Aion Oceanid (Cornish OC-1) unwanted amplification

[mrtzly74]

Thank you antonis!

Do you know of any way to reduce the output that doesn`t affect the general tone so much? Is there a way to just change the range of the volume pot? Right now you can dial it in from "louder" to "very loud". My goal would be to be able to dial it from slightly under unity (or unity) to "louder", but without changing anything dramatic soundwise.

I am thinking of a place which doesn't affect clean and wet signals (as altering R12 does?)..

[antonis]

R12 with C7 form a LPF (low-pass filter) of about 34kHz cut-off frequency..
(frequencies above that cut-off point are attenuated - or more presicely, less amplified..)

By making R12 1k say, you raise LPF's  cut-off frequency 10 times (340kHz) so you need to raise C7 cap value 10 times (4,7nF from 470pF)..
(just follow f = 0.159/(R x C) for the frequecny of your interest..)

Of course, by shorting pins 1 & 2, R12 value equals zero and C7 needs to be made infinite..

[idy]

You are asking good questions, assuming the pedal should be capable of putting out unity gain or less.

The tranistors are not the issue. They are buffers (output from emitter) and have a gain very close to 1, unity.

The opamps are apparently boosting a bit too much. IC1A: the two 10ks make a voltage divider, and feedback makes things "opposite", so gain of 2. That 2.2uf cap keeps DC voltage steady and maybe limits the low end. The 220pf allows super high freqs to stay at unity, so no squealing. Good design means limiting bandwidth among other things.

If you are going to look to adjust the gain, you have to decide if you are thinking about the clean signal only, or clean and compressed. Both go through IC1A, and the mixer IC2B. The clean alone goes through IC2A.

Any of those stages could be off, any could be adjusted. The gain is set by elements in the feedback loop and their series R in inverting opamps (like R17 and part of the  blend pot vs 
R19 and the other part of the blend pot.)
There are just so many ways to change the gain: R20, R15 can change the clean part of the mixer. But tinkering inside the circuit may cause other issues, and randomly pulling things out is a great way to damage your project.

I can think of three main possibilities: 1) the design boosts. Others say that is not so.
2) a single resistor is the wrong value. You say no, but eyes are fallible. 3) your bypass signal is actually below unity. But you say problem persists with buffered bypass. Another would be the "ground leg" (components to ground at inverting input) of 1A or 2B is open circuit, But you've checked your solder.

[SprinkleSpraycan]

I have the same volume issue with my build too. I'm loving the possibilities to try here. I've been thinking of just adding a small trimmer inside to act as a set and forget volume once I have it to unity.

[mrtzly74]

Thank you so much antonis and idy!

Like SprinkleSpraycan said, lots of possibilities to try! Please let me know what worked for you in the end!

Since you are having the same problem, i really think this might be "part" of the design. So my goal would be to drop to volume at the least invasive position.
What do you guys think this would be? Is it possible to drop it right at the output by increasing R22?

[antonis]

Is it possible to drop it right at the output by increasing R22?

Νο..

(actually yes, but you need to know next effect input impedance..)