VAS buffer

GEirin · 17th November 2009, 07:20 PM

Hi all.

Mr Self has 2 VAS buffer type. (Attached bellow).
1- VAS with CCS + buffer with CCS
2- VAS + Buffer with CCS

I´m very interested in to know the pro and cons the each type of VAS.
Thanks

GEirin · 18th November 2009, 09:32 AM

Reply?

OK.

Grundig SV 2000.
T404 VAS
T405 Buffer

Is better?
VAS NPN and Buffer NPN?
Separate CCS, one for VAS other for Buffer?
Opinions, please reply.
Thanks

forr · 18th November 2009, 08:30 PM

A few weeks ago, I was wondering in a post about the reason why such buffers are almost never seen on schematics, at leat on the recent ones. No answer at all.
Is there some rebuttal towards single ended buffers ? In that case, why not to use a White buffer (with a clean power supply) which has the nice feature of a well defined quiescent current.

AKSA · 18th November 2009, 09:03 PM

Geirin,

I prefer (f), because it is simpler (one CCS), and should lean more towards even order distortion. I have not simmed it, however.

Both work well.

Hugh

GEirin · 18th November 2009, 09:44 PM

Hi Hugh
Thank you very much.

A question:
Which transistors you suggest to use for VAS and buffer?
VAS: BC546?
Buffer: 2SA1358, 2SA1360?

Guillermo

AKSA · 19th November 2009, 07:10 AM

Guillermo,

I like 2SC1845 for VAS (110MHz, Cob 1.6pF, beta 600, super low noise, 50mA but watch the dissipation, only 500mW, don't run it over about 150mW), and 2SC1360 for the buffer. However, since the buffer is an EF, and intrinsically fast, you could use any relatively high voltage device here, such as a 2SA1837, BF470, or even a cheap BD140 if operating at low voltage.

Cheers,

Hugh

Lumba Ogir · 19th November 2009, 07:57 AM

forr,

Quote:

A few weeks ago, I was wondering in a post about the reason why such buffers are almost never seen on schematics

Because they do more harm than good. Is that a good reason for you?

GEirin · 19th November 2009, 09:48 AM

Hugh
Thank you very much for you help.
I will try to use this VAS type in my amplifier project.
regards
Guillermo

forr · 19th November 2009, 10:07 AM

Quote:

Originally Posted by Lumba Ogir

forr,

Because they do more harm than good. Is that a good reason for you?

Not at all. Because you don't give the slightest idea of harm it could introduce and some very good reasons have already been mentionned wihout any caution in D. Self's litterature.

AKSA · 19th November 2009, 10:41 AM

Lumba,

With respect, you are wrong. I support Sebastien. The buffer makes the VAS act as a voltage, not a current source, and this makes for less correction as it negotiates the erratic load of the output stage.

I notice better sonics, too, a stronger performance all round, and more resolution.

Hugh

18th November 2009, 09:03 PM	#4
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Geirin, I prefer (f), because it is simpler (one CCS), and should lean more towards even order distortion. I have not simmed it, however. Both work well. Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

19th November 2009, 07:10 AM	#6
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Guillermo, I like 2SC1845 for VAS (110MHz, Cob 1.6pF, beta 600, super low noise, 50mA but watch the dissipation, only 500mW, don't run it over about 150mW), and 2SC1360 for the buffer. However, since the buffer is an EF, and intrinsically fast, you could use any relatively high voltage device here, such as a 2SA1837, BF470, or even a cheap BD140 if operating at low voltage. Cheers, Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

19th November 2009, 10:41 AM	#10
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Lumba, With respect, you are wrong. I support Sebastien. The buffer makes the VAS act as a voltage, not a current source, and this makes for less correction as it negotiates the erratic load of the output stage. I notice better sonics, too, a stronger performance all round, and more resolution. Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

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18th November 2009, 08:30 PM	#3
forr diyAudio Member Join Date: Dec 2004 Location: Next door	A few weeks ago, I was wondering in a post about the reason why such buffers are almost never seen on schematics, at leat on the recent ones. No answer at all. Is there some rebuttal towards single ended buffers ? In that case, why not to use a White buffer (with a clean power supply) which has the nice feature of a well defined quiescent current.

18th November 2009, 09:44 PM	#5
GEirin diyAudio Member Join Date: Jun 2004 Location: Mendoza	Hi Hugh Thank you very much. A question: Which transistors you suggest to use for VAS and buffer? VAS: BC546? Buffer: 2SA1358, 2SA1360? Guillermo

19th November 2009, 09:48 AM	#8
GEirin diyAudio Member Join Date: Jun 2004 Location: Mendoza	Hugh Thank you very much for you help. I will try to use this VAS type in my amplifier project. regards Guillermo

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