Me too in 1997. I tried a similar approach with bipolar transistors and found out fast that to get sufficient gain for negative feedback you have to add current sources, for better performance get a differential input stage, then improve it with Wilson current mirrors, and still the DC performance was meagre and very temperature dependent.
Hi thanks a lot I am attaching the circuit i simulated It is just a gain block The recommended Vsupply is +60VDC but also with +48VDC the distortion spectrum of a 1kHz sine was very satisfying with a 2nd order harmonic at -90dB
I used other bjts because i did not find the models of the originals But the option of different bjts pairs is endless
The original preamp is the Radford ZD22 The line stage is made complex for the presence of a tone control stage between an input amp and an output amp that share the same topology This preamp was used as a reference by an Italian audio magazine in the late '70s
if i can get sufficient performance from a 2 bjts circuit i would not be motivated to try a 20 bjts design for sure
Regarding current sources i understand it is possible to get very low distortion also without them I read a lab report confirming this
Again the problem will be to check if the instruments will confirm the good results obtained with the simulation
Looking at the last circuit I'd tried I realized that it makes much more sense to use an opamp which contains all this and more in a thermocoupled package with tightly matched components, and all this for almost no money. I just kept a power Mosfet for sufficient output current.
Yes i will try also the opamp i have been suggested I like the fact that it works also with low voltage and low consumption
I could use batteries and therefore avoid the power supply design and build
