[brj]

... although I can't think of any shipping amps offhand that use this configuration) while many class D (switching) amps use a linear power supply.
...

FWIW, NuForce is probably one.  I dont' think they have room or dissapation capability for a linear supply in their little case.

You cut of my quote too early!

I mentioned a non-switching amp module with a switching supply.  NuForce amps have a SMPS in front of a switching amp module.

[cab]

CAB, it is entirely possible that Tommy doesn't have the same design philosophy, especially regarding feedback, that UcD does, in which case you wouldn't expect identical specs.  Certainly many amps play better with some types of speakers than others, but work exceedingly well for the subset they target.  (I'd never use a tube amp to drive a demanding woofer, for example, but many people will use nothing but tubes on a sensitive speaker or the mid-tweet of a more demanding speaker - even if tube amp specs aren't always as impressive as the specs of other amp topologies.)  Personally, specs alone wouldn't preclude me from listening to any amp, especially as I'm pretty convinced that the commonly reported measurements don't go far enough in fully characterizing what we can actually hear.  (For example, when people discuss distortion in amps or jitter in sources, I'd like to see the spectra involved, not just a single max value.)

The UcD is designed to function the same regardless of speaker load, while the Cherry specs vary with changing loads. Since nearly all speakers present a varying load, this is less than desirable, although as you remark, it may be less of a problem with certain speakers, i.e., those with a relatively flat impedance. How large a subset is that?

Personally, I wouldn't claim that an amp with output dependent on load to be a superior design.

[brj]

I agree that load invariant power is an excellent design goal, but my point was that the common mechanism to achieve this - negative feedback - isn't "free" in terms of the acoustic signature it lends an amp.  Some people don't like the sound of GNFB amps, just like others don't like tubes, or solid state, or class D, or any other over-generalized term that may or may apply to a specific amp.  Like everything else, it is a matter of degree.  (I'd very much recommend the Nelson Pass article I linked to further up this thread - I don't know how much I'm personally concerned about feedback, but I found it educational regardless.)

I would also add that there are other ways to deal with a significantly non-flat impedance curves, for example, from a Zobel network to a fully active rig where suitable amps are slaved directly to drivers.  If the curve is significantly problematic, I would also tend to lay some of the criticism on the speaker designer, rather than expect every amp to handle it without oscillating!

Of course, this thread is now veering pretty heavily into general amp and system design philosophy and away from Tommy's specific products, so I will attempt to avoid further excursions off-topic.  Sorry, Tommy!

[cab]

I agree that load invariant power is an excellent design goal, but my point was that the common mechanism to achieve this - negative feedback - isn't "free" in terms of the acoustic signature it lends an amp. 

His amp uses feedback....

[TomS]

... although I can't think of any shipping amps offhand that use this configuration) while many class D (switching) amps use a linear power supply.
...

FWIW, NuForce is probably one.  I dont' think they have room or dissapation capability for a linear supply in their little case.

You cut of my quote too early!

I mentioned a non-switching amp module with a switching supply.  NuForce amps have a SMPS in front of a switching amp module.

Sorry, I got caught by the double negative sort of thing - doh...

I meant switching output with a switching supply.... like the NuForce   I have seen a few DIY efforts with a SMPS feeding class AB output stages, but you're right, can't think of commercial efforts on this.

[AmpDesigner333]

There are a few key differences.  For one, UCD takes feedback after the filter which allows less phase margin and relies on the capacitance of the output to control the modulation.  There is also more than a decade of R&D behind the Digital Amp Co. methods involving much more than the general topology of the amp.  We use innovation in our modulation method, component selection, and practical implementation matters (layout, partitioning, etc.).

Sorry this can't go to the "exactly" level without divulging some "secret sauce" info.  We believe UCD is one of our more worthy competitors, and we have the greatest respect for Bruno P who created the technology.  I'd like to hear some more opinions from people who have heard both, preferably in an A/B comparison.  So far, we have heard that the Cherry and DAC4800A sound better all around, but keep in mind the speakers, source, power output, and setup can make all the difference.

Thanks for your post!

The Ucd uses feedback, your amp doesn't, we know that. Why is yours better from a theoretical standpoint? I am guessing the UcD has much better distortion specs, which in theory, should make it superior.

10 years of time developing your amp means nothing as far as why it is superior from a theoretical or implementation standpoint.

You seem reluctant to discuss EMI data on your amp... Has it passed the EU requirements for radiated EMF? What makes your layout, etc., better? UcD is well known to have passed and has very little EMI, unlike most other class d amps....

