Tube-O-phile
Contrary to what my close audio buddies might think about how I feel about tube gear, I happen to be a huge fan of tube equipment. Within certain applications tube equipment seems to capture some of those magical qualities that will allow recorded music to get you so close to the real thing that the presentation can sometimes be short of jaw dropping. But for all of the benefits of tube equipment sometimes I’ve encountered a few inconveniences such as biasing tubes, low power, and depending on the power tubes, soft bass lines. But after hearing a myriad of tube products over the last few years I am forced to rethink my position on tube gear.

During this years visit to CES 2007, I was fortunate enough to stop into a number of rooms that I felt were able to work out some of those anomalies that I just mentioned and judging by the sound coming from the Margules Audio room I felt confident that a review of the companies tube power amp would be an entertaining endeavor.

Call me Julian
Margules Audio is run by Julian Margules a dapper and highly accomplished man who has his Masters degree in Electrical Engineering. He is no stranger to tube equipment because Margules Audio is a family run business that has manufactured commercial electronics since the mid 1920’s and the companies successes have been passed down from generation to generation. With the institutional tube business as a foundation, he decided to transfer some of his vast knowledge into the development of tube and solid state products for two channel and home theatre retail applications. Margules Audio also makes loudspeakers and a high end I-pod interface that I had a chance to hear at CES that is pretty impressive sounding. But this review is about the U280sc power amplifier.

Turn up the power
The U280sc ($3450.00) is a Class A tube amplifier that can operate in either ultra-linear or triode mode. It is a push-pull design that can be used as a stereo amplifier or turned into a pair of monoblocks with the simple twist of a knob; and of course another amplifier. In ultra linear stereo it delivers 70 watts per channel into 8 ohms or 35 watts into 8 ohms while in stereo triode mode. The U280sc doubles its power output when it is used in a mono configuration. It uses KT88’s, 6550’s, or KT99’s. You can also use KT100’s but I hardly ever see them available new or on the used market.

The U280sc uses four power tubes and has a proprietary active bias circuit so I was able to put away my normal tools that are used for manual biasing such as the mini screwdriver and my Radio Shack multi-meter. This circuit has an additional feature that according to Julian Margules “actively tracks the input signal and permits full Class-A operation without saturating the output transformer and overdriving the tubes”. The U280sc also uses (2) 12au7’s per channel, one for the driver stage and the other one for the phase splitter. The binding posts are manufactured by ‘Vampire Wire’ and there are only one negative and one positive post per channel on the back. Instead of changing speaker wire taps to adjust for impedance, there is a military grade rotator knob on the front that allows the user to switch from 2 to 4 to 8 ohms. There are also volume pots for both channels so that you can connect a source component directly into the unit without a preamp. Although functional, it sounds better with a preamp.

The U280sc should be considered heavy at a little over 67 lbs and care should be taken when moving due to most of its weight being distributed toward the back where all three of its transformers, one input and two outputs reside. All are enclosed inside an attractively built steel cover plate. The U280sc is an attractive amplifier that has polished wood side panels and feels extremely solid like a 1960’s era Lincoln Continental sedan.

There are a number of technological innovations that contributes to its wonderful sound. The U280sc has full Class-A differential output and active damping control that helps to control low-frequency (woofer) excursion while at the same time delivering tremendous bass which negates the need for any amount of negative feedback. Margules Audio has also developed the Back Electromotive Force Sensor or BEFS for short. This is a sensor that detects the amount of resistance and changes the amplifiers output impedance which allows the U280sc to drive loudspeakers that pose a difficult load.

Mr. Margules is so proud of his amplifier that he encouraged me to take a look inside and after I unscrewed the bottom panel I didn’t see one ounce of unused space. In times past I have explored the inside of a component and was shocked to see just a small number of parts with a lot of wasted real estate. That’s not the case here; this unit is packed and gives you the feel that you are getting a lot more value than the stated retail price! There are a multitude of circuit boards that are firmly isolated from each other. Each one is made of epoxy fiberglass and coated with silver. The polypropylene capacitors and the metal film resistors and the semiconductors are top grade and in abundance. There are also three user replaceable fuses and a circuit breaker to protect the unit from a high voltage overload.

