Hi, I am working with a SWR Bass750. I am studying the power amp portion of the schematic. I have limited experience with solid state power sections and I am trying to grow in my understanding of the theory. I attached the schematic for this amp. I am wondering about what the purpose of Q15 and Q16 in the upper left corner of the power amp section. wisdom would be appreciated. thanks in advance. I am likely to have some follow up questions. LOL Fred
Q15/16 form a CCS, constant current source, for the differential pair, Q1/2. Also could be a form of turn on/off control since the DC voltage developed by D7 needs to be present to overcome the -VDC on the base of Q15. Once the base of Q15 is + Q16 is turned on providing current flow to the input diff., Q1/2. As soon as the AC power is cut the base of Q15 goes negative, Q16 turns off and the circuit is unable to pass a signal.
Craig
Craig
That’s awesome, thanks for the replies. I was suspecting that there was a turn on delay due the charging of c16. More questions if you don’t mind........ I am considering building this circuit to experiment with. The power supply I have in mind is +-90v. This one is +-100v. My gut says it will work just fine with the reduction of voltage. Are there any areas of the circuit that should be modified or adjusted?
I’m a little confused by your question. If you’re asking why I want to build the circuit it’s because I think it would be fun, rewarding, and a great opportunity to learn something. If you’re asking why I would want to modify it, that would be because the change in the rail voltage. I am wondering if other component values would better suit lower rail voltage
Q4 is the Vbe multiplier, Q3 is the VAS.
Typo, I'm sure, just wanted to correct it so the OP isn't confused.
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