Saturday, October 24, 2015

SR-88 Mods

The Sound Master SR-88 is a royal pain to sequence with. Mostly because it only has clock (and trig) out in a nonstandard PPQN(pulse per quarter note).

There are a few solutions:

  1. Make it generate a more normal 24PPQN. I like the idea of reworking its clock, speeding it up and dividing down internally. Maybe generate start/stop signals from the buttons then have a full DIN sync.
  2. Add a clock/sync in. Slave it to something that makes a better master clock and/or is MIDI compatible.
  3. Add trigger ins. The problem with both of the other approaches is that you still have to use its internal, very limited and fiddly sequencer. This avoids the clock and sequencer entirely. Trigger ins cure all ails.
Triggers it is. This is a pretty simple mod: just disconnect the TC5501 RAM from the sound generator and connect your triggers. This has already been documented here, but I found the images unclear. Since I'm performing the same mod, I used the opportunity to take my own pictures.

First cut out the TC5501 that generates the triggers. Just sever its data lines: pins 10, 12, 14, 16.


Then solder wires for the new jacks. Red wires are the original trigger outputs. White wires are the trigger inputs.


Attach switched jacks such that the original triggers are used in the absence of external triggers. Ground to the ring, red to the switch, white to the tip.
Mount the jacks and you're all done. I used the battery area since it had lots of room. Also shown is an added LM7805 regulator that allows the SR-88 to use a standard 9v power supply.


9 comments:

  1. Stupid question, but how do you then trigger it ? by connecting what?

    ReplyDelete
    Replies
    1. Personally, I use an Artura Beatstep Pro. It's nice because you adjust the trigger lengths, but there are lots of other options.

      Delete
  2. Do you have any schematics or service manual for the EDC sr-99?

    ReplyDelete
    Replies
    1. I don't, sadly. It's probably very similar to this and the other DR-55 work-alikes.
      Are you trying to troubleshoot a problem, or just curious about the design?

      Delete
  3. Hi, so I just finished this mod and everything is working as expected except the BD seems to trigger on note on and again on note off. Is this normal?

    ReplyDelete
    Replies
    1. Hello,

      Yes, that's normal if you have very long triggers. You can use something like a 555 to generate a short, consistent trigger from your longer one. Let me know if you need more info.

      Thanks,
      Zack

      Delete
  4. Thanks for the info, I found a temporary solution in Silent Way. In envelope mode it eliminates the second trigger when using a mid-length decay setting to the trigger. You should also add a warning to this page only to plug in gate connections while the sr-88 is off... I fried my 4011 while playing around with the connections ;)

    ReplyDelete
    Replies
    1. Ok. I haven't run into that, and I'm not sure how that took out the 4011. I could see there being issues with the SRAM, since your trigger could short to its output while inserting.
      It's probably best to add a low value resistor on either side of the jack.

      Delete