Active vs. Passive EQ

[sile2001]

Ok, I could use a little education here folks!

I have two main amps that I use. One is a Tech21 Trademark 60 with active EQ controls. The other is a Peavey Classic 30 with passive EQ controls.

I know the Trademark 60's active EQ allows me to cut OR boost lows, mids or highs. If I leave the controls at the center detent then it is flat. Move it up and it boosts, down and it cuts. Simple enough.

Now, I had always kind of treated the passive EQ in the Classic 30 the same way, but now I'm wondering if it isn't more like the tone control on a guitar. Obviously on a guitar, turning the tone all the way up keeps the signal wide open, and rolling back the tone starts to cut stuff out. Does the EQ on the amp work the same way? Would it be best to leave the EQ maxed at 12 on the lows, mids and highs, and then just cut as needed for the desired sound?

Thanks!

 

[reshp1]

The tone control in an passive circuit are going to be subtractive EQ. Most amps utilize a "tone stack" circuit. The separate controls are all potentiometers in a single circuit, each affects the frequency response of the circuit in a different way, but they aren't independent. I.E., if you turn down the mid with the bass knob all the way down, the frequencies cut will be different than with the bass knob all the way up. There was a website with a simulation of the frequency response of such a circuit, but I can't seem to find it right now. Google "tone stack" if you're interested.
EDIT: here you go http://www.duncanamps.com/tsc/
I did a project in school designing a DSP guitar amp and we modeled this circuit.

 

[sile2001]

Hmmm...that's a pretty cool little program! thanks for the link!