for the TR-808
Sound mods, 4 Level Accent mods and 32 Banks of Memory.
Whittle, Real World Interfaces
Daylesford Victoria Australia
firstname.lastname@example.org 20 October 2015
prices-au/ Prices for Australian customers.
prices-int/ Prices for customers outside Australia.
To the Real
World Interfaces page, including links to TB-303 and TR-606 modifications.
to the main
ABN 29 836 876
samples. MP3, WAVs and via SoundCloud.
For technicians: notes on repairing or replacing TR-808 switches and pots, especially the Start / Stop and Tap switches: TR-808-switches/ .
I have been modifying TR-808s since the early 1980s. In September
2012 I made these modifications available again, with some
improvements. Please see sounds/ for some demo sound recordings.
I was planning a MIDI In and Out system, but am no longer working on
this. I can however install a system to receive MIDI and generate
Roland/DIN Sync. This receives MIDI In via the Sync socket, drives the
TR-808's internal sequencer, and can drive up to three external
devices, such as TB-303s, TR-606s or another TR-808 via the Sync Lead:
Sound Mods, 4 Level Accent Mods and 32 Banks or Memory
The 32 Bank Memory System is identical in principle to that for the Devil Fish:
There are 5 toggle switches, moving side-to-side, and a pushbutton
switch. These are located on the front left side panel.
This provides 32 complete sets of the TR-808's original memory.
The main purpose is not so much to provide more pattern and track
memory, but to allow the switching of memory banks while the machine is
playing patterns. The CPU reads from memory for each beat, so
this enables switching to another pattern in the middle of a pattern
rather than waiting for the current pattern to end. This means
fresh notes can be dropped in with the flick of one or more
The 32 banks are selected by the 32 combinations of the 5
toggle-switches. The pushbutton reverses the bit produced by the
This memory system is now available with a two or four channel Dynamic Bank Switching (DBS) system, which is not shown in these photos. This enables externally applied audio or CV signals, via
3.5mm sockets on the left side of the machine, to alter which of the 32
memory banks is selected. This means that the internal sequencer
will play different patterns and one or more individual beats from
different patterns in response to these signals.
Please see the Devil Fish 32 Bank Memory system with DBS manual, which also covers DBS for the TR-606 and TR-808: http://www.firstpr.com.au/rwi/dfish/DF-32-Bank-Mem-DBS-Manual.pdf
The 32 Bank Memory System is available with two or four channels
of Dynamic Channel Switching: either two or four 3.5mm Audio/CV input
sockets (each with a detector circuit and LED, with a threshold of
about +1.15 volts) which, when activated, inverts the address bit
produced by two or four of the four toggle-switches which supply four of
the five address bits to the 32 Bank system. It is possible to
add to this a centre-off Enable switch for these inputs and so their
address inversion functions. Left and Right positions enable the
inputs, with Centre disabling them. The Right position is
momentary: it is spring return to centre.
(In the 1980s I installed 11 and 21 bank memory systems, with bank
selection via a thumb-wheel switch or pushbuttons and a 7-segment LED
display. Information about these mods is at the end of this page.)
The TR-808's drum circuits are triggered by pulses which start at 0
volts, rise to a certain voltage for 1 millisecond, and then fall to 0
The 4 Level Accent Mods enable normal operation of the Accent system (a 5 volt trigger pulse on
non-accented notes with a 5 to 14 volt trigger pulse for accented
notes) and a new mode of operation. In the new mode, the trigger
voltage for triggering all the activated drum sounds on the current
beat comes from one of four pots. One of these will be selected
on each beat depending on whether the Accent and the Cowbell is
programmed. Each such selection is
signaled by a flash of the LED below the knob.
|ACC & CB
playing a pattern, one of these LEDs flashes for every 1/16th note, and
setting of the corresponding pot determines the trigger voltage for all
drums which are programmed on that beat. The range is between
about 2 volts (fully anti-clockwise, about 8 o'clock) and 14 volts
(fully clockwise, about 4 o'clock). The ~2 volt level is adjusted
just triggers the drum sounds. (This mod also changes some
internal circuitry to make the Cymbal and HiHat circuits have the same
threshold of about 2 volts. Normally, they require about 4.5
volts before they will make a sound.)
