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Positive Feedback ISSUE 48
march/april 2010



U280SC amplifier

as reviewed by Francisco Duran







Tonian Labs TL-D1 Loudspeakers with custom cabinet with real wood Bamboo finish.

Margules U280SC Class A tube amplifier (new Version), Marantz PM-15S1G Reference Series Integrated amplifier, Antique Sound Labs MG-SPM25DT SE mono block tube amplifiers modified by Response Audio, Monarchy Audio SM-70 Class-A amplifier.

Marantz SA-15S2 Reference Series SACD/CD player, Kuzma Stabi S turntable, Stogi arm, Audioquest 4004i cartridge modified by van den Hul, Sony BDP-S350 Blue Ray Player, Onkyo Model T4 Servo Locked Stereo tuner. Stock MM/MC Phono preamplifier in Marantz SA-15S2.

JPS Labs Superconductor Q Series interconnects and speaker cables, Power AC+ , GPA2, and Digital AC power cords, Analysis Plus Solo Crystal Oval interconnects, Oval 12 speaker cables, Soundstring Tricormaxiel speaker cable, PC 30A and 10A power cords, and Octaphase "Alpha Series and Omega Pro Line" interconnects. Oyaide power cord, PS Audio C-4 power cord., Monster Cable M Series HDMI 1.3 cable, Parts Express HDMI cable.

Can't Live Without's; Gingko Audio Cloud Ten (2), Vibrapod Isolators (various sizes), and Cones, Ultra Systems' Hi-Fi Tuning Fuses, (various sizes peppered throughout my gear), Ultra Systems Cathedral Sound Panels, (4), Custom made gear racks for turntable and gear. Support staff; Balanced Power Technologies BPT 4SE power unit, Brick Wall Series Mode Surge filter (2 outlet), Quiet Line Parallel Power Line Filters, Bybee filters (inside ASL amps), Nitty Gritty record cleaning machine, PS Audio Zero Static record brush, Flitz Metal Polish, Caig ProGold, and Deoxit, Mondial Antenna Ground Isolation Circuit (for incoming Time Warner cable), Walker SST Extreme, Mapleshade Mikro-smooth CD polishing kit and Ionoclast Ion Generator, Bright Star Isonodes, EAT Cool Dampers, Hal O Rings, Cardas, Clearaudio, Hi-Fi News Test LP's, Smoke On The Water, Senor Coconut and his Orchestra used as test LP, generic ferrite rings, ERS paper, Custom made wooden cable lifters by Mr. Clark senior, Ceramic Insulator cable lifters, J&J, EI, Sovtek/Electro Harmonix, Ruby, SED, Jan Phillips, Sylvania Electron Tubes, Amoeba Music Store record bag!


A few years ago my wife and I decided it was time to shop for a new house. Now folks we don't live in Enid, Oklahoma, Osh Gosh, Wisconsin, or Williams, Arizona. We live in Los Angeles, or at least the eastern suburbs of L.A. Finding a house in this market place is a daunting task to say the least. We wanted a better house in a better neighborhood. It didn't have to be new and it should not be far from our jobs. Now the little community we live in is nice, but there are better. The more we looked the more we realized that the houses we looked at weren't much better than ours. We either had to go way out of our price range or move way out to the next county and buy in a new tract. That was two years ago. We are still here.

I had a similar problem recently when shopping for a new amplifier. My old Margules U280SC was ailing slightly and I wanted to fix it or replace it. So it was time to shop. You know how it is with gear heads once we get the itch for new gear. The problem was there was very little that could touch my old amp's sound and features without going to an extreme jump in price. Besides it always seemed that the more expensive amps lacked some feature or another that I took for granted on my old amp. It didn't seem worth it to spend more money on a new amp but I needed one. The solution was simple, why not upgrade to a new U280SC? Actually Margules Audio upgraded their U280SC model a few years ago (see my CES and T.H.E. Show report issue 24). Margules Audio products are manufactured in Mexico District Federal, Mexico. That is Mexico City to us northerners. I contacted Julian Margules who put me in touch with Ben Goldman of Margules Group USA, and as they say in the stud horse business, the deed was done. I soon had a brand spanking new model Margules U280SC in my house. So, what's so special about this new amplifier?

