Feedback Gain/Amount

[kr2p]

I’ve tried searching for the answer to this but haven’t had any luck. Could someone explain the difference between the feedback gain and feedback amount? The manual says that the amount is the amount of left channel output fed back into the signal path, and that the gain is the gain applied to the feedback - but aren’t these the exact same thing?

My only guess is that the “amount” goes from 0 feedback to unity gain, and the “gain” starts at unity and increases to whatever the max is. But if this is the case why not have a single knob with a unity gain marker? I’m so confused!

[chysn]

They are related, and you'll have no feedback if both are at 0.

If I recall, Feedback Gain can be used to boost a low signal, while Feedback Volume attenuates the feedback signal.

Why not a single knob? Well, in the original Mopho yellow brick, the gain was not under voltage control, it was just a knob, probably there for the purpose of increasing a guitar level or something. Future versions of Mopho Keyboard, etc., made it a programmable control.

[kr2p]

Thanks for the response, it’s interesting how the two knob approach appears to be historical rather than practical.

They are related, and you'll have no feedback if both are at 0.

I think this is the issue I’m having, as the manual says the same thing but doesn’t give any indication as to how they are related.

If I recall, Feedback Gain can be used to boost a low signal, while Feedback Volume attenuates the feedback signal.

Thanks, that’s helpful. So my understanding is that the volume of the feedback signal is (feedback amount)*(feedback gain)*(output signal) where the feedback amount goes from 0 to 1 and the feedback gain goes from 1 to whatever the max gain is.

The manual saying that the two are “interactive” misled me to thinking there was a more complex relationship that I didn’t know about. It still seems nuts to me that there’s two knobs for literally the exact same thing (albeit in different parameter ranges).

I guess my takeaway from this is that if I want effects resulting from sub-unity gain (e.g. subtle distortion) then I should leave the gain knob at minimum and control the feedback through the amount, and if I want super-unity gain effects (e.g. squealing and weird distortion) then I should turn the amount to maximum and control it using the gain. I suppose unless you want to modulate the feedback then there isn’t much use having both knobs somewhere in the middle as you just end up controlling it blind to where unity is!

[wbajzek]

The two knob approach gives you two gain stages to work with. You might want to crank the gain to get a distorted signal, but then only send a little of that back into the filter.