Another no overall NFB amp

npnp · 8th April 2010, 12:37 AM

Hello!

Here's my idea for an amplifier without overall NFB. Output power is about 35W @ 8 ohm.
Output stage is Hawksford E.C. topology.
VAS has a diamond structure.
DC servo circuit is taken from here.
Simulation results are promising.

Any suggestions are welcome!

Bigun · 8th April 2010, 01:36 AM

Looks very interesting. Is this to be operated in Class AB ?

npnp · 8th April 2010, 03:56 AM

Yes. Quiescent current is 50mA.

AKSA · 8th April 2010, 05:27 AM

A tour de force, no less.....

Have you built it, npnp? Does it sound sensational?

npnp · 8th April 2010, 06:21 AM

Quote:

Originally Posted by AKSA

A tour de force, no less.....

Have you built it, npnp?

Not yet

ontoaba · 8th April 2010, 01:07 PM

Quote:

Originally Posted by AKSA

Does it sound sensational?

Buffered current amplifier.
OnlyC5200 & A1953 has linearity, and there is local feedback in pre-driver stage low linearity V->I conversion and some low linearity mirror gain.

darkfenriz · 8th April 2010, 05:39 PM

What's the current in VAS stage? I think you could reduce it while kepping the same gain.
Overally a nice schematic with a terribly overengineered servo

bogdan_borko · 8th April 2010, 06:05 PM

I made similar input (voltage amplifier) and it sounded lot better with 6dB feedback (taken from the VAS output) then with zero feedback...
Also tried (open loop) mosfet error-correction output stage but it can`t come near bipolar "simple" triple EF.

npnp · 8th April 2010, 06:09 PM

Quote:

Originally Posted by onto aban

Buffered current amplifier.
OnlyC5200 & A1953 has linearity, and there is local feedback in pre-driver stage low linearity V->I conversion and some low linearity mirror gain.

According simulator nonlinearities is not that great (THD 0.02% @ 1kHz @ 30W).

Quote:

Originally Posted by darkfenriz

What's the current in VAS stage? I think you could reduce it while kepping the same gain.
Overally a nice schematic with a terribly overengineered servo

Q8, Q17 - 1mA
Q5, Q19 - 2.5mA
Q9, Q16 - 7mA (to work permanently in class A mode)

npnp · 8th April 2010, 09:12 PM

Quote:

Originally Posted by bogdan_borko

I made similar input (voltage amplifier) and it sounded lot better with 6dB feedback (taken from the VAS output) then with zero feedback...

You're right

THD decreased twice!
Thanks!

8th April 2010, 01:36 AM	#2
Bigun diyAudio Member Join Date: Jan 2009 Location: K-W Ontario Blog Entries: 2	Looks very interesting. Is this to be operated in Class AB ? __________________ "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

8th April 2010, 05:27 AM	#4
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	A tour de force, no less..... Have you built it, npnp? Does it sound sensational? __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

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8th April 2010, 03:56 AM	#3
npnp diyAudio Member Join Date: Aug 2009	Yes. Quiescent current is 50mA.

8th April 2010, 05:39 PM	#7
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	What's the current in VAS stage? I think you could reduce it while kepping the same gain. Overally a nice schematic with a terribly overengineered servo

8th April 2010, 06:05 PM	#8
bogdan_borko diyAudio Member Join Date: Nov 2005 Location: serbia, zajecar	I made similar input (voltage amplifier) and it sounded lot better with 6dB feedback (taken from the VAS output) then with zero feedback... Also tried (open loop) mosfet error-correction output stage but it can`t come near bipolar "simple" triple EF.

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