My 1024W RMS CLASS A+ amplifier.

[ChocoHolic]

...OK we all seem to agree that the high frequency PSRR of the class A output stage is important to suppress the distorsions from the class B part.
And of course it is a combination of the parasitic capacitances and the transistor transconductance. But transconductance might be poorer than many people expect. In my Rookie amp examinations especially most PNPs did not really show great properties, - already in DC examination.... together with capacitances...
That's why I was considering to adjust AB instead of B. Your heat sinks could probably handle that.

[GK]

Okaayyy.....the error corrected class A power module is now added to the list:

http://users.picknowl.com.au/~glenk/MAIN.HTM (previous)
http://users.picknowl.com.au/~glenk/CLASSA.HTM (+new one)

Haven't got time to do a technical write up ATM though.........


To be continued.........

[ChocoHolic]

...uahu... even if I am a fan of simple designs. This design I do like even with that giant component count.
Hope you get it running properly.

... I can't resist to ask:
Do you really need a tripple darlington for the output stage? I mean your main amp is sophisticated enough to be modified without additional components to drive a little bit more current.
Don't bother, it is my passion to strip down circuits
And there are also people here, who clearly state that I tend to strip down my circuits to much for their taste.

[GK]

Originally posted by ChocoHolic
...uahu... even if I am a fan of simple designs. This design I do like even with that giant component count.
Hope you get it running properly.

... I can't resist to ask:
Do you really need a tripple darlington for the output stage? I mean your main amp is sophisticated enough to be modified without additional components to drive a little bit more current.
Don't bother, it is my passion to strip down circuits
And there are also people here, who clearly state that I tend to strip down my circuits to much for their taste.

It's actually a quad darlington output!
And yes, it is required, as the error correction circuit requires a high input impedance to work as best as possible. The EC circuit develops an exact voltage across the 750 ohm input resistor to counter and compensate for any deviation between the input and output voltages. This input resistor should be presented with little loading from the output stage.
The output current is limited to 64A, which is a nice safety factor of 100% over the peak current at the rated power of 1000Wrms into 2 ohms.

All BJT's used are high fT devices (especially the pre drivers), so speed isn't a problem.


Cheers,
Glen

[anatech]

Hi Glen,
I just caught your thread. Nice project.

Look up the Carver Lightstar amplifier. They used about 13 VDC differential between the outputs and the tracking power supply. Now, if you use switching mosfets for the PWM "down convertor" you will end up with a simplified, reliable amplifier. The high frequency switchers are easier to filter out than class B types. I think they ran about 40 KHz.

Don't forget, Carver left the class B supply tracking for PWM voltage control at high frequency. You could lose most of that heatsink material.

Just a thought.

-Chris

[Terry Demol]

Originally posted by G.Kleinschmidt



It's actually a quad darlington output!
And yes, it is required, as the error correction circuit requires a high input impedance to work as best as possible. The EC circuit develops an exact voltage across the 750 ohm input resistor to counter and compensate for any deviation between the input and output voltages. This input resistor should be presented with little loading from the output stage.
The output current is limited to 64A, which is a nice safety factor of 100% over the peak current at the rated power of 1000Wrms into 2 ohms.

All BJT's used are high fT devices (especially the pre drivers), so speed isn't a problem.


Cheers,
Glen

Glen,

I haven't had time to go over the design thoroughly, so quick
question - does amp have global FB or is OP EC sole means of
linearising OP stage?

Also, WRT OP stage only and at full power - what do you envisage
the EC voltage swing will be. IOW the total non linearity from IP to
OP (of the OP stage), that the 750R IP R will be correcting for?

It is quite complex but should be very linear.

cheers

Terry

[ChocoHolic]

Originally posted by G.Kleinschmidt



It's actually a quad darlington output!


Cheers,
Glen

Ooohps, right.
You are crazy
What do you smoke? I am just on chocolate....

But it is a fantastic project! Go on, I am curiously reading.

[jacco vermeulen]

Judging by the 240 Re's and GK's avatar pic, XTC by the ounce.

[myhrrhleine]

Originally posted by G.Kleinschmidt


Well I’ve got a 50A@240V outlet in my shed for dummy load testing things such as this:
http://users.picknowl.com.au/~glenk/CTM2K.HTM
So testing the amplifier at it’s maximum power output shouldn’t be much of a hassle.
The complete stereo amplifier will only have an idle dissipation of about 650W in total. Most of this is provided by the quiescent dissipation of the class A stages, which remain constant, regardless of what the amplifier is doing. 650W is less than the “low” setting of a typical fan heater.[/quote

I don't know the codes in Oz, but in the US a 15 amp breaker is typical.
Breakers are derated to 80% or 12A in this case.
So, at 650 watts, 2 channels would work OK on one ckt.

The amp is indeed *very* impressive.
Similar to one I have been working on. (mine will be of much lower power)
How is the Hawksford EC working out (I hope to include it in mine)
Mr. Cordell seems to think the outputs may be at too low a voltage for a BJT follower?

Glen

[myhrrhleine]

BTW,

Do you find the Hawkford EC effective for "class A"
Any idea how much distortion reduction?