eq "shelving"

[km-r]

hi!
i wanted to know how to create a shelving eq, i think thats what its called.
you see a friend of mine wanted to recreate the freq response of his cranked up tube amp so we fx-looped a graphic eq after the preamp.
the result is a flat freq in the bass and a increased/"shelved" response of about 10db at about 2khz flat to 20khz.
i wanted a cheaper and discrete circuit that resembles this freq response. certainly not a high pass filter because it will suck out plenty of bass.

thanks in advance!

[zyxwyvu]

Try paralleling a 220k resistor and a 680p capacitor before a 100k resistor to ground.
Change the capacitor to change the frequency, and the resistors to change the attenuation at low frequencies.
If you want a boost instead of just attenuation, you can add a simple amplifier to this circuit.

Here's a picture to show the circuit and frequency response.

[Ben N]

You'd have to calculate the values, but I have the impression (from O'Connor's book, maybe?) that a cathode bypass cap in a tube amp creates a shelving response. That may be where it comes from in your friends amp (could also be the speaker). If so, the same thing ought to work in a SS single stage as well, using the emitter or source bypass cap. Not sure if you have to scale values, though, but try something like a simple NPN boost with the same cap value as on the amp's input stage on the emitter?

Hopefully someone a little smarter can chime in on this.

[stm]

km-r, do you have access to a 2N5457 FET?  If so I can provide you a suitable circuit.

[jayp5150]

Try paralleling a 220k resistor and a 680p capacitor before a 100k resistor to ground.
Change the capacitor to change the frequency, and the resistors to change the attenuation at low frequencies.
If you want a boost instead of just attenuation, you can add a simple amplifier to this circuit.

Here's a picture to show the circuit and frequency response.

What program is that? I was just thinking about trying to find something like that earlier today.

[zyxwyvu]

What program is that? I was just thinking about trying to find something like that earlier today.

It's called Simetrix. I use the trial version that you can download for free here: http://www.catena.uk.com/

The trial just has a circuit size limit (that's pretty big), so it works fine for just about any stompbox circuit.

[jayp5150]

It's called Simetrix. I use the trial version that you can download for free here: http://www.catena.uk.com/

The trial just has a circuit size limit (that's pretty big), so it works fine for just about any stompbox circuit.

Cool, thanks. I'll check that out.

[flo]

This is also a freeware option:
http://www.5spice.com/

[km-r]

thanks for the help guys,
i just downloaded Simetrix software demo... this will be great! you can actually simulate circuits' frequency response here?

[zyxwyvu]

thanks for the help guys,
i just downloaded Simetrix software demo... this will be great! you can actually simulate circuits' frequency response here?

Yes, just put in an AC source, connect it to the input, then put a voltage probe on the output of the circuit. Go to Simulator->Choose Analysis... , and check AC, and run the simulation.

[rogeryu_ph]

Hi Km-r,
Welcome me back   , I'm still eyeing on our project for insanity box just give me some times.
well i get suck with GT forum for a while. Is the eq your using was a ten band unit co'z it has more bass reponse isn't it. Well it also depend on Amp send/return direct mix level, some high-end amp provide or design control for this, most of these are solid state amp but I know some modern tube amp nowadays has too.

Roger