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Class D Switching Power Amplifiers and Power D/A conversion

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Old 9th November 2008, 02:30 PM   #21
iand is offline iand  United Kingdom
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Quote:
Originally posted by oon_the_kid
Bwaslo,

Yes, I am aware of the operations of the class D amp. However, in a normal sound system, the signal is converted from SPDIF/I2S to current in a DAC, which in turn goes through an I-V stage for final conversion to voltage. This in turn goes through a VR for volume control and another circiut for pre-amp(sometimes). This in turn is fed into the input of the Tripath chip which has an inverting amp to bias it to before the final conversion to PWM in the DSP. This is a rather long winded of achieving the right PWM duty cycle. It should be possible to figure out the right PWM duty cycle without having to go through the analogue path from the SPDIF/I2S by usage of a DSP. Volume control could be implemented there too.

I think that would reduce the degradation of the signal a long way....

Oon
You've just described the Zetex DDFA...

http://www.zetex.com/audio/audio06.asp

Their latest measured results show around 120dB dynamic range at the speaker outputs, which rivals the best standalone DACs (which then have added noise and distortion from power amplifier stages etc)

http://www.zetex.com/audio/audio06_4.asp

Unfortunately the chips (and any design support) are only available to OEMs as far as I'm aware :-(

http://www.zetex.com/audio/audio06_2.asp

Ian

P.S. Disclosure -- I don't work for Zetex, but I did design the ZXCZM800 clock and PWM modulator output stages which would limit the dynamic range if they had jitter of more than a few picoseconds :-)
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Old 9th November 2008, 02:36 PM   #22
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Quote:
Originally posted by Workhorse
I think yes, but i found T-amps attract many guys except me.
And many of those guys don't have your knowledge or experience in regards to class-d; including myself. Anything more than a class-d "chipamp" is beyond my reach. Does that mean I have no right to post here and discuss what little I do understand (or at least try to), even if the subject of the discussion happens to be a non-UcD design?

No one is stopping you or anyone else from discussing other designs, and you are free to skip any lame Tripath threads or posts.

Maybe the class-d elites here should start their own forum where they are free to heckle and ban people with less knowledge.
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Old 9th November 2008, 02:42 PM   #23
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Quote:
Originally posted by theAnonymous1


And many of those guys don't have your knowledge or experience in regards to class-d; including myself. Anything more than a class-d "chipamp" is beyond my reach. Does that mean I have no right to post here and discuss what little I do understand (or at least try to), even if the subject of the discussion happens to be a non-UcD design?

No one is stopping you or anyone else from discussing other designs, and you are free to skip any lame Tripath threads or posts.

Maybe the class-d elites here should start their own forum where they are free to heckle and ban people with less knowledge.
Dude, dont hype the statement, i never said that T-amp lovers should be banned or not allowed to post, i was just saying that this forum is comprised more of T-amp Diyers, thats all........

I still regard myself as a learner in Class-D field, not an elite..........but i love to take part in discussions involving non-T-amps & non-UCD amps...
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Old 9th November 2008, 06:59 PM   #24
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Quote:
Originally posted by bwaslo
Oon -

You do know that Class-D amplifiers, in general, are analog amplifiers, not digital, right?. Sorry if this is obvious, just making sure because many people equate "Class D" with quantized "digital" and it just isn't so.

Class D is analogue if you start with an analogue signal and then make a PWM via triangle+comparator or by hysteresis selfresonance or by UCD. Because in all this constellations you start with analogue and code the information in a PWM which allows any duty cycle values - without quantization steps. The information remains 100% analogue.

If you go through a signal processor and generate a digitalized PWM with quantization steps for your power switches, then I would tend to call it digital - even if there is usually something like a passive power DAC in the end of the chain, formed by the output filter and the speaker.

What is better? Good question.
But I would also guess that digital-analogue-digital-analogue is not straight forward and might cause more damage to the signal than a chain with less conversions.
If we compare:
Digital-analogue and staying analogue with traditional class D designs.
Versus
Digital-into a digital class D and convert to analogue in the passive end stage....
Then I would guess it will end up in the question of how good the chosen digital coding & filtering + D-A conversion of each system and output filter are fitting together. I am sure you can mess up both ways.

