[quote author="Kit"]John and Wavebourn, thanks for your replys.
RCs inserted between the internal long tail PNP pair either from base to base or collector to collector
Yes, that is a smarter and better solution. Thanks.
Output signal swing will not be great but some gain in a following diff to SE convertor will improve both swing and drive capability.
The idea was for this to be a "stand alone, diff in diff out module" for mic pre duty. Run it on +48V. Beefy BDXXX devices for the followers.
Couple with caps of you choice, gain set switch/pot and youre done.
There is a possibility to "CCS" the pnp collector load´s for larger open loop gain.
If one wants to go the discrete BJT into opamp route, theres is really no need for the followers, at all.
2 stages and emitter follower only, it is not an oscillation
nightmare.
Even the simplest circuits have an odd way of swinging by itself on my bench.......... :razz:
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To drive the outside world you will need more substantial output circuitry and/or pretty heavy class A current.
Upon reflection, my caution about inadequate GBW may be wrong. This topology will get a boost in open loop gain from the emitter connected gain resistor just like the Cohen, Transamp, et al topologies. So the G may be OK, BW will depend on device selection and current density.
Some very low noise devices have limited breakdown voltages so you may need to cascode devices if a problem.
This topology may be pretty similar to what's inside the sundry mic preamp chips being sold so perhaps a quick review of their internal schematics might reveal some compensation or other useful tricks.
JR
