Devil Fish mods to the TB-303:

Release notes version 4.1

This is: http://www.firstpr.com.au/rwi/dfish/release.html  Return to the main Devil Fish page, where MIDI In, 32 Banks of Memory and other related modifications are described. For the latest updates in reverse date order, click here!

Preliminaries

These release notes describe the modifications and give some guidance to usage.  A bundle of blank patch and pattern sheets are supplied with each Devil Fish. Patch and pattern sheets are available from patch-sheet/ .

New Inputs, Outputs, Controls and Functionality

Limiting the Devil Fish to TB-303 sounds

The Devil Fish's "sound-space" is immense.  A mild-mannered subset of this space is that of a standard TB-303.  Some users wish to restrict themselves to that space on certain sacred occasions.  Here are the limitations to observe.  The original pot settings are specified in terms of a clock face.  For instance the third line from the far left position is 9 o'clock

Filter Cut Off.  Between about 10.30 and 3 o'clock.

Resonance.  No limits.

Env Mod.  Between 12 and  4 o'clock. (The lower limit of envelope modulation was not zero in the TB-303, but it is in the Devil Fish. The upper limit in the Devil Fish is about 3 times what it was in the TB-303.)

Decay.  Fix at 12 o'clock.  This pot now controls the Volume Envelope Generator, which had a fixed decay time in the TB-303.

Accent.  No limits.

Overdrive.  Fix at 2.

Normal Decay.  No lower than 2.  This pot performs the function which the Decay pot on the TB-303 did.

Accent Decay.  Fix at about 2.7.

Filter Tracking.  Fix at 0.

Soft Attack.  Fix at 2.

Muffler.  Fix at 0.

Slide Time when using internal sequencer.  Fix at 0.

Slide Time with External CV.  Fix it at 5.  See the Usage Notes below on details of the Slide In input and how it may or may not drive the Gate of the synthesiser.

Sweep Speed.  Fix on Norm.

Acc Sweep. Fix on 2.

Filter FM.  Fix on 0.

Bass EQ. The TB-303 has a weaker bass response, so if you really want to replicate that, roll off the 30 to 60 Hz band by a few dB!

What Does it Sound Like?

Sound samples are available at the web site's sounds/ directory.

The musical implications of all the above changes are diverse and extreme. If you are interested in solid, heavy bass sounds, idiosyncratic synthesis or weird-and-wonderful sounds you have never heard before, then I promise you that you will really enjoy the Devil Fish. The expressiveness and pushiness of the Accent system – especially with the Filter FM which is boosted by the higher VCA output on accented notes – gives a unique range of dynamics. The Devil Fish can produce extreme output levels. Caution and/or a limiter should be used during live performance.

The TB-303 has five pots (not counting the tuning pot and the square/sawtooth switch) which define its sound – so there is a five dimensional space of sonic possibilities. In the Devil Fish, the range of four of these is expanded, and in addition, six new pots (not counting the Slide Time pot) and three new switches are added, so the sonic possibilities inhabit a 14 dimensional space, not counting the external inputs for audio into the filter and audio Filter FM.

I have discovered all sorts of exciting musical possibilities within this space – which is of course entirely dependent on the notes and accents the machine is playing. You will discover some of these and many that I have not yet found. If you have an exploratory nature, the Devil Fish will enable you to prowl powerful, exquisite, grungy and bizarre musical hunting grounds. All normal TB-303 operations are still possible, including "acid" type filter sweeps. Only minute details such as the delay in the start of the note and the lag at the end are not possible with the Devil Fish, but these delays would generally be regarded as problems rather than a part of the TB-303 sound.

You don't really need documentation to get great sounds from the Devil Fish. Just treat it like a child's activity set – play with the knobs and switches and you will find some good settings. I recommend that you write them down because it is impossible to remember the positions of 13 knobs and three switches. I recommend you roll tape and make music directly as you explore it. Don't try to make yourself an expert before you start recording.
 

Safety and Reliability

Devil Fish sounds may be seductive and powerful. Minor safety problems include the phenomenon of small household items being vibrated so as to fall from shelves. More serious a problem is the level of sound you can subject your ears to without realising it. Late at night, my ears become fatigued and I get low frequency tinnitus – I hear tones constantly droning. Please use this machine with caution!

Live sound with the Devil Fish could be problematic, since some sounds are extremely loud and contain large bass transients. I try not to leave mine sequencing away to itself audibly for no good purpose – it does something unpleasant to my brain.  The long-term effects of Devil Fish exposure have not been properly researched, so caution with this brain-frying instrument is indicated. The person who first took possession of a Devil Fish (actually, its the other way round . . . one places oneself in the care of the Devil Fish) in 1993, emailed me in 1997 – four years after writing something like "We were jumping up and down, literally bouncing off the walls, shouting This is what we want! This is what we want!" The time had come, he wrote, to pass the Devil Fish to someone else. I have serious concerns about the state of his remaining brain-cells, because he was talking about settling down, leading a healthy life . . . following simple pursuits . . . Its a worry!  So beware. Four years under the spell of the Devil Fish and this spirited artist was signing his emails . . . "mooooooo".

Please try to avoid spilling things into the Devil Fish. The basic machine, and especially the modified machine, is difficult to work on. Never spray anything inside the Devil Fish, or any other item of electronic equipment, ever. Pure water does the machine little or no harm, so don't worry if it gets rained on. Any other liquid is a cause for concern – so take it to a technician to have them investigate. Sticky things like rum and coke can be washed away with water, but only by someone working very carefully inside the machine.

The pots and switches are made by Alps (Japan) and C& K (USA) and are of the highest quality. However they could be damaged by excessive force. Always pack the Devil Fish in soft cloth inside a sturdy case. Never leave it floating around with other gear. Try to keep dust out of the machine.  Dust will ultimately make the pushbutton switches bounce. Avoid packing it directly in plastic/rubber foam. Sometimes fragments of foam can become wedged between the Accent pushbutton and its surround.

Only use a 9V DC adaptor – not a 12 volt or an AC adaptor. Some, probably most, "9V" adaptors actually put out higher voltages depending on the load current. A properly regulated supply is best, but the machine generally seems to tolerate moderate over-voltages gracefully.  (However, see the notes below under the Q45 part of the Reliability section.)  Don't leave batteries in the machine, unless you are about to use it without a power supply. There is serious danger of the machine being left on, or the volume/power knob being turned when in transit. This would flatten the C cell batteries and may cause leakage of corrosive liquids. Corrosion from battery leakage is a very common problem with TB- 303s and the damage can be hard to fix.

When you are turning the pots (of the original TB-303 or Devil Fish) do not press down excessively. With the original pots at least, this can wear out the conductive tracks and destroy the pot.  Please note that the standard TB-303 pots can fail – they are all at least 21 years old. In particular the Resonance pot, which is a dual pot, can fail without warning. The problem is often where the lugs are crimped to the conductive tracks – and no repair is possible (though some success has been reported with silver-loaded conductive epoxy). These pots have not been manufactured for a decade or so and the Resonance pot is short supply.  By all reports, Roland have none left, but if you try to find one, here are the details. Its part number in the TB-303 service notes is incorrect – it is a dual 50 k linear pot and its part number is different from that stated in the manual: 13219775 (K162T00W-50kB).  In 2003, complete replacement sets of the original six pots (and the volume and tempo pots separately) have become available from technologytransplant.com.  (See the 303-mods.html page. for contact details.) These seem to be of a high quality, but there is a problem with some pots not fitting the TB-303 knobs well.  The resonance pot has wider splines, and only fits some of the TB-303 knobs.  Also available are longer-shaft versions of this six pot set.  I trim these to about 2mm longer than the normal pots so as to raise the knobs this amount, which makes them easier to grasp and turn.  All these long-shaft pots, in my experience, have the wide-spline problem and since only a subset of TB-303 knobs fit them.  Since it is effectively impossible to file down the shafts, I modify the knobs to suit by using a drill to widen their hole to a depth of 1.5 or 2mm, which generally makes them fit.


As noted in the Reliability section, the three-position toggleswitches used in the Devil Fish can be worn out by lots of usage.  They remain functional, but lose their clear three-position tactile feel.  Don't flick these switches unnecessarily or with excessive force.

