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How close are JMP's vs Plexi's


5150Watts

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How close is a master volume JMP and a Plexi? I have a JMP and wondered how close it is. Mainly I am wondering how the gain structure is related. For instance, If you crank a plexi, what would the related pre-amp settings be on the JMP? Only reason I ask is I have never played a plexi, and have always been currious.

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A plexi is way different from a JMP. They look alike from the panel, but it's what's underneath the hood is where the difference is.

 

Until you've heard a plexi in person, you'll never understand. They have a bark unlike any amp I have heard. It's not the preamp, it's the power amp - that's where the tone is.

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They're actually not too much different. The big thing on the master volume models is that the driver tube is two cascaded gain stages as opposed to one for each channel, every thing else is very very minor. So overall the amp has a little bit more hair on it than does a Plexi. The power amps of the two are 100% identical.

 

So it really comes down to what you like the sound of better. You can get a helluva lotta grind out of an older Superlead.

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The master leads have more gain and are more compressed sounding. The super leads are more percussive and have more dynamic range. Super leads are also much darker sounding and the distortion has more grit.

 

The plexis had less filtering in the power sections, which made them have more sag and sensitivity to your playing.

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A master volume JMP has more in common with a JCM800 than a Plexi. However I prefer them over the Plexi or the JCM800. Especially with those big ass 6550's.

 

I had the pleasure of using a 1978 JMP for a while and I wish I had the money to buy it from the guy who owned it.

 

-Zach Omega

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Originally posted by 5150Watts

So how different is the poweramp section then? I was always lead to beleive that there really wasn't too many differences.

 

 

They're identical from the same era. If you compare a JMP Super Lead to the JMP Master Lead (is that the correct name - either way it's model 2203), the power amps are 100% identical. There are some minor differences if you go back to the plexi-era. There's much debate over how much difference in tone this really makes. Also, every one of these older Marshalls sounds different from the others.

 

The real difference is the preamp. The Super Lead has two parallel channels, like a lot of older amps. All Marshall did to get the Master Lead was remove the 2nd channel and cascade it into the 1st for more gain. You can get a similar sound to the Super Lead by cranking the master volume completely on your amp and then setting preamp somewhere in the 2-4 range. (There's a lot of variation in both amp models, so it's really hard to say without being there.) Dial in EQ to taste - it's identical between the two amps. As mentioned, this will be a little brighter and thinner than the Super Lead would be, but it's definitely related.

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I have both and think that although they both sound great, they sound very different. My not-quite-Plexi '72 Superlead sounds much more aggressive and brighter than my '79 JMP - both have EL34's. The Superlead sounds like early VH and the JMP sounds like GNR. Also, the Superlead really needs to be cranked to sound good (at least to 4) which is incredibly loud - at low settings, it is thin and brittle. An attenuator is a must. The JMP can sound good (but different) at any setting but doesn't have the tear-your-head-off aggressivness that my Superlead does.

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as compared to the metal panel early 70's 4-input superleads, my JMP doesn't sound as different as you might imagine...

 

when the master is turned up near 10 and the preamp is backed off, it's very similar

 

i've played a other JMP 2203s that sound less like my JMP than a couple of the 1959s i've played

 

as an aside, i'm no tech-head--when i jumper the channels in a 4-input superlead, is that akin to cascading those preamps, or is it just getting the 2 channels blended?

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