Converting a 9v transitor circuit to run on 4.5v bipolar

[jbm222]

I have this circuit on my breadboard right now that's using bipolar 4.5v power for opamps (voltage divider right off the battery with the signal ground in the middle).  But I want to add a section to it out of a transistor circuit that's using 9v.  How do I go about adjusting the transistor circuit (a distortion using two 2n3904's and 1n914's for clipping)  so that I can power it on the 4.5v and still get the same sound?

Oh, and I know I can modify the opamp sections to run on 9v, but I was having a much harder time getting the opamps to do what I wanted when I took that approach.

[davebungo]

AC coupling?

[toneman]

what's the circuit???

[sean k]

I would suppose you just do it normally as per collector and emitter resistors and realise that instead of,say,one volt on the emitter you'd have -3.5 and the caps before and after the transistor will take care of this but you'd maybe still have to have a positive potential on the base to keep it turned on.I don't know really and an answer to this query will help me to undersatnd it better.I've applied negative voltage to the cathodes of tubes for bias but haven't done it too transistors.

[davebungo]

Everything is relative.  If you wire your transistor circuit across the 9V supply as usual and AC couple it you should not have any problems.  In fact, if you bias your transistor circuit in the ideal place it will be close to half the supply rail anyway i.e. 0V as far as your op-amp circuitry is concerned.  What you want to avoid is DC coupling the two circuits as you may end up having an unwanted offset in your op-amp circuit, or your op-amp may end up sourcing/sinking a DC current which will affect performance and power consumption.  If you study a few of the transistor pre-amps on this site you will notice that they are usually connected via capacitors (observing correct DC polarity - don't reverse bias electrolytics); this is to maintain the independant bias within each transistor stage.  I hope this is helpful.