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Old 3rd October 2007, 02:40 PM   #1
ColinS is offline ColinS  England
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Join Date: Oct 2007
Default Headphone amp

By piecing bits and pieces together, and reading many sources I've come up with a design which seems to simulate ok. I was hoping to get any thoughts about it people may have, and improvements, or why it is so terrible before I purchase components to try it out.

The schematic can be found here

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Old 3rd October 2007, 03:07 PM   #2
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Join Date: Jul 2007
Location: South Worcestershire
You don't have any provision for adjusting the output stage bias. Why not replace R12 by a pot (say 220R).

Nothing is shown for trimming the offset.

You have no bias path at the input, so you absolutely require a DC coupled source, and must never power this up with the source disconnected.

You are running over 30mA through the LEDs, and I think that is a bit on the high side. You could replace R20 by either a higher value, or slip in a CC diode - say a J511, to get some extra PSRR.

No HF compensation is shown, and I don't think this is likely to be stable without it.

You might also want to consider putting emitter degeneration resistors into the input pairs, to bring the open loop gain down.
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Old 3rd October 2007, 03:38 PM   #3
jcx is offline jcx  United States
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A Classic pitfall circuit

the bias in the VAS is not firmly fixed by this circuit and may vary with component tolerance from simply nonfunctional to self-destructive extemes

Unstable VAS current in amp from Slone book

a possible solution:
optoisolator VAS bias for Comp Diff?

but I usually dismiss the diff complementary front end as little more than "eye candy" having little advantage in audio amplification

many headphone amp designs are collected at
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