RMI-FC100 MKII, single ended folded cascode VAS

roender · 30th September 2008, 07:20 AM

Enjoy

roender · 30th September 2008, 07:22 AM

SR > 120V/uS

OLG gain

AKSA · 30th September 2008, 08:40 AM

Exceptional performance.....

Congratulations, Mihai!

Hugh

mlloyd1 · 30th September 2008, 12:19 PM

i don't think i've seen a current mirror used that way with a VAS like that before. it seems strange that it would work so well.
very clever!
when's the first model ready?
( i had to ask

)

mlloyd1

tvicol · 30th September 2008, 12:19 PM

I'm really impressed !

Keep up good work and I'm waiting you for a listening session.

Regards,
Tibi

Cambe · 30th September 2008, 12:32 PM

Well done! Mihai.

Cambe

roender · 30th September 2008, 09:13 PM

Thank you all for your kind words.
I have a question for all of you. Did you see this type of folded cascode VAS used before in a commercial or DIY amplifier?
With the help of Q14 I was able to obtain an almost constant current over R14 which means a very high and linear OLG.
The current mirror is inherited from MKI version but isn't necessary and can be replaced with a bootstrap CCS. In this configuration, colector of Q14 can be conected to ground.
R13 can be used to null the offset

Cheers,
Mihai

AKSA · 30th September 2008, 09:49 PM

Mihai,

Your (unique) circuit appears to be a combination of a topology attributed to a German named Lender, and a folded cascode. I'm pretty sure Borbely has used it.

Lender arranged the two resistor loaded collector outputs from the LTP so that one was connected to the VAS base, and the other to the VAS emitter, enhancing OLG with diff drive. You've interposed an additional transistor cleverly.... I have not seen this before but that's not to say it hasn't been done. The truth is, almost nothing is new...... but I do not criticise, it is very clever.

Cheers,

Hugh

roender · 30th September 2008, 10:10 PM

I make big efforts to decrease components count but without loose sonic quality.
I will compare two version of this type of VAS. The one as in posted schematics and the other without mirror and with a simple bootstrapped 3ma CCS form the (-) rail to folded cascode transistor.

homemodder · 30th September 2008, 10:51 PM

I dont think anyone has used that vas single ended before, but with dual differencial Ltps. Nearly all of Pavel dudeks amps use the scheme. For reference you could look at his DPA range of amps, Im pretty sure Bobberly would also have gone dual differencial.

Congrats on a nice design, very good performance.

30th September 2008, 08:40 AM	#3
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Exceptional performance..... Congratulations, Mihai! Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

30th September 2008, 09:49 PM	#8
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Mihai, Your (unique) circuit appears to be a combination of a topology attributed to a German named Lender, and a folded cascode. I'm pretty sure Borbely has used it. Lender arranged the two resistor loaded collector outputs from the LTP so that one was connected to the VAS base, and the other to the VAS emitter, enhancing OLG with diff drive. You've interposed an additional transistor cleverly.... I have not seen this before but that's not to say it hasn't been done. The truth is, almost nothing is new...... but I do not criticise, it is very clever. Cheers, Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

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30th September 2008, 12:19 PM	#4
mlloyd1 diyAudio Member Join Date: Feb 2001 Location: illinois	i don't think i've seen a current mirror used that way with a VAS like that before. it seems strange that it would work so well. very clever! when's the first model ready? ( i had to ask ) mlloyd1

30th September 2008, 12:19 PM	#5
tvicol diyAudio Member Join Date: Jan 2005 Location: Bucharest	I'm really impressed ! Keep up good work and I'm waiting you for a listening session. Regards, Tibi

30th September 2008, 12:32 PM	#6
Cambe diyAudio Member Join Date: Aug 2001 Location: USA,NorthCarolina	Well done! Mihai. Cambe

30th September 2008, 09:13 PM	#7
roender diyAudio Member Join Date: Sep 2006	Thank you all for your kind words. I have a question for all of you. Did you see this type of folded cascode VAS used before in a commercial or DIY amplifier? With the help of Q14 I was able to obtain an almost constant current over R14 which means a very high and linear OLG. The current mirror is inherited from MKI version but isn't necessary and can be replaced with a bootstrap CCS. In this configuration, colector of Q14 can be conected to ground. R13 can be used to null the offset Cheers, Mihai

30th September 2008, 10:10 PM	#9
roender diyAudio Member Join Date: Sep 2006	I make big efforts to decrease components count but without loose sonic quality. I will compare two version of this type of VAS. The one as in posted schematics and the other without mirror and with a simple bootstrapped 3ma CCS form the (-) rail to folded cascode transistor.

30th September 2008, 10:51 PM	#10
homemodder diyAudio Member Join Date: May 2006	I dont think anyone has used that vas single ended before, but with dual differencial Ltps. Nearly all of Pavel dudeks amps use the scheme. For reference you could look at his DPA range of amps, Im pretty sure Bobberly would also have gone dual differencial. Congrats on a nice design, very good performance.

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