All Devil Fish's controls, inputs and outputs are fully tested before I return them to the owner. I cannot be responsible for failed TB-303 pots or other faults in the basic machine during or after shipment. The modifications are guaranteed for 2 years. Since the exact cause of the fault may not be apparent until after the machine has been repaired, faulty machines must be shipped at the owner's expense to me and I will refund freight costs in the event of a warranty repair – or charge for labour, parts and return freight if the problem is not covered by the warranty. Before sending a machine, be sure to email, fax or phone me with a precise description of the problem. There may be no real problem at all – or perhaps it would be better to take it to a local technician who I will help via phone, fax or email. In fact, Devil Fishes have proven to be remarkably reliable. I think there has only been one or two develop problems in the past ten years. On other occasions when faults were suspected, the problem was in fact flat batteries or a faulty external power supply.  One suspected noise fault turned out to be too high a gain in an external mixer, combined with low Overdrive and perhaps Volume settings making naturally occurring clicks seem more significant than they normally are.


See the section below on the Lithium battery for retaining memory data.
 

Usage Notes

Audio Input Voltages

The two audio inputs – Filter FM (Tip of what used to be the Headphone jack) and Audio In to Filter (Mix In jack) require line level signals. Microphone or guitar signals are not high enough. -10 dBm line level signals will be OK, but you may want to drive something harder so you will need a higher level. You can't do any damage by driving large audio signals into these inputs.

Gate, Slide and Accent Inputs

The three new inputs – Gate, Slide and Accent are all high impedance inputs expecting a positive input voltage. Impedance is at least 10k ohms and no damage will result from putting + or - 15 volt signals into these inputs. They are all "On or Off" inputs – where a positive voltage above about 2 to 4 volts is seen as "On". The typical thresholds are: Gate In 3.5 V (1.5 V for versions 2.1C and earlier), Accent In 2.3 V and Slide In 2.3 and 4.0 volts for the two aspects of its operation.  (This is for version 2.1D and later - see the more detailed information below in the Slide section).  A typical application is the Accent In voltage being driven by the velocity output of a MIDI to CV converter, so that those notes with a velocity above some particular value get played with Accent on. Similarly, the Slide In could be driven from another output voltage from the MIDI to CV converter – such as a mod wheel output voltage.

Filter CV Input

This enables an external control voltage to affect the filter frequency, in addition the internal processes which are driving the filter frequency, and in addition to the audio frequency modulation input on the tip of what used to be the headphone socket.  That audio frequency input is capacitively (AC) coupled.  It only passes rapid changes in voltage, so it does not enable normal CV control of the filter frequency.

The Filter CV Input socket is directly (DC) coupled, so all components of the input voltage will affect the filter frequency.  An audio signal into this input can cause audio FM of the filter, but the primary purpose of this input is to enable an external voltage, such as that produced by a MIDI to CV converter from MIDI Mod Wheel messages, to control the filter frequency.

Beginning with version 2.1C, the Filter CV input is approximately 1 volt per octave. (Previous versions were linear and are described below.)  The "resting" voltage of this input is approximately 3.3 volts and its input impedance is about 105k ohms.  When no signal is applied to it, its voltage is 3.3 volts.  If a higher voltage than this is applied, the filter frequency will rise.  For instance, if 4.3 volts is applied, this will raise the filter frequency approximately an octave above what it would otherwise be, as a result of the internal factors which affect the filter frequency (Cut Off, Env Mod, Filter Tracking, Accent and Filter FM) plus the AC-coupled audio modulation from the tip of the old headphone socket.

The filter is not a precise system and this input has a nominal 1 volt per octave response.  This response is not tested or guaranteed.  It may change with temperature, and with the many other things which are driving the filter frequency.

A good way of driving the Filter CV In would be a 0 to 5 volt Mod Wheel output from a MIDI to CV converter.  That will give approximately a 5 octave frequency range, which is pretty drastic.  If your MIDI to CV converter only has a 0 to 10 Volt or 0 to 12 volt output, or if you find the input too sensitive with 0 to 5 volt, then drive this input via an external 100k resistor, or something higher.  You can use a 500k pot in series to provide a good range of sensitivities.  If you don't know how to solder a lead with a resistor in series, then ask a technician to make one for you.

Due to the nature of the TB-303 / Devil Fish circuitry, large step-like changes to the filter frequency (those from the external CV input or the Filter Tracking pot) do not cause a perfect change to the filter frequency.  Perhaps 99.8% of the change occurs instantaneously (less then 1 millisecond), but there is a residual drift towards the final frequency over the next 500 msec or so.  This is caused by a number of capacitors in the machine, which are resistively coupled to a summing point for filter frequency which changes its voltage slightly.  This is only noticeable with the filter self-resonating, and with relatively large changes in filter frequency.


Notes on Filter CV In for Devil Fishes prior to 2.1C.  With versions 2.1A and earlier, this input had an unloaded voltage of about 1.0 volts.  Applying a voltage below this would lower the filter frequency. With version 2.1B, the unloaded voltage was about 3.7 volts.  Any voltage below this will lower the filter frequency and any voltage above this will raise it.  The 2.1B arrangement is a lot more sensitive then 2.1A – a given range of input voltages will achieve a wider variation of filter frequency.  For voltages below about 4.2 volts, the sensitivity is about twice as sensitive.  Above 4.2 volts it is about ten times as sensitive.  This enables finer control of lower frequencies, whilst still allowing for very high filter frequencies. Like the other CV inputs, any input voltage in the +/- 15 volt range is safe.  Probably a 0 to 10 volt range is ideal for driving the Filter CV Input.


Version 2.x Devil Fishes prior to 2.1C had linear responses to the external CV (albeit with two slopes in 2.1B).  This the system more musically sensitive at lower filter frequencies compared to higher ones.  Version 2.1C and later has an exponential - approximately 1 volt per octave - response.  This means that whatever frequency the filter is with in input of, say, 3 volts, it will be at twice that frequency with 4 volts, and four times that frequency with 5 volts etc.

The function of internal Filter Tracking system remains linear.  While the pot is actually a log pot, which I have made a little more linear, the relationship between the internal CV (from the internal sequencer or external CV In) and the filter frequency is linear in a volts to Hertz sense.  So, for instance, with a particular setting of the Filter Tracking pot, and the CV equal to say 2 volts, and with all the other settings (Cutoff pot etc.) the filter might have a cutoff / self-resonant frequency of say 1 kHz.  With a CV of 3 volts this would become 1.5 kHz and with 4 volts it would become 2 kHz.   The result of the linear system is that high notes (CVs of 3 to 5 volts) lead to only moderate increased in filter pitch (when considered in octaves or semitones), while low notes (1 to 2 volts) lead to dramatic drops in pitch (again when considered by an exponential scale such as octaves or semitones). 


I tried an exponential approach (1 volt/octave and beyond, to 0.33 volt/octave - as is typically found on other synthesisers) and decided the linear approach was much more musically interesting.

The final frequency of the filter depends on a number of internal and external factors.  


• The Cutoff Pot.
• The Main Envelope Generator via the Env Mod Pot.
• On accented notes, the Main Envelope Generator via the Accent Sweep Circuit (three modes controlled by the Sweep Speed switch), if the Sweep-Resonance switch is in positions 1 or 2.
• The AC coupled output of the VCA (which incorporates the Muffler) via the Filter FM Pot.
• The CV (from the internal sequencer or from the external CV input) via the Filter Tracking Pot. (Linear.)
• AC coupled signal from the Audio Filter FM input (tip of old headphone socket).  (Linear as well.)
• DC coupled signal from the Filter CV Input. (Exponential: ~ 1 volt / octave.)
  

The Tuning pot does not affect the filter frequency.  It only affects the Voltage Controlled Oscillator.

Synthesizer Accent and Accent Out

The Accent function of the internal synthesizer and the Accent Out signal are both activated when any of the following are true:


1. The internal sequencer is running and an accented note is currently being played.
2. The internal sequencer is not running, but the last note had the accent on.
3. The Accent In socket has more than about 2.3 volts going into it.
4. The red "Accent Pushbutton" on the right of the front panel is pushed.

Point 2 is worth remembering, since you may be driving the Devil Fish from an external CV, Gate and perhaps from and external Accent voltage, but you may not hear every note being accented in the sound coming from the machine. It may not sound this way, but the constant activity of the Accent MEG LED, and the lack of activity of the Normal MEG LED should alert you to the problem. The likely cause is that you were playing the machine from its internal sequencer and stopped it on an accented note. The solution is to start it again and stop on an unaccented note, or to turn the machine off and on again. According to one report, depending on the contents of the memory and the settings of the Track/Pattern and the Mode switches it is possible that when you turn the machine on, the internal sequencer will be in this accented state. I have not observed this, but it can probably be fixed by clearing pattern 1A, or the first pattern of the song in whatever group you have selected when you turn the machine on.

