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Class D Switching Power Amplifiers and Power D/A conversion

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Old 12th August 2007, 01:48 PM   #21
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Quote:
Originally posted by BWRX
It is possible but the OPA1632 is not an instrumentation amp (inamp for short). The method I described is best done using an inamp. Something like TI's INA128 http://focus.ti.com/docs/prod/folders/print/ina128.html would probably work well.
I realise the OPA1632 isn't an instrumentation amp, but will the circuit I posted work? I sure hope so because I already made a layout.

I already have some OPA and not any INA, so I might as well give it a go.
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Old 12th August 2007, 02:23 PM   #22
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It will work because you can set the common mode output voltage to the bias voltage of the Tripath input stage. The input impedance will be low if you ground one of the input resistors for use with a single ended input, and you may benefit from using a buffer between the source and the other input resistor. You could make the OPA134 an OPA2134 and now use both opamps. I would also add the option to use a resistive load between the differential outputs.
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Old 12th August 2007, 03:11 PM   #23
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Quote:
Originally posted by BWRX
I would also add the option to use a resistive load between the differential outputs.
Between the two outputs, or from the outputs to ground? What value should the load be?
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Old 12th August 2007, 03:58 PM   #24
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Between the two outputs. A value in the 5k to 10k range would be good.
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Old 16th August 2007, 10:11 PM   #25
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I was just about to etch some boards when an idea popped into my head. In the pic above I made a DC trim board, but is it possible to add one to the dc coupling/buffer circuit instead? I would like to kill two birds with one stone if possible.

Something like this......

Click the image to open in full size.
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Old 20th August 2007, 02:02 PM   #26
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Default Hmmmmm

OK guy's, time to entertain the novices here please?

When removing the input caps you are saying that there should be no voltage potential between the source/power grounds but I thought that the grounds must be connected at the chip? I thought that the analog ground and source ground were the same thing
Do you need to break any links between these on the board if you are going to convert a T-amp board?

Any further elightenement would be very much appreciated chaps...please
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Old 21st August 2007, 06:32 AM   #27
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Come on chaps, a schematic maybe?....please!

theAnonymous1 ? Pano ? pretty please?
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Old 21st August 2007, 11:01 AM   #28
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Hi Lostcause. If you're just going to remove the coupling caps you need to use a floating power supply for the T-amp so that you can connect the source ground to the biascap pin (which is at 2.5V with respect to the power ground).
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Old 21st August 2007, 11:49 AM   #29
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Quote:
Originally posted by BWRX
Hi Lostcause. If you're just going to remove the coupling caps you need to use a floating power supply for the T-amp so that you can connect the source ground to the biascap pin (which is at 2.5V with respect to the power ground).
Hi there.

Interesting tweak.

I am running my Charlize on batteries. I guess I am floating.


One question from my side:

I connected my DDDAC directly to Charlize. I've thrown out one coupling cap (DAC-output) already.
The DDDAC outputs needs to be DC decoupled. That's taken care of by the Charlize input cap for now.

Can I apply the biascap tweak for above scenario without getting into trouble?

EDIT: I forgot. I am currently using the input cap of Charlize as a 1st order high-pass to filter the low frequencies below 100Hz.
Would there be an alternative to do that differently if considering above. Because I wouldn't really like to drop the benefits achieved with this filter-tweak!

Cheers
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Old 21st August 2007, 11:56 AM   #30
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Quote:
Originally posted by BWRX
Hi Lostcause. If you're just going to remove the coupling caps you need to use a floating power supply for the T-amp so that you can connect the source ground to the biascap pin (which is at 2.5V with respect to the power ground).
Hi Brian, thanks for the reply sir but I'm still a bit confused by the 'floating' aspect of the power supply..... On most T-amps the power ground and the input ground are the same aren't they?
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