I try to avoid quoting from manufacturer's web sites but sometimes exceptions are made. Like right now. To reiterate, "pure class A tube audio amplifier with active bias servo-controlled output stage, does not require at any time bias adjustments, high precision regulated voltage in the input and inverter tubes, active damping control, bias meter, 70 W/channel, can work in triode, ultralinear, among other things can work either as a mono or stereo, the main design attribute is its great versatility, variable output impedance, independent gain controls for each channel, precision metal film resistors, polypropylene capacitors, etc, 4 output tubes can use 6550, KT90, KT99, KT88 (KT-88's, my favorite), KT100." It was named most wanted component in another online audio publicationówait a minute, I named it one of my Products of the Year in 2009 in this publication! If you didn't look back to issue 24 the transformers were upgraded, circuit changes and some new parts all add to the new model.

As one can see, this is a modern tube amplifier chock full of features and innovative, practical, and useful electrical design elements. One can set it up and forget it, or have hours of fun playing with all the knobs, switches, dials, and tubes. There are left and right volume controls, left and right triode/ultralinear switches, two mono/stereo switches, and an impedance switch for 2, 4, or 8 Ohms on the front of this baby. Oh and don't forget the cool meter. Believe me; I do have plenty of fun with this amp depending on mood, source material, or its interaction with other components in my system. . Not only listening to music but trying out all the different features and listening to what each one can do to the music. With this amp, you have options.

With my efficient speakers, I doubt there will ever be the need to have to strap another U280SC to my system and switch the mono switch on both amps. But there are several features I really appreciate on this amp. First is the active bias servo-controlled output stage. It actively tracks the input signal to keep the output in full class A without the amp overheating. The active servo bias sets DC bias and active drive levels therefore there is no need for manual adjustment. The amplifier is automatically doing it for you constantly. Just pop in the quad of designated power tubes of your desire and voila, you are off and running. Another design element that is very interesting is the BEFS or back electromotive force sensor. This changes the amplifiers output impedance as the load demands. This permits the U280SC to "drive difficult speaker loads with exceptional dynamics and extended controlled bass". As for the active servo bias, I have three sets of KT-88's and two sets of KT-90's at my disposal. Now I don't want to wear out my tube sockets but this is a really cool feature for any tube lover. The fact that one can change or tailor the sound of your amp to fit the need or mood makes ownership of this amp even more rewarding. And knowing that those tubes won't be overdriven or overheated in that class A amplifier is built in insurance and peace of mind in one's investment. And believe me it works as a testament to this amplifier's solid and taut bass output and grip on dynamics. I almost forgot to mention the three minute soft start up at turn on. This might seem like an eternity for an impatient guy like me, but it is definitely worth the wait. Oh, and if your unit comes with inexpensive Chinese 12AU7 driver and phase splitter tubes try rolling them with some nice J and J's or RCA's or even some nice JAN 5963's. Believe me the difference in price is worth it.

Before we get to the sound a word about the preamplifier that I use with it is in order. I have used a Reference Line passive line stage for years with all of my amplifiers. The electrical characteristics of my amps have matched this passive quite well. Not only did my U280SC wear out but my old passive wore out as well. Julian Margules has mentioned to me more than once that to hear his creation in full glory, I need to mate it to his SF 220 active tube preamplifier, or at least a high quality active preamplifier. That and a current stint with the preamp section of my Marantz Reference integrated have not deterred me from buying another passive line stage recently. This time it is an Audio Limits passive (review to come) from Canada. Some day I hope to have that perfect preamplifier in my system but for now this little affordable passive from the great white north is doing an excellent job.

Well with all of the options for changing the sound of this amplifier, how can you tell how it sounds? The main features that will change the sound dramatically are the ultralinear/triode switches. We will get to that in a minute. The sound of this amplifier is fast, clean, and detailed across the frequency extremes. Its pace is fast but natural and not exaggerated. With the recent addition of Transparent speaker cables in my system, the ability to listen far into the recording has seemed to jump exponentially, especially when listening to vinyl. The Margules brings forth these details effortlessly but most importantly naturally. From the upper most reaches of my ribbon tweeters the top end is extended, clean and grainless. The sound up high is never dull or flat or grainy unless the recording exhibits those traits. There is plenty of air and extension up top and a little sweetness too.

As low as my Tonian Labs speakers will reach, the bass is taut, solid, and has a nice grip on the bass frequencies. It is not too tight and over damped as it sounds on some solid state amplifiers. There is a nice presentation of dynamic shading and articulation. As with the top end, bass frequencies are clean and textured with excellent pace. The rhythm this amp reproduces is definitely one of its strong points and which I might add showcases what the Tonian Labs speakers do with this aspect of sound. The Tonian's are very fast and clean reproducers. There is nothing sloppy, fuzzy, loose or overly warm or under damped about this amp's sound.

The midrange is usually the deal breaker. Again with this amplifier, there is little to worry about here. Vocals sound free from colorations or aberrations. I hear no nasality, squawks, or tonal imbalances. Instead the midrange sounded clean (there are those words again) and yes natural. There is a holographic and dimensional sound in this range that gives music that slight warmth and dimension that the best designed tube amplifiers exhibit. But it doesn't over do it with this aspect of its performance. These traits were heard on the Monteverdi Vespers LP on Nonsuch with the layering of vocals and ambiance heard in the Church of Saint John at Hackney where it was recorded. The guttural grumblings and distorted guitar of Billy Gibbons on the song "Mescalero" from the ZZ Top CD of the same name were also brought out, ahem, well by this amplifier. This is great, I love this CD.

One could say that the U280SC is chameleon like in its presentation of the soundstage. Every recording's sound staging personality is clearly drawn out. On Ron Nelson's Rocky Point Holiday from Reference Recordings, the sweep of the orchestra took over the whole front of my listening room. There is no one size fits all soundstage in this area of performance though. My son and I were surprised to find out we actually liked the sound of Jack Johnson's release Brushfire Fairytales on CD better than the album. The U280SC easily and painfully revealed the stifling conditions of the recording venue for that session when we listened to the LP. This is one time where the CD even though not great in and of itself, actually sounded better to us. In any case the soundstage performance of the new U280SC surpassed the old amp in regards to width and depth and solid image placement.

As for the triode/ultralinear switch I found its performance pretty similar to other amps with this feature. In triode mode the sound was a tad warmer and handled inner details with slightly more delicacy and spaciousness. In ultralinear the sound took on a bit more dynamic grip and timbres sounded a bit more neutral or cooler. I am very glad this feature is on this amplifier. Again, one has choices.

Since no amplifier is perfect, are there any downsides to ownership of this amp? Well with its tight, clean, extended, and fast sound there are a few small moments that this unabashed tube lover would like to hear a smidge more tube lushness and a bit more warmth. But this could be a symptom of my system as well as the amp. It seems I am always trying to "warm it up" a bit. There is no shortage of that tube holographic and dimensional airy presentation with this amplifier though. Halfway through my review of the Almarro A-340 mono block amplifiers the Margules arrived. While the Margules had it all over these amps in speed, dynamics, and grip on the music, the Almarro pair had greater warmth, tube glow, and a slight slowness in pace that mixed together to easily draw one into the music. Which one I preferred should seem obvious or I wouldn't be doing this review. Although this amplifier has its share of warmth and fullness, it leans towards the fast, clean, and taut as opposed to the more classical or traditional golden glow of the old tube sound. And yes I have heard amplifiers with more resolution, gut wrenching dynamics and a squeaky clean sound but they are usually much more expensive than the U280SC.

The innards of the U280SC amp are built to exceptional standards, and the exterior is very handsome. Now there are amplifiers both tube and solid state that are built, or make that overbuilt with slabs of solid aluminum, etc. But that kind of build is going to up the cost many times as compared to the actual musical performance of the unit itself. In other words, those kinds of amps can seem overbuilt. The Margules U280SC on the other hand uses Plexiglas and wood along with metal in its creation. Plexiglas and wood are two materials that I feel outperform heavy metal in the area of EMF/RFI. I use four Herbie's Audio Labs Big Tenderfeet to great effect to help eliminate vibrations on this amp and the effects were noticeable. An application of four EAT tube coolers also brought about a change for the positive. So the U280 SC is not impervious to tweaks. All together I give this amplifier an A+ for looks and an A and C+ for build quality. The A is for the beautiful wiring and circuit boards and the C+ for the metal work.