Synthesizer Gate and Gate Out

The Gate Out follows the Synthesizer Gate which is on when either of the following are true:


1. The internal sequencer is playing a note.  This will happen when the sequencer is running or when you are playing notes in the programming mode.
2. The Gate In socket has more than about 3.5 volts (1.5 volts for version 2.1C and earlier) coming into it.
3. The Slide In voltage is above its second threshold.  (Version 2.1D and later only.)
   

If you are playing the Devil Fish from external CV and Gate, and you have the internal sequencer running as well, then both these will be driving the synthesizer gate, so you may get weird sounding notes. You can use this to advantage if you want some out-of-sync notes playing in addition to the normal ones. You can also have the machine running from external CV and Gate, but add in your own notes (Gates) by putting the machine into Pattern Write, Pitch Mode, and pressing any of the 13 note buttons.

The Devil Fish uses the standard TB-303 Gate Out circuit.  This is driven by a diode and a 1K resistor inside the machine. It goes high to 12 volts when the Gate is on. If you short it to ground (for instance as you plug a lead carrying this signal into a socket), the extra current could upset the Devil Fish / TB-303, but will not cause damage. This is a high gate voltage. If you need to drive a Moog or Korg active low gate, you will need a little circuit comprising of two resistors and a transistor to invert the polarity of the signal.  (In my experience, Mini-Moogs are entirely unsuitable for driving from external CV and Gate, unless they are extensively modified.)

CV Out

The standard TB-303 CV Out is connected directly to the output of an op-amp – this ensures an accurate voltage even when it is driving a lower impedance device. The output can handle being shorted to ground but the Devil Fish / TB-303 machine will not like it. You should ensure that it never gets connected to a signal which tries to drive it below ground or to any other voltage – since this could damage the op-amp. The CV Out carries the voltage of the internal DAC, after it has passed through the slide circuit. If an external CV is driving the machine through CV In, then the internal DAC is ignored and the input CV is passed through the slide circuit to drive the internal synthesizer and the CV Out.

The tuning knob only affects the tuning of the oscillator of the internal synthesizer.  It has no effect on CV Out or the Filter Frequency.  The range of the CV Out is 1 to 5 volts when driven by the internal sequencer. It may range a little above or below this when an external CV is used.  The internal sequencer produces a voltage in the range of 1 to 5 volts. This represents the 3 octave range of a pattern which can be transposed by up to an octave. 2 Volts is the normal C at the left of the keyboard, 1 volt is the C an octave below. 3 Volts is the C at the right of the "keyboard" and 4 volts is that C transposed up an octave. In pattern play mode, you can press "Pitch" and one of the 12 keys to transpose the pattern up by 0 to 12 semitones, so the normal 1 to 4 volt range can be transposed to as high as 2 to 5 volts.

CV In

The CV may be usable somewhat below 1 volt. Do not put voltages below 0 or above +5 volts into the CV input. The Devil Fish has a protection circuit to guard against these voltages, but it is best that you avoid them nonetheless. Many MIDI to CV converters are capable of going below 0 volts or above 5 volts.

Slide Slew Times

The Slide Time pot gives you longer slide times than normal and can give you shorter times when running from CV In.

The slide time - how long it takes for the internal CV to the Oscillator (and Filter Tracking Pot and CV Out) to slew from one level (and therefore oscillator pitch) to another - is proportional to the sum of three separate resistances. Resistance is an electrical term similar to impedance. A firehose has a low resistance to water flow while a drinking straw has a high resistance.  The slew time is theoretically infinite.  The times mentioned above, in the New and Changed Controls section, of 360 milliseconds etc. refer to the approximate audible time it takes to reach the final frequency.  But in any resistor capacitor arrangement, the final voltage is never precisely reached - it is only approached closer and closer over time.


When the Slide is activated, the internal DAC or the CV In drives a capacitor – which is like a large tank. If the source of Control Voltage (Voltage is like the pressure or level of water) has a high resistance, then it will take longer to bring the capacitor (tank) to the final level, so the slide time will be longer. The three resistances in the slide circuit are:
 

1. The resistance of the DAC (Digital to Analogue Converter) in the TB-303's internal sequencer. This is 100K Ohms (100,000 Ohms). Alternatively, if you are using an external source of CV, the resistance of the source of CV which is likely to be very low – 100 Ohms or less (equivalent to a firehose).
2. A 3.3K Ohm (3,300 Ohm) resistor in the Devil Fish CV voltage protection circuit. When thinking about slide, this is a very low value – close enough to zero.
3. The resistance of the Slide pot: between 0 Ohms (anti-clockwise) and 500K Ohms (500,000 Ohms = very high resistance equivalent to a long, narrow drinking straw) when turned fully clockwise.


The usual rather fast slide of a TB-303 is caused by the 100K resistance of the DAC feeding a 0.22uF capacitor. If you are using the internal sequencer and have the Slide pot turned fully anti-clockwise, you will get almost the same slide speed, due to the 100K DAC resistance and the 3.3K protection circuit voltage giving a total of 103.3K Ohms. By turning the Slide pot you can add to this resistance to give a slower slide time – up to a total of 603.3K Ohms, or a time 6 times longer than normal.

If you are running from an external CV, and the Slide pot is fully anti-clockwise, then the resistance will only be 3.3K Ohms (assuming that the source of CV has a very low resistance). This low value will give you a very short slide time: so short that you will not hear it. If you turn the Slide pot a little towards the clockwise position, you will be able to find a position which gives you the usual slide time, where the Slide pot is at about 100K Ohms. By turning it fully clockwise, you will get a total of 503.3K Ohms – about 5 times the usual slide time. If you want extremely long slide times, feed the CV into the Devil Fish through a resistor, where the value is 470K Ohms or above. Values above several Meg Ohms may result in a loss of pitch accuracy. There is a trimpot inside the Devil Fish to adjust for the bias current of the slide buffer op-amp, to minimise the mistuning which would otherwise occur with high impedance inputs, but this may not be entirely accurate over all temperatures, or at the highest and lowest pitches

Slide In Thresholds and Gate

In versions 2.1C and earlier, the Slide In had a single function - to turn on the slide slew circuit.  Slide In did not turn on the Gate of the synthesiser.  This meant that if the internal sequencer or external source of Gate (such as a MIDI to CV converter) was producing two separate periods of Gate On (that is two discrete notes in time) at different pitches (different CV voltages) then this input could not "tie" the two notes together, as is commonly desired for the musical concept of "Slide". 

In versions 2.1D and later, the above functionality can still be achieved, by driving Slide In to about +3 volts.  The first threshold voltage is about +2.3 volts - to turn on the slide slew circuit.   There is a second voltage threshold, present only in versions 2.1D and later, at about +4.0 volts.  This turns on the synthesiser's Gate and the Gate Out signal as well.   Thus, when Slide In is driven above +4 volts, not only is the slide slew circuit enabled, but Gate is turned on, which has the musical effect of making the Gate In signal irrelevant: it "ties" any and all "notes" into one long note event, as long as the Slide In is above 4.0 volts.  

For most musical purposes, simply drive Slide In with 5 volts or more - anything up to 15 or 30 volts will do.  Use about 3.0 volts if you want to turn on the slide-slew circuit whilst leaving the synthesiser notes to be driven independently by Gate In or the internal sequencer.

Devil Fishes prior to version 2.1C can't, internally, use the Slide In voltage to turn on the internal Gate.  However, a simple arrangement of wiring outside the machine will perform the same function.  A technician can easily create a set of cables, or a small adaptor box, with diodes so that either the Slide or the Gate voltage from the MIDI to CV converter drives the Devil Fish's Gate In:

MIDI-CV  Gate Out   >---------->|-----*------>   Devil Fish Gate In
                                     /
                           *--->|---*
                          /
MIDI-CV  Slide Out  >----*------------------->   Devil Fish Slide In

See also the discussion below in the Version History.

Accent Sweep Switch and Resonance

Here is a tabular description of the two functions of this three-position toggle switch.
 

Accent   Accent    Resonance            Use it for: Sweep    Sweep     High means the Switch   circuit   filter will self          enabled   resonate at mid &                    high frequencies                    when the Resonance                    pot is past about                    2 o'clock.  --------------------------------------------------------------- 2        Yes       Normal               Acidee sounds with the                                          Resonance pot fully                                          clockwise. 1        Yes       High                 Whistly filter sweep                                          sounds.   0        No        High                 Self resonant filter                                         with no sweep on                                         accented notes.

Overdrive, Filter Resonance and Audio Filter FM

Audio Filter FM has the most effect when the filter is most resonant. Audio signals for Filter FM come from the Filter FM pot and from the tip of what used to be the Headphone jack.  The resonance of the filter is quenched when the filter is driven by a heavy input signal – the filter hits its limits at the high and low extremes of the waveform and cannot resonate at these limits. The filter can be driven hard with the Overdrive pot and/or an external signal plugged into the Mix In socket.