While the internal sequencer is playing a pattern (or being switched
between patterns with the 32 Bank Memory System), the dynamics of the
pattern can be completely altered by turning the four knobs.
selects between normal and 4 Level Accent mode. The blue and
yellow pushbuttons over-ride the Instrument Select switch so the
buttons and LEDs work with the Accent and Cowbell respectively, rather
than whatever drum channel the Instrument Select switch selects.
it easier to program the desired Accent-Cowbell combination on any of
the 16 beats.
These 4 Level Accent mods are identical to what I installed in the
early 1980s, except that I am now using slightly smaller knobs with
metal-shaft pots. The earlier pots were not as robust as I
The User Manual contains the same text as above: TR-808-Four-Level-Accent-Mods.pdf
Please see sounds/ for some sound recordings in which I demonstrate the operation of the Sound Mods and the Four Level Accent system.
The Sound Modifications
are an extension of what I first installed in the early 1980s, with new
pots and knobs, three small pots for the Tom/Conga Decay function
(instead of toggle switches and trimpots) and three additional functions
marked * below. The User Manual TR-808-Sound-Mods.pdf contains the following description of features:
- * The Bass Drum decay range
is extended to include self-oscillation, so any decay time from the
normal minimum to infinity can be achieved with the Decay knob.
- * The Bass Drum Tuning knob enables higher and lower tuning. (Top white knob.)
- The Snare sound is changed in a number of respects:
- Sharper attack for the Snappy noise pulse.
- Reduced cutoff frequency in the Snappy noise pulse high pass filter, to make it gutsier in the lower mid-range.
- The two tonal components of the sound are boosted in level.
Snare sound is composed of the Snappy noise pulse and the ringing
of two "Bridged T-Network" (as the Roland service manual describes
them) resonators, with the Tone pot controlling the mix of the outputs
of the two resonators. There are two Snare Tuning pots,
one for the upper resonator (blue knob) and one for the lower (yellow knob). Tuning
is at the normal pitch when these pots are anticlockwise (ACW) and is
reduced by around an octave when they are clockwise (CW).
- The Cymbal Soft Attack switch (above the three small pots) gives more of a ride cymbal sound, compared to the normal crash sound. The attack is soft and the decay is somewhat extended.
- The Toms have a pulse of filtered noise, which is barely
perceptible, but gives them something of a rumbling sound. These
pulses are shortened somewhat. (In Conga mode, there is no such
- The Tom/Conga circuits each have a Decay
pot, where ACW is the normal decay time and CW is a much shorter decay
time. These are the three small pots with silver indicator lines.
- The Hand Clap sound is composed of a series of close-spaced
pulses of filtered and distorted noise plus a softer pseudo-reverb
exponential decay pulse of softly filtered noise. The Clap Reverb Disable
switch (below the three small pots) turns off this pulse, leaving the
dry, stark, and potentially extremely loud main pulse-cluster of the
- The Hand Clap Density pot
(red knob) controls the density of this cluster of pulses, from being very light
(ACW) through normal, to each pulse being bigger, to all pulses being
much louder and joined together (CW).
- The Noise Level pot (white knob) controls the
output level of the internal White Noise Generator. ACW creates a
somewhat lower than normal level of noise. 12 o-clock creates a
somewhat higher level. 3 o-clock creates a much higher
level. Fully CW produces an extreme level of noise such that the
Tom "rumble" circuits are occasionally overloaded, even when not being
triggered, so there will be sporadic crackles through each of whichever
of the Tom/Conga channels are in Tom mode.
The internal White Noise Generator runs from a noisy transistor and is genuinely random broadband noise. It is used for:
- The Snappy pulse of the Snare Drum. Increased noise levels make this a very strong pulse indeed.
- The Rumble pulse of the Toms. High noise levels lead to
more rumble to the point of completely unphysical rumbles and muffled
- The Maracas sound is based on this signal, but it is hardly affected by the noise level.
