EQ Design

[AR1]

I need a reliable 3 band EQ design for a guitar amp, anybody have any op amp based designs to share?

[rsavas]

I can suggest a few,

1) Doug Self's 2-band variable tone control as used in the Precision Preamp'96
2) A state variable filter type with a least two filter stages, hi and low.
3) Baxandall, as shown in many National Semiconductor device data sheets and application notes.

The state variable design would give the most control as it is infinitely variable. Not sure if you need a typical 3-band Baxandall as the mid-ban is rather redundant.

Good Luck
Rick

[Enzo]

EQ circuits are about as old and well explored as any circuit in an amp.

Are you specifically looking for active EQ circuits? Because a passive tone stack works pretty well, and doesn;t care what you drive it with, op amp, transistor, tube.

The needs of a guitar amp are not the same as for hifi, guitar amps are not intended to be flat in the first place. Look at any of the long list of Bandit models from Peavey as examples. Or something like a Fender Princeton Stereo Chorus.

Go over to Duncan's Amp Pages and download his VERY cool Tone Stack Calculator. A nifty bit of FREE software that lets you exploare in ral time the response curves of a variety of tonje stack circuits. It lets you vary the controls while watching the curve change. Plus you can even alter the individual component values to see what changing teh cap here or slope resistor there does.

[AR1]

Originally Posted by Enzo

EQ circuits are about as old and well explored as any circuit in an amp.

Are you specifically looking for active EQ circuits? Because a passive tone stack works pretty well, and doesn;t care what you drive it with, op amp, transistor, tube.

The needs of a guitar amp are not the same as for hifi, guitar amps are not intended to be flat in the first place. Look at any of the long list of Bandit models from Peavey as examples. Or something like a Fender Princeton Stereo Chorus.

Go over to Duncan's Amp Pages and download his VERY cool Tone Stack Calculator. A nifty bit of FREE software that lets you exploare in ral time the response curves of a variety of tonje stack circuits. It lets you vary the controls while watching the curve change. Plus you can even alter the individual component values to see what changing teh cap here or slope resistor there does.

Thanks for that info, Duncan Amps looks like an awesome site, it will make a great referance page. The design I am working on is a front end for an amp that will be used for with an emulator so I would like a fairly linar resopnce with as little coloration as possiable. I have attached a potental design as an example, I am testing this circuit now. I am lwill most likley look for an active design and go with that.

[AR1]

Originally Posted by rsavas

I can suggest a few,

1) Doug Self's 2-band variable tone control as used in the Precision Preamp'96
2) A state variable filter type with a least two filter stages, hi and low.
3) Baxandall, as shown in many National Semiconductor device data sheets and application notes.

The state variable design would give the most control as it is infinitely variable. Not sure if you need a typical 3-band Baxandall as the mid-ban is rather redundant.

Good Luck
Rick

The typical 3-band Baxandall looks like a potential candidate, likley would need to tweek the crossover bands to make all three bands useful, thanks for that info....

[Enzo]

If you liked Duncan's site - and there is other cool stuff there besides the tone stack thingie - you might also find useful:

Aiken AMps Aiken Amplification (Right now the site appears to be under re-construction) An internet archive site might still have the old one.

London Power Tube Amp Kits, Tube Amp Books, Tube Amplifiers by London Power

And many others...


Sounds then like you don;t want a guitar amp tone stack, you want more like a hifi stack. Not my area of expertise. Instead of looking specifically for tone controls, maybe also look into graphic EQ circuits, make them low-Q enough. Or for that matter, three parametric circuits set up to meet your needs.

[AR1]

Originally Posted by Enzo

If you liked Duncan's site - and there is other cool stuff there besides the tone stack thingie - you might also find useful:

Aiken AMps Aiken Amplification (Right now the site appears to be under re-construction) An internet archive site might still have the old one.

London Power Tube Amp Kits, Tube Amp Books, Tube Amplifiers by London Power

And many others...


Sounds then like you don;t want a guitar amp tone stack, you want more like a hifi stack. Not my area of expertise. Instead of looking specifically for tone controls, maybe also look into graphic EQ circuits, make them low-Q enough. Or for that matter, three parametric circuits set up to meet your needs.

WOW amazing, Thanks so much, I am a gear head 4 sure, I'll have loads of browseing fun their, thanks man, be well.

[Keriwena]

If you're running an emulator into it, then you probably want something closer to the tone controls on a mixing console. As you can tell from Duncan's app, regular guitar tone controls have heavy speaker EQ built in. I assume you'll be using a FRFR speaker? (Full Range, Flat Response)

[Enzo]

OK, one more post on it and I will stop.

Geofex New Page 1 RG has an interesting web site with some great little ideas.

And a forum i frequent more devoted to instrument amps:
Music Electronics Forum