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Help, my Perreaux amp has "mosfet mist"

144.139.227.182

Posted by Doug Flynn on December 19, 2004 at 00:30:46

Hi chaps

Let me first start by saying that I am a DIY tube person who doesn't usually dabble in solid state (the "Dark Side"....).

Anyway, I recently bought a used Perreaux 900B MOSFET power amp on eBay. I bought it to use on the JBL horn system I am currently building (I want it to drive a pair of 15 inch JBL 2235 woofers per channel in reflex boxes up to 500Hz). The amp has very impressive specs - 450 Watts into 8 Ohms, 900W into 4 Ohms, 4kW peaks, etc, etc.

I tested the amp on my Tannoy 15 inch dual concentric speakers. I drove the amp via the inverting input (with + and gnd grounded), using my SE linestage. OK, what did it sound like? Well, if you nailed a mattress to the front of my speakers it would go some way to describing the sound I encountered. The sound had very little of the detail I am used to with tube amps. It sounded smooth, but very blurred. The term "mosfet mist" comes to mind. I have a friend who also has a similar Perreaux who reports similar sound.

What can I do to improve this amp? What's causing the crappy sound? Is this what all SS amps sound like (remember, I'm a tube guy with little SS experience)? Is it the input op-amp? Should I re-bias the output stages? Or should I just reserve it for subwoofer duty and build a big mofo tube amp to drive my JBL woofers? :-)

Cheers. Doug

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