No offense, but Bruno, based on his work, publications, and patents, is recognized as one of the leading authorities, if not the authority, in the world, on class d amp design. Other than this amp, what publications, patents, and research have you published which would lend credence to your claims that you have out designed and out implemented the leading expert on class d?

To say that some people think it sounds better is not proof in my book-too subjective and too dependent on a multitude of other factors...besides, I am sure there are plenty of people who would disagree...such is the subjective nature of audio....

I have no doubt your product is a good one; it simply seems to me that the claims that it is a better design and implementation than the UcD is a bold statement that requires more than hand waving to back up.....

First, our amps DO use feedback.  Where did you read or hear otherwise?
Second, we are a private company and don't divulge information haphazardly.  The proof is in the sound.
Third, we trust our customers 100% and none of them have ever said that they like the sound of UCD better than DAC.  Have you ever heard this anywhere?  Have you ever heard one of our amps?  Specs wise, it's easy enough to visit www.DigitalAmp.com and check our specs.  They are very, VERY good, but like I say often, bench measurements don't tell the whole story.  You can also search the net for patents, publications, and the like that I have published.  Consider that it takes quite a bit of knowledge in the field to make such products.  I have been at this since the 1980s.  Also, Bruno can vouch for me, so feel free to ask him!  He even posted to this thread (check it out).  Thanks again for your post.

WR,
Tommy

[AmpDesigner333]

The Ucd uses feedback, your amp doesn't, we know that. Why is yours better from a theoretical standpoint? I am guessing the UcD has much better distortion specs, which in theory, should make it superior.

I think what Tommy is trying to say is that his feedback is taken before the output filter rather than after, not that it doesn't use feedback.  As long as the output filter is of high quality, it will contribute very little distortion of its own.  In tube amplifiers, for example, it is most common to take feedback after the output transformer - but stability gains can be had by taking it before, with comparable distortion-reduction.

Judging by the measurements posted on the website, his amp should have no problem competing with a UcD.  I am mighty impressed, and proud to see it is a product of Pennsylvania

Great post!  Are you from PA?  Thanks.

[cab]

Here is what I am talking about:

Frequency response vs load:

Cherry Amp (4 and 8 ohm loads):



UcD Amp



The UcD is FLAT for 3, 6 and infinite ohms (open circuit).

One can see that the frequency response for the Cherry varies depending on the load. Figures aren't provided for less than 4 or greater than 8 ohm loads, but the trend is apparent.

Well, if you don't wish to back up your statements objectively or address the EMI issues, and I understand why you would rather not, can you at least address the above issue as it concerns data that you have published?

Many people prefer the euphonic "tube sound" as well, but then most people are aware that is isn't a more accurate amplification scheme, simply "agreeable" distortion. Perhaps the fact that your amp is not flat with load is much the same....

[AmpDesigner333]

Here is what I am talking about:

Frequency response vs load:

Cherry Amp (4 and 8 ohm loads):



UcD Amp



The UcD is FLAT for 3, 6 and infinite ohms (open circuit).

One can see that the frequency response for the Cherry varies depending on the load. Figures aren't provided for less than 4 or greater than 8 ohm loads, but the trend is apparent.

Well, if you don't wish to back up your statements objectively or address the EMI issues, and I understand why you would rather not, can you at least address the above issue as it concerns data that you have published?

Many people prefer the euphonic "tube sound" as well, but then most people are aware that is isn't a more accurate amplification scheme, simply "agreeable" distortion. Perhaps the fact that your amp is not flat with load is much the same....

Take a look at the frequencies!  It's a little hard to read the UCD graph, but you can see from the DAC plot that there is less than a 1dB difference between 4 and 8 ohms load at 20KHz.  Once again, this comes down to sound.  I have designed several amps that use after-filter feedback, and it certainly takes away from clarity, especially for "guitar pluck" and "cymbal tap" type dynamics.  That is based on years of research and development.  Thanks again.

BR,
Tommy

[cab]

Here is what I am talking about:

Frequency response vs load:

Cherry Amp (4 and 8 ohm loads):



UcD Amp



The UcD is FLAT for 3, 6 and infinite ohms (open circuit).

One can see that the frequency response for the Cherry varies depending on the load. Figures aren't provided for less than 4 or greater than 8 ohm loads, but the trend is apparent.

Well, if you don't wish to back up your statements objectively or address the EMI issues, and I understand why you would rather not, can you at least address the above issue as it concerns data that you have published?

Many people prefer the euphonic "tube sound" as well, but then most people are aware that is isn't a more accurate amplification scheme, simply "agreeable" distortion. Perhaps the fact that your amp is not flat with load is much the same....

