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Yamaha PS-30 : Solo Section Filter and De-tune Mods

Behind the Yamaha PS-30's "Solo" section, there's a simple monophonic analogue synth. Here's how I brought the filter and tuning controls to the front panel...Quite simple, it's involves removing 3 trimmer pots from the PCB and replacing them with regular potentiometers mounted on the front panel.
First, however, much gratitude goes to the excellent Table Hooters site for the detailed information on this keyboard's inner workings:
http://weltenschule.de/TableHooters/Yamaha_PS-30_PS-20.html
     (click images to enlarge)
My Yamaha PS-30 - the green, blue and red knobs (top right) control de-tune, cut-off frequency and resonance respectively


You can already access the solo section's tuning control via a removable plug on the back of the case:


Removing this plug allows access to a trimmer pot on the PCB. I replaced this with a regular pot mounted on the front panel.

Back of case removed...


The solo section PCB is the shaded area on the right - close up below



Two screws hold the PCB in place. With these removed, it can be lifted out but a little care is needed to release the switches from their front panel tabs. In addition, the solo section's volume control is on a separate PCB connected by a short wiring strip, and this also needs to be removed from the case along with the main PCB.


This is the solo section PCB - in fact it is two boards held at a right angle by metal brackets.
Everything is nicely labelled on the PCBs - here's a close up of the oscillator's master tuning coil.


Unfortunately, I'd already performed the mod by the time I took these pictures, so I can't show the original trimmer pots in place, but here you can see where they used to be and the wires I patched in for the replacement pots.


For the resonance (Q) I used shielded cable as it's highly prone to interference - hence the thick black cable - I soldered the shield to ground at the leg of the nearest capacitor.

Holes drilled...

Pots mounted...

Knobs added.

This is a fairly simple mod. There are probably other adjustments that could be made and ways to improve the results. The filter can add a bit of spice to the overall sound ranging from 'funky quacking' to 'howling' when self-oscillating. One obvious improvement would be adding control voltage capabilities but the PS-30 PCBs operate on negative voltages (-9v) and I'm not sure how to work around this...using vactrols might be a workaround? In addition, the detune control has a fairly limited range - something like a quarter tone across the entire sweep. The oscillator tuning is set by a coil and the potentiometer only allows fine adjustment. Perhaps there is a way to modify the circuit to allow a greater range? As it is, I set it so that it is in tune when fully clockwise from where it can be subtly de-tuned - so no thirds and fifths sadly.

How does it sound? A video will follow shortly...hopefully

EDIT: Here's a sample of sounds



Questions, comments, suggestions....please share.


Comments

  1. Patrick Bartmess11 April 2019 at 21:28

    Great modification! Thank you for the detailed process notes.

    ReplyDelete
  2. Simon20 July 2020 at 10:26

    What value are the pots? Looking at the schematic it might also be possible to modify the different oscillator footages used to create the polyphonic presets. My understanding is that there’s limited filtering in this section, but being an analog keyboard plenty of potential.

    ReplyDelete
    Replies
    1. Lord of the Hertz20 July 2020 at 20:14

      Hi,
      I'm afraid I don't recall the exact values except that they are identical to the trimmer pots I removed. I seem to remember 10K and 20K values but I'd have to open it up to confirm - I could do that if you wish.
      Unfortunately, I only have the service manual/schematics for the PS-20 which omits the solo section but there are no doubt plenty further modifications doable. If you discover anything, please share.

      Delete
    2. grillmaus18 September 2023 at 07:53

      Hi. I just opened my PS30b only to discover that there's only two pots on the pcb. The Q resonance pot is missing. It's just a resistor there, right from the factory. Pot is marked on the pcb, though.

      Did you really replaced a pot there?

      Cheers

      Delete
    3. Lord of the Hertz19 September 2023 at 03:24

      Hi, thanks for checking it out. Yes, there was a trimmer pot on the PCB for the resonance in my PS30 - it sounds like you don't believe me!
      Perhaps, yours is a later build and Yamaha decided a fixed resistor was sufficient for the task? What value is it, I wonder?
      Anyway, since making this mod, I've found the service manual online which may be helpful or interesting, if you haven't already got a copy:
      https://www.vintagesynthparts.com/wp-content/uploads/2018/01/Yamaha-PS-30-Service-Manual.pdf
      I'm really pleased with the filter mod. However, the detune option is a little tame. It can thicken the sounds a little but I'd prefer it if the range were wider.
      I'm assuming you have 'dark' model which seems very rare - I've only seen a few photos online and can't tell if it's black or a very dark brown, like the PS3.
      Cheers!

      Delete
    4. grillmaus19 September 2023 at 13:33

      Thanks for your answer :)
      I did not daubt your mod description, but since you took the pictures after the modification i was just wondering...

      I think i'll skip the tuning knob. The keyboard color is indeed a dark brown, wood-like finish.

      :)

      Delete
    5. Lord of the Hertz25 September 2023 at 21:57

      Yeah, I should have taken photos before removing the pots but I sometimes forget to document stuff when in the middle of a project.
      There're only a couple of settings where I find the tuning knob useful, with it being so subtle. One is with the Violin voice combined with the Strings, it thickens the sound a little.
      I have a Casiotone 403 with the faux woodgrain finish. It's a good look!
      Cheers!

      Delete

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