Comments on this symmetric design

danfo098 · 30th June 2009, 10:16 PM

Do you have any comments on a design like this?

homemodder · 30th June 2009, 10:38 PM

Dont think it will work, vas biasing currents are undefined by using the mirrors, do a search here for Randy Slone s designs for more details.

blueskynis · 30th June 2009, 11:19 PM

It will not work. The VAS standing current will not be well defined when using current mirrors. Try searching G.Kleinschmidt symmetrical design posted here on forum.

danfo098 · 1st July 2009, 12:22 AM

Ok, thanks for confirming my doubts. It worked when I first simulated it but after reading your comments I tried doubling the supply voltage and the quiescent current through the output transistors increased from ~70mA to ~700mA.

I modified the circuit to this:

There should be no further problems with this modified circuit right?

cbdb · 1st July 2009, 01:15 AM

How suceptible to R5 R12 mismatches is the output bias current and output offset voltage? (change one to 101 ohms)

danfo098 · 1st July 2009, 02:29 AM

The output bias current changes about 1mA/ohm and the output offset 1mV/ohm if I change R5 or R12.

cbdb · 1st July 2009, 05:24 AM

OK, no worries there.

jaycee · 1st July 2009, 12:11 PM

Keep the emitter followers on the VAS stages. Also consider cascodes.

AndrewT · 1st July 2009, 04:38 PM

where are you getting your resistor values from?
E24 values are common.
E48 and E96 values are difficult to source at sensible prices.

danfo098 · 1st July 2009, 07:19 PM

I just pick the values (from thin air

) then I source the closest/best compromise mostly from farnell.

But don't get hung up on the values in the above modified schematic I will most likely change them.

30th June 2009, 10:16 PM	#1
danfo098 diyAudio Member Join Date: Apr 2005 Location: Linköping	Comments on this symmetric design Do you have any comments on a design like this?

30th June 2009, 11:19 PM	#3
blueskynis diyAudio Member Join Date: Aug 2007 Location: Serbia, Nis	It will not work. The VAS standing current will not be well defined when using current mirrors. Try searching G.Kleinschmidt symmetrical design posted here on forum. __________________ Windows-free with Fedora 10

1st July 2009, 04:38 PM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	where are you getting your resistor values from? E24 values are common. E48 and E96 values are difficult to source at sensible prices. __________________ regards Andrew T.

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30th June 2009, 10:38 PM	#2
homemodder diyAudio Member Join Date: May 2006	Dont think it will work, vas biasing currents are undefined by using the mirrors, do a search here for Randy Slone s designs for more details.

1st July 2009, 12:22 AM	#4
danfo098 diyAudio Member Join Date: Apr 2005 Location: Linköping	Ok, thanks for confirming my doubts. It worked when I first simulated it but after reading your comments I tried doubling the supply voltage and the quiescent current through the output transistors increased from ~70mA to ~700mA. I modified the circuit to this: There should be no further problems with this modified circuit right?

1st July 2009, 01:15 AM	#5
cbdb Sin Bin Join Date: Oct 2008	How suceptible to R5 R12 mismatches is the output bias current and output offset voltage? (change one to 101 ohms)

1st July 2009, 02:29 AM	#6
danfo098 diyAudio Member Join Date: Apr 2005 Location: Linköping	The output bias current changes about 1mA/ohm and the output offset 1mV/ohm if I change R5 or R12.

1st July 2009, 05:24 AM	#7
cbdb Sin Bin Join Date: Oct 2008	OK, no worries there.

1st July 2009, 12:11 PM	#8
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Keep the emitter followers on the VAS stages. Also consider cascodes.

1st July 2009, 07:19 PM	#10
danfo098 diyAudio Member Join Date: Apr 2005 Location: Linköping	I just pick the values (from thin air ) then I source the closest/best compromise mostly from farnell. But don't get hung up on the values in the above modified schematic I will most likely change them.

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