convert tone job/box and all to ±12v bipolar

[maertz13]

plotting a power amp build and want to put an EQ and volume control out front. basically a take on a SD powerstage. The power amp module has a built in PSU and an auxilery bipolar 12v output. I've heard people say that running an op amp circuit off of ±V instead of +V/VREF is an easy mod, but I can't seem to google the right words to find an example.

can anyone provide/point me to a schematic for such a thing? thanks

 

[jwin615]

The simplest way is probably lift the V- leg of each opamp and run a bodge wire or -12v to it. Then, convert other vref points to ground.

You could maybe just ground the vref point in the power section.
Rig up voltage protection and smoothing on the -12 line and up the protection on the +12.

Not really simple. Definitely messy. Probably not reliable in an amp.
I also haven't looked at the schem. If there are any feta or bjts, they'll need to be delt with.

 

[maertz13]

It’s 100% op amp driven

 

[jwin615]

I think this would be correct
Someone feel free to check my work.
I drew it up for virtual ground(Vg) as Vref as we don't know how well matched or steady the bipolar supply is. Thought being that id one sags, our headroom doesn't go to shit, as that's the whole point.
You'll need to life the legs of the opamps and run bodge wire to -V, or cut the traces and run wire to the back of the pins.
The goal here is to basically change part of the previous ground plane to -V and Vref to Vg, which is "ground" but not earth, instead a virtual ground, a point electrically centered between the two voltage rails. This may not totally be necessary, but it prevents unnecessary offset. Say actual supply voltages are +12.3 and -11.8. If you just use ground as Vref, you're going to have 500mV DC offset, which will decrease headroom...
Hope this helps. Again, please check my work. It's early.

 

[maertz13]

Suppose it’s also worth mentioning that I’d be building this on Vero. Makes a lot of this easier logistically.

 

[jwin615]

Suppose it’s also worth mentioning that I’d be building this on Vero. Makes a lot of this easier logistically.

I'd take a look at some schematics for bipolar input stages of other audio circuits. Particularly the decoupling and filtering. Should give a clearer picture. And if on vero, you can maybe filter for ripple and noise a bit more, perhaps including a couple of ferrite beads, if you so wished.