"Good" Feedback

[cminor9]

Using a semi hollow body guitar makes it easy. I play an epiphone dot and I have figured out how to make it feed back whenever I want it to in a good way, as in infinite sustain. Room acoustics matter, but I was able to do it outside at a gig.

Everything has a resonant frequency. If you can figure out what your guitar's resonant frequency is, then you can exploit that.

[TopOfTheMountain]

Yes, I've got a 335 and of course it's a feedback machine. Look out Nugent!



>You think so, eh? Look at the classic 30. It has a 470pf coupling cap !

Yes, I know. I took it out of my 30 to warm it up or so I thought.




> But the thing is, nothing is too small when it's used with a resistor to form > a filter like i described. Marshall uses 470pf caps all the time like that and > as long as it's parallel to a resistor you're passing ALL frequencies but they > are attenuated a bit due to the resistor.

Yeah, I understand all that. There again, I sometimes take those 470pf caps out to warm it up. Hmm, might change my thinking.




> By the way, when you say "it's a wonder it's not flabby" i'm not sure what > you mean,

I meant by using a .022uf coupled to a 1Meg to ground between stages has the -6db cutoff at such a low frequency. That's a lot of needless low end.



> but a .0047 wouldn't cause flab unless you DUMPED the frequencies it
> passes such as if you connected it to the signal and ground. But in this
> case you are accentuating it and in effect as i explained CUTTING flab.

Yes, I understand. Lots of ideas.

[Joey Voltage]

You think so, eh? Look at the classic 30. It has a 470pf coupling cap ! But the thing is, nothing is too small when it's used with a resistor to form a filter like i described. Marshall uses 470pf caps all the time like that and as long as it's parallel to a resistor you're passing ALL frequencies but they are attenuated a bit due to the resistor. But the frequencies the cap passes get thru w/o being attenuated so they *in effect* are boosted the same as if you took a EQ and cut all the frequencies you want less of and left the sliders that you want more of at 0 Db. By the way, when you say "it's a wonder it's not flabby" i'm not sure what you mean, but a .0047 wouldn't cause flab unless you DUMPED the frequencies it passes such as if you connected it to the signal and ground. But in this case you are accentuating it and in effect as i explained CUTTING flab.

two different sonic effects. a coupling cap and resistor combination is just a single pole filter with a gentle 6db per octave degrade. the "marshall" filter you describe is a passive shelving filter usually in conjunction with a first order RC filter. while the Shelving filter gives the sonic impression of a boost (the first just cut), it is still passive, so it is not exactly the same as your Active GEQ analogy, and it relies heavily on the divider network to determine the degree of cut for the frequencies not of interest, and for the peak frequency. for example a shelving filter comprised of a 470K/220K (shunt) divider with a 470pf cap will sound more intense, and have a higher peak frequency (frequency at full gain), than one with the typical 470k/470K (shunt) divider network even though the initial slope upwards starts at about 720hz for both.