The Truth About Digital (Class D) Amplifiers

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ruadmaa

Banned
I have read the above audioholics article and, quite frankly, it doesn't make a whole bunch of sense. I have directly compared a Panasonic Digital XR-55 with a Yamaha RX-V1400 for almost a month and could not tell one bit of difference in audio quality. The Audioholics article made a digital amp sound like it was nothing but garbage. My ears certainly don't tell me that.
 
S

silversurfer

Senior Audioholic
The Hypex UcD amps by Bruno Putzeys are suppose to be very good too.

I notice you use Rotel amps, they are using an ICEpower module in their new class D amps.
 
mike c

mike c

Audioholic Warlord
yup ... there's quite a lot of discussion about class D rotel amps at htguide.coom
-one of the reasons I considered the 1077
 
S

silversurfer

Senior Audioholic
How do you like the 1077? What other amps can you compare it too?
 
mike c

mike c

Audioholic Warlord
I can only compare it with the Rotel RMB1066 bridged to 150wpc x 3.
I can hear NO difference, except that I miss the "louder" 1066. (watts is watts ... the more the merrier)

I like and chose the 1077 for both space and heat concerns. I only have space under the TV, and to even fit a 100 x 5 amp + a dvd player would be impossible.

I haven't given the amp a thorough music test (especially with my more demanding r&b music) I will post back after I put the test CD in.
 
mike c

mike c

Audioholic Warlord
silversurfer,

while the test conditions are NOT the same ... I have finally listened to the 1077 using the same material. (I added curtains and couches since the last time I compared a yammy 640, rotel 1066 and an HK3480)

results: 100wpc of the 1077 simply cannot boom the bass on my tower speakers. the 1066, did a better job of giving excursion to the bass drivers.
the 1066 is rated at 150wpc x 3. but when I tested it, I only used 2 channels ... I'm guessing, that added more headroom to the amp.

I bi-amped the towers using 4 channels of the 1077 and tested again with the same material, this time there is driver excursion, but it barely gave me the chest thump (most probably attributed to the room changes).

don't get me wrong, the 1077 is a pretty good amp ... it achieves what it was designed to do, which is to give 100wpc or more x 7 in a small package, lighter unit and "cooler" running amp.
 
S

silversurfer

Senior Audioholic
Very interesting Mike. Thank you.

How did the mids and highs sound?
 
S

Sleestack

Senior Audioholic
ruadmaa said:
I have read the above audioholics article and, quite frankly, it doesn't make a whole bunch of sense. I have directly compared a Panasonic Digital XR-55 with a Yamaha RX-V1400 for almost a month and could not tell one bit of difference in audio quality. The Audioholics article made a digital amp sound like it was nothing but garbage. My ears certainly don't tell me that.

The problem with that article is that it makes sweeping assertions based on a very few product samples. Also, the article seems to talk more about interference issues than sound quality issues. I converted to all digital amps in both my HT and 2.2. channel systems. I use the TACT BOZ216/2200s to bi-map and externally crossover each of my Andra IIs. I definitely prefer the TACT setup over the Parasound A51 and Meridian G57 I was using and really seee no reason to ever go back to SS or tube amps.
 
jaxvon

jaxvon

Audioholic Ninja
One of the consultants, Bruno Putzeys (I believe I spelled that correctly), does work for Phillips. He seems to have a bias against TACT and their design, basically calling their high output-DAC design junk (though I have never seen any justification for his claim). Obviously not all digital amps are good, and sadly many are crap. But like Sleestack mentioned, sweeping generalizations can give false information on what's actually available and possible.
 
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mike c

mike c

Audioholic Warlord
silversurfer, as much as I have read a LOT of comments that the mids and highs of this amp is much improved over the analog offerings of Rotel double the wattage (one of the reasons I bought it) ...
I can only imagine because I simply cannot remember the difference.
I am afraid to conclude because it could simply be my weak memory or imagination of hearing "new" things.
 
S

Sleestack

Senior Audioholic
jaxvon said:
One of the consultants, Bruno Prutzeys (I believe I spelled that correctly), does work for Phillips. He seems to have a bias against TACT and their design, basically calling their high output-DAC design junk (though I have never seen any justification for his claim). Obviously not all digital amps are good, and sadly many are crap. But like Sleestack mentioned, sweeping generalizations can give false information on what's actually available and possible.

I would like to hear what he has to say about it, however, if he's talking about the audible qualities of their amps, he's either smoking crack or has an agenda. Nevertheless, the room correction is why primarily why I use TACT. The 216/220 amps are great, but versatility is their differentiating strength. Other than that, they just sound like clean amps. You could easily get more power using a SS setup if you didn't need the versatility of the amps. I have no comment on the other TACT amps b/c I have no experience with them. If radio interference is his primary issue, it really is a non-issue for me.
 
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jaxvon

jaxvon

Audioholic Ninja
I'll try to get a quote tomorrow. I have access to a lot of journals via UofM, but I can't access them from home. When I'm at the U tomorrow I'll try to pull up the article I read.
 
S

silversurfer

Senior Audioholic
mike c said:
silversurfer, as much as I have read a LOT of comments that the mids and highs of this amp is much improved over the analog offerings of Rotel double the wattage (one of the reasons I bought it) ...
I can only imagine because I simply cannot remember the difference.
I am afraid to conclude because it could simply be my weak memory or imagination of hearing "new" things.
That is very fair of you. Thanks.
 
