Question about Pioneer A35R 2-Channel Amplifier

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Pioneer SA100 integrated - low, distorted output

Pioneer SA1000 integrated amp - low, distorted output to headphones and speakers. I loaned this out and I believe it was overdriven or overloaded with too many speakers. I replaced all 4 output power xisters with no discernable improvement.

Thanks

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  • 4,234 Answers

At this point, I would be looking at the main power suply for the final output stage. You may be attempting to drive the output with the driver section rather than the final amp stage. The center pin of the output transistors should have B+/B- on them. Measure that to ground and report the value here.

Dan

Posted on Jul 13, 2010

  • 7 more comments 
  • jamesvalenza Jul 13, 2010

    Thanks for your input. I have a very rudimentry meter so measurements are approximate. There are 4 transistirs and there is no center pin - the 2 pins are base and emitter; the case is the collector; measurements are transistor# then Base, Emitter, Collector -
    #1: 0 0 45
    #2: -40 -40 -25
    #3: -40 -40 0
    #4 0 0 45

    Thanks again and standing by . . . Jim

  • jamesvalenza Jul 13, 2010

    Thanks for your input. I have a very rudimentry meter so measurements are approximate. There are 4 transistirs and there is no center pin - the 2 pins are base and emitter; the case is the collector; measurements are transistor# then Base, Emitter, Collector -
    #1: 0 0 45
    #2: -40 -40 -25
    #3: -40 -40 0
    #4 0 0 45

    Thanks again and standing by . . . Jim

  • jamesvalenza Jul 13, 2010

    Thanks for your input. I have a very rudimentry meter so measurements are approximate. There are 4 transistirs and there is no center pin - the 2 pins are base and emitter; the case is the collector; measurements are transistor# then Base, Emitter, Collector -
    #1: 0 0 45 #2: -40 -40 -25 #3: -40 -40 0 #4 0 0 45

    Thanks again and standing by . . . Jim

  • jamesvalenza Jul 13, 2010

    Thanks for your input. I have a very rudimentry meter so measurements are approximate. There are 4 transistirs and there is no center pin - the 2 pins are base and emitter; the case is the collector; measurements are transistor# then Base, Emitter, Collector -
    #1: 0 0 45 #2: -40 -40 -25 #3: -40 -40 0 #4 0 0 45
    Thanks again and standing by . . . Jim

  • jamesvalenza Jul 13, 2010

    Thanks for your input. I have a very rudimentry meter so measurements are approximate. There are 4 transistirs and there is no center pin - the 2 pins are base and emitter; the case is the collector; measurements are transistor# then Base, Emitter, Collector -
    #1: 0, 0, 45 #2: -40 -40 -25 #3: -40 -40 0 #4 0 0 45
    Thanks again and standing by . . . Jim

  • jamesvalenza Jul 13, 2010

    Thanks for your input. I have a very rudimentry meter so measurements are approximate. There are 4 transistirs and there is no center pin - the 2 pins are base and emitter; the case is the collector; measurements are transistor# then Base, Emitter, Collector -#1: 0, 0, 45 #2: -40 -40 -25 #3: -40 -40 0 #4 0 0 45
    Thanks again and standing by . . . Jim

  • jamesvalenza Jul 13, 2010

    Thanks for your input. I have a very rudimentry meter so measurements are approximate. There are 4 transistirs and there is no center pin - the 2 pins are base and emitter; the case is the collector; measurements are transistor# then Base, Emitter, Collector -#1: 0, 0, 45 #2: -40 -40 -25 #3: -40 -40 0 #4 0 0 45 Thanks again and standing by . . . Jim

  • ABRsvcs Jul 13, 2010

    The voltages are wrong. You are missing a voltage somewhere. If the outputs are not shorted, then you should see either a 0.6 or 1.2V reading on one of the legs (plus or minus). Given the readings you posted, there is a supply problem in the driver area or bias circuit. I don't have the schematic for this model handy, so I can't give you specifics, but there is a problem between the preamp section and the final stage. Lift the center pin of the output transistors and look in the driver circuit for open resistors or open transistors.



    Dan

  • jamesvalenza Jul 18, 2010

    Dan,

    there is a protection circuit governed by a 4-pole relay. I cheked measurements hre and only fqund input power - nothing on the output(s). I found one of these on line and am takeing a flyer that this is the source. Your prognosis about a supply problem kind of points here, also in the past another volume freak (while house sitting) also overdrove this amp and my recollection is the relay was replaced. I have very limited knowledge and tools for this kind of work but trial had error can sometin=mes get me through. I'll let you lnow the outcome.
    Jim

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