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Class D Switching Power Amplifiers and Power D/A conversion

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Old 17th May 2005, 06:57 AM   #1
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I'm posting this here since there doesn't seem to be a forum that better matches my topic.

I see that some people on the forum (percy, Bruno and dutch among others) are discussing the difference between Class-D and Digital amplifiers. TI calls their products in the latter category True Digital Audio Amplifiers (TDAA). I believe this term is a much better way to refer to the devices in question.

TDAA's typically accepts PCM/I2S digital audio streams as inputs, convert these to PWM signals to drive their (Class-D style) digital/switching power stages and then filters the signal to produce the amplified signal which goes to the speakers.

I am a firm believer that TDAA's (not necessarily TI's) are the way forward and I would like to build some of these myself in the near future. Has anyone here already done so?

Does anyone know how some of these TDAA's compare to each other and/or to other (ie Class-D) amps?

Any other views/thoughts welcome!
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Old 18th May 2005, 07:14 AM   #2
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Originally posted by theodoric
Does anyone know how some of these TDAA's compare to each other and/or to other (ie Class-D) amps?
Most of these are limited by the performance of the power stage. Usually a lot of attention has gone into making a good modulator and that the power stage would be the limiting factor was realised only afterwards.

I'd consider the TI chip sets the best open-loop digital offering on the market if you stay with one supplier. The TI modulators are quite good and the power chips are OK. Other options are combining TI modulators with power chips by Philips and ST. I would suggest reading the other threads, because the fact that a certain chipset is the best in the open-loop digital field does not imply I think it's good. I'm not going to argue that case here because I don't think it was your question.
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Old 18th May 2005, 11:26 AM   #3
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Hmm... I have some of the TI chipsets lying around which I suppose I could use to build a prototype amp for evaluation purposes. I could then combine that with my existing TI digital crossover (if I'm happy with the results of said crossover) and work my way towards a full-on digital system from there (again if all results are satisfactory). Perhaps I'll even do wireless, anyone have any experience with Bluetooth etc?

Let me munch these thoughts over for a day or so. If I decide to do this, I might even put up a website for it.
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Old 19th May 2005, 11:17 AM   #4
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Theodoric: Ja well, no fine. There is already a thread on the forum called something like 'Anyone interested in building a digital amplifier...' under Class D. It's very worthwhile reading it all.

Bruno and John Westlake have been building TDAAs for many years and John Westlake's latest design - which uses closed loop feedback around the power stage - has the best measured performance of any TDAA anywhere, at any price. I've been designing and building open TDAAs since about 1995 and am presently working on yet another one. It's a serious addction and challenge to a variety of one's theoretical and technical skills.

If I were you I would start off by building a stereo TDAA based on the TI modulator chip (which is probably the best available today), coupled to a discrete output stage (OPS) of your own design. Some of John Westlake's discrete OPS schematics have been posted on the forum and my own PowerDAC 2 OPS schematic - based on a HIP4081A bridge driver - is also out there somewhere. These can serve as a good base and the design and layout of an OPS with low THD will keep you out of mischief for long enough for you to forget all this BlueGum. . .Bluee teeth...Buck teeth - whatever - computerry stuff!

I've attached a pic of PowerDAC 2 to whet your interest.

Veels geluk

John Hope
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Old 19th May 2005, 11:28 AM   #5
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Originally posted by John Hope
Bruno and John Westlake have been building TDAAs for many years and John Westlake's latest design - which uses closed loop feedback around the power stage - has the best measured performance of any TDAA anywhere, at any price.
But then again - closed loop. I think by TDAA Theodoric means open-loop ie. no op amps or other analogue parts in the circuit.
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Old 19th May 2005, 12:15 PM   #6
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Bruno: Yes, open loop (like TacT Millenium and my PowerDAC 2 and the TI OPS ) is what I'm suggesting Theodoric build. As you say, once one starts putting blatant analog stuff in . . .

But hey, let's not embroil this innocent newcomer in the Digital Amplifier nomenclature wars!

Cheers

John
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Old 19th May 2005, 12:35 PM   #7
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Originally posted by John Hope
But hey, let's not embroil this innocent newcomer in the Digital Amplifier nomenclature wars!
Exactly
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Old 20th May 2005, 09:33 AM   #8
wytco0 is offline wytco0  United Kingdom
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John Hope is the powerdac avaiable as a product or plans anywhere? I have tried searching but ended up with confusing results !

I understand its your own design, but have you made any thing available?

I assume its not relkated to the Wadia product? or is it?

Apologies if these are silly questions with obvious answers !
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Old 20th May 2005, 09:59 AM   #9
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I assume it is his own DIY product, although looking veeeeeeery commercial (i.e. clean and professional).

Regards

Charles
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Old 20th May 2005, 10:00 AM   #10
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Sorry John, I'm a computery type of guy. Like I said, I plan to first get the actual system up and running (piece by piece that is) and then much later on hopefully make it wireless.

I also find your PowerDAC quite interesting looking and wouldn't mind some more info to chew over.
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