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Thread: the puzzle

  1. #1
    Join Date: Dec 2008

    Location: penzance,cornwall uk

    Posts: 319
    I'm paul.

    Default the puzzle

    hi everyone
    i keep looking at this circuit diagram of my amplifier power section in the hope of trying to mark out and highlight on it the route the audio signal takes from input to output...never was much good at puzzles
    anyone up to the task and has the knowledge to sort and mark it out for me...pretty please,its driving me nuts,and i was nuts to start with

    regards
    paul
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  2. #2
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,300
    I'm Andrew.

    Default

    You're starting with a misconception in my opinion. It's commonly assumed that the signal goes in at one end and follows a path through a maze of resistors/capacitors/transistors and comes out at the other end. No, it doesn't really do that. It's more like a complex set of cogs and wheels and pulleys where you turn a bit at "the input" and everything else turns simultaneously, and "the output" is just another one of the bits turning.

    You need to recognize bits of the circuit such as the long tail pair, constant current sources, the output stage etc. Actually, that's quite a sophisticated circuit with bits that are often just a single transistor being complex two-transistor arrangements. There's also a current mirror in there.
    Anyway, try spotting the long tail pair first (aka the differential input).

  3. #3
    Join Date: May 2008

    Location: Surrey

    Posts: 6,135
    I'm Rob.

    Default

    Are they TR3/TR2 and TR4 and the one linked to it? When you blow it up the numbers just get harder to read. Are they the Sziklai pairs I can see?
    Buy Bose...And get your parking validated!.

  4. #4
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,300
    I'm Andrew.

    Default

    Yes, the diagram is too small to see the numbers clearly but the long tail pair seems to be TR21/27/28/29. A simpler and more common circuit would have just two transistors there. The "long tail" is sometimes just a resistor but in this instance has been replaced by a constant current source formed by TR36 and TR37. Again, a single transistor is more common. Sorry, I can't even find TR2, TR3 and TR4. I think a bigger, clearer diagram is needed.

    Really, all parts of the total circuit are doing something (or else why have them there?) and although the idea of a simple "signal path" is appealing it's actually quite misleading and explains why people say "resistor X is in the signal path, but resistor Y is not" when it's really not that simple.

  5. #5
    Join Date: Aug 2008

    Location: Suffolk, UK

    Posts: 1,250
    I'm Paul.

    Default

    An anology I use is that an amplifier is like a tap.

    Imagine you (the signal) turning the tap handle (the tap being the amplifier) so that the flow of water (water - the amplifiers power suppy) is being modulated and flowing into the sink (the speakers) at a flow rate that depends on the position of the tap handle.

    So the signal just controls the tap which in turn controls the flow of water. You the signal are not sucked into the tap and spat out harder and faster, you just use a little bit of energy to control the flow of a much larger source of energy.

    As LTPs go that’s a complicated one, current sources, current sink, current mirror. I do wonder if it really needs to be that complicated sometimes.
    ~Paul~

  6. #6
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 36,174
    I'm Geoff.

    Default

    Well I regard a triode as a tap. But to me a whole amp is like a Newton Cradle, you bang one end and bits bounce all the way through.


  7. #7
    Join Date: Aug 2008

    Location: Suffolk, UK

    Posts: 1,250
    I'm Paul.

    Default

    Quote Originally Posted by walpurgis View Post
    Well I regard a triode as a tap. But to me a whole amp is like a Newton Cradle, you bang one end and bits bounce all the way through.

    A triode is a valve, a tap is a valve, so it would be the right way to think of it.
    ~Paul~

  8. #8
    Join Date: Dec 2008

    Location: Berks

    Posts: 90
    I'm Alan.

    Default

    Heres the original diag......
    Modified SB Receiver, SB Touch, Schiit Gungnir Multibit, AVI Lab Series S21, Custom Speakers, Modified Rega RP3. Pioneer PL550 (thanks Andrew) Various TDA1541 CDP's, too much shit I dont use to list.

  9. #9
    Join Date: Dec 2008

    Location: Berks

    Posts: 90
    I'm Alan.

    Default

    I thought you might be able to zoom in on it but it appears not....
    Modified SB Receiver, SB Touch, Schiit Gungnir Multibit, AVI Lab Series S21, Custom Speakers, Modified Rega RP3. Pioneer PL550 (thanks Andrew) Various TDA1541 CDP's, too much shit I dont use to list.

  10. #10
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 46,019
    I'm Grant.

    Default

    this might help...

    Regards,
    Grant ....

    I've said it before and I'll say it again: democracy simply-doesn't-work
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