On the other hand, since the internal Filter FM pot is driven by the output of the VCA, and this VCA output signal is likely to be much higher with the Overdrive pot turned clockwise, extreme internal Filter FM will occur, at the same time as the filter is being overdriven by the 66.6 times normal level of oscillator signal.  Seriously loud and complex sounds!


Furthermore, if you carefully use a mono or stereo plug in what used to be the headphone socket you can achieve something still more drastic. Whether or not the tip of the plug connects to anything (such as a mixer or reverb input) and assuming it is not driven by some external signal, then you can use the tip of this plug to connect the "ring" of this socket (Audio Out from the Filter, before the VCA/Muffler) straight to the "tip" of the socket: Filter FM In.  There is a position just a few millimetres short of full insertion which connects the two parts of the socket together.   This is different from the Filter FM pot system in several ways.  Firstly, there is no control over the level of this type of Filter FM. (Use a proper stereo plug and lead, with external pot, mixer, gain control, etc. if you want to control it.)  Secondly, the level is potentially more intense than with the Filter FM pot.  Thirdly, this is continual FM, not dependent on "notes" via the VCA being turned on.  Finally, the polarity relationship between Filter audio output voltage and its control voltage is the opposite of that of the Filter FM pot, so depending on the gain of the VCA, the two may cancel to some extent, or more likely greatly complexify the final audible result. 


Rather than try to analyse and understand, its better to simply try this! 


Turning up the Overdrive towards maximum, and then with Filter FM turned up high, it is possible to have sounds which, depending on other things, descend into a spluttering chaotic mess.  At times, I have had this arrangement with the controls finely tweaked so that on some cycles through a pattern, the filter  resonates with the spiky, "nutty" sounding intense Filter FM at about the frequency of the Oscillator, but at other times at half the rate (an octave below), or less.  This is somewhat like not quite blowing a trombone into its second octave.  Thus, a totally repetitive sequence can result in randomly very different sounds.  I have had settings where the state of this self-oscillation for a particular note in the bar varies from bar to bar, but remains stuck in one state or the other for the duration of each note. 

Muffler and Audio Filter FM

The muffler works on the output of the VCA, and it is the output of the VCA which drives the Filter FM pot. Since the Muffler decreases the level – and particularly the extremes of level – it will reduce the effect of Filter FM and change its nature.  Likewise, the Filter FM pot will have less effect if the VCA output level is low due to the Overdrive pot being set low.

Lithium Battery

The Lithium battery is soldered to the main internal Devil Fish circuit board.  Replacement involves dismantling the machine and the use of a soldering iron.  Under normal circumstances, replacement should not be necessary for a long time - probably several decades.

The battery is a Varta CR 1/2 AA.  It is not rechargeable and will never leak.  It has a capacity of about 1,000 mA hours.  The drain of the memory chips is always less than 1 uA – I test it.  At this rate, 8.76 mA hours will be drained per year, so the life of the battery is theoretically 114 years.  In fact the battery does have a slow self-discharge characteristic which is more significant than the current drawn by the memory system.  This self-discharge rate is temperature-dependent. Varta predicts that at 25° C only 10% of the charge will be lost after ten years, whilst at 45° C 40% would be lost.  Assuming that no faults develop with the battery or the circuitry, battery life will be at least ten years and quite likely thirty years or more.

To test the battery voltage, remove the Mode knob. (Use adhesive masking tape to grip it, if necessary.)  Connect the negative lead of a Digital Volt Meter (DVM) to the ground of the machine.  The best way is to clip on to the ground of one of the 3.5mm jacks at the rear, or to plug a lead into any of the sockets and connect to the ground of that lead.  Note that the metal ring on the outside of the 1/4" jacks is not grounded.  Place the positive lead of the DVM on the test point near the Mode Switch.  This is the Lithium battery voltage via a 3.3k resistor.  Any voltage above 3.0 volts is fine.

To "clear" the memory it is necessary to remove the battery backup supply from the memory chips.  This can be achieved by removing the Track/Pattern Knob and shorting to ground the test point which is underneath the knob.  Do this while the machine is turned off and has no C-cell batteries installed.  Short the test point to ground for 1 second or more.  "Clearing" means that the memory chips will have patterns of data in them determined by subtle physical characteristics of each flip-flop - each memory cell.  Chips from different factories tend to have different sorts of patterns.  The chips used for the 23 bank memory systems tend to have quite random and potentially quirkily interesting patterns.  Clearing does not mean that all cells are set to zero - which would probably result in blank patterns, or patterns of all the same timing and pitch.


To measure the current drain of the memory system, turn the machine off, and remove any C-cell batteries.  Connect a micro-amp meter between these two test points. Current will take a while to stabilise due to the presence of a capacitor on the RAM chips' VDD.  The final current should be less than 1uA.

Operation from C-cell batteries

Please be wary of inadequate supply voltage from batteries or the external power adaptor if you experience faulty behaviour with the Devil Fish's sequencer.  There can be all sorts of trouble, such as the sequencer stopping (and not responding to front panel buttons) or playing patterns incorrectly or not at all.  There have been many instances of Devil Fish users being perplexed at a malfunction, only to find the problems are resolved with a fresh set of batteries. 

Please use Alkaline C-cell batteries, rather than ordinary dry-cells.  NiCad or Nickel Metal Hydride rechargeable batteries are 1.2 volts per cell, and generally will not provide sufficient voltage to run a TB-303 or Devil Fish reliably.

The TB-303 is fussy about the voltage of its C-cell batteries.  Likewise, if it gets too little voltage from an external power supply, then the internally regulated version of that supply voltage will drop below 6.0 volts, and trouble may occur.  The Devil Fish draws more current and therefore is still fussier about these low voltages, however in August 2005 I began making additional changes to the Devil Fish (Version 3.0C and 4.0C as described below) which improve the way the CPU voltage is generated and so make these machines somewhat less sensitive to low battery (or adaptor) voltages than a standard TB-303.  Please see the Version 4.0C notes for technical details.  This discussion concerns the TB-303's original CPU.  The CPU I use for the MIDI In system has a separate power supply, and should not be affected by marginal drops in battery or external supply voltage.

Devil Fishes before August 2005 generally could only work from the "top 25% or so" of the energy available from alkaline C-cells.  I estimate that a fresh set of C-cells would run the machine reliably for 3 or 4 hours.  Some machines may be more robust and others more flaky - depending on how fussy the CPU chip is.  After these changes, I expect machines should run for 5 or 6 hours before the battery voltage falls to the point where the CPU may malfunction.  These times are not guaranteed.  The actual running times depend on the batteries, the temperature, what the Devil Fish is doing, and especially on the characteristics of the particular CPU chip.

When the on-load voltage of the 4 cells combined dropped below about 5.5 volts (1.375 volts / cell), the TB-303's CPU chip would generally be running from 4.5 volts or less.  The CPU chips are only specified to run from 4.5 to 5.5 volts, so if they malfunction below 4.5 volts, it would not be surprising.  Each individual CPU has its own lower limit, and this may vary with temperature.  The lower limit for proper operation may also rise with age.  I have seen particular TB-303s or Devil Fishes become more fussy about supply voltage.  This is not common, but it may happen to any machine.  Replacement CPU chips are not available, and in 2005, these devices are around 23 years old.  The failure mode may be the CPU freezing - so there will be no sequencer or front panel activity.  Another failure mode may be it stepping through a pattern, displaying things on the front panel etc, but failing to trigger the Gate of the synthesiser - so no sound is played and no Devil Fish LEDs are turned on.

The Version 4.0C changes reduce the voltage drop to the CPU and so enable any given CPU to operate at correspondingly lower battery (or external supply) voltages.  I estimate the voltage at the batteries which is required for 4.5 volts to the CPU is reduced from 5.5 volts to about 5.05 volts.  This means that the machine will run properly for longer on a particular set of C-cells.  However, the machine will stop running reliably when the batteries are still a long way from being fully discharged.  The discharge curve for alkaline C-cell batteries can be seen at: http://data.energizer.com/PDFs/e93.pdf .  The voltage drops steadily down to about 1.1 or 1.0 volts and then drops more rapidly.  Generally, the 1.5 to 1.0 volt range is where most of the battery's power can be extracted.  However, a (post August 2005) Devil Fish will only be able to run from C-cells down to about 1.25 volts per cell.  The C-cells should then be used for some other purpose, such as a torch / flash-light, or some other less fussy electronic device.

