July 2015

World Premiere Review!
GamuT Limited Edition Di150 Solid-State Integrated Stereo Amplifier Review
The most transparent integrated amplifier I have ever had the pleasure of auditioning.
Review By Ron Nagle

  Let us take a look back to the Enjoy the Music.com archives. In October of 2006 our friend and colleague Phil Gold evaluated a three-piece GamuT audio system. That Danish system was comprised of the CD3 compact disc player, the Di150integrated amplifier and a pair of L5 speakers. Now more than eight years have passed and we can now listen to an evolutionary new GamuT Limited Edition version of their Di150 integrated amplifier. At first glance, both old and new versions of the GamuT Di150 integrated amplifiers look the same. All of the advances are on the inside incorporating a revised circuit design and higher quality internal components. This is how the GamuT company answered my preliminary questions.

"Concerning the Limited Edition model, we have improved and refined the output stage for a cleaner sound with even lower distortion. We are offering this Limited Edition for the same price as the regular Di150, $11,990." Now this is only a guess, but it sounds like they stiffened the power supply by increasing the amount of storage capacitance. That upgrade should have been part of the modifications. In my crazy days of modifying old Dynaco amplifiers, increasing the power supply capacitance did improve all frequencies, but it had the greatest audible effect near the mid bass and bass frequencies.

The companies name, GamuT, seems very odd yet it is actually derived from a Latin word. As referenced from Websters Dictionary. I will cite one particular attribution meaning: "A whole series of recognized musical notes". The GamuT company applies this as their raison d'ete. "Our goal is not missing out on one single element among the myriads of information that create a realistic sound."

Electron Messaging Circuits
The Danes are great designers and engineers. I don't think I have to tell you that with such incredible brands including Gryphon Audio, which is Enjoy the Music.com's Editor and Creative Director Steven R. Rochlin's reference. The GamuT Limited Edition Di150 integrated amplifier, or Di150 LE, will certainly bear that out with its clean lines and built like a tank construction. The exterior is constructed of stainless steel and aluminum while internally it features a heavy non-magnetic chassis for stability. About one month after I started this project the GamuT people finally supplied me with additional circuit information, the following is my paraphrased description.

The GamuT Di150LE preamplifier circuit uses a combination of JFET and bipolar transistors. They are all identical negative types no complementary transistors are used. The input section of the output board uses a similar buffer configuration. The driver stage consists of NPN bipolar transistors, capable of producing 25 watts of power, which is needed to drive the 100 Ampere MOSFET NPN output transistors. Each transistor can handle more than 300 Amperes peak. Compared with the original GamuT Di150, the Limited Edition uses a new output transistor and a refined driver stage, which is so stable that the industry-standard Zobel Network (a resistor + coil in series with the speaker output) is no longer necessary.

This is claimed to yield even more control and help produce a better soundstage. The GamuT single MOSFET principle is based upon the use of only one output transistor per rail. Audio-grade complementary transistors are only available with a 20 Ampere maximum rating. The advantage is that you can avoid having 20 separate transistors on each rail trying to work together. Even with transistors closely matched there remains differences between them that results in phase-smearing which is clearly audible. Using one huge MOSFET effectively eliminates the disadvantages of the traditional multi-transistor output stage.

The MOSFET GamuT uses is an industrial grade NPN. Instead, GamuT has implemented the NPN MOSFETs where one of them actually powers the positive rail. This special arrangement has the added benefit that the difference between these two identical transistors is 100 times less than it would be in the usual complementary based output, the result of this is an output section without crossover distortion, no emitter resistors, and an extremely low distortion. Distortion is mainly of even-order harmonics. This also means that the GamuT's single MOSFET design does not use what many traditional audiophiles desire, which is Class A bias all the way to full output.

Instead, the GamuT Limited Edition Di150 integrated amplifier is a Class AB design, yet biased to 14 watts Class A in order to run the transistors at the best sounding temperature and to get the best sound during the first few watts of output. GamuT's Limited Edition Di150 integrated amplifier is a true dual mono design utilizing separate power transformers with separate secondary windings for the pre and power amplifier circuits. The amplifiers protection circuitry can detect DC errors, high level subsonic signals, long-term ultrasonic signals, high temperatures and low impedance loads. And so to summarize, the GamuT Di150LE use a dual-FET hybrid input buffer, a single Power MOSFET for each stereo output circuit along with an extremely robust power supply.

A Pretty Face?
The owner's manual tells us to do two things. "Please allow the new amplifier to burn in by playing music for 100 hundred hours" and "Allow the amplifier to warm up for at least one hour before optimum performance can be achieved". Well both of these instructions are just common sense procedure, but both of the suggested time intervals seem unusually long. Lucky for me the unit I received was broken in. The most eye-catching design element is a large 2.25" diameter volume control knob. It is positioned dead center on a 3/8" thick, 17" wide brushed aluminum front panel. The large central volume control conceals an ALPS dual logarithmic potentiometer. The knob overlays a rectangular dark plastic insert.

