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Old 16th August 2011, 10:41 AM   #11
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Quote:
Originally Posted by trevmar View Post
The TA3020 chip, on the other hand, uses the Tripath clocked-sample encoding technology. You can see from the test measurements in my first post that the I-R Delta-Sigma technology produces higher fidelity, distortion numbers which are much better than any of the Tripath chips.
No. The TA3020 like all Tripath chip use Sigma-Delta converters. No input frequency is around 700MHz. With input it's spread spectrum from 200KHz to 1.5MHz.

The TA3020 as you can see in the link above has a THD+N vs. Power that over the whole range until clipping is beneath your testing equipments noise floor at -80dB (0.01%), so it's a far cry better than the IRS2092 in that respect.

How it sounds, I don't really know but I would assume it would perform similar to the TA3020. Though probably not as good.

It's cheap though... and still in production so for a new design the choice is obvious.
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Old 16th August 2011, 10:58 AM   #12
trevmar is offline trevmar  United States
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Show me the results, please. Where is your test data showing that a real circuit board can give a distortion vs power and distortion vs frequency with total distortion levels remaining below -80dB? I don't want to show disrespect, but please point me to a third party test where such a level of performance was achieved
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Last edited by trevmar; 16th August 2011 at 11:00 AM.
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Old 16th August 2011, 11:19 AM   #13
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I trust the measurements from Jan at 41hz completely. They have always been accurate.

That's also why the noise floor of the testing equipment was shown so that you can test for yourself... if you got good enough testing equipment.

Click the image to open in full size.

That's for the assembled finished version of the Amp15, ie. a complete amp. Not just the chip.

Last edited by Saturnus; 16th August 2011 at 11:22 AM.
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Old 16th August 2011, 12:06 PM   #14
trevmar is offline trevmar  United States
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Saturnus,
I found the curve attached below on Page 8 of the Tripath application note for the TA3020, titled "Class T Digital Audio Amplifier Evaluation Board," part number Bridged RB-TA3020-1-3 MC/1.0/06-01, EAD003.

It seems remarkably similar to the curve I measured on the L20D (also attached below), not to the curve the manufacturer gave you for its AMP15 performance. Here is an explanation of why such differences are frequently seen in power electronics, and why they are unimportant.

My test equipment actually goes down to the noise floor of the 16bit input A-D converter. There are problems involved in measuring a distortion vs power curve such as you have shown, the input level at 1W (vs 100W) is already 40dB below the peak threshold, requiring a 120dB total dynamic range in the measuring circuitry. That sweep you are showing for the AMP15 must have been very carefully measured indeed.

I didn't worry about the rising noise floor in my L20D measurements (caused by my test input's 'limited' dynamic range) because the THD+noise values were already so low as to be negligible. No listening room on this planet can achieve a 120dB ratio between background noise and peak loudspeaker level. A typical noise room level rarely falls below 20dBA and most listeners don't want sound levels above about 120dBA, a total dynamic range of 100dBA. The situation is more complex than that, of course, but that is a good rule of thumb.

If you are going to directly compare my L20D data to that AMP15 curve, however, it looks like I need to make a better effort at identifying the actual L20D noise level below 10W, rather than have readers assume that the AMP15 is actually better than the L20D.

The IR amp did hit -80dB at higher signal levels, and may well have maintained it down to 1W, just as the AMP15 curve says it does. Who knows? I certainly paid little attention to any THD below -60dB, which is lower than any available speaker can reproduce Although it is always nice to publish great specs on an amplifier, they usually turn out to be meaningless.

I don't really want to split hairs, the quickest thing is for me to do is look around for a TA3020 chip and test it out more closely
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Attached Images
File Type: gif Tripath_TA3020_Pdist_curve.gif (46.3 KB, 1400 views)
File Type: gif Pdist_L20D_8ohm_200W.gif (16.4 KB, 1387 views)
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Old 16th August 2011, 01:42 PM   #15
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The FETs used by Tripath in their application note and the application note board are very inferior to those used by 41hz, and other manufacturers who actually use the TA3020 chip, so you can't read anything into that. The vast majority of distortion will be a in the output FETs and the board layout of the output section. This will be especially note worthy at lower power levels.

Last edited by Saturnus; 16th August 2011 at 01:46 PM.
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Old 16th August 2011, 02:07 PM   #16
trevmar is offline trevmar  United States
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Are you suggesting that International Rectifier don't have the best range of output FETs in the business right now?

When I see a one on one comparison of the L20D with the AMP15 I can draw some meaningful conclusions. Until then I will continue to accept that the L20D is a superb amplifier.

But look, I have had enough discussion of phantoms. I was careful to use identical test conditions when I prepared my own data for this series of posts. Please post a third-party comparison data set to support your assertions that '41Hz rules the world'
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Old 16th August 2011, 02:15 PM   #17
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Your assumptions are completely wrong. Anyways, until you get a TA3020 based amp (41hz or other manufacturer) for comparison I'd regard the whole subject here as irrelevant.

Let me also note that even though the amp15 is the amp for 41Hz with least distortion. It's not their best sounding amp. There's a lot more to sound quality than distortion.

And I'm sure that the L20D is a superb sounding amp. Never doubted that for a second. You just don't seem to graps that the whole point of this comparison was unfair as it involved chips and chip sets developed for completely different uses and as such the whole subject is moot.

If you're comparing something, at least compare fruits to other fruit types.
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Old 16th August 2011, 02:33 PM   #18
trevmar is offline trevmar  United States
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Wow. Well, excuse me for breathing! Am I indeed completely wrong, Sir?

Fundamentally, all amplifiers are designed to take an electrical signal and produce enough energy to drive loudspeakers in such a way that the brain appreciates the result as "pleasant."

I have designed many amplifiers, speakers, and other audio systems, some of which have been acclaimed as "pleasant" (or better). Would you rather I not share my perspectives? I have tried to be totally objective...
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Old 16th August 2011, 04:08 PM   #19
lithoc is offline lithoc  Malaysia
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Hi Trevmar,

How about TDA8950 measurement?

As TDA8920 is pin to pin compatible with TDA8950, may be you can do some comparison as well using yuanjing TDA8920 board
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Old 16th August 2011, 04:35 PM   #20
trevmar is offline trevmar  United States
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Lithoc,
I have a YuanJing board with the chip desoldered right now, so I could mount a TDA8950 on that one, I guess. In any case, I will post a complete set of graphs for the YuanJing TDA8920B boards, and I might also look and see if I can see any differences between the two fully assembled boards which I have working now. One has a chip I bought from Mouser, one has the original Chinese-sourced TDA8920B on it It will take me a day or two to run the tests, I will post them here when they are ready

I also have a TDA7498L winging its way from Mouser to me right now, so I can check whether the SURE board works better with a (presumed) full-spec chip
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