I was attempting to single out the white noise generator of Kinks, and noted the transistor arrangement and op amp on page 3 of the schematic. C13 is explicitly connected to one of the transistors, but I noticed C9 calls for an identical capacitor. Is C9 implicitly correlated to the noise generator?
I have forgotten quite a bit about my experiments with this, but C13’s value has been decided according to an amplitude/whiteness trade-off ; and C9 has been added to prevent power supply noise or whine to leak through the circuit (and be amplified 15 times by IC4a!).
In production I used a tantalum for C13 because ceramic caps are prone to microphonics, and given the huge gain of the circuit, the module acted kind of like Ears (a tester of an early revision thought it was an “easter egg”).
Hope this helps!
Thanks that explains it!