# Diminishing parts list of Greengage overdrive



## D45T4N (Sep 12, 2020)

Greetings everyone.

I've been looking at the schematics of Greengage overdrive, and the purpose of capacitors C2 and C8 remains unclear to me. (De)coupling capacitors are used for two things: 1) to separate parts of the circuit with different DC bias; 2) to make high pass filters. Thanks to bipolar power supply the entire audio route is biased to the ground and negative feedback cap of the gain stage provides more than enough of high pass fitering. Furthermore, in a very similar Bullrush overdrive there is no cap between input buffer and gain stage.

So, will there be any negative consequences after replacing C2 and C8 caps with jumpers, or they can be safely removed for the sake of reducing the price of the build and deducting the (microscopic) noise of those two caps?


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## BurntFingers (Sep 12, 2020)

Socket them. Try with the caps, try with a jumper wire. Job jobbed.


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## Chuck D. Bones (Sep 13, 2020)

"Decoupling" doesn't mean what you think it means.  Those are_ coupling_ caps and their purpose is to couple AC and block DC. A natural consequence of that is they act as high-pass filters. Some pedals use the coupling caps to tailor the bass response, particularly before the distortion stages. The high-pass cutoff freq is low enough in both the Greengage & Bullrush that removing the caps listed below won't alter the sound.

The Greengage has split power supplies and biases everything at ground. The DC voltage on both sides of C2 is zero volts ± a few millivolts.  It's perfectly reasonable to replace C2 with a jumper and delete R4.  Same holds true for C8, C9 & R12.  Jumper C8 & C9, delete R12.  It's an EQD design, 'nuff said.

The Bullrush also has split power supplies and biases everything at ground.  You can jumper C6 and C7, delete R13.  You could apply the same reasoning to C9 & R18, however I'm inclined to leave them in just to ensure that we don't upset anything after that pedal in the chain.  The thing Providence did that looks goofy to me is running the ICs on +18V & -9V.  You could run them on ±9V and have essentially the same amount of headroom.  If you decide to do that, replace D101 & D102 with jumpers, delete C102 & C103.  

On both pedals, use whatever opamps you like because neither pedal drives the opamps into saturation.  The only caveat is make sure the opamps are rated for the power supply voltages.  90% of them are.


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## D45T4N (Sep 13, 2020)

Chuck D. Bones said:


> The thing Providence did that looks goofy to me is running the ICs on +18V & -9V.


Thanks for the great answer! And sorry for the late night typo, I meant coupling caps indeed. The original Providence (Free the Tone) SOV overdrive has bizzare power schematic — voltage is lowered to 5V and then increased to +-15V by NMA0515SC converter which is quite expensive, meanwhile TC1044 chip which used in all pedalpcb projects cannot quadruple the voltage of two opamps because output current will be something around 6 mA, so audio artifacts may start to appear. I guess Bugg decided to increase the current by reducing the voltage to the Klon level, but forgot to change bias to 4.5V.


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