Help please for opamp challenged..........

[rabbitz]

What I've got is a stereo amp which I'm using as a sub power amp. The tone control section and preamp was was removed as it was faulty. I've added a sub bass processor which provides gain, low pass filter, equaliser, 20Hz filter and inverter/buffer output.

The circuit diagram is for the buffer/gain stage (LM833) which gives ±12dB or a gain of 4/0.25 via a pot RV1 (varies the input attenuation at R4 and the opamp's negative feedback at R6). The circuit is balanced, gain of 1, with RV1 in the centre position. What I want to do is increase the gain to 8/0.125 to give me ±24dB as when the preamp was removed, a lot of gain was lost.

Being opamp challenged, I think it's just a matter of:
increasing R4 and R6 to 100k?
or decreasing R3 to 51k?
or decreasing R5 to 7K5?
or am I way off course?

What would be the maximum gain that could be used?

Any advice would be appreciated.

[rabbitz]

In the too hard basket, hey.

I've had my books out and can't figure out how they get a gain of 4/0.25 with this circuit.

[dimitri]

decreasing R5 to 7K5 will give you 8/0.125 or ±18dB

[rabbitz]

Excellent, thanks very much.