This Week on the Breadboard: The EHX Black Finger Sustainer

Interesting. They probably exist, but I don’t know that I’ve ever heard a fuzz with OTA chips. I have some I’ve been trying to decide what to use them in.
 
The Moog Lab Series L5 amp has 2 OTAs in the preamp. One is a compressor and the other is an OD. The Aphex Aural Exciter II also used an OTA to generate mild distortion. The both do it by feeding signal to the amplifier input and to the gain control (Iabc) input.

I breadboarded the Aural Exciter II and it is very subtle. IMHO, it was not all that useful as a guitar pedal. I disassembled it so that I had a place to build the Black Finger.
 
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gtt said:
What's the input to the one OTA at R14 doing? Why doesn't that go to the other one?
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Good question!
R14 biases the linearizing diodes on U2C. Since U2A's and U2C's inputs are wired in parallel (pin 4 to 13, pin 3 to 14), the two OTAs can share one set of linearizing diodes. If we look inside the OTA, we can see that the linearizing diodes (D2 & D3) are connected to the input pins.

1775342324614.png
 
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