Behind that dark window is a series of blue LED's that tracks the position of the volume control. Stacked vertically on either side of the volume control are eight function select push buttons. There are four buttons are on the right side labeled from the top down, Bal 1, Bal 2, CD, and Dim. The four buttons on the left side are designated Tuner, Tape, HTH Preamp bypass and last one being for Mute. When the HTH function is selected, you can bypass the preamplifier section and use the Di150 as a power amplifier to drive two channels of an AV surround system. When any input is selected, a small blue LED is illuminated next the selected button.

At the top of the rear panel are the left and right pairs of speaker binding posts. Just below these are rows of unbalanced RCA and balanced XLR jacks. From left to right there are two pair RCA inputs labeled TAPE OUT and OUT. Side by side two XLR sockets they are R out and L out. Just to the right is a small toggle switch designated HTH enable. Next in line are four pairs of RCA inputs in order they are, HTH, Tape, Tuner, and CD. On the right rear are four XLR sockets, two are designated Bal 2 and the last Bal 1. Not to be omitted is the fused IEC 120 Volt line input.

My Wish List
Note: None of the following comments in any way effect the performance of the Di150 LE Amplifier. There are a some things I believe would benefit the Di150LE. First, GamuT should replace the inexpensive plastic remote control. There are 21 buttons on this remote control,14 of these are used for, in my case, a nonexistent CD player. Then there are two function buttons Standby and Phase they are present but not used. And that leaves just 5 functioning buttons of the 21 for the integrated amplifier. These are: Volume up, Volume Down, Source toggle, Previous source toggle, and last a mute function. Each of the DI150 LE amplifier's eight front panel buttons should be included on the remote control so you could go directly to each selection without stepping past some other functions. Finally, the rear panel RCA connections are not commensurate with the cost of this amplifier.

These connections are actually mounted on a Printed Circuit board and sticking through holes in the back panel. These remind me of low-fi $400 receiver versus a $12,000 high-end audio product. It would be far better if they were individual hardware jacks bolted to the rear panel with much more space between each one to support high quality audio cables. When you are investing this much money in a piece of gear, there are set minimums one should expect. A plastic remote control with only a few buttons being usable plus the apparently low quality RCA jacks are not the norm. Our industry is much better than this for anything costing over $8000, generally.

Performance
It don't come easy. A reviewers task is to isolate the performance of one review component slotted into a system comprised of totally different components. This is exactly why it requires an intimate knowledge of a very well-known set up we call a, Reference System. This may be characterized as cheating but I have been playing Vinyl records with the Merrill Audio Jens Moving Coil amplifier reviewed in April and with a Denon DL103 moving coil cartridge feeding the GamuT Di150LE. This may not be strictly Kosher since the Jens is on loan as a review sample. But damn, I can't help myself as these two components love each other, and who am I to tear them asunder. The recording was The Very Best Of Diana Krall [Verve 06025 74683 13] and it was the most lifelike rendition yet. Getting back to my reference system, let us try my $2500 British Creek Wyndsor phono preamplifier plugged into the GamuT.

Again, using the Denon DL103 cartridge feeding into the Creek loaded at 100 Ohms. Let us listen to that same Diana Krall album a second time. The track is called The Look of Love seemed that all the exact same musical information is present and accounted for. Maybe I sense a small image shift. Now more of Diana's voice is to the right of center. Also, there is noticeably more warmth to her voice. Mind you I can't say there is anything obviously wrong, yet my $ 2500 Wyndsor phonostage just cannot delineate the same expansive soundscape. And without that expansive sound I don't really feel as immersed within the music. At this point I realize just how transparent the GamuT Di150LE is to whatever characteristic is inherent in the line sources used.

Surround Sound?
Because the Di150LE includes a HGH bypass option we can separate the preamplifier section and use just the power amplifier to drive my speakers. The manufacturer includes this bypass feature as an option to use the separated amplifier in an audio/video surround system. This opens up a new path of investigation. Let us compare my reference preamplifier to the preamplifier built into the Di150LE. With the HTH bypass feature switched on, all of the line level sources were rerouted to my Parasound P5 preamplifier, with the Parasound preamplifier now up front driving the power amplifier.

At this point with my own preamplifier in the system I can determine if the power amplifier changes anything. It takes nearly an hour of playing music for the GamuT power amplifier to fully open up. After that hour long wait, the Di150LE very low noise floor is so transparent that not just the soundstage but the space separating individual players on the stage comes into focus. By a slight margin the details of that open stage surpassed even my reference Sanders ESL muscle amplifier. Now at this juncture with both halves of the Di150EL separated we can listen to my reference digital source. It is a Marantz 8400 Universal CD, DVD, DVD-Audio, SACD deck feeding Roy Hall's tube buffered up-sampling DAC25.3 DAC.

