Class D amps

Occam · « **Reply #40 on:** 7 Mar 2006, 02:16 pm »

Dan, et al.....

I guess you all should be flattered. A few posts back, I voiced my frustration with the direction this thread had taken. I mentioned that we'd seemed to get tied up with conventional vs.switching amps, whereas the real nature of the Audioholics article was the tremendous variability in the actual implementation among switching amps themselves. And I came out and said that one of the amps discussed in the article appears tremendously flawed, with substantial shoot-trough as an ONGOING problem was a NuForce9. This, I assume, is the reason for NuForce amps incompatibility with FM radio reception.

Well, it appears that we've had a coyote in the henhouse, an agent provocotuer, if you will. Our prime diverter, who has shown a great interest in the economics of chipamps for reasons that are now painfully clear, is noneother than the CEO of NPhysics/NuForce, Tranh, aka TNT. You just can't make crap like this up.

Its painfully obvious whyTNT wished to divert the nature of this discussion away from the specifics of the NuForce amps.

Dan, you specifically should be quite flattered.
TNT, you're on heck of a 'piece of work'.

Discuss amongst yourselves......

skrivis · « **Reply #41 on:** 7 Mar 2006, 04:53 pm »

Quote from: randytsuch

.
But the bottom line point I think you are getting at is that it is silly to group all class D amps together, just like it would be silly to group tube or even chip amps together. It comes down to implem ...

I was actually questioning the entire concept.

To me, the reasons for going with Class D would be smaller, lighter, cooler, cheaper, more efficient.

A lot of the Class D amps don't have all of those characteristics.

I've also seen some speculation that Class D uses the output devices in a more ideal way.

But... I've seen several people comment that Class D isn't better than a linear amp. It's possible that they're approaching just as good...

UCD and Coldamp do seem to be at the top of the heap.

But I still have to question why I'd want to pay more for less?

skrivis · « **Reply #42 on:** 7 Mar 2006, 04:57 pm »

Quote from: ctviggen

I'm seriously considering class D (Hypex UcD) because I need 8 (or 10, if I use a center channel) of amplification for my front right/left speakers, if I build the Linkwitz Orions. With the Orions, which have active filters and you put the amps between the active filters and the drivers, I'm thinking that there will be little difference between amps. Therefore, why not use something light, low power (in terms of power when "off"), easy to build, etc.? A four channel amp with Hypex modules would be relati ...

It seems to me that this is a perfect place for Class D amps, assuming they do sound as good as conventional linear amps can.

skrivis · « **Reply #43 on:** 7 Mar 2006, 05:04 pm »

Quote from: MarkM

Take AVA's OmegaStar line, not the very best products they offer, but solid values. Consumers choose OmegaStar products based on hmmm, budget, tastes, preferences, etc. That is what you own, correct?

If you haven't heard the Hypex designs, perhaps you don't have a decent reference as to where it has advanced. AVA makes some great gear, but Frank is always developing new product that offers better sonics than previous models.

"Class D" is still delevoping and who knows where it will end up. The ...

Fair enough. I'll be interested to see what you think of Kevin's amp.

Kevin Haskins · « **Reply #44 on:** 7 Mar 2006, 05:18 pm »

Quote from: skrivis

I was actually questioning the entire concept.

To me, the reasons for going with Class D would be smaller, lighter, cooler, cheaper, more efficient.

A lot of the Class D amps don't have all of those characteristics.

I've also seen some speculation that Class D uses the output devices in a more ideal way.

But... I've seen several people comment that Class D isn't better than a linear amp. It's possible that they're approaching just as good...

UCD and Coldamp do seem to be at the top of the heap.

But I still have to question why I'd want to pay more for less?

I don't think you have to pay more for one.... there are Class D solutions at a number of price points. Energy efficiency is also a nice feature of any product. Lower heat also translates to longer component life.

You are assuming that the Class D solutions sound WORSE than other solutions. There are a lot of people who don't concur with your premise.

TheChairGuy · « **Reply #45 on:** 7 Mar 2006, 05:36 pm »

At least to me, the promise of Class D is equivalent sound quality to 'conventional' amplifiers. Better for many is not the goal....but better for less is. I know it is for me, and tho not always in tune with the majority, I rarely fly solo.

'The best' is a very, very subjective consensus to reach - 'superb value for the money' is a more achievable goal. I hope some day the small cadre of Class D amplifier manufacturers wil understand this mission better. Until then, I think you're all beating your heads against the wall uneccesarily.

I'm no raving environmentalist, but I find the greater efficiency of these new architectures to be very appealling. Give me more reason than that (and it's more decor friendly size) to buy one....and I will

Dan Banquer · « **Reply #46 on:** 7 Mar 2006, 05:37 pm »

I have an article coming that will give scope shots and an FFT plot out to 1 MHZ of one unit that uses a switching amp. I am awaiting additional data from one other source to include in the article. I ask your patience, I want a relatively complete article that does not leave things open to question.
d.b.

