More on Class D amps

Dan Banquer · « **on:** 10 Apr 2006, 11:52 pm »

For those of you who may be interested There is another article on Class D amps at Audioholics.com
Go Here:
http://www.audioholics.com/techtips/audioprinciples/amplifiers/SwitchingAmplifierIssues.php

JoshK · « **Reply #1 on:** 11 Apr 2006, 12:28 am »

Interesting read. Did you examine the UcD modules? I can loan you a pair if you like to test them on the bench.

Dan Banquer · « **Reply #2 on:** 11 Apr 2006, 12:23 pm »

Can I take a rain check?
d.b.

Hogg · « **Reply #3 on:** 11 Apr 2006, 02:20 pm »

Good article. I'm not surprised by your findings. I believe the chip used in the Panasonic is the TI. These are inexpensive and designed primarily for cars and other non-audiophile uses. Measurement of ICE or UcD would be a better indicator of audiophile designs.

Jim

warnerwh · « **Reply #4 on:** 11 Apr 2006, 09:09 pm »

Are these tests typical of switching amplifiers? If you could elaborate just a little I'd appreciate it. If you don't want to I understand why. Thank you very much for the notice of this article.

After reading this article I'm left with somewhat of a dizzy feeling regarding this type of amplifier architecture. It appears these amps are less accurate than what we were using in the 70's. The high output impedance should be clearly audible. I'd think this would damage the sound in speakers with a high quality bass reproduction. Overall it appears there are a few generations of these switching amps to go before they equal the standard linear amplifier.

Dan Banquer · « **Reply #5 on:** 11 Apr 2006, 11:04 pm »

These measurements are NOT typical. Most measurements, if they are done at all, will only include measurements in the audio band with 6 or 8 octave filter just after the 20kHz to severly attenuate all of the out of band components.
One of the purposes of the article is to inform people that switching amplifers do produce these out of band components to some degree. The amount of which is entirely dependent on the design, parts and how well it is implemented. See Bruno's article for more info.
Gene may decide to do a part two of this article on some of the in band measurements. Gene has taken some in band measurements not published in the article and they have basically described what I heard here; before he took the measurements. And no, I am not going to talk about this aspect of the unit further.
Hope this helps.
d.b.

warnerwh · « **Reply #6 on:** 12 Apr 2006, 02:05 am »

Thanks Dan, that helps. It still appears that switching and linear amplifiers are two different animals with regards to "linearity".

Ric Schultz · « **Reply #7 on:** 12 Apr 2006, 06:45 pm »

The article is very misleading about switching amplifiers....yes, those particular amps do measure relatively high output impedance...part of their design, not inherent of the type. The UCD modules have less than 20 milliohm (.02 ohm) output impedance to 1K and about 150 milliohm (.15 ohm) at 20K....this will give flat frequency response with ANY speaker. The Ice amps and Nuforce actually have even lower output impedance...along with less good sound.... he he. Many linear amps do not have 20 milliohm output impedance at any frequency. The Sony and Panny probably use no feedback around the output filter, hence the poor readings. UCD, ICE and Nuforce all use feedback around the output filter giving very LINEAR performance into any load.

Occam · « **Reply #8 on:** 12 Apr 2006, 06:57 pm »

Quote from: Ric Schultz

The article is very misleading about switching amplifiers...

Really? First, FrankVanA -
http://www.audiocircle.com/index.php?topic=27269
and now you....
Until recently I'd thought that a reasonably good education covered what was necessary and sufficient to draw conclusions from empirical data.
I found absolutely nothing in the article that was in any way misleading.
I do despair....

Occam · « **Reply #9 on:** 12 Apr 2006, 07:32 pm »

Rick - I'm just yanking your chain

I believe what you are really saying is that you don't want your potential customers drawing unfounded conclusions based upon a specific implementation of a digital amp that has nothing to do with the switching amp that you are currently using.

Quote

The Sony and Panny probably use no feedback around the output filter, hence the poor readings. UCD, ICE and Nuforce all use feedback around the output filter giving very LINEAR performance into any load.

Indeed, closing the feedback loop around the output filter does address that specific issue, but sadly that does not preclude a your last vendor from taking a good topology and botching it.
http://www.audiocircle.com/index.php?topic=26197&postdays=0&postorder=asc&start=0

Dan Banquer · « **Reply #10 on:** 12 Apr 2006, 11:27 pm »

Quote from: Ric Schultz

The article is very misleading about switching amplifiers....yes, those particular amps do measure relatively high output impedance...part of their design, not inherent of the type. The UCD modules have less than 20 milliohm (.02 ohm) output impedance to 1K and about 150 milliohm (.15 ohm) at 20K....this will give flat frequency response with ANY speaker. The Ice amps and Nuforce actually have even lower output impedance...along with less good sound.... he he. Many linear amps do not have 20 milliohm out ...

If you read the article carefully, you will find a long quote from Bruno Putzeys, who just happens to be Mr. UCD if you will. The quote went in the article with Bruno's permission.
Please also note that throughout the process of writing this article, all of the initial through final drafts went to Bruno, Mike, Dick, and Gene for comment and correction. There are about three or four other engineers who reviewed this who will remain un-named.
If any conclusions can be made about this article, it's that what Panasonic did is not a very good way to implement a switching amp.
d.b.

CSMR · « **Reply #11 on:** 18 Aug 2006, 07:37 pm »

Maybe if the article were called "issues in certain switching amps" there would be no chance of its being misleading. Or even "Problems with a certain switching amp"!