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Just wondering what the hell MOSFET stands for and what that means if an amp says MOSFET on it. I saw a "Marshall MOSFET 100 Lead" amp or something like that, and WTF does that mean??? :scratch:
 

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MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. They behave more similarly to tubes compared to standard BJT transistors. Standard transistors are prown to fold over, that is to say that once they clip, the clipped part of the wave, instead of flattening, begins to invert or go upside down.... it looks like someone folded the sine wave in half at the clipping point when viewed on a scope. MOSFET's don't do this. This is part of the reason that MOSFET's sound more like tubes. MOSFET's also exhibit a negative temperature coefficient so bias tracking is less critical. Also, because of this, MOSFET's cannot go into thermal runaway and self destruct like 'normal' transistors can. And, like tubes, MOSFET's operate by fluctuations of input voltage, instead of fluctuations of input current (like standard transistors do).

I know, it's probably more than you wanted(or needed) to know :dance:
 

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Good post Crumb...and all true in case anybody thinks you are making stuff up.

MOSFET's do act more like tubes and it's a hell of a lot easier to design an amp using them. Those solid state power amps Ed always uses in his live rigs are MOSFET.

Here's a link that gives lot's of info:

http://mr5150.vhvault.com/evh-brown-sound.html
 

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So how is the SOUND of a MOSFET amp compared to say a good old fashioned Marshall tube amp?


Rj
 

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I seem to remember Van Halen using a couple of MOSFET HHV800s in his stack , i used a couple in my PA , cracking Amps , if you see one , and sometimes they pop up cheap , buy it .!
 

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rjfoster said:
So how is the SOUND of a MOSFET amp compared to say a good old fashioned Marshall tube amp?


Rj
MOSFET (solid-state) power amps are designed to supply as clean a signal as possible... with the lowest signal-to-noise ratio.... and the lowest Total Harmonic Distortion (THD)... so they are used primarily for Public Address (PA) systems for mixing boards, for amplifying vocals (through a microphone), keyboards and bass instruments which need clean volume.

Unlike a tube amplifier... MOSFET amps are generally not going to sound very "musical" when driven hard or into clipping... unless they are designed to do so... as I believe the Marshall "Valvestate" series amps are.
 

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It all depends on where you get your tone, and harmonics. In my post above with the link to Ed's set-up...he turns a head into a preamp and get's the exact sound he wants...then powers it though a MOSfet amp. If he used a tube power amp (which he could no doubt afford) it would screw up his sound. They have their place if you know what you are doing.
 

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VHfanOU812 said:
It all depends on where you get your tone, and harmonics. In my post above with the link to Ed's set-up...he turns a head into a preamp and get's the exact sound he wants...then powers it though a MOSfet amp. If he used a tube power amp (which he could no doubt afford) it would screw up his sound. They have their place if you know what you are doing.
I fully agree... especially about Ed using his Marshall head as an entire preamp and the MOSFET H&H's as true clean "power amps". And it's absolutely correct that his tone would have changed if Ed had used a tube power amp which would have directly altered his overall tone... perhaps in a good way or even bad... we'll never know. :dunno:

Ed has always said his early set-up was like a "... home stereo amplified". The way his amplified signal chain was structured back then, using the floor pedal effects and Marshall head as a preamped "tone stack", and with the echo delay last in the tone chain, finally through the clean "PA" power amps to drive his Marshall Celestion G12H/JBL D120F cabinets was sheer, audio engineering genius!! :jam:
 
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