Take a look at the frequencies!  It's a little hard to read the UCD graph, but you can see from the DAC plot that there is less than a 1dB difference between 4 and 8 ohms load at 20KHz.  Once again, this comes down to sound.  I have designed several amps that use after-filter feedback, and it certainly takes away from clarity, especially for "guitar pluck" and "cymbal tap" type dynamics.  That is based on years of research and development.  Thanks again.

BR,
Tommy

We don't know what the figures are for 1~2 ohm loads or those greater than 8 ohms, except that the response will be worse than what is shown. The UcD response is independent of load and is flat to 20Khz...

The discussion was about the comment that your amp is a better design and implementation than the UcD. Sound quality is subjective while specs, such as a flat response to a varying load and low EMI, are valid criteria upon which to judge the design and implementation. Objectively, I still fail to see why your amp is superior in design and implementation....Talking about your years of experience and happy customers does nothing to support the claim.

If you have patents and published papers, I can't find them....have any links?

[satfrat]

Hey cab, why don't you compare the 2 amps for yourself and see which design you prefer? Seems mfsoa has done this and he made his statement based on an opinion. Myself, I'll take an actual listener's(that being mfsoa) opinion over your charts, specs, and rants anyday.

Cheers,
Robin

edit, I too was pestimistic as my early posts in this thread will attest but I have heard this amp a few times, thanks to Tommy's participation in past RAVES and I have liked what I heard,,, really liked in some cases depending on the preamp matchups. I myself haven't ever had the chance to hear a UcD amp or compare the 2 so i have no opionion as to any superiority claims between the 2 designs myself.

[cab]

Hey cab, why don't you compare the 2 amps for yourself and see which design you prefer? Seems mfsoa has done this and he made his statement based on an opinion. Myself, I'll take an actual listener's(that being mfsoa) opinion over your charts, specs, and rants anyday.

Cheers,
Robin

edit, I too was pestimistic as my early posts in this thread will attest but I have heard this amp a few times, thanks to Tommy's participation in past RAVES and I have liked what I heard,,, really liked in some cases depending on the preamp matchups. I myself haven't ever had the chance to hear a UcD amp or compare the 2 so i have no opionion as to any superiority claims between the 2 designs myself.

It is strictly a matter of engineering, not subjective performance. Claiming it is superior in design and implementation means charts and specs not customer reviews. Not sure where you are getting the rant portion....

It's like claiming car b, which is slower, costs more, and emits more emissions than car a, is a better design than car a because some drivers liked driving it better than car a.

Glad you and others like it. I'm just asking for proof that supports the marketing.....

[jman66]

Proof, specs and other nomenclature can be the equivalent of toilet paper when it comes to audio performance.
Take for example the measurements conducted on tube amps versus solid state. They typically measure poorer than solid state.
But in the listening, there's an entirely different story being told...

[cab]

Proof, specs and other nomenclature can be the equivalent of toilet paper when it comes to audio performance.
Take for example the measurements conducted on tube amps versus solid state. They typically measure poorer than solid state.
But in the listening, there's an entirely different story being told...

Yeah, some people like it and some don't. It's SUBJECTIVE.....

The claims made were OBJECTIVE.

[orientalexpress]

i have the opputunity to compare between Spectron amp and DAC 4800A with sp tech revalation speakers.at first i thought this not going to be even close,after i read all the rave review on the spectron.as soon as i aquired the Spectron i put my DAC for sale here at AC.but no one seem to be interested.over the weekend i got a couple friends come over to do A-B comparison.I try to use different genre music to comnpare them.playing about 4 different CDs.Alison Krause,Rodrigo Gabriela,Fredric Chopin,Opus3 test CD.ouput is about the same.seem like DAC have better image ,bass,more live ,better mid,the high ia about the same..That why i decided to sell the spectron .ask Tommy to send u a DAC amp for try out.i think u going to like DAC amp.even tho they're not well known in Hi end audio.they're real deal.


lapsan

[mfsoa]

To All, but especially Cab,

I feel bad I started all this with my comments, and I have put words in Tommy's mouth and said things in public that he told me in private that maybe I shouldn't have repeated  .