On top the tube sockets are gold plated ceramic and there is a panel meter in between the tubes that measures the amount of amperage that is passing through the right front tubes. If it is at the far left which is 100a the tubes are being overdriven. Normal readings are generally around 35a.

The power switch is located on the back and once it’s engaged after approximately three minutes the U280sc is ready for play. During this time it is going through a soft start up and a number of system checks.

Bright Lights
The unit comes standard with Chinese KT88’s and 12AU7’s, but one of the benefits of using tube gear for amplification is that you can tube roll to cater to the sound that you feel is most comfortable to your ears; plus its fun to play around and try out different tubes. But as you know, even the same type of tubes from different manufactures can have an entirely different effect.

I know there are a lot of KT88 fans out there but I settled on new production Tung Sol 6550’s. In addition to the stock tubes I tried Electro Harmonix, SED Wing-C 6550’s, and Valve Art KT88’s but I preferred the sound of the Tung Sol’s. Even though the Tung Sol 6550’s had a little bit more tube noise than the SED Wing-C’s, this tube performed the best in all areas of the musical spectrum and was the only power tube that I tried that excelled in both ultra linear and triode modes without compromising low end integrity or rolling off the top end. Finally I tried out four KT90’s from Ei. Unfortunately when I plugged them into the system the tubes were a little grainy so I went back to the Tung Sols. I’m not saying that it is indicative of the Ei KT90 sound or that there were quality control issues because it could have been just a bad batch of tubes similar to the three or four of the SED Wing-C 6550’s that I had to return.

For this review I have on hand a number of 12au7’s from new production JJ/Tesla’s and Electro Harmonix, to NOS Ei’s, and Tung Sols. I also have some NOS Telefunkens but at $125.00 per tube, that’s $600.00 for the quads and I normally save those for special occasions. Although I did try the Telefunkens with the Margules U280sc the German wonder tubes did make an improvement in the sound however it was not as profound a difference as I experienced in another make of amplifier. So I primarily used the NOS Tung Sol 12AU7 and found the tubes more than sufficient and cost justifiable with a detailed, musical, and robust sound that was much better than the stock tubes or the other 12AU7’S that I had available.

I would say that my listening sessions were about seventy/thirty ultra linear to triode. In ultra linear mode I sacrificed more of that three dimensional holographic sound that is a signature trait of triode designs but I gained in the areas of bass slam and rhythm and drive. But in triode mode the presentation is much more detailed with warmer, more romantic lines.

Candle-Opera
In ultra linear the Margules Audio U280sc exhibits tremendous bass that is tuneful, has plenty of impact as well as wonderful extension. Bass drums notes are revealed with power and authority and lower organ notes have presence and body. If the U280sc were produced in colors other than black I would choose green because this amplifier is a chameleon and emulates the sound of many top notch solid state amplifiers that have a firm, tight fisted grip on the low end.

The midrange portion of the presentation is wonderfully crafted. It is clear with beautiful tonality and musical pleasantries. Midrange notes do not stand out because the presentation is overly warm or romantic but stands out because of how well it is integrated within the musical spectrum. There is nothing that is over emphasized or over exemplified.

High frequency information is also handled very well. There is no hint of roll off and the amount of information that is presented is just enough that if you had a tone control you could leave it positioned at dead center.

Not to long ago I had an opportunity to hear Joyce Cooling live during the summer and I’ve been playing a number of her discs quite frequently. The Third Wish CD [314 549 850-2] on GRP a division of Universal Records is one of the discs that I prefer in ultra linear mode. The tune that I like the most is “Daddy –O” with Joyce Cooling on guitar, close companion Jay Wagner on keyboards, Gary Calvin on bass and Billy Johnson on drums. This is a funky tune with a stellar guitar performance, strong bass lines, and supportive play on electric keyboards along with tight drum work. What makes this piece so enjoyable is the Margules U280sc is able to perform a number of tasks admirably. Bass is firm but doesn’t extend up into the lower bass which is a good thing because that might cause congestion in the all import middle portion of the frequency range. Transient response, pace, rhythm, and timing are also one of the amplifiers strengths and the tight and fast presentation reminded me of how some members at the concert reacted positively to what was being played by getting up and dancing and clearly having a good time.