Please see the discussion below (Known reliability problems) on how the Run/Stop LED is an indicator of power supply voltage.  A dim Run/Stop LED indicates that the battery or external power supply voltage is too low.

Power Adaptors

The Devil Fish, with MIDI In and the headphone amp operating, draws 180 mA from the external power adaptor.  The lowest current drawn, with few LEDs on and no sequencer, synthesiser, headphone out or MIDI activity is around 150 mA.  It is vital that the power adaptor used for the Devil Fish (or any TB-303 or TR-606) be an independent adaptor for this machine alone, and that it be close to 9 volts. 8.5 to 9.5 volts is best. 

I recommend a Boss PSA-240 adaptor for Australia.  I similar adaptor can probably be found for various countries depending on the supply voltage: PSA-100, PSA-120, PSA-230 etc.  These put out a reliable 9 volts with quite sufficient current for the Devil Fish.  Search for things like:

Boss PSA-120

at www.google.com/search?q=Boss+PSA-120 .

Beware of other adaptors.  Just because an adaptor is labelled as "9 volts 300mA" does not mean it actually puts out 9 volts when powering the Devil Fish.  It may be designed to put out at least 9 volts under worst-case conditions (usually when warm, which increases the resistance of the copper windings of the transformer) with a load of 300mA and a slightly lower than normal mains voltage.  But this means that with a good mains voltage and a lighter load, it will probably put out 10 or 11 volts.  If you are going to use unregulated adaptors (almost all of them are unregulated) then it is best to choose a 9 volt one with a lower rated current than a higher.  For instance, the voltage supplied under a 150 mA load by a "300 mA" adaptor might be an OK 9.7 volts, while with a "1000 mA" adaptor the voltage might be a damaging 11 volts.

I can't tell you exactly which adaptor in your country is suitable for the Devil Fish.  A good one will put out 9.0 to 9.5 or maybe 10 volts maximum when the Devil Fish is running from it.  If the Run/Stop LED does not light fully and without fluctuation when the sequencer is running, then the external power adaptor (or the C-cell batteries if this is what you are using) are not supplying sufficient voltage.  

The machine may work OK with higher input voltages, for a while - but the internal regulator transistor will be asked to drop 180 mA through more than its intended 3.0 volts (9 volts external dropped to 6 volts internally means a 3.0 volt drop across this power transistor and therefore a 0.54 watt dissipation).  If you notice the back right of the machine getting too hot, then you are probably driving it with an adaptor which is putting out too high a voltage.  This probably won't damage the transistor immediately, but extended use will damage it and make the machine unusable except from C-cell batteries.  I have replaced many of these transistors - the TO-220 power transistor at Q-45 2SB596 - with a TIP-30.  Some of them have turned brown and have been so hot that solder has melted inside them and been forced out of the package

Do not use share one power adaptor amongst multiple machines.  Theoretically it may work if the two machines are identical, such as two TB-303s etc.  However, this sharing of 9 volt adaptors with other machines is likely to damage machines such as the TR-606 or TB-303 / Devil Fish.  These use a regulator in the negative lead, so this lead drops to -3 volts for a 9 volt input, causing the positive lead to be the +6 volts the internal power supply requires.  However, most other musical instrument devices ground the negative lead - and the TB-303 / Devil Fish will have its ground connected via audio leads to the ground of the other device.  This bypasses the TB-303's internal regulator, and forces the positive lead to +9 volts, or whatever higher voltage the adaptor is putting out.  This is likely to damage the internal power supply and it would not be surprising if it destroyed the CPU chip, which would then be running from 8.0 or more volts, while its absolute maximum voltage is 6.0 and while it is only specified to operate properly on 4.5 to 5.5 volts.  TB-303 CPU chips are Unobtainium - they cannot be obtained from anywhere.

Idiosyncrasies

The Devil Fish is a denizen of the catacombs of Idiosyncrasy City. Here are some of its peccadilloes.

With version 2.1 and earlier, there used to be a certain amount of clicking at the start of notes and sometimes at the end of notes – even when no sound was being produced, on un-accented notes when the Soft Attack pot was fully clockwise and the Decay pot was fully anti-clockwise. Version 2.1A largely fixed these clicks, but due to a mistake I made with the choice of a diode, clicks may appear with some machines at high temperatures.  In Version 2.1B I further refined the circuit to minimise these clicks under all circumstances.

The TB-303 filter is a diode-capacitor ladder filter – comparable to those in many Moog synthesizers. The filter is unchanged in the Devil Fish, although its audio input can be driven harder and its frequency control can be driven over a wider range by a large number of signals.  Electronically its behaviour far from the perfect model of a filter. I still don't know exactly why it sounds the way it does, but it has a fantastic vocal/nasal twang that gives it a really musical spirit. The filter will only self oscillate at mid and high frequencies. Surgical intervention, aimed at improving its gain at lower frequencies, made it sound more like a normal filter, so I abandoned this line of investigation.

With high levels of VCO and/or external signal into the filter, some clipping can occur – depending on the filter frequency and resonance.

With high levels of signal coming out of the VCA and with the Volume pot set at or near maximum, some clipping can occur in the output amplifier.  This typically only happens on the loudest (for instance the accented) notes, and can be quite a useful effect.

The polarity of the main output signal is opposite that of the Filter Audio Out signal.  If you mix the two into mono, then depending on the VCA gain, the two resulting contributions to the final mix may be equal but opposite signals and so will cancel out.

A useful, convenient and drastic effect is to partially insert a 1/4" (6.5mm) mono or stereo plug into the old headphone output socket.  This form of Filter FM is described above in the Overdrive, Filter Resonance and Audio Filter FM section above.

Reasons for no audible output

The filter can have such a low frequency that it passes no audio at all.  For instance, with notes below the low C (2.0 volts) of the standard range (i.e. in the octave accessible with the transpose down function: 1.0 to 2.0 volts) the Filter Tracking pot will lower the filter frequency.

The Cutoff Pot can be turned anti-clockwise to the point where the filter passes no audio at the frequencies the VCO is producing.

The external Filter CV input can lower the filter frequency, including when 0 volts is applied.  Any voltage below about 3.3 volts will lower the filter frequency.

If you hear no sound when the Gate is On (as indicated by the LED in the "e" of "Devil Fish") and the Overdrive pot is not at zero, then try turning up the Cutoff pot, turning down the Filter Tracking pot, removing or changing the Filter CV input voltage.  Another reason for not hearing any sound is the Decay pot being fully anti-clockwise whilst the Soft Attack pot is is fully clockwise – but only for non-accented notes.  Beware too of the waveform switch being in mid-position!
 

Known reliability problems

In general I have been very happy with Devil Fish reliability.  However, the TB-303's CPU may freeze or misbehave when operating from C-cell batteries or an external power supply which does not provide sufficient voltage.  When the sequencer is running, the Run/Stop LED functions as a power supply voltage indicator (its behaviour is not altered by installing different colour LEDs).  The Run/Stop LED should be on brightly, or perhaps just dimming a little when more current is drawn by the Devil Fish LEDs.  If it is dim, then the batteries or external supply are not providing enough voltage, and you cannot expect the CPU to function correctly.  Failure may involve cessation of sequencing and front panel activity until the machine is turned off and then on again.  Failure may also include playing patterns in an erratic manner, problems writing patterns, playing patterns but not driving the Gate (so there is no sound) etc.  Please see the section above on operation from C-cell batteries.

With over 190 units in use, for a cumulative total of, I guess, around 800 years service, there have been no reports of failure other than these battery problems and those noted below.  There has been occasional incidents of damage, such as a switch being hit by an external object.  Also, there may have been troubles which I have not heard of.

CV In socket: internal sequencer CV misbehaving

An occasional problem is that the internal sequencer does not drive the Devil Fish oscillator and Filter Tracking correctly.  (Likewise, the CV Out socket will not respond as it should to the internal sequencer.)  There may be no pitch variation or an incorrect variation.  The cause is the rear-panel external CV In 3.5mm socket.  This socket's tip contact also functions as a switch to another contact in the socket so that the internal sequencer's CV is used when no plug is inserted.  This connection between the contacts is metal-to-metal and so should be perfectly reliable.  However, it seems that it is possible for the connection to fail or to be flaky.  The most likely cause is dust getting into the contact area, but there have been instances where the problem developed with the socket not having been used recently or at all.  Fortunately, it seems that the problem can be fixed simply by inserting a plug into the CV In socket and removing it.  This may need to be done a few times before the contact area is freed of whatever dust or other contaminants was causing the trouble.  If this doesn't work, try twisting the plug clockwise and anti-clockwise as you slowly press it into the socket.  This will cause the spring contact to move sideways against the fixed contact.

