While on a run of compressors, I thought this one looked interesting. ThorpyFX Fat General is an optical compressor with a treble control and a blend function.
Schematic can be found on PedalPcb here.
It's said to be a progression of the Dan Coggins designed Lovetone OCT-201 - based on the trace at Aion FX,
THORPY FX FAT GENERAL - VERO LAYOUT
The layout works - I have tested it using standard true bypass, but please read the comments below. Seems to be some switching issues.
I used some proper vactrols that I forgot that I had in a draw and subbed a couple of resistor values as I was short a few.
Sounds fine, although after playing with a few compressor/limiters recently, I think I prefer diode compressors. The tone control is subtle and only obvious on certain pickup/compressor settings. Still quite useful. The blend is a cool feature, but not one that I tend to use on guitar.
Hi,
ReplyDeleteIt seems the "mute/fx to ground" is part of a fancy bypass scheme. (on the aion schematic it connects to ground via the footswitch).
Thanks for all these great posts !
So it does - I should have looked harder. That makes sense, and thanks for letting me know.
DeleteThe compression sounds cool. But I think maybe the switch wiring is a bit off. I can't quite figure out how it should go. First lug 3 of the Blend switch should go to ground. Beyond that, I can't say. Mute, might go to lug 6 of the bypass switch. Buffer out goes to the Blend switch only. Bypass switch 2-3 go to ground. I don't know if this is correct. But as it is currently, the Bypass switch mutes the signal entirely when the effect is disengaged. Do you have a reference off board diagram that you can share?
ReplyDeleteOr...ground to pin 3 of the 2PDT and Buffer to pin 2 and to the SPDT 1. Mute to pin 6 of the 2PDT. It sounds more like the demos this way but I can't quite confirm.
DeleteI haven’t looked at this one for a while - try removing the mute wire and ground to pin 3 SPDT as mentioned above. The. Schematics are linked to the post in the text.
DeleteI tried that and had no luck. I found the switch wiring diagram on PPCB. It makes no sense to me that people are wiring this thing up this way and getting a working circuit. I looked the schematic over again and didn't see anything obviously wrong.
DeleteThe way I have it working is like my first guess but buffered out is lug 3 of the footswitch which also leads to the spdt switch lug 1. Lug 2 is grounded as PPCB has it. Lug 3 of the spdt is also grounded. The buffer is working and it sounds correct I think. I can't tell if it's as squishy as the demos but it does sound nice. Either way, thanks as always for the layout Andy.
The polarized 1uf near the FET should in fact be a 470nf film cap.
DeleteHi Tom. Good spotting, however 1uf vs 470n makes no difference here, apart from the 1uf taking up less space on the board than a 470n film cap. It's part of the power filtering for vref.
DeleteOh, is it really? Interesting. Trying to track down possible issues. It's a really nice sounding compressor. Albeit somewhat subtle.
DeleteSometimes it’s a case of vactrols not matching the original design - you end up with too much or too little compression.
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DeleteCould it be ground related? Does the circuit require a second path to ground?
DeleteHi Tom. normally one path to ground is enough.
DeleteHey Tom - when I have a minute, I might try modelling the buffer / switching in LTspice, to see what happens.
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DeleteFound the issue. It was my fault. I misplaced the 180r connecting input to buffer out. I must've looked this layout over 100x. I just disconnected this build and stuffed it in a box only to pull it out tonight and instantly see an error!!! 40 minutes of off-board wiring later and voila, So sorry for the confusion Andy. Sounds great and works great. Cheers.
DeleteWe’ve all been there - glad you got it working properly
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