Tweakers' Asylum

• Hey Doug ! - djk 23:31:31 12/22/04 (0)
  In Reply to: Help, my Perreaux amp has "mosfet mist" posted by Doug Flynn on December 19, 2004 at 00:30:46:

  At one time I was a Perreaux dealer, we were also the largest single JBL dealer in the midwest.

  The Perreaux has mosfet mist in spades, if you don't like that kind of sound, get rid of it. Short of replacing the mosfets with bipolars (a major redesign) it will still sound like it has mosfets, no matter what you do to it.

  Send me an e-mail if you really want to discuss it.
  
  

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• Re: Help, my Perreaux amp has "mosfet mist" - Anthony Dockrill 22:45:23 12/22/04 (0)
  In Reply to: Help, my Perreaux amp has "mosfet mist" posted by Doug Flynn on December 19, 2004 at 00:30:46:

  Hi Doug,

  I recently moved to solid state and much of the hard grainy flat sound that I remember sand amps having is now gone in most modern designs.

  So assuming your amp is one of the good ones....First thing I would look at are you cables. Solid state even the good ones are less forgiving then valves. Also check your system to see nothing in your system is overly forward. One of the down sides of having a neutral amp is it doesn't suffer fools gladly.

  Sand amps are not as plug and play as valves in that you need to get everything just right and then they can sing.

  Having said that you may have bad amp but from what I've heard of recent designs it won't be the mosfets as such to blame but the guy who designed it.

  
  Cheers,
  Anthony
  
  

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• Re: Help, my Perreaux amp has "mosfet mist" - Cobra2 08:50:16 12/21/04 (0)
  In Reply to: Help, my Perreaux amp has "mosfet mist" posted by Doug Flynn on December 19, 2004 at 00:30:46:

  I would check caps...maybe also AC-filter.

  Sound quality does not come from MosFets, BJT, or Tubes alone, as you can have a just as muddy tubes, or tubes with "digital-glare"...

  Arne K
  
  

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• Re: Help, my Perreaux amp has "mosfet mist" - Lou S 08:19:49 12/21/04 (0)
  In Reply to: Help, my Perreaux amp has "mosfet mist" posted by Doug Flynn on December 19, 2004 at 00:30:46:

  Hi Doug. Your amp is most likely suffering from 2 things. Bad rectification, and poor quality caps. Any electrolytic caps on the circuit cards ought to be replaced with Black Gates, or Nichocons if you cannot use Black Gates. The bridge rectifiers should be replaced with either Ixys bridges which Percy Audio sells, or if you feel creative, you can use Stealth diodes and make your own bridge. This may clear up the muddy sound, unless it is in part related to design, and it will clean up midrange glare as well. You would do well to bypass the PS caps with at least .1uF RTX caps too.
  
  

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• Check the AC supply. - Al Sekela 09:22:05 12/19/04 (0)
  In Reply to: Help, my Perreaux amp has "mosfet mist" posted by Doug Flynn on December 19, 2004 at 00:30:46:

  Monster amps can generate lots of RFI in their power supply and inject it back into the AC supply. The bigger the power transformer, and the lower the filter capacitor impedance, the worse this is. If your source shares this supply circuit, you could be suffering from the effects of this noise on the source component.

  There is little point in trying to filter the AC to the power amp, but you might find improvement from a filter to the source. Separate, dedicated circuits are a big help.

  You might be able to reduce the noise, if that is the problem, with HexFRED rectifiers and a soft-start circuit (to keep from burning up the 'FREDs) in the SS amp.

  Also be sure the SS amp's power transformers do not suffer from weak mechanical support. If they are on thin sheet metal panels and can bounce around, this will reduce the deep bass clarity.
  
  

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• Wish I had an answer - Russ57 08:30:11 12/19/04 (0)
  In Reply to: Help, my Perreaux amp has "mosfet mist" posted by Doug Flynn on December 19, 2004 at 00:30:46:

  I don't know your amp. But I can say that in my limited experience I find MOSFETS to be a soft and loose in the low bass. A little like a tubey vintage tube amp can be. I thinkk you'd be better off with BJT based outputs. If you handle the price and only want it for bass freqs a Krell is a great bass amp.

  
  Russ
  
  

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