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Old 30th June 2009, 10:16 PM   #1
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Default Comments on this symmetric design

Do you have any comments on a design like this?

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Old 30th June 2009, 10:38 PM   #2
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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.
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Old 30th June 2009, 11:19 PM   #3
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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.
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Old 1st July 2009, 12:22 AM   #4
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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:

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There should be no further problems with this modified circuit right?
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Old 1st July 2009, 01:15 AM   #5
cbdb is offline cbdb  Canada
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How suceptible to R5 R12 mismatches is the output bias current and output offset voltage? (change one to 101 ohms)
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Old 1st July 2009, 02:29 AM   #6
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The output bias current changes about 1mA/ohm and the output offset 1mV/ohm if I change R5 or R12.
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Old 1st July 2009, 05:24 AM   #7
cbdb is offline cbdb  Canada
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OK, no worries there.
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Old 1st July 2009, 12:11 PM   #8
jaycee is offline jaycee  United Kingdom
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Keep the emitter followers on the VAS stages. Also consider cascodes.
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Old 1st July 2009, 04:38 PM   #9
AndrewT is offline AndrewT  Scotland
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where are you getting your resistor values from?
E24 values are common.
E48 and E96 values are difficult to source at sensible prices.
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Old 1st July 2009, 07:19 PM   #10
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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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