Is this output arrangement OK?

[NVD33]

Hi ,

I am given an old amplifier, schematic is not available so I draw output stage from the circuit. I have checked many times to be sure of it. See attached scan.

The amp is singing but its output arrangement puzzles me. Is this output arrangement correct and can perform well? I never see this arrangement before .

[DF96]

It could be correct, although rather unusual. You appear to have two complementary pairs, but used in common emitter mode rather than emitter follower mode. I assume the two bases Q1 and Q3 are not connected essentially to the same point apart from a Vbe multiplier for bias, but instead have separate drives at potentials near the two supply rails.

Are you sure you haven't got them upside down? i.e. the output connects to the junction of the two 0.47 resistors?

The arrangement you have drawn would have high output impedance, but this could be reduced via global negative feedback.

[AndrewT]

Hi,
check the NPN or PNP of the two outputs.

Now that others have been talking about the Baxandall Super Pair, I recognise both pairs as BSP.

Read the other threads to see if any of it's stability problems might apply to your output stage.

[NVD33]

Hi,

The amp is singing but I am not happy with the sound (too harsh, lack of dynamic, sound seems restrained). That 's why I decided to look at the schematic.

I was surprised to see this strange output arrangement, I have checked many times I am pretty sure that I did not make mistake on my drawing. I do not know how can work Q2 and Q4 they are polarized backward right? Can it be a mistake during production? They swapped Q2 and Q4 may be? My first idea was to swap Q2 and Q4 but I changed my mind to post for help.

- 0.47R resistors are in the supply lines and ouput is as in my drawing,

- I have checked also for the NPN and PNP output (Q2, Q4) they are as in my drawing,

I will check again, tomorrow I will also post a more complete schematic.

Thanks for your replies,

[nigelwright7557]

It looks very wrong to me.

Two of the transistors (q2 and q4) are wired the wrong way around.

[DF96]

Yes, it is wrong - I didn't look closely enough at it. Q2 and Q4 have emitter and collector mixed up. With this corrected it is then a strange circuit, rather than a wrong circuit.

My guess is that this is really a standard complementary feedback pair output, but the OP has got confused somehow. Seeing the previous stage which drives it would confirm this: VAS plus Vbe multiplier says this is a conventional CFP, separate drivers fed from an earlier phase splitter would suggest that it is not a CFP.

[NVD33]

We are "in phase now" this arrangement is wrong.

Assuming that my drawing is correct and that q2 & q4 are wired this way can the amp produce sound? As I stated above it produces sound!

[AndrewT]

yes, it works, it is the common emitter output stage requiring a driver stage that uses current through a resistor to the supply rail to control the CFP.
OOPs,
I hold this until I see the corrected schematic.
(The big difference is that the output stage uses two transistors in Baxandall Super Pair arrangement)

[sakis]

state brand and model you will be syrprized to see that schmatic might exist somewhere

regards sakis

[homemodder]

It looks to me like the Hiraga amp, its the only amp I know of that uses this arangement, it is strange you say the sound is bad as builders of the hiraga are very pleased with their amps saying it sounds very tube like. Maybe in your case something is wrong or its a different amp. Look up threads here about these amps, theyre called hiraga 8w monster amp and hiraga super class A amp, the builders might be able to give some good advice.