the puzzle

[smithie]

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

[RothwellAudio]

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).

[Puffin]

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?

[RothwellAudio]

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 The "long tail" is sometimes just a resistor but in this instance has been replaced by a constant current source formed by TR36 and TR37.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.

[Dawg]

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 The "long tail" is sometimes just a resistor but in this instance has been replaced by a constant current source formed by TR36 and TR37.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.

AVI started numbering them at the pre section.

[smithie]

hi guys
thanks for all the posts and responses....sorry i haven't replied earlier....had my mod and tweaking head on and had my grubby hands and soldering iron in the amp
so no ones cracked it???
as pointed out,it is rather complicated,also pointed out,the signal does ebb and flow in lots of ways at times due to the design
ive gone with plan "B" and decided to take it slowly,start at the beginning (the preamp section) and then take the various stages bit by bit if i need to.
once again thanks for all the input and help and sorry for my delay in replying.
ive done a mod on the preamp section but ill probably share that as a new post

regards
paul

[Primalsea]

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.

[walpurgis]

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.

[Primalsea]

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.

[Dawg]

Heres the original diag......