I later switched to triode mode and the music took on a magical quality and more of a ‘you are there’ effect. The music shoots off of a black panoramic background and because of the lower distortion it is like listening to the same track remixed with additional percussive instruments; details are just that sharp and abundant with greater musical hues. The soundstage also exhibits some drastic differences. Music has more of a three dimensional effect with greater ambience retrieval and its like adding a rear firing tweeter to my loudspeakers and creating a greater depth perspective. Dynamics are still very impressive but do not posses the amount of force as in ultra linear mode.

A good example of a CD with depth is Joe Sample’s Spellbound on Warner Bros. [9 25781-2]. The fourth track ‘All God’s Children’ starts off tender and peaceful yet further into the song dynamic intensity increases slightly. There are a number of memorable moments from Joe’s inspirational touching display on the keyboards, to Marcus Miller’s stylistic manipulation of the strings on bass, to Omar Hakim’s stimulating play on drums. Collectively it is like listening to this touching selection via a single full range driver because there is an unmistakable coherence amongst the musicians that is smooth and effervescent.

If there were ever a disc that is well suited for triode play, it is Juanita Bynum’s Morning Glory Vol. 1: Peace [CD11659]. This is a powerful spiritual disc that allows her to speak from the heart. The songs are very tranquil and are a perfect example for the U280sc to showcase its ability to demonstrate a warm and inviting sound that has the chance to give you a goose bump experience. Through the U280sc music glistens like the dew in the early morning and the sounds in triode mode are more palpable with focused intensity. Spatial cues are better realized including capturing the ‘hall effect’ because of the airiness of the presentation.

A Sweet Ending
The Margules U280sc is a superbly crafted amplifier that has a marvelous sound and is an excellent choice for amplification whether you’re a fan of solid state or tubes. Its build quality is first rate and it has great bass, a nicely textured midrange, and reveals high frequency information with wonderful extension and clarity. It combines some of the better qualities of solid state devices with the magical quality of tubes and presents music with an ultra smooth and silky sweet midrange that is one of the hot selling points of tube electronics.

It also has a list of features that rivals the accomplishments of a Nobel Prize winner. As an end user you have the flexibility to match the impedance levels to your favorite brand of loudspeaker and alternate between triode and ultra linear mode with the ease of flicking a switch or turning a knob. There is also the ability to switch from mono to stereo without sending the amplifiers back to the factory. After all, who wants to go through the trouble of repackaging two seventy pound amplifiers and waiting several weeks for the upgraded amps to return and then hoping that there wasn’t any damage during transport? And if that’s not enough you have the option to install your favorite power tubes without the hassles of manual bias. Top that off with a price of less than $3500.00 (which is a steal), and what have you got? That’s right, a product worthy of our “Most Wanted Component” award.

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Manufacturer:
Margules Audio
Uruapan #17-4
Col. Roma
Mexico D.F. 06700
Mexico.
Tel. 52(55) 5514 7448
52(55) 5533 4654
52(55) 19987171
Collect 1-888-538 8605
FAX 52(55) 19987272
Website: www.margules.com.mx
Price: $3450.00 USD

U.S. Distributor:
Margules Audio USA
Harwil Corporation
8390 E. Via De Ventura
F110-194
Scottsdale, Arizona 85258
Tel:(866) 590-1616 Toll Free USA and Canada
Tel:(310) 601-7976
Website: www.margulesaudio.com

Specifications:
Power utralinear: 70 watts per channel
Power mono ultralinear: 130 watts per channel
Power triode: 35 watts per channel
Power mono triode 70 watts per channel
Distortion: >0.15%
Frequency response: 20-55 khz
Signal to noise ratio: >83db
Maximum power consumption: 590 watts
Weight: 30.5 kg