moid wrote:First as the feedback is increased the three high strings on the guitar lose the ability to produce sound (the three lower strings still work) and the effect is high E is lost first, and as you increase the feedback the B string goes, followed by the D. I am sure that you once said something to me about adding a certain capacitor value somewhere to enable high pitched frequencies to travel through more, but I cannot recall it or find where you wrote it... does that mean anything to you?
Yeah, I might have been talking while referencing a schematic on another build? I don't recall taking that plunge on this thread..
Stupid question time: do you have an o-scope? I'd be interested in watching screen while you increase feedback. Guessing the answer is no, so....
It sounds like you'd like more HF in the feedback mode and less HF oscillation when the gain is cranked? These are interactive fronts, and diving into the circuit to fix one might tamper with the other. Everything affects everything.
My thoughts (disorganized) are:
0.01 is a fairly small coupling cap, so it will, as a general rule, allow more HF and less low frequency to pass. Depending on the impedance of the surrounding elements it might be high passing the upper strings while going into a supersonic oscillation that effects that way the circuit handles the lower registers. Experimenting with cap size might be illuminating to see if you can push the "knee" or crossover point up or down in relation to capacitor size (simply piggybacking one over the existing in parallel will make the capacitance larger).
You can stick a bypass cap on an emitter and increase AC conductance through that stage - the only emitter resistor I see is on the far right hand resistor. Increasing HF only would entail selecting smaller value caps, and the 390 ohm emitter resistor is probably not going to attenuate the other frequencies to a large degree..
To snub HF, you can grab a SMALL value (pf) cap and either ground reference that along a signal path or try the feedback approach of giving a high frequency path from the collector to base, though this entire section is really getting close to tampering with the sound to a larger degree.
Apologies if that's hard to read, I'm not in a solid translate stuff to something readable head space at present, I might revisit with coffee tomorrow.