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Old 8th April 2010, 01:37 AM   #1
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Default Another no overall NFB amp

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!
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Old 8th April 2010, 02:36 AM   #2
Bigun is offline Bigun  Canada
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Looks very interesting. Is this to be operated in Class AB ?
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Old 8th April 2010, 04:56 AM   #3
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Yes. Quiescent current is 50mA.
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Old 8th April 2010, 06:27 AM   #4
AKSA is offline AKSA  Australia
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A tour de force, no less.....

Have you built it, npnp? Does it sound sensational?
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Old 8th April 2010, 07:21 AM   #5
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Quote:
Originally Posted by AKSA View Post
A tour de force, no less.....

Have you built it, npnp?
Not yet
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Old 8th April 2010, 02:07 PM   #6
ontoaba is offline ontoaba  Indonesia
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Quote:
Originally Posted by AKSA View Post

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.
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Old 8th April 2010, 06:39 PM   #7
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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
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Old 8th April 2010, 07:05 PM   #8
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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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Old 8th April 2010, 07:09 PM   #9
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Quote:
Originally Posted by onto aban View Post
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 View Post
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)
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Old 8th April 2010, 10:12 PM   #10
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Quote:
Originally Posted by bogdan_borko View Post
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!
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