_scotty_ · « **Reply #47 on:** 7 Mar 2006, 06:10 pm »

Occam,thanks for calling attention to TNT's true identity, his motives for posting are now transparently obvious. I also noticed that he did not dispute your claim that the scope photo of the amp showing the high magnitude shoot through current was his latest Ref 9 amp.
Scotty

randytsuch · « **Reply #48 on:** 7 Mar 2006, 06:33 pm »

Take a look over here,
http://www.audiocircle.com/index.php?topic=25308&postdays=0&postorder=asc&start=120

This is where TNT's identity was revealed, as he was buying an amp my ampguru

I thought yesterday was funny, when I saw a thread with this email from a audio manufacturer in it

EDIT FOR CLARIFICATION.
THIS IS NOT FROM AN AUDIOCIRCLE VENDOR!

update: still hadn't heard back from XXXXX about an $253.05 unexplained difference in my refund until today. i got this. must have been an internal message mistakenly sent to me. i'm still laughing.

- - -
From: Sales <XXXXXXXX>
Date: Mar 2, 2006 2:44 PM
Subject: Re: rma
To: (my name and email)

should i tell him to go F--k himself? this is the jackass who wrote the horrible review

On Mar 1, 2006, at 12:41 PM, (my name) wrote:

> I haven't heard back from anyone about this. Please clear up the recent billing mistake and the shipping billing error from months ago.
>
> (my name)
- - -

i guess they read my cnet review. ; )

Randy

Charles Calkins · « **Reply #49 on:** 7 Mar 2006, 11:18 pm »

skrivis:
You have a lot to say about a lot of audio gear and such on the audiocircle. I respect your opinion. I know just by reading your posts you are very knowlegeble about audio gear. I'm curious now as to what kind of gear you have in your audio system. Now don't tell me it's Radio Shack!

Cheers
Charlie

dwc · « **Reply #50 on:** 7 Mar 2006, 11:37 pm »

Randy,
I think you should take extra steps to be clear that that email snippet you included has nothing to do with N-Force or any of the vendors with forums on this board.
-Dan

randytsuch · « **Reply #51 on:** 7 Mar 2006, 11:59 pm »

Quote from: dwc

Randy,
I think you should take extra steps to be clear that that email snippet you included has nothing to do with N-Force or any of the vendors with forums on this board.
-Dan

Done (at least tried to)

skrivis · « **Reply #52 on:** 8 Mar 2006, 01:07 am »

Quote from: Charles Calkins

skrivis:
You have a lot to say about a lot of audio gear and such on the audiocircle. I respect your opinion. I know just by reading your posts you are very knowlegeble about audio gear. I'm curious now as to what kind of gear you have in your audio system. Now don't tell me it's Radio Shack!

Cheers
Charlie

I'm interested in audio gear, and strongly opinionated about it. I even know about some of the engineering behind it. I'm allergic to snake oil and BS too. hehe

The only Rat Shack stuff in my system is some ICs, and I may even have replaced those with some newer ones from PartsExpress.

My electronics are all AVA, and my speakers are a Fried design that is related to the current Monitor 7. (I also have a pair of C/6's and some Pinnacles that I'm not very fond of.) Oh, and I have a pair of Wharfedale towers that my wife uses when she'd in the basement doing the laundry.

Dan Banquer · « **Reply #53 on:** 8 Mar 2006, 01:55 am »

Well I thought I bring us back to the subject matter at hand, and mention that the first two scope shots shown in the article looks like somebody forgot to put in a snubber across the Mosfets. That's an educated guess on my part. Anyone else have any ideas?
d.b.

art · « **Reply #54 on:** 8 Mar 2006, 02:15 am »

You are talking about Bruno's article, right? (Too many weird threads today to keep track of.)

If you are, I think Bruno said it best. Connectors and bits of groundplane everywhere...........about sums it up.

Pat

Occam · « **Reply #55 on:** 8 Mar 2006, 03:45 am »

Quote from: Dan Banquer

Well I thought I bring us back to the subject matter at hand, and mention that the first two scope shots shown in the article looks like somebody forgot to put in a snubber across the Mosfets. That's an educated guess on my part. Anyone else have any ideas?
d.b.

Well I guess someone could design the traces around the half bridges so badly so that the circulating currents were soooooo bad, but that would require an effort to do it that badly..... but I'd have to agree, I really don't see how you could get that shoot-through with any level of snubbering with the proper capacitors. Slightly off topic - its not the periodicity of the spikes, its their spectrum.

Whats really funny (not in a ha ha sense) is over on the bitch slap thread,
http://www.audiocircle.com/index.php?topic=26273&postdays=0&postorder=asc&start=30
we've got a no doubt earnest, unaffiliated with Nuforce vendor (other than raving about their products) arguing that the screenshots couldn't be from a NuForce because they've passed FCC sec. 15. But absolutely NO ONE from NuForce has the stones to publish a screenshot, or APS graphs for that matter.

