Danish designer Ole Lund Christianson's Gamut D-200 amplifier differs from its competitors in the high power sweepstakes in its use of a single high power MOSFET to produce its rated power. Previously, most high power amplifiers made use of multiple transistors operated in a parallel fashion to produce their rated power. The major drawback to this design philosophy is that no matter how hard you try; you are never able to completely match the transistors. As a result the signal that is produced is a mixture of the signals from all the parallel-coupled transistors. According to GamuT, the result is that the fine details found in music can be lost.
The MOSFET used in the D-200 was originally for use in switch-mode power supplies and is capable of handling more than 500 watts and passing a peak current of more than 300A. The stereo D-200 utilizes two of these single MOSFETs per channel, one on the positive rail and one on the negative rail. A push-pull amplifier operating in Class A drives each output device. This amplifier has the ability to charge the gate either up or down. The driver stage has a voltage source 15V higher than the output device voltage rail to help control the MOSFET when it is approaching its maximum output. The power source for the D-200 is two 500VA toroidal transformers with 32,000 µF of capacitance.
Due to the high current capability of the MOSFETs, GamuT designed a sophisticated protection circuit for the D-200. Through the use of both thermal and current sensors, the circuit detects DC errors, high-level subsonic signals, long-term ultrasonic signals, high temperature, low impedance loads and short circuits. In addition, the circuit monitors the voltage, current and phase of the load being presented to the amplifier. If any of these conditions are detected, the protection will simply mute the input signal or if necessary, open the output relay. GamuT has designed the relay to open only after the input has been muted to prevent the contacts of the relay from being damaged by switching current as the relay reacts to the situation.
Okay, so how does it work? Say for instance the circuit detects a short. The protection circuit will immediately mute the input for about a second and the output relays will then open. The circuit then sends out a 1-millisecond long pulse to test the circuit. If the condition is still present, the protection circuit remains engaged. As soon as the circuit determines the problem has been corrected, the system automatically resets itself and the music begins playing.
The protection circuit precludes the D-200's use with loudspeakers who have an impedance of less than 2 Ohms. GamuT has set the protection circuit so that the amplifier will deliver its full output into loads greater than 1.5 ohm. Should the amplifier's protection circuit detect an impedance load lower than 1.5 ohm, the circuit will alert you by muting the input for a second. In most real world situations, this should not be a problem.
The D-200 measures a diminutive 17 inches wide, 18 inches deep and 6 inches high and weighs a gut-wrenching 68 pounds. The review sample was finished in the traditional GamuT black livery with the optional chromed faceplate. The faceplate has a center mounted power switch with a single green LED to indicate that the unit is powered up. The chassis is made of stainless steel while the front panel and heat sinks are sanded three times to obtain a very smooth surface. The rear panel is nicely laid out. There are provisions for both unbalanced and balanced operation by way of the traditional RCA and XLR connections. If you decide to use the amplifier unbalanced, remember to insert the supplied shorting plugs tying pin 1 and 3 together.
Loudspeaker connection is by way of two sets of beefy WBT connectors. One pair of the connectors is a direct connection, which bypasses the filter network that protects most amplifiers against capacitive speaker and cable loads. According to Christensen, the using the direct connection increases the fidelity of the sound particularly in the upper registers. Also, he says the only difference between Direct and Normal output is the coil/resistor network for electrostatic loudspeakers, both are protected for shorts. If you bi-wire your speakers, Gamut recommends using the filtered connectors for the bass and the direct connections for your midrange/treble connections. If electrostatics are your thing, reverse the above convention. Please be warned, if you use the direct connection, make absolutely sure that you do not short the connections, as there is no guarantee that the amp will survive. Thankfully this is extremely hard to do as the Gamut uses European specification WBT's that are completely encased in plastic. There is also one small negative associated with these connectors. Certain cables may not fit the posts due to the small opening in the plastic sheath through which they must be inserted.
The D-200 replaced my reference Pass Labs Aleph 1.2 monoblocks on the twin towers of the Nearfield Acoustics Performance 924 loudspeakers. The GamuT drove the 924's full range with all but the lowest octave handled by the superb REL Stadium III subwoofer, which was crossed over to the towers at 32Hz. The D-200 that I received came to me directly from CES so it was pretty well broken in when I received it therefore I cannot give you much insight into the unit as it goes through the break-in process. In any case, I let it play non-stop for 72 hours before I sat down to do any critical listening. During this 72-hour period, the sound of the unit changed very little from when it was first inserted into the system.
The first thing that grabbed my attention about this amplifier was the quality of its soundstage, which is among the very best I have ever heard. The sense of depth produced by this diminutive amplifier rivals some of the best tube amplifiers out there. On orchestral recordings, the rows of instruments were very nicely layered with the proper amount of separation between them. Lateral placement of the instruments within the soundstage was equally precise. John Rutter's Requiem (Reference Recordings, RR57) as performed by the Turtle Creek Chorale and the Women's Chorus of Dallas really showcases the superb soundstaging capabilities of this amplifier. The Morton H. Meyerson Symphony Center that the Chorale and Chorus call home is fast earning a reputation as being one of the best halls in the country. My favorite cut from this album is "Pie Jesu", which features soprano Nancy Keith. As Ms. Keith performs, the entire chorus swells up behind her filling the hall with glorious sound that will almost bring tears to your eyes.
