suggestions - Amp Fig11.12 (Slone)

Havenwood · 27th April 2009, 06:26 PM

Hi!
What think about this modification?

The amplifier is in Randy Slone, pag 368 (Figure 11.12)

The amplifier works, but I thinkThe VAS is not ok

Iq is very very small (nV or pV on 0.1ohms)
What say about this?

Here the simulation:
http://www.megaupload.com/?d=2FHZYHTY
With MultiSim10

blueskynis · 27th April 2009, 06:47 PM

I think it will not work very well. Because of use of current mirrors in LTP the standing current is ill defined in VA stage. There are numerous threads about the problems that arise when using current mirrors in symmetrical designs. I remember G.Kleinschmidt was trying to use current mirrors in his symmetrical designs.

Edit: Have a look here
Unstable VAS current in amp from Slone book

CBS240 · 27th April 2009, 07:10 PM

Yes, you have to scrap the mirrors and replace them with resistors to define the bias in the VAS. Try about 680 Ohms. Also a small emitter resistor on the VAS transistors may help.

blueskynis · 27th April 2009, 07:23 PM

Also, how could mr. Slone publish his book with those big mistakes?? Even I noticed mistakes in his designs and I am not an expert.

homemodder · 27th April 2009, 10:06 PM

This design is bad, Slone realised his mistake, he has a newer version of the amp called optimos, this is a very good solid design, sounds darn good and is powerful. Worth a build.

Havenwood · 28th April 2009, 12:53 AM

Hi

blueskynis, what is LPT?

CBS240, ok, I will try simulate with the resistors R=680 (ie) in diferential transistor in the input stage.

VAS cascode is an option? like this:

Schematics:
http://www.pcpaudio.com/pcpfiles/pro.../Vag/etapa.pdf

from PCPAudio

Thanks!

Lumba Ogir · 28th April 2009, 01:37 AM

Havenwood,
the input stage cascode should have its own Vref /current source.

GK · 28th April 2009, 02:26 AM

Quote:

Originally posted by Havenwood
The amplifier is in Randy Slone, pag 368 (Figure 11.12)

The amplifier works, but I thinkThe VAS is not ok
Iq is very very small (nV or pV on 0.1ohms)

There is nothing to bias the VAS.

See here for one solution:
http://users.picknowl.com.au/~glenk/K12A.HTM

Havenwood · 28th April 2009, 03:24 AM

Quote:

Originally posted by G.Kleinschmidt
There is nothing to bias the VAS.

See here for one solution:
http://users.picknowl.com.au/~glenk/K12A.HTM

thanks for the link!
Very interesting

CBS240 · 28th April 2009, 06:19 AM

Quote:

Originally posted by Havenwood
Hi

blueskynis, what is LPT?

CBS240, ok, I will try simulate with the resistors R=680 (ie) in diferential transistor in the input stage.

VAS cascode is an option?

Schematics:
http://www.pcpaudio.com/pcpfiles/pro.../Vag/etapa.pdf

from PCPAudio

Thanks!

Hi

What is the purpose of the pots that source the cascode zeners?

The base of the Vbe multiplier should not be tied to the wiper, but the pot should be between the base and emitter. If the pot fails open (quite common) the outputs will fry.

27th April 2009, 06:47 PM	#2
blueskynis diyAudio Member Join Date: Aug 2007 Location: Niš	I think it will not work very well. Because of use of current mirrors in LTP the standing current is ill defined in VA stage. There are numerous threads about the problems that arise when using current mirrors in symmetrical designs. I remember G.Kleinschmidt was trying to use current mirrors in his symmetrical designs. Edit: Have a look here Unstable VAS current in amp from Slone book __________________ Windows-free with Linux == blueskynet.dyndns-server.com ==

27th April 2009, 07:10 PM	#3
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Yes, you have to scrap the mirrors and replace them with resistors to define the bias in the VAS. Try about 680 Ohms. Also a small emitter resistor on the VAS transistors may help. __________________ All the trouble I've ever been in started out as fun......

27th April 2009, 07:23 PM	#4
blueskynis diyAudio Member Join Date: Aug 2007 Location: Niš	Also, how could mr. Slone publish his book with those big mistakes?? Even I noticed mistakes in his designs and I am not an expert. __________________ Windows-free with Linux == blueskynet.dyndns-server.com ==

28th April 2009, 12:53 AM	#6
Havenwood diyAudio Member Join Date: Mar 2008	Hi blueskynis, what is LPT? CBS240, ok, I will try simulate with the resistors R=680 (ie) in diferential transistor in the input stage. VAS cascode is an option? like this: Schematics: http://www.pcpaudio.com/pcpfiles/pro.../Vag/etapa.pdf from PCPAudio Thanks! __________________ - Music by John Williams -

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27th April 2009, 10:06 PM	#5
homemodder diyAudio Member Join Date: May 2006	This design is bad, Slone realised his mistake, he has a newer version of the amp called optimos, this is a very good solid design, sounds darn good and is powerful. Worth a build.

28th April 2009, 01:37 AM	#7
Lumba Ogir Banned Join Date: Apr 2005 Location: Stockholm	Havenwood, the input stage cascode should have its own Vref /current source.

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