Request: TC Sustain + Parametric EQ

This one’s an experiment and there’s a real chance this initial version won’t work correctly, so keep that in mind if you’re trying this right away.

I took the service manual schematic that’s floating around and removed the portions related to the effect switching and the buffered bypass (or so I believe at least).


And from this I put together a fairly large layout.


There are a few uncertainties here. I grounded the now-unused parts of the LM339 (from the switching stuff I left out). The original uses an XR4212, but unless there’s something special about this particular IC I’m sure most quad opamps with a compatible pinout would work (e.g. TL074). The circuit contains two trim pots that presumably will need to be adjusted for proper circuit operation. The schematic also hinted at two resistors possibly having to be adjusted based on some setup routine (R53 and R60; see the schematic notes). I’m also assuming you’ll have a hard time finding a dual C100k pot, but a linear taper one is probably a second best.

I’m going to try building this (I do like those compressors), but I’m missing a few components and will have to source them, probably from over-seas. Let me know what your experiences are if you are brave enough to give this an attempt. (A quick google search seems to suggest the AA/119 is in fact the 1N60 germanium diode which I have a few of, but I’d like suggestions on a replacement for the BC558Bs).

Update (16.03.2013): Built this and it seems to work 🙂 All controls respond as expected, and there’s lots of compression and equalization happening.

SustainParametricEq board

First off, I had a small typo on the initial layout that has now been fixed.

I kept R53 at 1M, but didn’t have a 6M8 so I used a 10M for R60. Both trim pots were initially set at 50% and I didn’t try tweaking them as it seemed to work (I’ll experiment with these when I stuff this thing in an enclosure). I used an LF347 for IC1, though a TL074 would have probably worked just as fine. I found a couple of BC558Bs in my drawer so I haven’t experimented with any replacement for these.

Next step; how to fit this in a 1590BB without using a hammer…

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8 thoughts on “Request: TC Sustain + Parametric EQ

  1. Hello Harald, Just noticed while going over your vero board layout that it doesn’t appear you have VR2 wired in correct. The schematic shows VR2 pins 1 and 2 linked, and yet your layout doesn’t. might need a fix. Also noticed just to confuse us, you swapped around some of those internal Quad op amps, compared to the schematic, no biggy, just had me pondering for a bit.
    Cheers, Trevor

  2. Hello Harald, I am putting this together on a PCB design, So much appreciated your efforts for putting the design together easy to understand, whereby the switching is omitted. Thankyou.
    Cheers, Trevor

  3. Hi Alex,
    Looking at the schematic now and I think it’s going to be a major challenge for anyone without a lot of experience (that includes me), and will be quite a bit of work/redesign. Sorry 🙁

  4. Hey all..
    I’d love to be able to engage/disengage the EQ and comp circuit independently. I’m still a bit of a burgeoning DIY guy, I could use your help… does this circuit lend itself to a mod like this easy enough without overhauling the entire circuit?
    Thank you in advance for your help.. anything is appreciated!

  5. Ah, right. Well, I agree you should do the ET first just because of the complexity of the TC, but do both eventually 😉 Good luck.

  6. I was referring to your instruction (going by memory after a brief glance), “Update (14.08.2012): Some of you have asked how to modify this to opt out of all the extra controls and have just the “ratio” and “level” ones. Here’s how to do t with the current layout:” and realize now after a second reading that the instruction was for those only wanting two controls. The TC is definitely more comprehensive, and I am still recovering from the Echo Base which all but destroyed what confidence I had in building skills.Maybe ET fisrt and save TC for later. Thanks for your reply.

  7. Does my ET build omit three controls? Not sure I understand you there.
    Anyways, they’re two very different compressors. The ET is professional and clean sounding with more or less transparent operation, where the TC adds a lot of character to the sound (not to forget the EQ part as well). I like them both, but for different reasons and situations (also I haven’t really played that much with the TC yet as I haven’t boxed it).

  8. Harald,
    I recently built the TransMORGrifier and was not happy with the results. Likely requires more troubleshooting, except I am shot or my ears are shot. I am torn between this build and the Engineer’s Thumb. Having built both, I would like your feedback. Also, I see where your ET build omits three of the controls, which matches the two knob version I have seen demoed. Comments in this regard would also be greatly appreciated. Thanks in advance.

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