Preamp concept - Page 2

PMA · 24th September 2005, 02:40 PM

Quote:

Originally posted by darkfenriz

Applied along the section of voltage gain of 1....?
On this RC there is a buffer error voltage drop, dividing by RC impedance you get parasitic error current drawn from VAS.
I think you are trying to be mysterious about the point of this arrangement...

As you know, the followers have 100% voltage feedback. Do you think they are unconditionally stable?

anli · 24th September 2005, 02:40 PM

Pavel,

No, I don't

There are no resistance values on the schematics. I have suggested output emiter resistors are about 10-50 ohm. In such case to move out stage to class A some emiter resitors are necessary for pre-out pair too. Where is my mistake? Or - what is your concept in words?

PMA · 24th September 2005, 02:47 PM

Andrej,

you are right. There are no values, which makes the case more interesting. The output emitter resistors are only 2.7 Ohms. Bias current is a game of Vbe voltages and thermal coupling.

darkfenriz · 24th September 2005, 03:00 PM

With emitter resistors of both 'drivres' and output stage you could add some local modulation or error correction or feedback or whatever one would call it.
Maybe you would be interested in my use of diamond buffer with modulated current sources (error correction).???
Perfect buffer for unity gain preamp, headphone class A amplifier or filters.
Needs some adjustment of bias and offset: 321R/339R are pots.
What do you think?

schematic:

darkfenriz · 24th September 2005, 03:02 PM

Forgot to add:
for low power speaker amp/ headphone amp one could take advantage of sweeping bias point.

PMA · 24th September 2005, 03:26 PM

You mean to use it as an output stage? The circuit I have shown can have a voltage gain up to 40 dB without problems.

darkfenriz · 24th September 2005, 03:28 PM

yes

anli · 24th September 2005, 03:51 PM

As for preamp (before output buffer) concept, I have selected (and am listening now) this topology:

http://gaydenko.com/preamp/final.jpg

PMA · 24th September 2005, 03:53 PM

Andrej - how does it sound and how does it measure?

anli · 24th September 2005, 04:03 PM

Pavel,

I have no experience in listening to nice amps. In such conditions it is the best

This is card's own spectrum:

http://gaydenko.com/preamp/card-own-4KHz-500mV.png

This is the preamp bridge-half spectrum:

http://gaydenko.com/preamp/un-4KHz-500mV.png

Last one was measured for prototype. In real preamp input fets were selected, and 2d harmonic is about -92db. All others are below my card resolution.

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24th September 2005, 02:40 PM	#12
anli diyAudio Member Join Date: Oct 2004	Pavel, No, I don't There are no resistance values on the schematics. I have suggested output emiter resistors are about 10-50 ohm. In such case to move out stage to class A some emiter resitors are necessary for pre-out pair too. Where is my mistake? Or - what is your concept in words?

24th September 2005, 02:47 PM	#13
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Andrej, you are right. There are no values, which makes the case more interesting. The output emitter resistors are only 2.7 Ohms. Bias current is a game of Vbe voltages and thermal coupling.

24th September 2005, 03:02 PM	#15
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Forgot to add: for low power speaker amp/ headphone amp one could take advantage of sweeping bias point.

24th September 2005, 03:26 PM	#16
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	You mean to use it as an output stage? The circuit I have shown can have a voltage gain up to 40 dB without problems.

24th September 2005, 03:28 PM	#17
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	yes

24th September 2005, 03:51 PM	#18
anli diyAudio Member Join Date: Oct 2004	As for preamp (before output buffer) concept, I have selected (and am listening now) this topology: http://gaydenko.com/preamp/final.jpg

24th September 2005, 03:53 PM	#19
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Andrej - how does it sound and how does it measure?

24th September 2005, 04:03 PM	#20
anli diyAudio Member Join Date: Oct 2004	Pavel, I have no experience in listening to nice amps. In such conditions it is the best This is card's own spectrum: http://gaydenko.com/preamp/card-own-4KHz-500mV.png This is the preamp bridge-half spectrum: http://gaydenko.com/preamp/un-4KHz-500mV.png Last one was measured for prototype. In real preamp input fets were selected, and 2d harmonic is about -92db. All others are below my card resolution.