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Old 28th August 2007, 02:19 PM   #1
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Default DC coupling circuit for Tripath amps

This idea started in another post......

Charlize 2

I think this is a novel solution and it deserves it's own thread that others can easily find.

The point of this circuit is to be able to DC couple Tripath amps. These amps have a 2.5v bias on the inputs that would normally require coupling capacitors. It also happens to act as a buffer and DC offset trim.

I have already built this and it works great. It gave my AMP32 a new set of ****s. Very authoritative and tight bass for such a small amp. Any suggestions and comments are welcome on how this circuit can be improved.

http://i18.tinypic.com/54n6q2p.jpg
http://i19.tinypic.com/52p5soh.jpg
http://i15.tinypic.com/6auhyqc.jpg
http://i10.tinypic.com/4z1ecma.jpg
http://i13.tinypic.com/4tjo7rc.jpg

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Old 10th September 2007, 12:54 PM   #2
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Well, there seems to be a small issue with this circuit. It works as it should and it sounds fine, but there is some major thermal drift going on.

The OPA1632 get blazing hot and this causes an offset drift of nearly 15mv after the board temp normalizes. This causes the amp to have almost 400mv of offset from a cold start.

I think I'll start from scratch and get some INA134. I used the OPA1632 because I already had them. I didn't realize how hot they get.
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Old 14th September 2007, 04:50 PM   #3
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Success at last.

I redid the circuit, but I am too cheap and impatient to buy any INA134 so I just copied the block diagram from the datasheet and used an op-amp instead. It worked like a charm.

The board stays nice and cool now and there is no more offset drift. I included a reference voltage buffer this time. I'm not sure if the fact I left it out of the first board was part of the problem or not.

I'll post some pics of the amp this goes to when it's all finished.

The completed board uses one OPA2134 and one OPA4134......

http://i18.tinypic.com/4oswozs.jpg
http://i2.tinypic.com/63kc1he.jpg

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Old 23rd June 2009, 06:08 PM   #4
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hello theAnonymous1,

i also have a t2020, and finanly i'm gonna mod it a bit further.

1)are you still running on your 2.5dc design ? just curious if things are still stable and doing fine.

2)you design is to overcome the input caps of the t2020
but what if there is dc on the source ?

3)about the floating psu; in the simple mod : take out the capacitor the psu has to be floating. But isn't it so that when the powercords of the other devices do not have a ground or earth that you can always rip out the capacitors? (none of my equipment has usb dac or tuner has a ground connection)

4)with your design, i suppose there is no problem with floating psu, or any other ground loop problems ?

thank you very much
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