The sockets I use seem to be robust and have plenty of spring-pressure on the contacts.  I don't know of any other "better" sockets and the problem is so rare I cannot reproduce it – so at present I have no means of entirely eradicating it.  The problem is occasional, since there have been only two reports from users and one instance with a newly modified Devil Fish I was testing.  It is possible to imagine the spring contact becoming deformed by the use of a thick 3.5 mm plug, or that plug being pressured from the outside so its tip is forced upwards inside the Devil Fish, which would bend the contact more and so perhaps deform it and reduce its pressure on the fixed contact.  The sockets I use seem to be capable of withstanding excessive pressure on the spring contact.  Generally these sockets are indestructible.

Starting with serial number 084 (13 April 2000) I bent the fixed contact of the CV In sockets a little to increase the pressure the spring contact makes on it.  Hopefully this will improve reliability, but the problem is so rare it will be hard to prove this.
 

32 bank memory system – problems when fresh C-cell batteries are installed

This problem has been resolved in current-production Devil Fishes.

Three customers have reported flaky 32 bank memory behaviour when running from batteries.  Symptoms included the pattern length being re-written to something shorter than 16 after the notes were entered.  I don't know the state of these batteries but proper operation was restored when they operated their machines from a 9 volt DC adaptor.  I am yet to reproduce this problem myself.  I suspect that the problem was caused by using fresh C-cells – probably alkaline batteries – and that these had a total voltage significantly higher than 6.0 volts.  The supply voltage for the memory chips in the standard TB-303 and on Devil Fishes with 32 banks of memory up to serial number 079 (24 February 2000) are driven via diodes from two sources: firstly the internal 6 volt supply and secondly from the battery voltage directly.  The diodes introduce a voltage drop of 0.3 to 0.5 volts and so the memory chips can be running from a voltage as high as 6 volts or more, depending on the voltage of the batteries.  The chips are usually rated to operate at no more than 5.5 volts, so this higher voltage could cause malfunction.  (The paint dots on some of the 1k x 4 bit chips Roland installed indicates they may have been selected to operate correctly at these higher than normal voltage.)

Starting with serial number 081 (4 April 2000) I modified this circuit to reduce the supply voltage the RAM chips receive.  Firstly D38 is removed.  This powered the chips continually from the C-cells, but this is not needed with the Devil Fish, since the internal lithium battery should power the chips for several decades.  Secondly, I install a second diode in series with D39 to add further voltage drop to the voltage supplied from the internal 6 volt supply.  When operating from batteries, this supply is not regulated and follows the battery voltage.  These modifications should reduce the tendency for high C-cell voltages to disrupt memory operation.  A sufficiently high C-cell voltage will still cause trouble and there is no solid specification for C-cell voltage – so it cannot be ruled out that particularly high voltage C-cells will not cause trouble.  While I am yet to observe the flaky behaviour directly, I believe that these changes will largely or completely eliminate the problems experienced by users.  Since I began these mods, there have been no further reports of trouble.
 

Q45 overheating

This is not a problem for the Devil Fish as such, but a general problem with TB-303s and other devices operating from AC adaptors.

A common problem for TB-303s and I assume Devil Fishes is that the machine is sometimes connected to an AC adaptor or to a DC adaptor which produces significantly more than the required 9 volts.  The machine my run properly, but the main regulator transistor in the internal power supply section – Q45 (type "B569") – can become overheated.  Over time, this may damage the transistor and it may fail completely, or more likely fail to operate properly.  You may be able to feel this overheating in the rear right of the machine.  Damaged transistors typically show discolouration of the green plastic case and plated copper heatsink.  Some are remarkably resilient, operating correctly despite having their plastic and heatsink blackened and even showing blobs of solder leaking from within the transistor itself!  I replace the "B569" with a commonly available transistor called a "TIP30".  As is often the case with electronics, many weird and wonderful fault conditions turn out to be caused by inadequate supply voltage, or a faulty power supply.

Generally the Roland or Boss adaptors are fine.  Cheaper adaptors may say something like "9 volts 400 mA".  This means they are supposedly capable of producing 400 mA of current (milliamps are like pints of water per minute flowing through a pipe) whilst still maintaining a 9 volt (volts are like pounds-per-square-inch of pressure in a water pipe) output.  The Devil Fish uses around 85 mA in idle mode and no more than 155 mA when running.  The latter figure includes 15 mA drawn by the old headphone amp if a plug is inserted into the socket which is not Filter Out and Filter FM In.  Most power adaptors do not have internal regulators.  Their output results from a transformer secondary winding going through some silicon diodes and being smoothed by a capacitor.  To achieve a minimum voltage of 9 volts (not the average, the minimum after allowing for the 100 or 120 Hz hum variation as the mains charges the capacitor in pulses) at maximum output current (say 400 mA) when the transformer's windings are hot and have a high resistance, when the mains voltage is rather low (say 110V or 220V AC) then the same power supply, when cool, unloaded and running from a higher mains voltage (120 volts or greater than 240 volts) is bound to put out significantly more than 9 volts.  The question is: what voltage is the adaptor putting out in practice, when loaded by the Devil Fish?  10 or perhaps 11 volts is probably OK.  Anything above this risks overheating Q45, and so causing damage soon or in the long-term.  This is a general problem for TB-303s and all similar machines which run from a power adaptor.  I don't know of a specific instance of a Devil Fish being damaged in this way, but I wouldn't be surprised if it occurred.

There is no rule which enables users to choose their external supplies with bullet-proof safety.  In general, stick to Boss or other quality Japanese adaptors which are 9 volt DC, and which have a current rating between 150 and 500 mA.  If in doubt, have a technician check the voltage of your adaptor when it is operating the Devil Fish.  The easiest approach to this is to take the back off the machine and use a volt meter on the circuit board where the power jack is mounted.
 

Switches and pots

Once the tact switches (the 24 click switches behind the silver buttons) have been replaced and the dust-guard installed, it seems their life is extended to many years of active use.  In late 2003, I have no reports of switch trouble from those machines I modified in 1993 and 1994 - but in 2002 I did replace one set of switches in a machine I modified in 1996.  This was a very intensively used Devil Fish.  The dust guard clearly greatly extends the life of the tact switches. 


Tact switches which are erratic make the machine difficult or impossible to program.  There is no way of repairing them or improving them by spraying stuff inside them.  In my view, stuff should never be sprayed inside anything electronic, unless the component is able to be dismantled and the cleaning done with isopropyl alcohol in a way that it can be completely cleaned off in a visible way.  These tact switches cannot be dismantled or improved with any such liquids.


There have never been any problems with the beautiful little ALPS pots used in the Devil Fish.  Likewise the C&K 8121 (or 8125 - and C&K was bought out by ITT Canon) switches used beneath the Accent button (and in the memory system) seem to last forever. There have never been any failures of the 6mm sockets used in the TB-303 (Filter In, Filter Out/FM and Audio Out) - these are remarkably reliable sockets.  There have never been any failures of the 3.5 mm sockets of the TB-303 (CV and Gate Out).  The only problem with the Devil Fish 3.5 mm jacks is discussed in a section above on the Gate In socket


There is a lifetime "wear out" problem with the three three-position toggleswitches used in the Devil Fish panel.  These are of the highest quality, and are made by only one manufacturer, C&K (now ITT Canon).  They are a T211 SHCQE.  Their three-position operation depends on the interaction of a small piece of red fibreglass-reinforced  plastic with the sides of the case, which is made of a similar material.  With a lot of use, the sides of the moving plastic piece become rounded from friction against the case.  The result is that there is progressively less of a clear distinction between the three positions.  There still are three positions, so the switch remains electrically fully functional, but it does not have its original clear positive tactile action.  I haven't tested this to find out how many hundreds or thousands of operations cause a deterioration.  I encourage users not to flick these switches back and forth for no good purpose.  Repairing the problem is non-trivial.  The best approach is not to de-solder the switch, but to leave its base intact on the circuit board, and to unclip the metal part.  A new toggle, metal surround and internal contacts and plastic piece can then be clipped to the switch base.  Of course this involves complete disassembly and re-assembly of the Devil Fish, which is not for the faint hearted.



Replacement Resonance pot with narrower active rotational range


Technology Transplant (http://www.technologytransplant.com) sell a set of replacement pots for the 6 small pots along the top of the TB-303.  (They also sell replacement Tempo and Volume pots.)  There have been several versions of these pots over the years.  In March 2006 I received some and when I first used a set in August I found that the Resonance pot is not a linear pot, as it should be.  The Resonance pot is a dual 50k pot, with a linear taper, which is 'B' in the arcane world of potentiometer nomenclature.  So "50KB" is the label of the original and the replacement pots.  The Resonance pots I received concentrate most of their resistance variation into the centre of the rotational range. That is to say that very little happens between fully anticlockwise and about 10 o'clock, and likewise very little happens from clockwise back to about 2 o'clock. 


