Combining single- and dual-rail supply devices. How to?

[meffcio]

I want to merge an old Marshall Lead 12 (3005, schematic) preamp with Taylor's Tiny Giant amplifier (schematic and info). What disturbs me is that TG is a single-rail supply amplifier, and the Lead 12 preamp is designed for dual-rail supply use. I'll be using this setup with a regulated laptop power supply, because I don't want to mess with transformers and stuff like that. How should I deal with the supply rails difference?[/quote]

I've come up with that kind of idea:
Schematic.
I suppose it is going to work, but I'm not sure about value of the input cap. However, I'm pretty sure there's impedance mismatch between pre- and power amp. How to deal with it? Should I restore the buffer? Or a simple tone stack scaling would do the trick?

[brett]

Hi
your schematic seems right (ie power the op-amps across the 'whole' supply and bias to 'half', and block the DC bias 'inside' with caps).
If you wanted to run the op-amps off Vb, then all you'd need to do is create a bias voltage of Vb/2.
Depending on the input impedance of the amp chip, the operation of the tone stack might be affected when the volume is turned up and there's a low impedance path to the chip.
A simple solution (3 parts) would be a Jfet buffer between the volume control and the amp. It would be very stable with that in place. A BJT buffer would be as good.
cheers

[PRR]

I wonder if the Marshall Volume is really 1Meg Log. It's pretty mis-matched into Marshall's 100K input power amp. Also the rest of the tone stack is similar to Fender except most values 10 times smaller. 100K would be in keeping with the trend.

You seem to have caught most of the conversion.

The power amp thumps the supply hard. The Marshall plan has a LOT more gain than Taylor's basic front end. My gut says there should be a power rail filter to the preamp (Marshall does). And that Vb should be filtered separate from power.