S

Sleestack

Senior Audioholic
jaxvon said:
I'll try to get a quote tomorrow. I have access to a lot of journals via UofM, but I can't access them from home. When I'm at the U tomorrow I'll try to pull up the article I read.
Thanks. The other consideration is that he may have been commenting on their older amps, which were designed back in the late 90s. TACT is on a new generation of amps which have a different design. The older amps were a single box design with 150w ouput at 8 ohms. The new 2200 amps, shown on the right below, utilize the external 216 power/control center and a new floating point DSP engine, and have 200w output at 8 ohms.

 
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jaxvon

jaxvon

Audioholic Ninja
Here's what Bruno had to say regarding digitally controlled amps like the Tact:

Bruno Putzeys said:
Digitally controlled class D initially delivered a success in the form of the Tact Millennium. However, by its mere existence this device (and another one of my own making, the "PPDSD" which performs marginally better) proves that obtaining good performance from such a contraption is largely an analog design exercise - a very complicated and expensive one at that. After all, the distortion phenomena that stand in the way between a perfectly formed digital control signal and a perfect analog replica are inherently analog. Similarly,cheaper digital class D’s (such as SonyS-Master and TI’s) go on to show that at practical price and complexity levels, performance is quite abysmal (better than 0.1% THD is unusual and be sure it ain’t just third harmonic!)

One should ask the question: would any D/A converter designer in his right mind build a DAC using power components? Probably not. Then how about the old argument that digital-to-the-end is best? Well, I should think the D/A barrier is best put precisely where it allows the whole signal chain to perform at its best and why should we believe that this is necessarily right at the end? Quite obviously the concept of a digital class D amplifier was dreamt up by DSP folks who presumed that the signal should be kept out of the big bad analog world as long as possible, at the same time expecting the power stage, power supply and filter (all highly analog in nature) to perform flawlessly.

Analog controlled class D is quite adifferent story. Although mostcommercially available implementationsare well short of this ideal, proper error control can be used to makeanalog class D amplifiers with performance figures giving thedigital variety a run for their money, at a price well below that of even the cheapest digital class D’s.They can have vanishingly low output impedance right across and beyond the audio range (which the digital ones can’t!) while frequency-independent distortion (for that “zero-feedback sound”) is actually easier to achieve than with digital ones.


[...]

"Digitally controlled class D: dead end street.Analog controlled class D: definitely the future, allthough you shouldn’t expect it to flatten competition from traditional solid-state and tube amps by a tremendous margin.

In the very high-end segment the three are bound to coexist for a very long time. In mainstream gear, class D is certain to take over the scene completely, although one serious problem remains: building a good class D amp is an order of magnitude tougher than a linear amp, and the knowledge required is much more diverse. It may take long before each large company has at least one knowledgeable designer. It won’t stop them from putting class D based products on the market, but until then and unless they buy completed amplifier modules from specialist vendors (which eastern companies rarely do, they’d rather commit harakiri than having to swallow their pride), they will be putting out seriously substandard products for years to come."
I read this article in a journal, though what I have posted (and more) is available on Bryston's website. Here's the link:

http://www.bryston.ca/newsletters/74_files/vol7is4.html
 
gene

gene

Audioholics Master Chief
Administrator
I have read the above audioholics article and, quite frankly, it doesn't make a whole bunch of sense. I have directly compared a Panasonic Digital XR-55 with a Yamaha RX-V1400 for almost a month and could not tell one bit of difference in audio quality. The Audioholics article made a digital amp sound like it was nothing but garbage. My ears certainly don't tell me that.
You can drive two different cars on a highway at 60mph and not notice much of a difference until you are faced with external influences such as weather conditions, road obstacles requiring quick maneuvers that the inferior car may not be up to task to handle.

My point is, alot of it depends on load conditions, quality of source material played back, quality of listening space, quality of speakers, discernability of your ears.

I personally purchased the older version of the Panasonic Class D receiver b/c I felt the amp section was so bad that it was a worthy piece of gear to add to my reference system for comparative purposes. I will be referencing this in up and coming listening tests once the primary theater room in the Showcase home is completed.

This article is NOT a knock on Class D amps as much as it is a reminder that there are technical hurdles manufacturers must jump in order to design them properly.

See our Article: Switching Amps: Technology & Issues

I just want to add that a class D amp is not necessarily a digital amp.
There is no such thing as a "Digital" amp really. All amps are analog in nature but some such as class D amps are Switchers.
 
gene

gene

Audioholics Master Chief
Administrator
One of the consultants, Bruno Putzeys (I believe I spelled that correctly), does work for Phillips. He seems to have a bias against TACT and their design, basically calling their high output-DAC design junk (though I have never seen any justification for his claim).
Actually he no longer works for Phillips. I don't recall him ever stating that their design DAC is junk and he gives good reasons as to why that type of method is NOT optimal.

But like Sleestack mentioned, sweeping generalizations can give false information on what's actually available and possible.
Yes I agree which is why its important to NOT put words in peoples mouths or misquote them when they write articles :rolleyes:
 
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