Modifications for the TR-808

I have been modifying TR-808s since the early 1980s.  I have not mentioned this on the website, primarily because I thought that shipping TR-808s to and from Australia is too much trouble.  However, maybe it's worth it – since it is such an excellent, musical, unique, drum machine.

I used to do 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.  I have run out of PCBs for this, and would have to go to some trouble to make more, but it's not out of the question.  (I do not provide any of these modifications as kits.)

The main modifications which I did, which can be found on TR-808s for sale on eBay, mainly in Australia, are:

• Extra memory banks, similar in concept to what I do with the TB-303 / Devil Fish, but with different control systems:

• 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.
  

• Sound controls.  A bunch of knobs, switches and inputs on the right of the machine.  See documentation below.
  
  
• Four level Accent system, also documented below.  This was four knobs, four LEDs, a toggleswitch and two pushbuttons on the left of the machine.  When enabled, this produced an internal trigger voltage for the drum sounds on that beat of between about 3V and the usual maximum of about 14V.  The trigger voltage is normally 5 volts on non-accented notes, with the value being 5 to 14 volts on accented notes, depending on the setting of the Accent knob.
  
  The four states each had their own knob, and a LED which flashed when each one was used.  The states were: 0 (the bottom knob and LED) = no Accent, no Cowbell;   1 = no Accent, Cowbell ON; 2 =  Accent ON, no Cowbell; 3 Accent ON, Cowbell ON.  This was a unique and lively system by which the one pattern could be smoothly and utterly transformed by turning the knobs, bringing up one or more beats independently of the others.
  
  

Please see this file for documentation of the Sound Controls, 4 Level Accent system an the 7 segment LED-based 11 or 21 bank memory system:



Documentation for the full MIDI In system is:

In late 2010 I am modifying a machine to have new Omron sealed tact switches, similar to those I am using in the Devil Fish, with Blue LEDs and a new Red LED for Run/Stop.  It is difficult to get these switches and LEDs to fit correctly with the special coloured plastic buttons and actuators which are used in the TR-808.  So the pricing is significantly higher than for the Devil Fish.  Please see Technology Transplant for replacement coloured buttons and actuators.

I am also installing the Sound Controls and the 4 Level Accent system.

I am installing a lithium battery in the original battery compartment, but soldered to the two wires which normally go to the contacts there.  This will be highly reliable.

I am installing a version of the 32 bank memory system similar in principle to that I do for the TB-303 and TR-606:  Devil-Fish-32-Bank-Mem-Manual.pdf  There will be 5 toggle switches, moving side-to-side, and a pushbutton switch.  These will be located on the right of the machine, just to the right of the Tap switch.

I am also installing a MIDI In system purely for Sync.  This will receive MIDI via the Sync socket and drive the Sync socket's pins, as with the Devil Fish MIDI In system.  There will be a small toggleswitch near the Sync socket to enable and disable it.  When the TR-808's Sync slider is set to Input, the machine will start, stop and run in time with MIDI Sync.  It will be possible to use the Sync Lead with this to receive MIDI In while driving Sync out to three other devices.