Margules Audio U280-SC Black power amplifier Manufacturers' Comment

Manufacturers' Comment

Editor: Thank you for your time and effort put into the measurements of our amplifiers for this review. Your measurements are correct, but we must point out that the Margules U280-SC Black is definitely not a conventional tube amplifier. It has a different design approach, so it should be treated as such, and your comments are a good opportunity to explain the engineering behind the amplifier and to shed light on why Jason Victor Serinus's auditory evaluation and your technical measurements have differing outcomes.

Respectfully, and in the interest of accuracy to best serve your readers' understanding, we submit that we consider this to be a case of misunderstanding our type of amplification technology that has led to the utilization of incorrect or inappropriate methodologies and metrics to measure our amplifiers, naturally yielding materially erroneous results that are misleading for the proper evaluation of our amplifier design and performance.

Please allow us to explain. The Margules U280-SC Black is a full class-A amplifier that tracks the input and output signals. Having said that, if this amplifier is fed with a continuous and constant signal, it will run, as [John Atkinson] commented, "unacceptably hot." But if you use it as an audio amplifier to reproduce music, which is its purpose, with a music signal it will run much cooler than most tube amps. Even after hours of operation at high volume levels, you can put your hand on any of the surfaces without burning yourself, and you can even touch the tubes without harm (of course, they will be hot). This in fact provides important benefits; among others, it will prolong the life expectancy of the tubes and equipment.

The U280-SC Black is the only tube amplifier that we know of capable of offering full class-A operation with almost the efficiency of class-AB while not requiring any adjustment, even when changing tubes or tube types. That is why no users or reviewers anywhere have mentioned any concerns with the heat output—quite the opposite.

To achieve low output impedance, distortion, and improved frequency response, most tube amplifiers use negative feedback; this technique has its drawbacks, as it tends to sound unnatural, and can imprint a "tube" sound lacking richness and detail. The Margules U280-SC Black is a full class-A amplifier that has no negative feedback. The control to achieve proper performance is taken care by the proprietary active servo controls, which dynamically change the tube characteristics to optimize power transfer and distortion.

The changes in the output impedance change not only the power transfer but also the damping control; our manual states that, for speakers of 4 to 8 ohms, we recommend that this amplifier be set to use the 4-ohm taps, and for speakers of 8 ohms and up we recommend that this amplifier be set to use the 8-ohm taps; we recommend that users optimize the taps to their systems. The Margules U280-SC Black amplifier, when set to be used as a monoblock, parallels the channels—because you double the current capability, the taps should be used differently, as stated in our manual.

It has to be noted that the specifications of the U280-SC Black are rare for this type of amplifier. In engineering and design work you deal with a large number of variables, and to make a proper product you are required to balance them to achieve the design goals. This amplifier was designed, first and foremost, as an audio amplifier with the sole purpose of music reproduction; the emphasis was not on the static signal (continuous signal), but rather on the dynamic behavior like music reproduction. It was designed to be able to operate with all its capabilities with any conventional loudspeaker and make it sing, even highly capacitive speakers like electrostatics, thereby covering most of the speakers in the market.

We believe that our products should be steady and reliable as a rock for decades of satisfying performance. Therefore, all of our amplifiers and preamplifiers have been and will be upgradable to our new technological improvements.

We do hope that this response, which is written in good faith and in the most constructive spirit, is of use to you for what is understandably an unusual design that incorporates proprietary elements. Therefore, in the interest of providing your readers with an accurate representation of the technical characteristics and performance of our amplifiers, we must respectfully request that you either reevaluate said technical aspects based on the corresponding and correct criteria, or publish our full explanation, again in the best interest of serving your readers. Thank you.

