Active Baxandall Pedal ?!?

[ct_anthony]

Hi everbody,

I'd like to build an active Baxandall pedal for my board. The EQ section should be placed in an amplifying TL072 sandwitch (one half before eq, one half after, both amplifying, no buffer stage).

During research/planning I found the following http://www.parasitstudio.se/vero-layouts/active-baxandall-tonestack, including the schematic within the PDF here: http://www.parasitstudio.se/uploads/2/4/4/9/2449159/active_bax_eq_pcb.pdf

I don't get the configuration of the second opamp stage... Won't the bass controll affect the gain? What is the deal here?

Regards,
anthony

[induction]

Won't the bass controll affect the gain?

Yes. That's how it works. The first op-amp is a simple gain stage, the second op-amp and all the passives after the coupling cap are the active baxandall circuit.

It's frequency-selective gain. It's different from a passive EQ with makeup gain, which might be what's throwing you off.

You might enjoy reading this.

[ct_anthony]

Won't the bass controll affect the gain?

Yes. That's how it works. The first op-amp is a simple gain stage, the second op-amp and all the passives after the coupling cap are the active baxandall circuit.

It's frequency-selective gain. It's different from a passive EQ with makeup gain, which might be what's throwing you off.

You might enjoy reading this.

This was a perfect link! Thanks so much! Everything is clear now 

A final word about the tone control circuit. Note that it is a 'virtual earth' circuit, so the feedback at all times will maintain the -ve input at zero volts. The bass and treble content of the input waveform will force the amplifier to provide just the amount of boost or cut at any frequency to maintain the 0V condition on -in. You will find this useful as you work towards an understanding of the complete circuit.

I think I got confused by the "Bax-in-a-box" you can find in this forum somewhere... it uses an dual opamp as input buffer and final make-up-stage with a passive baxandall (in fact its the james from the duncan tone stack calculator) in between...

Thanks again

Regards,
Anthony

[samhay]

Only thing to add to Rod's (ESP) excellent article is that you can add additional mid control(s) by doing this: