Margules Audio U280-SC Black power amplifier Specifications

Sidebar 1: Specifications

Description: Tubed stereo power amplifier, strappable for mono, with selectable output transformer taps (8, 4, or 2 ohms) and modes (Ultralinear, Triode). Tube complement: four 12AU7, four KT88 (or 6550, KT99, KT100, KT120, KT150). All measurements at 8 ohms 1 khz input voltage 127V AC. Rated power output before clipping: stereo mode, 50Wpc Ultralinear (17dBW), 25Wpc Triode (14dBW); monoblock mode, 100W Ultralinear (20dBW), 55W Triode (17.4dBW); Inputs: 1 pair unbalanced (RCA). Outputs: 2 pairs binding posts. THD at 7V RMS output: 0.08%. Power consumption: 170W idle, 585W maximum at 127V AC. Input impedance at 1kHz, stereo: 180k ohms. Triode: input voltage for maximum output at 8 ohms, 0.6V (gain: 28dB). Ultralinear mode: input voltage for maximum output, 0.5V (gain: 32dB). Input impedance at 1kHz, monoblock mode: 100k ohms. Triode mode: input voltage for maximum output, 0.6V (gain: 30dB). Ultralinear mode: input voltage for maximum output, 0.45V (gain: 35dB).
Dimensions: 17.7" (450mm) W by 8.7" (220mm) H by 13.8" (350mm) D. Weight: 67.25 lbs (30.5kg) net each; 73.85 lbs (33.5kg) shipping each.
Finish: Black, wooden side panels.
Serial numbers of units reviewed: B-50003950517, B-50003960517.
Price: $10,800/monoblock pair, $6000 each, stereo Approximate number of dealers: 5.
Manufacturer: Margules Group, Uruapan 17-4, Col. Roma Norte, Mexico DF 06700, Mexico. Tel: (52) 5514-7448. Fax: (52) 5533-4654. US: Margules Group USA, Columbus, GA. Tel: (888) 538-8605, (706) 575-0926. Web:

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.