Many songs and many hours can be summarized by describing the first track from Sting's album, The Dream of The Blue Turtles [AM+CD 2750]. If you love somebody set them free. This track is replete with tons of studio reverb and a big driving bass tempo. The reverberation may be artificial, but it is full of micro dynamic details that locate and separate all of the players onto a wide and deep front soundstage. Nothing is held back as the bass line is reproduced as a deep driving force and the repeating tempo compels you to become involved. So now we can directly compare the contribution of each preamplifier separately. The Parasound is bright and quick with a tendency to sound very slightly more bright at the treble end of things.

At the same time the higher frequencies do paint small details within the space between my speakers. However, the Di150LE preamplifier overall has a better balanced presentation from top to bottom. The treble does not stand out now and the midrange and mid bass are all in balanced proportion. My Parasound preamplifier did over emphasize the higher frequencies. Not that I found this to be objectionable as some of the warmth that should be part of a human voice was now missing.

If we take each component's sound, the preamplifier and the power amplifiers contribution we will find the components voice. So far each half of the GamuT Limited Edition Di150 integrated amplifier is completely complementary. If there are any weaknesses, they seem buried in the music. I could not find any obvious faults. But here is where the road gets a bit bumpy for a writer. Because when all is said and done the most outstanding characteristic of the Di150LE is its transparency to the source. All of my reference line sources retained all of their characteristic pluses and minuses and the GamuT did not impose any of its own sound. I have heard the Gamut Di150 LE reproduce micro dynamic sound that is crisp and lush, sounding with a wonderful expansive midrange when the source contains these qualities. Yet when presented, the Di150 LE will elicit nuance, speed, power and delicacy. It will open a wide and crystal clear window containing subtle micro details contained within the performance.

Conclusion
The ethics of performance. Can an amplifier change or even improve on what you feed into it, or should it? The answer has to be a resounding NO! I see the Di150LE as a bed rock starting point for building a system from scratch. Its very natural neutrality dictates that you must proceed carefully to match every source component. At 700 wpc it will drive even very difficult 2 Ohm loudspeaker loads. Feed it junk and what you hear will be junk. Appropriately, that old computer caution applies of Garbage In = Garbage Out. GamuT's Di150LE integrated solid-state stereo amplifier is the most transparent integrated amplifier I have ever had the pleasure of auditioning. The promise and the possibilities are endless!

Footnote
Writing this report I tried not to fall into the black hole. It is not my intention to tell you what I feed into any component, that would be reviewing software and some outboard processor. Rather than tell you I played a particular CD or vinyl recording that you almost certainly do not own through a system you do not have makes no sense to me. I have tried, instead, to isolate and focus on the effect Di150LE amplifier has on the signal passing through it. That to me is relevant.

Enjoy the music and remember… Semper Hi-Fi.

Review System Components
Source Components: Sota Sapphire 2 turn table and Denon 103 Cartridge, Sangean Digital tuner, Marantz 8400 Universal CD/SACD/DVD/DVDA player. Music Hall Up sampling DAC 25.3 and headphone amplifier.

Amplification: Sanders ESL power Amplifier, Parasound Halo P5 Preamplifier. Jens Phono Amplifier.

Speakers: Aurum Cantus Leisure 2 SE two way monitors on 24-inch stands, Mark Daniels  Omni Harmonizer tweeters, Onyx Rocket Strata Mini 3.5 way speakers.

Cables: Kimber Kable 12tc 11ft. Kimber Kable 8TC Jumpers, Nordost Red Dawn, Chord Silver Siren, Homemade Teflon and Autobahn digital.

AC Power: Wire World 10 gauge IEC line cord, Power Cords: Kaplan Cables 12 gauge IEC

Power Conditioning: Islatrol Industrial 20 Ampere AC line conditioner, Richard Gray 20 Ampere Sub Station. Alpha Core Balanced Transformer Power Supply, Audio Power PE-1 power enhancer, Triad 2 Ampere isolation transformer.

And a comfortable chair with a 12' X 19' room. 

Specifications
Type: Solid-state stereo integrated amplifier
Frequency Response: 10 Hz to 50 kHz (+/-1dB)
THD: @1kHz > 0.05% (mainly 2nd harmonic)
Signal To Noise Ratio: 100 dBA 
Power Output: 180 wpc @ 8 Ohms, 360wpc into 4 Ohms, and 700wpc @ 2 Ohms
Inputs: Two pairs XLR, four pairs RCA
Record Output: One pair RCA
Line Output: Balanced XLR and unbalanced RCA
Speaker Posts: WBT gold plated binding posts 
Power Supply Dual Mono: Two 500VA Toroidal transformers
Weight: 64 lbs
Dimensions: 16.9" x 6.1" x 16.1" (WxHxD)
Warranty: 5 years parts and labor
Price: $11,990

Company Information
GamuT Audio
6818 Årre
Denmark

Voice: (+45) 70 20 22 68
E-mail: info@gamutaudio.com 
Website: www.GamuTAudio.com

United States Distributor
GamuT USA, Inc.
Los Angeles, California 

Voice: (888) 252-2499
E-mail: usa@gamutaudio.com