2. amps-preamps
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SS amp mosfet 'haze' - ever experienced this?

Tried a new amp in my system on the weekend: the well-reviewed Gamut D200 mkIII (partly based on HP's great review), a single-mosfet SS design. At the dealers' place, it sounded great (speakers were Wilson Benesch Discovery, an isobarak, lower-efficiency design). I can't use a tube amp right now (unfortunately!) due to pending child and the system is on a LOT (2-ch/HT mix), so am looking for the most full-bodied SS amp I can find (prefer fully balanced design to match my modded SF Line 3 pre).

Well, to my surprise, the amp did NOT work out as well at my place. My speakers are 97db Coincident Total Victory. Yes, it was full-bodied, but I was definitely aware of this haze, or veiling around each note. I have a friend who designs amplifiers, and he said that this is inherent of mosfet designs. I called Israel (Coincident) and he was not surprised that I only heard this once I got back to my place, due to the high resolution abilities of my speaker vs the speakers at the dealer's. I guess I will be sticking with my Sim Audio W-3, as it is much 'cleaner' on my system (given that I must stay with SS). Too bad, 'cause my Sim W-3 definitely has the edge in clarity, but the Gamut was a touch more full-bodied.

Has anyone else experienced this 'haze' with a mosfet-based design? I admit, those with higher-efficiency speakers like mine (97db/14ohm) probably are NOT using higher-powered mosfet designs anyways, but I would like to know how others feel about mosfet designs and this issue I had.
sutts
kalan
185 posts
 
Sutts, I have also heard that among Gaincard fans, the 25-watt version was usually favored over the 50-watt S version. Since the S version could not come close to powering the Coincident Super Eclipse I's (at the time) properly, I figured the standard version---for all it's alleged better qualities---just wouldn't have the gusto to work well with the Super E's.

I can report on the GamuT M200 monos, though. They are breaking in nicely. All the elements over the already good D200 I had hoped for are present in the M200 monos: more solidity (palpability[?]) to their presentation, larger (particularly deeper) and better defined sound staging and just as musically engaging as the D200.

They M200's also sound considerably more powerful and controlled than the D200 stereo version with deeper, more commanding bass. The D200 is gone; so, I can't make a current, direct comparison. But I spent a month with the D200 and started using the M200's directly after the D200. No regrets.

If I had a bunch more money, I would consider two D200 amps in vertical bi-amp configuration. The extra cost (over M200's) and the additional cabling would kill me right now.

The M200's are working well with about 300 hours on them. I have heard they continue to improve beyond that. We'll see....
kalan
185 posts
 
Sutts, you also asked about the Plinus SA102 MkII amp. Yes, I used the same speakers I have now: Super Eclipse MkIII's. I liked the amp; among the other SS amps I was trying out (Goldmund SRM 150's, and Goldmund Mimesis 28M in quick succession) the Plinus seemed more alive, more coherent, more liquid, and maybe just mated with the First Sound pre-amp better compared to the Goldmund amps. I liked the Plinius amp, but not enough to buy one.

Now, I have heard the (significant) step up Goldmond 29M in another system that just worked wonderfully with the Placette Audio Active Linestage and Talon Firebirds. The 1.45 V input sensitivity of the 28M just may not be enough to let the First Sound drive the amp properly, or something.

To me, the Plinius SA102 MKII seemed to be a more complete amp, in my system.
sutts OP
702 posts
 
Kalan- thanks for the updates. How are the Gamut M200 monos on the ambient heat factor scale? are they warm to the touch; do they hear up the room? Incidentally, what is the size of your listening room?
kalan
185 posts
 
Sutts, Both the D200 and the M200's run cool, with the M200’s running cooler still than the D200. The M200’s are just barely warmer than the room itself. The two-only MOSFETs per channel are mounted on the side of the chassis, equal distant apart and in the middle of the flush side of two, large heat sink banks.

The M200’s space their transformers fairly far away from the main board and other signal-carrying wiring and have two, much bigger power capacitors per channel than the D200 has.

My room is a small-ish 12.5' x 17', with low-pile carpet & pad over concrete and lots of open cell acoustic panels--placed mainly at the first and second side reflection areas and behind my listening position. The speakers fire down the long walls and are positioned well forward into the room (from the wall behind them).

May I ask why you ask about the heat and room size?
musiklab
2 posts
 
Hi, I am Michael Edinger, of MusikLab.dk
Musiklab.dk
I made (designed) the latest 3 upgrade of the well received D200 amplifiers from GamuT , as well as all their other analog stuff- like S300, M250, D150, D3, etc. until 2005.
The D200 k mk2 and earlier were a bit less transparent in the midrange and treble, and the GamuT mk3 (2003 was last version for GamuT)upgrade adressed this with a complete redesign of the circuit board. The "Haze" mentioned occurs with sensitive speakers and ears- when listening to a cold started Mk2 or Mk3 for the first 1/2 hour or so.
Reason: the GamuT amps warm up very slowly (>30 min´s) due to high thermal mass and a slow bias circuit setting and regulation. To avoid Bias overshoot and meltdown it is set below the optimum value for sound.
In my self produced MusikLab D220 mkIV single MosFet power amplifiers this issue is adressed with a sophisticated redesign of the Bias circuit that allows a faster warmup( < 5min´s), and maintains an optimal Bias setting and thermal regulation by monitoring the output device crystal temperatures immediately.
The Musiklab products are available via the musiklab website above.
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