I was just trying to point out that Tommy/DAC has great confidence in his product's ability to compete w/ any of the most popular types of Class D circuits and that some of this belief is the result of his being familiar w/ the guts of the other ClassD designs. I don't think that there is harm in saying that he feels his product is superior - I sure hope that Bruno feels that his amps are better than Tommy's, that Krell/Audio Research etc. feels that their amps are better than Bruno's, that the Wyred4Sound folks think that their amps are better than UcDs, that VAC thinks that their stuff is better than ... - You get the picture. I was trying to make the point that DAC is not only hoping to "keep up" w/ the other amps designs, but to exceed them. I wouldn't want the makers of my equipment to think anything less!

I like the sound of the DAC amps. I feel that they are at least competitive with the UcD and ICE amps I've had in my house and that other's may benefit from (or be free to ignore if you want) my impressions. Tommy won't be hired to run the Marketing dept at Bose anytime soon (sorry buddy) but I'd rather pay for engineering expertise.

It would be nice to have a perfectly flat frequency response in my ears first, and then in my speakers, and then in my room, and then in my recorded material so that flat response from my electronics would actually mean something. But alas, I don't think I'll miss a dB or two at 20K 

The discussion was about the comment that your amp is a better design and implementation than the UcD

I made that comment and maybe shouldn't have. Let's not take Tommy to task for not defending my comment vigorously enough. 

So, sorry to have stirred things up.

-Mike




 

[satfrat]

Hey cab, why don't you compare the 2 amps for yourself and see which design you prefer? Seems mfsoa has done this and he made his statement based on an opinion. Myself, I'll take an actual listener's(that being mfsoa) opinion over your charts, specs, and rants anyday.

Cheers,
Robin

edit, I too was pestimistic as my early posts in this thread will attest but I have heard this amp a few times, thanks to Tommy's participation in past RAVES and I have liked what I heard,,, really liked in some cases depending on the preamp matchups. I myself haven't ever had the chance to hear a UcD amp or compare the 2 so i have no opionion as to any superiority claims between the 2 designs myself.

It is strictly a matter of engineering, not subjective performance. Claiming it is superior in design and implementation means charts and specs not customer reviews. Not sure where you are getting the rant portion....

It's like claiming car b, which is slower, costs more, and emits more emissions than car a, is a better design than car a because some drivers liked driving it better than car a.

Glad you and others like it. I'm just asking for proof that supports the marketing.....

Marketing cab?? Can you show me proof that DAC is marketing claims that their design is superior to the UcD? Thanks.

Cheers,
Robin

[AmpDesigner333]

I agree that load invariant power is an excellent design goal, but my point was that the common mechanism to achieve this - negative feedback - isn't "free" in terms of the acoustic signature it lends an amp.  Some people don't like the sound of GNFB amps, just like others don't like tubes, or solid state, or class D, or any other over-generalized term that may or may apply to a specific amp.  Like everything else, it is a matter of degree.  (I'd very much recommend the Nelson Pass article I linked to further up this thread - I don't know how much I'm personally concerned about feedback, but I found it educational regardless.)

I would also add that there are other ways to deal with a significantly non-flat impedance curves, for example, from a Zobel network to a fully active rig where suitable amps are slaved directly to drivers.  If the curve is significantly problematic, I would also tend to lay some of the criticism on the speaker designer, rather than expect every amp to handle it without oscillating!

Of course, this thread is now veering pretty heavily into general amp and system design philosophy and away from Tommy's specific products, so I will attempt to avoid further excursions off-topic.  Sorry, Tommy!

No problem.  I appreciate your comments.  This is going beyond "how is your design different" and into the "obvious affiliation" area...  Thanks as always.  You are a great contributor to this thread!

[cab]

"Marketing cab?? Can you show me proof that DAC is marketing claims that their design is superior to the UcD? Thanks. Very Happy

Cheers,
Robin"

Maybe you missed the post that started this where the OP, a customer I believe, related what he was told by the designer....I have quoted it below for you......

In any case, this horse is dead and there is no need to beat it further. Most manufacturers make such statements so it is best to just let it go for what it is.....

And since I've already blapped more than I should I can tell you guys that he is intimately familiar with the operation of the UcD and ICE modules, and feels absolutely confidant that his designs are superior in both theory and implementation. This may not mean much coming from him if it was ad copy, but this is what I asked him point blank in person. Is it true? I don't have the tech knowledge to know, but I wanted to give you some idea of what Tommy is about and what he's shooting for here.

Tommy - Hope I didn't blather too much or give away your shoe size- just giving my $0.02, FWIW.

-Mike

[mfsoa]

Most manufacturers make such statements so it is best to just let it go for what it is.....

Ahhh, very good. This is how my comments should be taken, thanks for understanding.

Wow I reread my comment you attached - Pretty over the top, I admit 

Happy listening, everyone!

-Mike