2. amps-preamps
  3. 1092643684

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, 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.
cdc
1,855 posts
 
Welcome to Audiogon, Michael and thanks for the post.
Hope you stick around. It's always nice to hear from people in the know.
taterworks
1 posts
 
Sutts (and others reporting 'haze'), how is your power? I modified a power strip with a small (< 1 uF) high-voltage (400V) film capacitor across the hot and neutral lines, and noticed immediately a reduction in 'grain' and 'haze' from my Hafler amplifier, which uses MOSFETs. My approach is very similar to the original Shunyata Hydra-4 power conditioner, which only uses a single 0.1 uF isolation capacitor across the hot and neutral of both duplex outlets in the unit. (Note: DO NOT try to build one of these if you don't have electrical training. AC power KILLS.) This very rudimentary power line conditioner made a startling difference in my system.

It's possible that what is being described as 'haze' is the result of dirty power.
pbb
1,140 posts
 

This is all idle talk.  Typical of audiophiles.  Not worth a plugged nickel I fear.

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