D1 bias currents

spzzzzkt · 26th June 2008, 01:21 AM

I'm about to start matching mosfets for a D1 output stage and I'm sure I'm not reading/understanding the schematic correctly:

http://www.diyaudio.com/forums/attac...amp=1062946522

from searching the archives I understand that R26 and R33 set bias for Q3 and Q6 respectively, and using the I = (V-3)/R formula I calculate a bias current of slightly more than 8mA.

For Q2 and Q5 am I right in assuming that R25 and R32 set bias current and that this is around 18mA?

cheers
Paul

Nelson Pass · 26th June 2008, 02:27 AM

Looks more like 10 mA @ 15V since the Gates should be at around
18V.

spzzzzkt · 26th June 2008, 02:45 AM

Hi Nelson,

thanks for clearing that up. I'm trying to learn how to make sense of the schematics but it's a slow process!! So the network of R24, R21, and P4 set the gate of Q3 to approximately 15V?

btw I discovered your diy opamps article explained why fets give better performance than the mosfets in situations like the I/V. I really should read before asking dumb questions :\

cheers
Paul

26th June 2008, 01:21 AM	#1
spzzzzkt diyAudio Member Join Date: May 2005 Location: Melbourne	D1 bias currents I'm about to start matching mosfets for a D1 output stage and I'm sure I'm not reading/understanding the schematic correctly: http://www.diyaudio.com/forums/attac...amp=1062946522 from searching the archives I understand that R26 and R33 set bias for Q3 and Q6 respectively, and using the I = (V-3)/R formula I calculate a bias current of slightly more than 8mA. For Q2 and Q5 am I right in assuming that R25 and R32 set bias current and that this is around 18mA? cheers Paul

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26th June 2008, 02:27 AM	#2
Nelson Pass The one and only Join Date: Mar 2001	Looks more like 10 mA @ 15V since the Gates should be at around 18V.

26th June 2008, 02:45 AM	#3
spzzzzkt diyAudio Member Join Date: May 2005 Location: Melbourne	Hi Nelson, thanks for clearing that up. I'm trying to learn how to make sense of the schematics but it's a slow process!! So the network of R24, R21, and P4 set the gate of Q3 to approximately 15V? btw I discovered your diy opamps article explained why fets give better performance than the mosfets in situations like the I/V. I really should read before asking dumb questions :\ cheers Paul

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