#1
Hey all,

Just curious here - I know each guitar amplifier is unique in its own way, but generally speaking:

-Do the bass and treble knobs generally behave as low/high shelf boosts?
-What is a standard frequency per knob (as the start of each shelf)?  Say, 85hz for the bass, and 5khz for the treble?
-Is the Middle knob generally shelving everything between the two?  I know some amps have a second knob that lets you 'move' the midrange frequency around for a bell curve; but most amps do not have this - do most of them pick a frequency and do a bell?  Or do they shelf everything between the bass & treble frequency knobs?

Thanks! and happy friday!
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#2
Not sure, but I think so. Or rather, if they are passive controls likely they will cut the other to boost itself. So there are only shelve cuts. To boost bass, you cut treble. Active controls can do whatever they want.

I do not think there is a standard frequency. Part of what gives an amp its sound is how the tone stack adjusts everything with knobs at 12, so adjusting those knobs will control different frequencies per amp methinks.

Typically its just a general parametric EQ with pre-determined Q width.
Last edited by Will Lane at Jun 2, 2017,
#3
-Do the bass and treble knobs generally behave as low/high shelf boosts?
They tend to be passive high/lowpass filters of some sort, so they act like shelf cuts mostly. It's not cut and dry like a software or studio EQ, though; amp tone stacks tend to be highly interactive and more than a bit messy. 
-What is a standard frequency per knob (as the start of each shelf)?  Say, 85hz for the bass, and 5khz for the treble?
No standard. Interaction in the circuit means there aren't set frequencies for each. You can ballpark it with a calculator (like this one http://www.duncanamps.com/tsc/ ) but again they aren't neat and clean like graphic or studio parametric EQs tend to be with their frequency ranges.
-Is the Middle knob generally shelving everything between the two?  
Depends on the design, but it's usually a bandpass filter, obviously between bass and treble. Some circuits like the Fender and Marshall stacks have interactions where, for example, the treble control affects the mid frequency. 
I know some amps have a second knob that lets you 'move' the midrange frequency around for a bell curve; but most amps do not have this - do most of them pick a frequency and do a bell?  Or do they shelf everything between the bass & treble frequency knobs?
There's spillover and interaction, usually, between mid and treble/bass. As mentioned above, the interaction means that the center frequency of the mid control isn't fixed, and can be altered by the settings of the other controls.