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Old 3rd November 2007, 10:34 AM   #1
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Default TPA6120 headphone amp with servo

The TPA6120 is a very good sounding opamp with great spec's. The problem is a very high input bias current causing a lot of DC-offset. Either you have to use a crappy opamp in front of it, or you have to use degrading coupling caps, or you have to use a DC-servo. Since there was no room for high grade output caps and I dislike opamps in general, I used a servo.

I didn't make the board myself. I bought it from a fellow Head-Fi:er. http://www.head-fi.org/forums/showthread.php?t=258698

There's an OPA690 as active ground and a TLE2426 as railsplitter/virtual ground. Since OPA690 is 12 V max, there's a 7812 to protect it from higher voltages. I haven't decided what enclosure to use - a mint tin or a Hammond C801. The servo opamp is an OPA2132. The DC-offset is 2 mV.

The sound is very clean, almost overly detailed. There's great slam and energy. It plays loud as hell with no effort. I'm not sure how good it is or if I'm going to like the sound signature of it, have to listen some more. I have nothing but a DMM, so I can't tell if there's ringing or oscillation. The current draw is what's expected - 32 mA quiescent.
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Old 3rd November 2007, 11:09 AM   #2
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Default Re: TPA6120 headphone amp with servo

Quote:
Originally posted by nelsonvandal
I dislike opamps in general, I used a servo....
1 The TPA6120 is an opamp but of current fedback type.....
2 The servo is also an oapmp and actually in the audio chain.....
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Old 3rd November 2007, 01:07 PM   #3
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Default Re: TPA6120 headphone amp with servo

Quote:
Originally posted by nelsonvandal
The TPA6120 is a very good sounding opamp...
1. Yes I know
2. This amp doen't sound a bit like OPA2132. I don't think it'll affect the sound that much compared to used in front of the TPA, but I'm not sure because I haven't tried it. I think the sound signature is about the same as before I added the servo. What are your experience using servos? I know you've used it quite a lot. Is there a more elegant way to solve the offset problem? Don't you think this is a great sounding opamp?

This gives hope about even better opamps. ADA4899-1 is also a very transparent sounding opamp, but without the power of TPA6120. Opamps are improving .
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Old 8th November 2007, 08:54 PM   #4
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After some more listening, I can tell this amp isn't as neutral as I thought. It has a kind of silky, shiny coloration - like as it smears out grains and make everything smoother. So I don't think it's more high-resolution than other amps, it just gives the impression of it. It still sounds very good with a highly enjoyable, easy-to-listen-to sound, smooth yet energetic. It's a little bit too lean for my taste. I like a fuller/meatier sound.

This leaves ADA4899-1 king of details and neutrality.
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