This is not disastrous, but it must be borne in mind when writing down knob settings, and transferring them to another machine with the original type of Resonance pot.  I inform all customers who have such a pot.  Unfortunately there are not alternatives.  Despite this problem, and the fact that the shafts of the new Resonance pots are too large (I drill out the knob's splined hole) we are fortunate that Technology Transplant has gone to the trouble of having these pots manufactured.



 

Applications

In November 2003, Devil Fishes have been in existence for ten and a half years now.  Still, it is early days in terms of exploring their musical potential.  It was quite a few years before the idiosyncratic personality of the TB-303 was fully recognised. Most of the things you do will be unique because the combination of your music and the new sounds have never been tried before. There is a great deal to be done, just with the machine as it stands, playing from its internal sequencer, synched up to other equipment. Still, I think, most people see the Devil Fish as a TB-303, typecast in techno or acid music, rather than an instrument, musical character / critter etc. in its own right.

One simple extension is to drive a synth from the CV and Gate outputs and mix the synth's signal into the Devil Fish with the Mix In or the Filter FM. Another is to treat the output of the Devil Fish with EQ, reverb, delay, flange etc. and bring it back into these inputs. One application of the CV, Gate and Accent In and Out signals is to have one Devil Fish slaved to another via these three signals. The two machines can have differing sounds and their outputs can be treated and mixed separately.  This sounds great with the two machines running together, but coming out of separate speakers.

Breeding pairs of Devil Fishes are rare, but if you can bring two together, the following "69" configuration is recommended. Have the two machines running as master and slave, via CV and Gate or by Sync. Have them playing similar or identical notes, with similar or identical settings and tuning. Take the audio out of the left one and feed it into the Filter FM input of the right.  Vice-versa from the right audio out to the left Filter FM in.  Listen to the two machines in stereo.  Turn both Devil Fish volumes down and start them playing.  Now slowly turn up the two volumes, and you will hear the increasing sound level and the similarly increasing levels of cross-pollination taking place, since the level of FM for one is dependent on the volume of the other . . . while the sound quality of the other is dependent on its interaction with the output of the first, which is getting louder and the product of the other's increasingly convoluted output . . .

Take a look at the dfspank.html file at this site.

Consider one of my definitions of techno: Machines cranking over – lovingly tended.
 

Version History

Version 1.0 and 1.1

[April 1993 to April 1994, serial numbers -001 to 016.]  There is no musical or functional difference between these versions. Version 1.1 used a more convenient value for the Accent and Normal Decay pots, which simplified the modification a little. In Version 1.0, I had to use different pots while I waited for the right ones to arrive from Japan. Some of these machines had the Sweep Speed switch retrofitted. All version 1.x machines had the Slide Time pot as a trimpot adjustable from the back – which meant it was hardly ever used. (Alternatively, if it was used a lot, it became hard to adjust because the little slot in the trimpot would become worn.) They did not have LEDs or the Filter Audio Output signal. They had a pitch shift problem with longer slide times. They had no Lithium battery. The front panel was laminated cardboard.

Version 2.0

[July to September 1996, serial numbers 017 to 022.] These were the first six printed circuit boards of the new design. The face-plate was of temporary cardboard. Apart from the correction of slide time pitch problems, and the addition of the Sweep Speed switch and the filter audio output, these sound identical to the previous versions, except for a problem with oscillation of the filter frequencies. In November 2003, four of these machines still need to have C14 replaced with a 22uF to correct this problem.

Version 2.1

[September to November 1996, serial numbers 023 to 028.]  This is a printed circuit update – removing a few problems in the 2.0 boards which had to corrected manually. 

Version 2.1A

[December 1996 to August 1998, serial numbers 029 to 051.] This is the same printed circuit as 2.1, but with some changes to components on the board and to the modifications on the TB-303 main board. These changes almost entirely eliminate clicking when the Decay pot is anti-clockwise and the Soft Attack pot is clockwise.

Version 2.1B

(February 1999) This is the same printed circuit as 2.1, but with further changes to achieve:


1. The reliable elimination of clicks when Decay is fully anti-clockwise and Soft Attack is fully clockwise.
2. The new, more sensitive, Filter CV input arrangement.  (Still linear, but with greatly increased sensitivity above 4.2 volts.)
   

In addition, I used a new label for the back panel of the Devil Fish.  A few details of the modifications were changed, such as replacing a resistor rather than adding one in parallel, but these changes do not alter the behaviour of the machine.

Version 2.1C

(30 May 1999) This is the same printed circuit as 2.1, but with further changes to achieve:
 
1. Filter CV in is now about 1 volt per octave (exponential response).  In 2.1A and earlier it was a linear arrangement – a certain number of Hertz per volt.  In 2.1B it was linear up to about 4.2 volts and then a more sensitive linear response above that.
2. Internal adjustment to ensure that the maximum resonant filter frequency (no Env Mod, Filter Tracking or external CV In) is 5 kHz – an octave above the standard frequency of the TB-303.  Previously component variations caused this frequency to vary somewhat from one Devil Fish to another.
3. The Filter Tracking circuit has been altered to give more tracking at lower settings of the pot.  The maximum tracking remains unaltered.
4. A small internal change to stabilise a voltage in the filter driver.

Starting with serial number 070 (19 November 1999) I added a resistor across TM6 to make it easier to adjust the 5.333 volt voltage correctly.  This has no effect whatsoever on the sound – it is just to make it easier to calibrate.  Sometimes the voltage cannot be calibrated properly with this resistor, so I remove it or replace it with a higher value.

Starting with serial number 081 (4 April 2000) I altered the battery supply arrangements for the 32 bank memory system to avoid potential problems when C-cell batteries are installed. See discussion above on known reliability problems.

Starting with serial number 084 (13 April 2000) I bent the fixed contact of the CV In sockets a little to increase the pressure the spring contact makes on it. See discussion above on known reliability problems.  

Version 2.1D - a new Slide In arrangement

(11 November 2003, starting with serial number 157)  This is the same as 2.1C, but with updates to the Slide In and Gate in circuit as described above and below.  This is to make it compatible with the forthcoming version 3.0. which is a new printed circuit design which embodies all these features which previously were modifications to the 2.1 circuit boards.  Therefore, version 2.1D is functionally identical to version 3.0.

The musical concept of a slide is for one note event (in terms of triggering envelopes) to begin at one pitch and to transition to another pitch with an audible slew between the two pitches.  In the TB-303 sequencer, this is achieved with two or more notes (that is a pitch with a timing value of one or more steps) where the first one or more notes has the Slide bit turned on.  The result is that what would otherwise be two note events, with two pitches, and two separate activations of the envelope generators, is turned into a single longer note event, starting at the start of the first note and ending at the end of the second. Thus, Slide in the TB-303 sequencer ties two notes together in time to become one, whilst turning on a "slide slew" circuit (IC11B following C35 driven by the 100K impedance of the DAC in the standard TB-303) which causes any pitch difference between the notes to be audibly slewed.  (Normally, without Slide, C35 is driven by the IC11B op-amp, which follows the DAC voltage directly.)

In MIDI there is no formal concept of a slide.  It is possible to use pitch-bend on a single note, but that does not relate to the musical notion of tying two note events into one over time, and it has technical problems including: the need to return at some stage to zero pitch-bend, the lack of reliable control of the amount of pitch bend the slave device implements and the typical inability to arrive at a precise final pitch.  Also, smooth slides of pitch are impossible with MIDI pitch-bend, since these are discrete commands.

Since musicians typically conceive of slide as something added to two or more pre-existing note events, rather than slide being a conversion of two or more static note events into one longer note event with a complex pitch variation over time, it is natural that a single control voltage be used to turn on Slide.  Prior to version 2.1D, the Devil Fish Slide In turned on the slew circuit, but did not affect the Gate of the synthesiser.  This provided maximum flexibility, since there are musically useful reasons for slewing the oscillator's control voltage with respect to the input CV (or the internal sequencer's DAC) without at the same time turning on the Gate.  However, in version 2.1D I implemented a system which can still work in this "isolated" way - turning on the slew circuit only - or which could also turn on the Gate.

The most usual concept of Slide is that when such an input is on, the synthesiser's Gate is also on, and that all changes to CV are slewed.  This is the "combined" slew and gate mode.

The Slide In voltage of version 2.1D has two thresholds:

1. +2.3 volts and above - turns on the slew circuit.  (As for all previous versions.)
   