Maybe if we're lucky, and if TNT (Tranh, CTO of NuForce) is finished with his diversionary discussions of Peter Daniels irellevant products, he could revisit this thread and actually contribute to this thread. Then again, monkeys may fly out of my arse.

art · « **Reply #56 on:** 8 Mar 2006, 04:05 am »

Well, if he is honed in on Peter Daniels, maybe we should encourage them.

Just joking.........don't have a cow. Man.

Pat

Occam · « **Reply #57 on:** 8 Mar 2006, 04:17 am »

Quote from: art

Well, if he is honed in on Peter Daniels, maybe we should encourage them. Just joking.........don't have a cow. Man.

But thems chassis sure are purty.

Occam · « **Reply #58 on:** 9 Mar 2006, 08:20 pm »

Tranh(TNT),

I'd like to comment on something you've said, as it pertains very much To the Nuforce amp discussed in Bruno's Audioholics article -
http://www.audioholics.com/techtips/audioprinciples/amplifiers/SwitchingAmplifierBasics.php

You made the following comment posting as koolkid731 -
http://www.diyaudio.com/forums/showthread.php?postid=865189#post865189
The whole thread is very interesting.

Quote

Very interesting to hear a digital hardware analyst analysing an analog system, Sassen.

I ran thousands of simulations on many different and possible schemes of self-oscillating class-D amps and always got lower even harmonics than odds. Oh maybe my models are incorrect.
__________________
Koolkid

Bolding added by me.
And I wonder whether I could make the categorical statement -

"Yes obviously, your models are indeed incorrect."

This is neither a criticsm of either your engineering skill and expertise, or your fluency with your modeling tools. It speaks to the modeling tools themselves. Do they have the requisite Markov Chain or Monte Carlo (or appropriate alternatives) techniques required to provide even an attempt to capture the random parasitic (secondary) characteristics in any real world circuit implementation. The circuit layout itself, potentially creates massive circulating currents. As Bruno descibes in the article -

Quote

Image 2: Amplifier A, Common Mode. 500us/div, 1V/div.

The amplifier is a full bridge. Note that the switching fundamental cancels neatly from the common mode output, the high frequencies do not. This is because it is impossible to match all parasitic circuit elements acting at this frequency. The surprising bit is that the common mode RFI is several factors larger than the differential mode RFI, although the output filter has grounded caps. This is caused by the “connectors everywhere” problem. The common mode RFI corresponds to the voltage developed across the “ground plane” of the board.

Ringing: The voltage on the power stage should stabilise immediately after each switching edge. Ringing corresponds to an enormous boost in emissions that even the best output filter can’t block. When left unchecked, the parasitic circuit elements present in all power components will produce up to 50% overshoot and ringing that can last up to a microsecond. As luck will have it, this ringing is usually smack in the middle of the FM band. Getting a nice, clean ringing-free square wave requires detailed attention to gate control, circuit layout and damping. Too many designers think that a high-speed H-bridge driver and four MOSFETs is all one needs to build an amplifier. It’s all you need to build a radio transmitter, so much is certain. If you see a gate driver capable of running a 10kW UPS, chuckle.

Regardless of whatever your models tell you, you know that secondary characteristics, loop and lead inductances, parasitic capacitances and especially their variances, make most anyone's model, an optimal mean, than cannot be aproached without wildly optimistic matching.
Wouldn't spectrum of your shoot-through exceeds the bandwidth of the amplifier? The result of the full bridge is that the net, resultant shoot-through is common mode, which isn't going to be adequately attenuated by any follow on CMCs....

FWIW,
Paul

[EDIT - Tranh, you really aren't going to respond? Is it that you can only enter a conversation from behind a veil of misrepresentation?]

Occam · « **Reply #59 on:** 24 Mar 2006, 02:14 pm »

I just got a chance to examine the innards of a brand spanking new (purportedly fully updated) Nufrorce Ref8. Sorry, I didn't make note of the serial numbers.....

As far as I can see, there are no snubbers on the ouput half-bridges. Its now quite apparent why these amps splay noise into the FM band (see the oscilloscope picture in the post above) ; its a result of Nuforces choice of 'dead time' in their upper to lower switch transition and their choice not to use snubbers, along with unmatched parasitic characteristics. That 'after the fact' kludged CMC will lessen the resulting crap, but isn't going to eliminated it.

I assume Nuforce has simply not been able to find a combination of timing and snubbers that result in acceptable 'audiophile' sound, for their chosen topology and implementation. Those using the similar topology B&O Ice modules do not appear to be so unlucky. (or the Hpex modules for that matter).

You pays your money, and you make your choices.