The D-200 is remarkably clean and coherent from top to bottom. Transients are cleanly produced and march along in perfect lockstep with the harmonics, which gives the music an excellent sense of drive. Music seemed to flow from speakers with a sense of ease. This amplifier is also very low in distortion. This allows low-level details to flow out of a seemingly endless black hole. This black background allowed silent passages to seem even darker, which gave even greater impact and power to each note played. The "Absolute Sound's" CD Hearts of Space really is an excellent test CD. While it is not the type of music I would listen to everyday, it has become a valuable tool in my reviewing process. Track 8 "Sama" is an excellent test of your systems ability to reproduce depth. The beginning of the cut features scrapped rocks and other sounds that seem to well up out of the depths. To hear these sounds at their lowest level requires a system capable of very high resolution. Many amplifiers that I have used in this system mask the first few notes of this track. The GamuT's noise floor is low enough that it does not seem to get in the way and cover up those wonderful low-level details.
The GamuT seems remarkably balanced from top to bottom. It does not seem to favor one part of the music spectrum over another. Low-level bass extension and dynamics are very good. My Pass Labs Aleph 1.2 monoblocks are not known for their superb bottom end performance. However, I find their bass performance to be exceptionally good. I place the Gamut in the same camp. Neither amplifier generates the same deep bass energy as say, one of the more expensive Krells. This may make the D-200 seem like it is missing measure of dynamics. I can assure you it is not. "Black Magic Woman" from Patricia Barber's Companion (Blue Note, 7243 5 22963 2 3) features a superb drum solo by Eric Montzka. Montzka's drum kit was presented accurately. The same could be said from Michael Arnopol's bass. There was none of the thick turgid mess that generally passes today for excellent bass performance.
Moving up through midbass all the way through the midrange, the D-200 remained crisp and very nicely detailed. Textures remained true to the original. It was in this area though that the D-200 gave up a little ground to my reference Pass Aleph 1.2 monoblocks. The Aleph is known for the quality of its midrange, which is very dimensional and harmonically rich. The Gamut's midrange, on the other hand, had an immediacy, airiness and clarity that created a sense of intimacy that was a pleasure to listen to. However, the slight lack of harmonic richness that I am used to with the Pass amps did take just a little bit off my listening pleasure.
This is particularly noticeable on female voices. My friend, Beth Chorneau has just released a new album, which was recorded live at a new club in Charlotte called the Evening Muse. The acoustics are absolutely wonderful! The album called Stage Presence, Live At The Evening Muse (available from Pamona Records at www.jimbrock.net) features Beth Chorneau on vocals, Van Sachs on guitar, Gerard Benson on bass and Jim Brock on percussion. Beth's voice has a smokey, sexy quality to it that has to be heard to be believed. This album comes the closest to of any album I have heard of hers to capturing the true sound of her voice. When reproducing her voice, the Gamut tends to smooth out some of the huskiness that gives her voice so much character. The Pass provides a slightly better recreation of her voice by its very nature of being more harmonically rich. There was nothing really wrong about the way it presented her voice; it was just a little lighter than I am used to. Please do not get me wrong, this is not meant to be a major criticism of the D-200, it is more of a nit-pick.
The top octaves are reproduced with all of the energy, air, life and detail that any music lover could ever want. There was no edge or hardness to upper frequencies that could ever be considered harmful to the musical truth. The amplifier also exhibits explosive speed and overall dynamics. Music seems to flow from this amplifier with a sense of ease as long as it is not driven hard. This leads me to my major criticism of this stereo amplifier.
If the D-200 has a weakness, it is that it seems to have less power than most similarly rated amplifiers. As the amplifier's power supply is used up and it is driven into clipping, the sound becomes brighter and edgier. The soundstage begins to collapse and the superb focus within the soundstage is lost. This is an amplifier that is best partnered with speakers that offer higher sensitivity. Speakers that offer lower sensitivity or electrostatics with wild impedance curves need not apply. For those speakers, Gamut offers the M-250 monoblocks or the exquisite S-300, at a much higher cost.
When used within its operating limits and partnered with speakers of moderate to high sensitivity, the D-200 is a true world-class amplifier that offers its owner a touch of sonic heaven at a real world price. My hat is off to Ole Lund Christensen for offering us mere mortals touch of sonic heaven. Highly recommended.
Power Output: 200 Watts per channel in 8 ohms load
Signal To Noise: <100dB below 100 Watts at 8 ohms
Input Impedance: 40kohms XLR (balanced), RCA input is 20kohms
Input Sensitivity: variable as set by dealer, 0.77V, 1.55V, 3.1V or 3.9V for full power
Shipping Weight: 31 kg.
Dimensions: 155 x 430 x 446 (HxWxD in mm)
GamuT Audio ApS