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Old 15th January 2014, 04:02 AM   #1
bimo is offline bimo  Indonesia
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Default How to optimize this CFA?

I have build VSSA and then inspire by Lazy Cat who achieve 0,0001% THD at 1kHz, 1W/8Ohm with his First One, I want to modify my VSSA.

Please help me to optimize this design for lower THD and to make stable. I want to make this design as simple as possible. Any suggestion are welcome.

Anistardi
Attached Files
File Type: pdf VSSA 2 Lateral OPS OK3.asc.pdf (27.3 KB, 79 views)
File Type: asc VSSA 2 Lateral OPS OK3.asc (11.3 KB, 31 views)
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Old 15th January 2014, 04:20 AM   #2
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It's a CFA , needs regulation /CCS's .. no way around it.

It's 2 big caps make THD .01% at 20hz. No way around that without
a servo. HF is extraordinary, PPM all the way to 100k.

Below is what I settled on for this design. It will be my second CFA
IPS. (with servo)

PS - make stable ???? It will run with NO compensation ...
Also , heck with the "THD fetish" , I want PSRR , no drift/DC , run cool and to last for 20 years.
.001% and below is a good target.
OS
Attached Images
File Type: jpg VSSA-H.jpg (112.1 KB, 361 views)
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Last edited by ostripper; 15th January 2014 at 04:26 AM.
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Old 15th January 2014, 04:36 AM   #3
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Quote:
Originally Posted by ostripper View Post
It's a CFA , needs regulation /CCS's .. no way around it.

It's 2 big caps make THD .01% at 20hz. No way around that without
a servo. HF is extraordinary, PPM all the way to 100k.

Below is what I settled on for this design. It will be my second CFA
IPS. (with servo)

PS - make stable ???? It will run with NO compensation ...
Also , heck with the "THD fetish" , I want PSRR , no drift/DC , run cool and to last for 20 years.
.001% and below is a good target.
OS
I want to trade THD 20 Hz for simplicities. Btw, my ears more sensitive at high freq . May be I add capacitance multiplier for IPS.
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Old 15th January 2014, 04:42 AM   #4
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Quote:
Originally Posted by bimo View Post
I want to trade THD 20 Hz for simplicities. Btw, my ears more sensitive at high freq . May be I add capacitance multiplier for IPS.
Yes , C mult. is "big one" ... CCS is also a real game changer.
Actually , the VSSA is the best of my simulated CFA's for LF WITH caps.
(.006% 20hz -2200u caps) ....

OS
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Old 15th January 2014, 05:31 AM   #5
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Quote:
Originally Posted by ostripper View Post
Actually , the VSSA is the best of my simulated CFA's for LF WITH caps.
(.006% 20hz -2200u caps) ....

OS
But this is 0.000363% at 12Vp.
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Old 15th January 2014, 08:01 AM   #6
bimo is offline bimo  Indonesia
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Default VSSA with 3EF

I change the OPS with 3EF.
To get lowest THD, the VAS current is around 13-14mA for all OPS. CCS setting is tricky.
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File Type: asc VSSA 3EF.asc (16.4 KB, 31 views)
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Old 15th January 2014, 12:14 PM   #7
bimo is offline bimo  Indonesia
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Quote:
Originally Posted by bimo View Post
I change the OPS with 3EF.
To get lowest THD, the VAS current is around 13-14mA for all OPS. CCS setting is tricky.
Almost finish. Very low THD
Attached Files
File Type: pdf VSSA 3EF.asc.pdf (37.5 KB, 66 views)
File Type: asc VSSA 3EF.asc (19.8 KB, 22 views)
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Old 15th January 2014, 12:33 PM   #8
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Quote:
Originally Posted by bimo View Post
Almost finish. Very low THD
With optimize bias current of output transistors, it give:
121W/8Ohm, 1kHz, 0.000076%
121W/8Ohm, 20kHz, 0.000559%

If implemented correctly, I'm sure it will comparable to LC's First One .
I was finished to draw OPS PCB like OS's style. But I must make some software for my friend now.
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Old 17th January 2014, 08:16 AM   #9
bimo is offline bimo  Indonesia
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Inspire by OS, I draw the OPS. I already send the file to PCB maker.
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File Type: pdf 3EF OUT AMP.brd.pdf (58.0 KB, 62 views)
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Old 17th January 2014, 08:27 AM   #10
bimo is offline bimo  Indonesia
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... and the IPS.
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File Type: pdf VSSA Haksford Cascode.brd.pdf (41.6 KB, 71 views)
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