Marshall sound clips

yek

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I stumbled upon these two sound clips of a Marshall JMP 2204 (EL34) and a Plexi 100W, in a thread on another forum.

Amazing tones, especially the modded* JMP, recorded with a Shure SM7B.

* Quotes: "I changed nfb 100k to 50k (or 47k), removed few bright caps and modified master volume a bit". And: "No PPIMV, just 100k with master volume".



 
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Thanks for posting.. The 1959SLP is currently my favorite amp in the Axe3. The last 3 months I probably have spent 80% of my time playing through it.
 
It is about swapping a resistor to increase the "negative feedback" of the amp. The first Marshalls hat 27k, what gives a lot of feedback to the main stage and tightens the amp. 100k gives more gain and distortion.
Cliff wrote about that, I think im the wiki or tech area.
 
that 2204 sounds absolut killer!
what does "changed NFB 100k to 50k" mean?

That is probably referring to Negative Feedback (if you are in Axe Edit, it is under the Power Amp section).

I've been playing with the 800's and got a lot closer with the 800 #34 rather than the normal 800 actually (most likely my guitar and IR choice).

Thanks for sharing this Yek, super nice to chase some stunning tones like that!
 
It is about swapping a resistor to increase the "negative feedback" of the amp. The first Marshalls hat 27k, what gives a lot of feedback to the main stage and tightens the amp. 100k gives more gain and distortion.
Cliff wrote about that, I think im the wiki or tech area.

Negative feedback in the Brit 800 model defaults to 1.xx. In one of the Plexi models it's 6.60. So I tried that value (and in between values) in the Brit 800 model, to simulate the nfb mod, but I don't really like it. The amp starts to feel stiff.
 
A JCM800 is NOT a Plexi. Very different circuit. Those clips sound like a Plexi. What you're hearing in the second clip is a LOT of room. I'm not even sure there is a mic on the speaker. Sound like two room mics or a stereo room mic.
 
So the guy in the 1st clip says the amp was ruined by adding more tubes and a reverb and other shit.

I think I probably would have liked it more with the mods. Moar gain! And if that shit included an FX loop sign me up for some shit.
 
The Plexi 2204 model doesn't really do it for me. But the Capt Hook 3A is surprisingly close, at almost default settings.
 
the takeaway from those vids should be just how much volume plays a part in forming a great tone. the interaction between the guitar and the amp is something really special. one of the amazing things about the axe fx is the ability to run amps at full tilt at whisper quiet volume....but it's also one of the drawbacks, because you lose that interaction.
i helped a guy on facebook some time ago who was complaining about some weird noise he was getting when he wasn't playing the guitar. turns out it was natural feedback. he'd actually turned his monitors up and didn't realise what was happening because he'd never played a real amp at volume. he had no idea that he needed to damp his strings or turn the guitar volume down. crazy.
 
A JCM800 is NOT a Plexi. Very different circuit. Those clips sound like a Plexi. What you're hearing in the second clip is a LOT of room. I'm not even sure there is a mic on the speaker. Sound like two room mics or a stereo room mic.

Of course. Should have selected the Plexi 2204 model, totally forgot about that one.

*walks away to power on the rig again..."
I'd be curious as to what differences there are between the actual JCM 800 2204 used for the Brit 800 model and the actual JMP 2204 used for the Plexi 2204 model. From what I've read there were few, if any, changes to the 2204 circuit during the JMP to JCM transition. It was basically just a cosmetic change. It does sound like the very early (mid-seventies) JMPs may not have had a cascaded preamp and there may have been some filtering changes made to the 800s at some point in the mid-eighties. But it doesn't sound like they are drastically different amps. Can't say I have any first-hand knowledge though, my only experience with these was owning a mid-eighties JCM 800 2203 about 20 years ago.
 
Early JMP 2204's did not have cascaded input gain stages. The low and high sensitivity inputs each fed separate 12AX7 gain stages in parallel and each was biased for the different gain levels. Their parallel outputs fed the preamp volume control.

Later 2204 amps from the JCM series have the first two preamp stages cascaded in series with the preamp volume control between them. When you plug into the low sensitivity input, you bypass the first stage and plug directly into the second stage through the preamp volume control. When you plug into the high sensitivity input, you feed the first stage which then in turn feeds the second. The result is more gain available and the ability to force another tube gain stage into overdrive with higher input levels.

Interestingly, the 100 watt JMP master volume (2203) did have the cascaded input stages, so it was much closer to the JCM version.
 
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I'd be curious as to what differences there are between the actual JCM 800 2204 used for the Brit 800 model and the actual JMP 2204 used for the Plexi 2204 model. From what I've read there were few, if any, changes to the 2204 circuit during the JMP to JCM transition. It was basically just a cosmetic change. It does sound like the very early (mid-seventies) JMPs may not have had a cascaded preamp and there may have been some filtering changes made to the 800s at some point in the mid-eighties. But it doesn't sound like they are drastically different amps. Can't say I have any first-hand knowledge though, my only experience with these was owning a mid-eighties JCM 800 2203 about 20 years ago.
There were several versions of the "2204" Plexi. Our model is based on a 1981 2204 Master Volume JMP. It has a different circuit than a JCM800.
 
It also depends on your definition of "Plexi". For many that's come to mean any vintage style non-channel switching Marshall amp, while others say it only applies to pre-1969 amps with actual Plexiglass faceplates. Marshall's model numbers and component values can kind of be all over the place so the lines tend to blur. When I see Plexi, I tend to think 4 input non-master volume amp regardless of the faceplate.
 
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