Note: The specifications, especially distortion and power, are obviously affected by the tubes. When products leave the factory, the measurements stated must be fully met. The supplied tubes undergo double tests, one by our supplier and one in our factory; even so, we offer a two-month tube warranty if failure is suspected. That is the nature of tubes; however, we will be happy to supply a new set to you for testing, as we do for our customers.—Carlos Smith, Sales & Service, Margules Group

Margules Group
US: Margules Group USA
Columbus, GA
(888) 538-8605

NeilS's picture

I'm not an engineer, so please excuse if this is a dumb question or I'm misusing terms. This amplifier's total harmonic distortion is stated as 0.08% at 7V RMS. Can the level of THD in an amplifier be converted to an effective bit depth resolution capabilty?

Ortofan's picture

... S/N ratio of 62dB which is equivalent to a resolution of 10 bits.

NeilS's picture

So if you play a 24/192 flac decoded by a 64 bit computer chip and converted by a DAC with 16+ bits of resolution and then sent to an amp with a 62dB S/N ratio (10 bit resolution), what gets sent to the speakers is 62dB (10 bit) resolution?

Ortofan's picture

... a random uncorrelated signal, THD is the sum of signals which are harmonically related to the fundamental tone. If you look at Fig. 16, note that the second harmonic is at about -40dB, the third harmonic at about -55dB, and all higher harmonics are at or below about -70dB.

Compare this with Fig. 9 from the test of the Benchmark AHB2, where all harmonics are below the level of -110dB:

You could argue that the higher level of THD - especially the level of second harmonic distortion - effectively limits or reduces the resolution of the playback system, yet some listeners may find the resultant sound quality preferable:

NeilS's picture

Thank you very much for the explanation. It makes sense that the resolving capability of the system can't exceed its 'lowest-res' component. Another way of looking at the THD in component measurements that I hadn't realized before.

Ortofan's picture

... the Harbeth Monitor 40.2 speakers and a pair of the Audio Research Reference 250 SE amplifiers.

Anton's picture

You know those follow ups where another reviewer compares experiences?

This would seem great to continue to try to wrap my head around this product.

Even the manufacturer is fascinating.

tonykaz's picture

what did the Wilson people have to say?

Wow, the Amp has beautiful engraving, I bet they'll start a trend of using a CNC machine to do this gorgeous chassis decoration. It's kinda like one of those artistic Tattoos we occasionally see.

It's a Beautiful Amp, I'd like it to be a success.

Some of this Company's other offerings are also beautiful.

Tony in Michigan

pma's picture

This amp has high output impedance and the frequency response will be strongly modulated by speaker impedance plot, as we can see in

This will be audible with most speaker, so we have an example of another effect box here, rather than an amplifier.

Anton's picture

I hadn't thought of the term 'effect box,' you said it well.

johnnythunder's picture

Obviously, something that deviates from absolute clinical technical perfection with no horrifying overtones or those terrible euphonic colorations. Definition of euphony:
1 :pleasing or sweet sound; especially :the acoustic effect produced by words so formed or combined as to please the ear
2 :a harmonious succession of words having a pleasing sound

Terrible things those amplifiers or source components that make pleasing sounds. Oh wait we cant call them truly amplifiers because they may make music sound pleasing to the ear. That's not what music is supposed to do.

pma's picture

Is the SET distorted sound still 'pleasing' when playing complex philharmonic orchestra, Beethoven, Mahler? Do we want a modified sound or true reproduction of the recorded sound?

Ortofan's picture

... was asking the very same question 30 years ago.
"Should an amplifier be pleasant sounding, or should it be accurate even if accuracy is not as pleasant?"
See the next to last paragraph:

pma's picture

Well, the question put this way is no good. Well designed and engineered amplifier is never "unpleasant sounding", in case you have good speakers, good listening room, good recordings and good signal source. If someone listens to commercial music only, I agree it is a pain since pocket audio started with iPod in 2001 (thank you, Steve) and huge dynamic compression took place almost everywhere (sounds good in subway for millions, right?). But with good classical recordings, good speakers and listening room, good DAC, the accurate amp never sounds boring or unpleasant. Please find a real fault in other parts of the audio chain.

Ortofan's picture

"Not as pleasant" is not the same as "unpleasant."
Also read the op-ed piece from AD linked above.