- The Hand Clap sound, both the pulse-cluster and the
pseudo-reverb, is based on this noise source. Higher noise levels
lead to gutsier and potentially very loud hand-clap sounds. It is
generally best to disable the Hand Clap Reverb when high noise levels
are used. The resulting clap sounds, especially with the Density
control turned somewhat to the ACW and with the Noise Level pot set to
about 2 o'clock, are a unique and gusty discrete sound. Since
these are generated from real analogue noise, no two Hand Clap sounds
are the same.
- * The Accent Button
forces Accent on even if the internal sequencer's pattern has no Accent
on the current beat. This Accent state also drives the 4 Level
In mid-2014 I introduced an optional Accent Input socket.
This 3.5mm input socket, mounted on the right of the machine, enables
external audio or CV input signals to turn on the Accent, if it was not
already turned on by the Internal Sequencer or the Accent Button.
The detector circuit and accompanying LED, next to the socket, uses a
+1.1 volt detector circuit similar to that of the Dynamic Bank
Switching system mentioned above.
are three audio signal inputs. (6.5mm mono sockets on right
side.) When an audio signal is plugged into one of these, that
signal takes over the
role of an internal noise signal. These are not to trigger drum
sounds - they are signals from which drum sounds are made.
- Cymbal / Hi Hat Alternative Noise Input.
Normally the Cymbal and Hi Hat sounds are created from a mix of 6
square-wave oscillators. This signals is filtered, distorted in a
gating circuit (which controls the volume) and filtered
again. By plugging an audio signal into this socket, the 6
square-wave oscillators are no longer used and the Cymbal and Hi Hat
sounds are made from the input signal instead. Bright, high,
chord sounds are an obvious choice of signal - they cause the Cymbal
and Hi Hat sounds to be metallic shimmering (low level) or mashed and
splattered chord-related sounds. Playing a single pitch into this
signal results in single-pitch high-pass filtered square-wave Cymbal and Hi Hat
Miking up a continual cymbal sound (such as from a large
cymbal hammered softly with a mallet) and feeding this signal into this input results in realistic sounding
Cymbal and Hi Hat sounds, depending on the level. (I did this in
the 1980s. If someone can send me a suitable long, constant
level, recording of a ride cymbal being hammered reasonably gently, I
will use it in this way in another sound demo.)
The Cymbal and Hi Hat circuitry is beautiful, inspired and unique to the TR-808 and TR-606. This Alternative Input enables
the creation of many bright, delicate and potentially wild
sounds. It is my favourite part of the TR-808.
Each TR-808 has a unique tonality to its Cymbal and Hi Hat sounds, due
to each machine's six square wave oscillators having a unique set of
frequencies. As demonstrated in one of the sound recordings sounds/
it is possible to use this socket as an output for this mix of six
square waves - by inserting a plug gently until it touches the tip
contact of the switch, but not hard enough to lift the tip contact from the
normally closed contact. Then, it is possible to record a few
minutes or whatever of this mix of square waves. This can be
played back into a second TR-808 via this Input, and the second
machine will have the tonality of the first machine, assuming the
playback level is adjusted to match the required signal level. Of
course, this recorded signal could be subject to manipulation by
changing its playback pitch, but distorting it, by adding reverb,
random vibrato or whatever via audio editing software, so the original
tonality could be used in the same machine, with various modifications.
- Hand Clap and Maracas Alternative Noise Input.
Whatever signal is input here replaces the internal white noise
generator in the Hand Clap and Maracas circuits. Random mid-range
to high frequency noise, chords, distorted and/or reverberated chords
or various other signals result in staccato Hand Clap sounds which
are unique to the Modified TR-808 and would never result from
conventional synthesis techniques. These can be musically dramatic - please check out the recordings in the sounds/ directory.
This socket (and the next) can be used as an output for the internal
noise source, with the same technique as described above for the CY/HH
Alternative Noise Input. It is (in audio terms) "white" noise -
real noise from a reverse-biased transistor junction going into
avalanche breakdown. There are many other sources of noise in the
modern world, but this is a source and it might be handy. The
volume and to some extent the character of the noise will vary with the
setting of the Noise Level pot. There's no significant difference
in the audible quality of the noise between one TR-808 and another,
other than the effects of TM4 inside the machine (for a standard
TR-808) or the Noise Level pot (on a modified TR-808) which affects the
white noise level sent to the Snare, Toms and the Hand Clap / Maracas
- Snare Drum Alternative Noise Input. This signal replaces the internal white noise generator for the Snare Snappy noise pulse circuit.
