SOLVED: HM-2 clone, high pitched shriek when Lo is dimed

[matopotato]

Forget all about DC here..
Impedance hates DC 'cause it neutralizes reactive components..
(caps turn into open circuit and inductors to short circuit.. - resistors, frankly, don't give a damn..)

Vs is signal amplitude and Vin is a portion of Vs, according to above mentioned formula..

About spectral view: IMHO, 3 measuremets at lower, higher and mid-band frequencies of interest should be adequate..

Thanks. It's the + and - that is confusing. AC don't really have any constant polarity in a specific location over long time. I thought. Of course momentarily there is a polarity unless "0", but not as connections would go.
So I didn't understand how to interpret the figure.
But if I scrach the polarities and think ~ instead, it should be ok. Or I misunderstood completely. (Again ;-) )

[idy]

Yes, for our purposes scratch the polarity and think AC source fro signal.

The example schematic shows the simplest example, with a series R and a shunt R. In real life a signal encounters R, C and L. L is usually left out because its so small. But in a power supply or wah-wah pedal, it becomes important.

Really we mostly deal with R and C. Those two values, Zs and Zl, stand for impedance in series with the signal and impedance loading the signal. That impedance can come from a resistance, capacitance or inductance. Or (in real life) all together. But we measure impedance in ohms, like R, but it changes with frequency.

The way a cap works we can think like this: at some high frequency it has no impedance to the signal. At some low frequency the cap treats it like DC. You can make that reactance into an ohm value. With a simple tone control type filter we are putting a C in one direction and an R in the other. At the frequency where the signal sees equal "resistance" (really impedance) in both directions you have 1/2 the voltage, 6db less signal.

[antonis]

Or I misunderstood completely. (Again ;-) )

No, you've got it absolutely right..

P.S.
It's a matter of convension for AC voltage sourses to be depicted with positive and negative poles for been distinguished the current send and return paths inside a closed loop (network)