geofx Graphic EQ for Dual Supply

[bartimaeus]

Hi all,

I've built this EQ in the past, and I like how it works. I'd like to add a few bands to a new circuit I'm building. That circuit already offers a dual power supply, so I'd like to save some components (such as the voltage divider resistors, and the input/output caps) by running it from the dual supply.

I'm pretty sure I can just omit the 1M resistor from Vb to the opamp +in. However, I'm not sure how to handle the 6.8K resistor to Vb in section A. I've tried grounding it, and it works for about 30 seconds, but then a fuzzy/distorted sound slowly fades in.

Your advice is much appreciated!

[samhay]

Everything that is connected to Vb in the schematic gets connected to ground.
This includes the 6.8k's and the 1M resistor, which you need unless you DC couple this circuit to a preceding stage.

[bartimaeus]

That did the trick, thanks very much!