Switch replacement and various repairs
TR-808s are now about 32+ years old. They typically require some cleaning and fixing as part of doing any modifications.
TR-808s use ALPS tact switches which are open to dust. I replace them with sealed Omron tact switches
which have a similar feel. Since these are sealed against dust
and liquids I expect they will last a very long time, such as decades,
rather than the few years it typically takes for the unsealed
ALPS switches to become erratic.
I fix Volume pot noise problems by
dismantling it and cleaning it with isopropyl alcohol. The 22
small pots (without knobs) sometimes become noisy. I clean them
in-situ with isopropyl alcohol and compressed air. Likewise the prescale switch and the toggle-switches and the Tempo
The output sockets, rotary switches and the small red pushbutton switch
have not, in my experience, given any trouble. The key-switches for Run/Stop and Tap
are prone to failure. I have a fairly involved method of repairing them, but
ideally there would be replacements for these which were less prone to
failure. I have used a set of replacement switches with matching 3D printed buttons from Social Entropy.com,
with great success. These kits are not yet officially available
but I have some here. I am developing self-adhesive laminated
replacement orange labels for the START / STOP and TAP buttons to
replace those which may have been lost, including if the top plastic
cover is missing.
There is a fault in all TR-808s which corrupts the first pattern and the first track.
It is caused by capacitive coupling of turn-off inductive transients
from the power transformer into the write-enable signal for the memory
system. I fix this with a simple low pass filter at the memory
and by tying the line inactive-high when the Mode Selector is in the
1st Part or 2nd Part positions. (Technicians: the details of this
mod are described in the TR-808-Memory-Backup.pdf file linked to below.)
Some TR-808s have corrosion on their
right-hand circuit-board (Cowbell, Cymbal and Hi Hat). This
appears to arise from contamination in the factory, and can develop
over decades into potentially severe corrosion of parts of the circuit
board and its components. This is not disastrous, but a bad case
can take several hours to fix.
I can install back-to-back high-current diodes in the ground lead so
that there is a 0.5 volt float between the ground pin of the mains
cable (assuming it is a three pin power plug) and the chassis and
ground of the TR-808. This will eliminate various ground noise problems which might otherwise be caused in some circumstances.
Some people in 220-240 volt countries such as Australia (230 volts) have a TR-808
which was built for the Japanese market (2 pin power cord and 100 volt
power transformer) of for the North American market, with a 115 volt
power transformer. I can install a toroidal power transformer and
make some changes to the internal power supply so that the machine runs
on 230 or 240 volts. If anyone from a
100V to 120V country has a 220V to 240V TR-808, I may be able to
transplant a power transformer or install a new toroidal power
transformer to make it operate from the lower mains voltage.
New Battery Arrangements for Retaining Memory Data
modifications will not apply to TR-808s with the forthcoming Quicksilver 808 system
installed, since that has its own internal non-volatile memory.
The TR-808's memory chips will be removed, and there will be no need for battery
power to retain the contents of the Quicksilver 808's memory.)
This is a separate set of modifications for the TR-808, whether or
the machine has a 32 Bank Memory system installed. (With the
TB-303, the new memory backup battery arrangements are part of the
mods.) The purpose is to provide a more robust and convenient
backup power system for the memory
system than is possible with the original arrangements, which involve
three AA batteries in the battery compartment in the bottom panel.
Prior to May 2015, I offered an optional memory powering system involving a
permanently installed (soldered connections) large capacity,
"1/2 AA" cylindrical lithium battery. In 2015, due to restrictions on
air-freight carriage of items including lithium batteries, I developed
customers outside Australia, we normally ship the modified machine
without the lithium battery in the internal battery holder, using
Australia Post's Express Courier International (EMS) service. The
customer can install their own 1/2AA cylindrical cell. We can also ship the
modified machine overseas with its lithium battery installed, with
For the full details of the original arrangement (option A, a permanently
installed lithium battery) and the two new Options B (for air-freight
shipping to overseas customers) and C (for road freight shipping to
customers in Australia, or via FedEx to customers overseas) please see the PDF manual: TR-808-Memory-Backup.pdf .
