True Digital Audio Amplifier

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!
theodoric said:
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.
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.

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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John Hope said:
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.
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 !
Hi, I haven't been about for a while now, but I spoted your thread today and thought that I would let you know what I'm supposed to be up to at the moment. This is basicaly trying to build up an amp based around the TI TAS5518 Digital audio processing chip, using a cirrus SPDIF converter, PIC micro to control things and some TAS5182 Driver chips going into an h-bridge output.

I've been (slowly) trying to put this together as a partof my final year project at university, and as my deadline is on the 1st of June I should hopefully be getting somewhere near to finishing it in the next week. And if it works (and I realy hope it does other wise I'm a bit stuffed when it somes to my project) I'll be happy to share my circuit designs and performance figures for the device (which basicaly does opperate as a high power DAC, without any feedback to improve the qouality of the output signal).

Either way, if it works or not, I would be interested to hear any views from people who have already heard this sort of technology in opperation.

John Hope said:

You are a lucky fellow to do such an interesting thesis project; I had to do stuff on Ternary Error Correcting Line Codes and could barely keep awake!

You may think so up untill the point where easy PC tells you you have reached the 500-pin limit of your software version and the only way round it is to pay £100 for the 1000-pin version because the engineering department are stuck back with version four (Number one are now up to version eight so thats quite some way behind). Actualy, in general when it comes to this project I wish I'd done something else as it's been such a pain to work with due to limited resources available. Oh for the days of having a proper workshop.

BigParsnip: I truly sympathise. There's nothing worse than being thwarted by the parsimony of university labs, and some companies, too. I think you need a real CAD; I use Protel DXP myself. (Now absorbed into Altium). They used to have a Free Trial Version that lasted 30 days before it keeled over, perhaps they still do. In which case you could download the Free Trial Version. (if you e-mail me I'll give you more information on this....)

Alternatively on the pages of this forum there is mention of other PC packages. Seek and ye shall find.


Well, on a pluss note I have finished what I think should be th edesign for my amp/dac so if it works once I have it together I'll quite happily put up the board layouts/schematics (or, if people want them, even the ones that don't work). One thing that the design does have which may be of interest as well is a board which will take in a standard coax or optical feed froma CD/DVD player and convert the data for use with a DAC chip or with this TI chip. But, I'll have ta wait and see if they do work first (and I should probably start a new thread for it seen as how this one has been hijaked a bit from the original point).

Hi wytc0:

Sorry I didn't see your previous posts because I unsubscribed from the thread, which seemed to be losing focus.

I have already posted some of the schematics of the existing PowerDAC 1 and 2, which I don't have any problem with sharing to the forum.

I am now developing PowerDAC3 - inbetween trying to work and live up to the high expectations of my cats - and there has been commercial interest shown in it by an established UK company. It wouldn't be appropriate for me to post details of the new developments at this time.

Kind regards

John Hope