thanks for your feedback sgrossklass,
input AC will be 12vac and the +/- DC rails should end up around 10vdc. the rectification i'm planning on using are mouser # 512-DF005M which are 4 pdip rated at 50v so keeping everything contained on board. regulation transistors are BD139/BD140 or should i look for something else?
if you know of something that has better regulation and compact that will fit on the board i'm all ears
output impedance, R17 (75r) and C4 (.82u) go to make a low pass filter to cut the output frequency to about 25Khz, i can change this about and use say a 0.22uf capacitor and 29r. or have i got that wrong and stick with a zobel?
the output bias on the opamp is a jfet cascode to bias the opamp into class A. the jfets will be graded so J1 will have a higher idss than J2. or have i got that wrong?
opamp trim, i'm using the OPA228PA at the moment and it takes very little to trim compared to the OPA134. i'm using 12K to get the output at 0.7mv at the headphone socket. my thinking is 50K variable trimmer should be plenty to play with.
all PNP/NPN will be BC337-25TA/BC327-25TA so should be ok putting 40-60ma through them. with the DC rails only running at 10vdc will this not drop the output to around 30ma and 1-1.3v?
i'm still confused about the buffer output and i'm thinking of removing the two extra transistors for the Sziklai pair.
i'll admit that its a copy of RJM's sapphire with things moved about. i added regulation and a bias cascode.
i'm planning on building it on one of those protoboards that you just plug components into , its practise to help me learn, that and i'm bored and this is fun so keeping me entertained.
i have tried getting to grips with LTspice but as yet i'm still confused.
some pretty pictures, values of components have not been configured yet.
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