This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Wednesday, November 9, 2016

Mad Professor Forest Green Compressor

Got a request for this one. It's very similar to Bjorn's Pale Green Compressor in his BearFoot Fx line, but with an extra stage for the Sustain mode. Here's the schematic for reference. From the product description:

FOREST GREEN COMPRESSOR (FGC) is designed to meet the highest standards of guitar and bass compression.  There is extremely low noise throughout the range and a high overload margin, which allows also a wide dynamic input range at minimum distortion and noise.  FGC is equipped with a special tone control to fine-tune the compressed sound for most transparent tone and effect.  The pedal has a switchable compressor and sustainer mode.  In Sustain mode you can get a very dynamic, touch sensitive tone with a long sustain. Here the attack is not lost, making the pedal suit-able even for blues players and works great with slide playing.




I've made 2 versions of the layout, one with SGD pinout for the 2SK170, and another with the more common GSD pinout for other JFETs (J201, 2N5457, etc)




18 comments:

  1. substitute for ci and transistors? Thanks a lot!

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    1. You can try some other JFETs for the 2SK170 (mind the pinout). For the other transistors, high gain NPN silicons for the BC550Cs (2N5089, MPSA18, etc) and a high gain PNP silicon for the BC560C (like 2N5087). As always, Google is your friend.

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    2. Hello. Is pinout of 2sk170 correct?I think Gate is center in this FET.

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  2. Replies
    1. Socket and experiment with any higher end single op amps you can find–NE5534 is where I'd start.

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  3. I have seen these... ( https://www.aliexpress.com/store/product/Single-OP-Amp-W-Discrete-Components-To-Replace-AD797-LME49710-OPA627-NE5534-LME49990-Free-Shipping/802369_32374567307.html ) which supposedly can replace these expensive chips... ANyone have a comment on this?

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    1. Not sure I would use one of those contraptions. Probably just use a higher end single op amp like a NE5534. You could even try using a TL071.

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  4. Hi! Thank you again for the great layout. Which Vactol do you suggest? VTL5C6 on Pale Green Comp?

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    1. Originals use an LED and LDR in a heat shrink tube, so not exactly sure which VTL5 to recommend. But this circuit is similar to the Pale Green Comp, so if the VTL5C6 works there I would think it would work on this.

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  5. Is the pinout of 2sk170 correct on this layout? Gate is in the mddle of this tranny. I'd tried twisting the pinout but i only get a humming sound.

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  6. Yeah I think you're right. Guess I got stuck in 2N5457/J201 pinout mode. I'll update the layout.

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  7. I'm always confused by those LED/LDR couplers. What specs should i look for? I already build a tremulus lune and an easyvibe (both with LED/LDR) and they seem to work fine but that could just have been luck :). Does anybody know what to look for?

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  8. Hi. I built this one, but have some problems. I get some compressed sound, but all the pots do not work. I will try another combo of LDR/LED, but am wondering why volume and tone do not work. As long as I traced the layout to the schematic, did not find any error.
    Does anyone have an idea for that?

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    1. Hello. I would think, in the schematic, output from pin6 goes to lug3 of volume via 1uFcap and 5k6 resistor, but in the layout it does not.
      And in the schematic, Vc from 78L05 goes to +side of LED, which makes LED always on.It set me wondering if a LED/LDR combo works properly.

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    2. Thanks for finding that error. The layouts have been fixed and should be correct now. Since it's an optical compressor I believe the LED needs to always be on a little. But the amount of resistance from the LED to ground varies based on signal being processed by the circuit. So I think that part of the schematic is fine.

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    3. Thank you for a quick fix! It seems that only PCB layout is fixed.
      I also think the 1uf cap, between the opamp pin6 and comp3,should be moved to right before 5k6 on the way to Vol3. Am I correct? It's my first experience to read a schematic, and have found it is a fun and tough job!

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    4. Вы правы! Должно быть соединено.

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