For both Options B and C, the three AA cells (it is best to install
only alkaline cells) can still be used to provide backup power to
the memory system. A large capacitor
enables the machine to retain memory contents for a longer period than
usual without these three AA batteries and without the machine being
run from an
external power supply. There is an internal holder for a
cylindrical "1/2 AA" lithium battery, which can be accessed by
removing the right part of the case. This is the same type of
battery we have been using in Devil Fishes, TR-808s and TR-606s since
1996, except that it is the version without leads, so it clips
directly into a suitable battery holder.
Overseas customers can
install a 1/2 AA lithium battery in this holder, after which there is no need for AA alkaline
batteries. The lithium battery should last for ten or more years.
modification includes a recessed switch and two LEDs which test the
charge and connectivity of both the three AA alkaline batteries (if any
are installed) and the 1/2 AA lithium battery (if this is
This modification is not essential, since the three AA alkaline battery
arrangements are generally reliable, provided fresh alkaline batteries
are installed every few years, and there is no corrosion or other
problems with the battery holder for these. It is a desirable
modification for anyone who wants a reliable memory, since the AA cells
and their six battery holder contacts are less than 100%
reliable. (If you use AA cells, be sure to insert adequate
packing between them and the battery compartment door, since the light
foam there - if it still exists - is typically too soft, to hold the
batteries in their holder.)
purpose of the modification is to provide an easy way of testing the
voltage and connectivity of the three AA batteries, if any are
installed, and the internal lithium battery, if one is installed - and to enable overseas customers to install their own
lithium battery, while avoiding the problem of air-freighting the
machine with a lithium battery installed. For overseas customers
we will ship the machine with three fresh AA batteries installed.
For Australian customers, we will ship the machine with a lithium
battery installed, but we do not install new AA alkaline batteries,
since these are not needed once the lithium battery is installed.
time is likely to be a month or more. We have some good boxes to
pack the TR-808 in for the return trip to customers.
I have not included a price for installing new LEDs - the A, B, 1st
Part and 2nd Part LEDs and the 16 LEDs in the Step buttons. I can
do it, but it is inordinately difficult to install new LEDs in the Step
buttons, even when I am removing the buttons to replace the tact
switches. The original Red LEDs are fine and I recommend leaving
them as they are.
Documentation for older modifications
about 1982 onwards, I worked on a few dozen TR-808s, which can now
sometimes be found for sale on eBay. All these were for
Australian customers, but some may now be in other countries. The
- Extra memory banks with two types of control system:
- The first ones had 10 or 20 extra banks and had a thumb-wheel
switch to select the banks with 0 to 4 or 0 to 9. There were 5 or
10 new banks accessible when a three position toggleswitch was in the
left position, the original bank of memory is accessible with the
middle position and 5 or 10 new banks of memory are accessible via the
right position. Changing the memory bank, by number or the
left-mid-right switch would normally reset the CPU, so the sequencer
firmware didn't get confused about pattern lengths and in track
mode. This was for people playing large numbers of songs, not
primarily for live switching between patterns in different banks.
However, the CPU reset could be disabled so the user could switch
between memory banks while the patterns were playing. There was
also a write-protect switch. (On one or more machines I may have
done the CPU reset with a pushbutton, so changing bank would not reset
the CPU at all.)
- The second and more common type had the same arrangement of
memory banks, but I replaced the thumb-wheel switch with two
push-buttons and a 7 segment LED display. See documentation below.
Please see this file for documentation of the 1980s versions of the Sound Controls, 4 Level
Accent system and the 7 segment LED-based 11 or 21 bank memory system:
I used to install a MIDI In system, with full velocity control of each drum
channel, an extra 0 to 12 volt velocity sensitive trigger output and
Sync reception. Documentation is in:
- Sound controls. As described above except for the items
with an asterisk and with different arrangements for the Alternative
- Four level Accent system, as described above.