So did the changes to this amplifier make it a better one? With improved bass extension, great timing, a solid grip on dynamics, a more open and spacious soundstage, and an easier presentation with inner details, I would say the answer to that question is a resounding yes. This is definitely a better sounding amp than the old one. Also if you are of the notion that tube amps play only certain types of music as in soft, look out, this baby can rock. And look, I am not heaping praise on this amplifier because I own it. I could have gone many different ways in replacing my old U280SC. Believe me! It's funny but with all the design and parts changes and minimal price difference Margules Audio chose not to designate this amplifier a Mark II status or even a fancy name such as reference or ultimate. It is still the U280SC. Also buying this amplifier from a company in the Americas, Mexico to be exact will guarantee that you won't see the same amp with about twenty different nameplates on the front or worries about grey market shenanigans. What you buy is what you buy from a company that has been around for decades!

And yes, it also draws you into the music. Those tubes aren't there just for decoration! Francisco Duran


I can't turn this article in without mentioning two accessories that have become absolute necessities in my system. In fact in one of the pictures you can see the first tweak. The other one is underneath the amp. The EAT Tube dampers are the red things that are slid over the 12AU7 tubes. The Herbie's Audio Labs Big Tenderfeet (4 each) were slid under the amp. EAT are famous for the manufacture of several tubes used in audio application and of course their tube dampers. Made of aluminum that is finned and anodized in several different colors, they have an ingenious method of adjustment with the use of four carbon/Teflon inserts inside the ring. The rings can be adjusted to fit a multitude of small signal tubes of various make and manufacture. These rings are said to reduce distortion and micro phonics. They also function as a device to dissipate heat.

The Herbie's Audio Labs Big Tenderfeet are one of many vibration products that are in the Herbie's line. File these under component isolation but he also makes vibration damping products for tubes but with a radically different approach than the EAT Tube Coolers. The Herbie's feet are said to absorb micro vibrations and block sound wave energies from components. I urge you to check out their website for a look at some interesting and fun stuff from them.

The words, "are said to", are definitely an understatement in regards to these two tweaks. They both work as advertised and then some. I listened to the U280SC without both of these tweaks, taking them out one at a time and listening and taking notes as I went. With both tweaks out the differences were quite noticeable. Bass depth and impact noticeably diminished and mids were not as clear and clean. Vocals sounded a tad less intelligible and there was an overall warmer, fuller and richer (colorations?) sound.

So one by one in went the tweaks. The first was the Herbie's Big Tenderfeet. My son helped me with this. He is definitely not an audiophile (I'm working on him) but he has a very sharp set of ears. As soon as the music started he almost did the classic jaw drop thing. "Wow Dad, I can't believe it," was his reaction. Suddenly the bass depth and impact noticeably improved, the mid range slightly cleaned up, and the soundstage opened up and deepened to a noticeable degree than without the feet under the amp. When I slipped the EAT Cool Dampers on the four 12AU7's we noticed the sound to shift to a tad cooler and sharper presentation. There was slightly more layering of the soundstage and images were slightly more defined. The sibilance was definitely more controlled. This last bit of artifice might be the deal breaker in the decision to purchase these tube coolers for some. Excessive sibilance for me has always been akin to the old finger nails running across the chalk board.

The biggest impact on the sound though was with the Herbie's Audio Labs Big Tenderfeet. The EAT's effects were more subtle but definitely noticeable. Although the claim that the EAT tube coolers actually cool the tube, therefore extending tube life, is another reason to seek these products out. If I had to live with just one of these products though, I would definitely pick the Herbie's Big Tenderfeet hands down. They are amazing products.

I have to emphasis that this is not a statement of the amplifier's poor performance. Because without these two tweaks the U280SC sounded quite good. But these tweaks helped to eliminate unwanted vibrations in the chassis and tubes to flesh out the true performance of this wonderful amplifier. Want proof? They also elevated the performance of my Antique Sound Labs mono block tube amps, my two solid state amps, the Marantz PM15S1 and the Monarchy SM-70 with very similar results. Let's not forget my Marantz SACD player and blue ray player that have Herbie's feet under them. Of course I couldn't use the tube coolers on my solid state amps. But perhaps someday Herbie's or EAT will manufacture a remedy for those pesky vibrating transistors! Francisco Duran

U280SC amplifier
Retail: $3450 USD

Margules Audio
Urapan #17-4
Col. Roma
Mexico DF 06700|
TEL: 52(55) 5514 7448 or 1-888-538-8605
web address:

Margules Group USA
Ben Goldman
820 Elm Dr.
Petaluma, Ca.
TEL: 707-581-1830

Herbie's Audio labs
web address:

web address: