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Old 26th June 2008, 12:21 AM   #1
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Default 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:


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?

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Old 26th June 2008, 01:27 AM   #2
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Looks more like 10 mA @ 15V since the Gates should be at around
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Old 26th June 2008, 01:45 AM   #3
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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 :\

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