   
2. +4.0 volts and above - turns on the Gate of the synthesiser, if it was not already turned on via the Gate In or the internal sequencer.
   

Therefore, for ordinary Slide operation, simply have your external MIDI to CV converter (or whatever you are using to control the Devil Fish) provide more than +4.0 volts.  5 volts to any other value, say as high as 30 volts, is fine. 

To turn on the slew circuit, without turning on the synthesiser's Gate, use a voltage such as 3.0 volts.  If you have only an on/off Gate signal and you want to provide 3.0 volts to the Slide In, then you will need to experiment with external resistors in series, or as a divider to create this voltage.

Also, with version 2.1D, I changed the Gate In threshold voltage from +1.5 volts to +3.5 volts.  This should not have any practical impact, since all MIDI to CV converters can be assumed to put out at least 5 volts for their Gate signal.  As before, there is no hard upper limit to the Gate In voltage - up to 30 volts is fine. 

Version 3.0

This is sonically identical to version 2.1D.  There are two changes:

1. The printed circuit board is a fresh design, integrating the changes listed above which were done as modifications to the 2.1 boards.
   
   
2. I pack the six small TB-303 knobs (Tuning to Accent) with a small insert, which together with the "Blu-Tack" which helps stop the knob from coming adrift, causes the knobs to be about 1.5mm higher.  This makes them easier to turn.
   

Version 3.0B

Version 3.0C

Three Devil Fishes were made with this version number, but others may be upgraded to it in the future.  These are 3.0 boards, but with the 4.0A,  4.0B and 4.0C upgrades as described below.  So this is like 3.0B but with longer C-cell battery life.

Version 4.0

This is functionally identical to Version 3.0 and therefore 2.1D.  The printed circuit boards have provision for the MIDI In system, which is described separately here: midi/ .

Version 4.0A

Apart from a minor matter of LED brightnesses, this is functionally identical to Version 4.0 and therefore 2.1D.  A diode has been added to cope with TL072 op-amps which can't output below their specified limit of 1.5 volts above their negative supply.  I was expecting them to go below this when driving the Normal and Accent Decay LEDs and this caused a slight continual glow on one of these LEDs at all times.  Serial numbers 168 and after (except perhaps where I use a 3.0 board for customers who don't need MIDI In) are version 4.0A.  The problem only affected the LED - not the sound - and may  be present on the three 4.0 machines.  

Version 4.0B

Apart from a minor matter of LED brightnesses, this is functionally identical to Version 4.0A and therefore 2.1D.  I changed the design slightly so that the Normal and Accent Decay LEDs are brighter when the times for these Decays are very short..  

Version 4.0C

This is sonically identical to version 2.1D. Please see the discussion above on operation from C-cell batteries. Beginning in August 2005, I added three changes which have the effect of increasing the battery life when running from C-cells.  These do not reduce the current consumption, but they reduce the voltage drop between the four C-cell batteries and the CPU, enabling the machine to run from a lower total 4 x C-cell voltage.  The standard TB-303 draws about 85 mA, or more depending on the number of LEDs illuminated, whether the headphone amplifier is on, and what signal it is driving into the headphone load.  The Devil Fish draws more current, depending on the three new LEDs it may be turning on - Gate and either the Normal or Accent Decay LED.  It may draw more current due to the headphone amplifier being on (if a lead is plugged into the old headphone socket) and the MIDI In system draws a little extra current too.  The new Blue and other colour LEDs do not draw more current.  The new Red LEDs draw the same current as the original LEDs and the other colours, especially the Blue, draw less current because the junction voltage of the LEDs gets higher with shorter-wavelength light.  The 32 Bank Memory system does not draw any extra current.

Peak currents for the Devil Fish may be 150mA or so.  This reduces the battery voltage more than the usual TB-303 currents, and induces greater than usual voltage drops in some of the internal power supply circuitry.  The three 4.0C modifications reduce these voltage drops between the battery (or the external power supply, after the internal 6 volt regulator) and various of the machine.  The first two reduce voltage drops to all sections of the machine's power supply - for the CPU and the switching supply which provides +15 volts.  The third one only reduces voltage drop to the CPU.  The aim of all these is to enable the CPU to operate with battery voltages which are lower than those which would otherwise be necessary.

1. A 1k resistor is wired across R169 (1.5k).  This more than doubles the base current to Q44, which - in one machine at least - reduced the voltage drop between Q44's emitter and collector from 112mV to 76mV.  (Actual voltages would depend on the particular Q44, on the temperature and on the current being drawn.)  This actually adds about 1mA to the total current drawn, but it saves around 36mV (or more at higher load currents) and so enables the machine to work from lower voltage batteries.
   
   
2. Short out R168 (2.7 ohms).  This is a special resistor, intended as a fuse.  It would only operate if there was a drastic problem with the internal circuitry, such as a dead-short failure of Q44, or perhaps a dead-short failure after R168 - but I doubt if a normally driven Q44 could pass enough current to blow this fuse.  In the 250 or 300 or so TB-303s and TR-606s I have worked on, I have never seen such a fault and I have never seen one of these "fuses" blow.  I have on two or more occasions found machines where this device has a higher than normal resistance - and so needed to be replaced.  Shorting out a protection fuse is not generally recommended, but since this is battery operated equipment, and since the fuse sometimes causes trouble (by developing a higher resistance) and has never been observed to prevent trouble, I say we are better off without it.  The benefit is that we no longer have a 368mV (in one machine) voltage drop.  This change significantly lowers the voltage the C-cells can go to before the machine will no longer operate.
   
   
3. A 1 amp silicon diode 1N4004 is wired across the lower current D2.  This reduces the voltage drop to the CPU from about 612mV to 545mV - a drop of 67mV.  The silicon junction voltage drop is intentional in the design, since (apart from the drops in Q44 and R168 above), D2 is the only mechanism for providing the CPU with its proper voltage.  Since four fresh alkaline batteries can provide as much as 6.4 volts no load - hopefully less under load - there needs to be a way of dropping the voltage down to the 4.5 to 5.5 volt range.  Chips such as the CPU typically have an absolute maximum rating of 6.0 volts, so there should be no danger to the CPU in reducing these voltage drops inside the machine. 
   

Altogether, these changes should enable the Devil Fish to function reliably with lower battery voltages.  However, the behaviour of particular CPU chips will vary, so it is not possible to specify exactly what voltages a Devil Fish will work reliably from.

Version 4.1

This is sonically and functionally (LED brightness etc.) identical to version 4.0C and therefore sonically identical to 2.1D.  This is a printed circuit board revision which does not change the functionality.

Updates sorted by date

• 31 August 2007  Revised Boss adaptor details to mention PSA-120. Fixed a formatting problem.
• 25 August 2006  Added note about restricted active rotational range of replacement Resonance pots.
  
• 22 November 2005  Added notes about Version 4.1.
  
• 26 August 2005 Added notes about Version 4.0C and 3.0C.  Added C-cell battery section and extra information on battery voltages and Run/Stop LED as a power supply voltage indicator.
  
• 15 August 2005  Added notes about Version 3.0B.
• 4 April 2005  Layout changes.
  
• 10 February 2005   Added notes about Version 4.0B.  Added a section on power adaptors.
  
• 18 January 2005   Added notes about Version 4.0A.
  
• 9 December 2004  Added notes on Version 4.0 and corrected erroneous resting voltage for Filter Frequency, which is 3.3 volts but was previously stated to be 2.3 volts.
  
• 12 February 2004  Added the Version 3.0 notes.
  
• 11 November 2003  Added section on Slide In for version 2.1D.  Split the Slide section into Slew and Threshold sections. Added schematic of diodes for pre 2.1C Slide In activation of Gate.  Mentioned replacement pots in normal and long-shaft lengths.  Minor improvements to the text, such as a description of "random" patterns of data in memory chips which are "cleared".
  
• 12 April 2000  Added to the "Known reliability problems":
• Discussion of the CV input socket problem.
• An update on the 32 bank memory system C-cell battery problem.
• 9 March 2000  Added a section on "Known reliability problems".
• 4 June 1999  Minor corrections.
• 1 June 1999  Reformatted and updated to release.html at the new web site, to reflect version 2.1C.
• 5 February 1999  Updated to dfrel21b.htm to reflect the "B" changes of version 2.1B.
• 22 September 1997 Updated to dfrel21a.htm to reflect the "A" changes of 2.1A and the concerns about long term exposure to the Devil Fish.
• 4 October 1996 Updated to reflect the availability of patch sheets.
• 3 October 1996 Updated to reflect the fact that the face-plates are ready.
• 13 September 1996 dfrel21.htm file created.