In fact most of our music, which we hear, is already digitzied with quantization steps and quite poor sampling rate.... And with respect to the catastrophic appearing CD standard, I am again and again wondering how well our ears do accept it.
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Old 10th November 2008, 12:45 AM   #25
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Quote:
Originally posted by iand

You've just described the Zetex DDFA...

http://www.zetex.com/audio/audio06.asp

Their latest measured results show around 120dB dynamic range at the speaker outputs, which rivals the best standalone DACs (which then have added noise and distortion from power amplifier stages etc)

http://www.zetex.com/audio/audio06_4.asp

Unfortunately the chips (and any design support) are only available to OEMs as far as I'm aware :-(

http://www.zetex.com/audio/audio06_2.asp

Ian

Yup, this is precisely what I am looking for. Unfortunately, only available to OEM, I guess. I saw the ad for inclusion in a NAD. Maybe we might see it in a NAD soon. I think the true genius of tripath, is the usage of a digital processor to achieve the accurate switching, which means it probably a very high speed PID, this tends to reduce the overshoot and instabilities etc normally associated with analogue.

Well Ian, if you find out which other products uses it, maybe we can get hold of one and modify it....
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Old 10th November 2008, 12:56 AM   #26
Pano is offline Pano  United States
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Well the Apogee DDX chips look interesting.

The power chips can even be driven by Tripath controllers, if you want analog input. Otherwise the Apogee DDX control chips sure have a ton of features.

It's all going to end up as variable duty square wave that gets low pass filtered on its way to the loudspeaker - but how you get to that square wave is the interesting part. The digital path up to that point "should" have some advantages.

But of course you have to deal wit the volume control, for better of for worse.
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Old 10th November 2008, 01:25 PM   #27
iand is offline iand  United Kingdom
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Quote:
Originally posted by oon_the_kid


Yup, this is precisely what I am looking for. Unfortunately, only available to OEM, I guess. I saw the ad for inclusion in a NAD. Maybe we might see it in a NAD soon. I think the true genius of tripath, is the usage of a digital processor to achieve the accurate switching, which means it probably a very high speed PID, this tends to reduce the overshoot and instabilities etc normally associated with analogue.

Well Ian, if you find out which other products uses it, maybe we can get hold of one and modify it....
The digital PWM modulation processor is clocked at over 100MHz in the DDFA, including the error digitiser in the feedback path -- this is how Zetex get very fast and accurate correction of errors (distortion) because the total delay round the digital correction loop is small (<20ns), so the feedback loop can have very wide bandwidth and high gain without any (analogue) stability issues.

NAD are presumably a flagship DDFA user to gain market acceptance of DDFA as a high-quality class-D amplifier, though I guess they're not exactly small volume. I believe Zetex are primarily targeting the high-volume Far East audio manufacturers in markets like home cinema, because this is where the big production volumes are and Zetex want to sell lots of chips (which would make us happy too since we manufacture them :-)

So I guess whatever product NAD come out with is likely to be the best candidate for class D/audiophile modding -- unless you want to try and reverse engineer a multichannel Chinese-sourced home cinema box...

Ian
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Old 10th November 2008, 03:20 PM   #28
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I just wonder why nobody talks about the texas chips
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Old 10th November 2008, 04:06 PM   #29
Steven is offline Steven  Netherlands
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Quote:
Originally posted by iand


You've just described the Zetex DDFA...


Or the D2Audio approach: http://www.d2audio.com/

Steven
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Old 11th November 2008, 12:23 AM   #30
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Quote:

originally posted by audiomaniac:
I just wonder why nobody talks about the texas chips
The nice part about tripath to diy is the simplicity of usage. One can easily buy a kit and modify from there. There are no programing needed, no support chips and just a normal analogue input.

The unfortunate thing, I believeabout fully digital system is, quite frequently they require you to have some sort of support chips to generate the volume control, remember the last setting of the volume control, booting up the system etc. There must be a reason for them to have so many legs.... So I would not probably do it unless there is a full kit or modify a preexisting set., since i know nuts about digital....

Oon
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