Polarity Reverser Circuit (RG Keen) as preamp?

[psw]

Hi all...

I am interested in this polarity reverser op-amp design for use with a preamp...
http://geofex.com/Article_Folders/polarity_reverser/polarity_reverser.htm

I want to provide variable gain with a trim pot...the intention is to use such a circuit in my sustainer circuitry to provide a signal for a LM386 or similar module to power the sustainer driver. The use of the polarity reversing is to flip the signal to create the harmonic drive effect. This effect is created by the sustainer driver attempting to dampen the fundumental and so drive the harmonics of the string. Previously I have achieved this by using a DPDT switch on the driver wires to produce the effect...recent developments in the sustainer thread now call for the control of this function to be in the preamp stage. The preamp stage needs to be overhauled anyway and a simple opamp design would seem ideal...

Any thoughts on adapting this circuit or other ideas? I had been thinking along the lines of a dual opamp inverting amplifiers and engaging the second to flip it back over...but I am not that proficient with design issues to be so confident of a good solution...

Any help or advice appreciated... pete

[slacker]

I don't think you could easily add gain control to this circuit, but you could use a dual opamp with the other half configured as a non inverting amplifer with variable gain. That would be fairly simple, or your idea of using 2 inverting opamps in series would work. You could make the first one have variable gain and set up the second one as an inverting buffer, then just tap the output from either after the first one or second one to get in and out of phase outputs.
If you're using a 386 in the design the simplest way would simply be to have a switch that sent the input into either the inverting or non inverting inputs. That would avoid the need for extra components just to invert the signal.