New amp question

[Captain archer]

Hello everybody

I have an question, Could someone give a opinion about the circuit I designed down here.
The idea came to mind when in found this beautiful To66 Japanese transistors (2SD292 NpN 13w dissipation) mounted on a heat sink.
This comes from a almost 45 year old Sony amp.
Although all the capacitors in the amp are still fine amazingly, it uses 470uf output capacitors and no this is not a type error this is just awful and all the cinch connectors are corroded.
And believe me the list goes on and on.
I have build some other retro amps before (see my posts in post your solid state pics here topic).
And they where all based on the most basic LIN topology circuits, like almost every amp was in the 1960 and 1970’s.
This was and still is my hobby to build or rebuild retro things.
I used to design these simple circuits to replicate the sound as I never used to hear because I am only 22 years old.
But with these transistors I wanted to go a little step further and use current sources, and for the first time use a long taled pair as input.
I used to design circuits that had a singleton pre transistor and they where all bootstrapped current sourced.
Also this is the first schematic I designed that utilizes a dual power supply, before all my amps where based on a single supply rail with output capacitors (like the Sony amp).
I have never done this before and this is my first try, simulations show some good results dough.
It doesn’t have to be anything super fancy or whatever since it is still based on a asymmetrical quasi complementary output pair with 45 year old slow slooww sloooowwww slooooowwwww transistors.
But is this circuit good enough to utilize or are there some mayor flaws here.
Or are there some minor adjustments possible to make this circuit better without using to many extra active devices.
The TIP41c transistors will off-course be the Sony 2SD292 transistors and my plan was to use either BC550C and BC560C transistors in the rest of the circuit or BC337-40 and BC327-40.
For the Vas i maybe planned to use a BC141-16.

P.S. don’t mind the bias circuit this will be properly designed this was merely for simulation purposes.

Thanks guys

I will post the schematic as a picture, and I will post the Multisim simulation file in a zipped package.
And I will also post the 2SD292 datasheet.

Damn it is hard to explain things in English when you are dutch but I hope my question is clear.

[Captain archer]

Sorry not 13 but 18 watt dissipation

[Captain archer]

Does nobody have an answer or opinion?
Is this circuit usable or does this need some modification?

Sorry for my last post but when i placed this thread to many people also replied on a thread en so my question just dissappeard is no time.

[Nelson Pass]

On the face of it, it will work. It might need a little tweaking
for thermal or frequency stability.

[godfrey]

Hi

A couple of ideas:
- Add an input coupling capacitor.
- Reduce R15 and R16 to help the output transistors switch off faster.
- Use BC560B or BC560C instead of BC560A, especially for the input stage.
- Q11 and Q12 should be something with higher power rating?

The Sony amp with 470uF output capacitors sounds familiar. I think the one I had was a TA70 - it worked OK but was a horrible design!

Cheers - Godfrey

[Captain archer]

Yes it was the TA-70 man you are good

I want to rebuild it with the power transistors inside.
Indeed i was planning for matched BC550C and BC560c transistors in the input.
and for the driver and maybe Vas BC141-16 and BC161-16?

Input coupling cap is a good idea Thanks forgot all about that.

What value would be better for those "switch off" resistors 150-Ohm maybe?

Thanks

[Captain archer]

Here's the new schematic with updates

And is it a good idea to make R8 a trimpot so i can adjust dc offset?
now i have about 5mv offset in simulation is this acceptable?
And the 22-Ohm emitter resistors on the long tailed pair what is there purpose i have read somewhere that these provide local feedback is this correct?

Thanks

[Captain archer]

Circuit is now completed Added a diode and resistor in the bottom sziklai pair to improve symmetry.
Distortion is now 0.009% at 15 watts output power and 1 volt input.
Almost no offset voltage ( off-course in real life situations there will be differences) but I will make R14 a trimpot so I can null the offset.

So if anybody wants to use this circuit feel free to do so.

High frequency stability can be improved with adding a coil of 15-20 turns or so to the ouput tightly wound.

Here’s the new circuit and Multisim File

Greets Captain Starlog stardate April 16, 2010

Captain out………………………………….!

[padamiecki]

Originally Posted by Captain archer

...

Hi Capitan,
please look at harmonics distribution,
your amp probably will sound harsh/bright/metallic/sand-like

[woody]

That bias transistor Q8 could use a bypass cap.