Metropoulos Forum

Johan Segeborn demos this beast a few days ago. He says it the best sounding amp he has ever played and thats quite big coming from him!



plexi

Sounds good - but got to see inside

sounds good and juicy. 2 gain stages is all you need. specs:"it is pretty much stock 10xxx series SL but with 0,68 caps as in 68-69 SL. The transformers are Dagnall C1998 OT and T2562 MT, they are original. Choke is an oddball an old RS 10 henry heavy duty, probably non original to this amp"
http://s139.photobucket.com/user/plexim ... 8.jpg.html

now get rid of that tone strangling attenuator and hear even more natural harmonics overtones and compression.

So it was a Super Bass that got tweaked to a Super Lead? That's what it looks like. Very cool amp. Me likes.

jnew wrote:So it was a Super Bass that got tweaked to a Super Lead? That's what it looks like. Very cool amp. Me likes.

Yes that fits with the rest of the spec, although the first superleads (with Drake -119OT) used 270k mixers with 560pF cap and the 56k/256pF tone stack too, but obviously different PI output caps and all 0.022uF in pteamp

As I look closer, it's more interesting. No bright cap on VOL I, still a 56K slope resistor but with a 500pF cap, and to me, it looks like the NFB resistor has a yellow band multiplier which would make it a 270K instead of a 27K. I like the dual 16uF for the pre-amp. .0022 on CH. I would yield some interesting results as well. Great amp in any config however.

EDIT: That cap in the tone stack might actually say 300 instead of 500. Kind of hard to tell.

Is it just me, or does something look a little fishy about it? Never seen brown McMurdo preamp sockets in that era amp either. Not saying they never used them, but I can't recall seeing them. And the Pihers look kind of weird, more like later era production. In fact, the whole preamp board looks like it could have been a restoration job.

I should read closer, as it seems it is indeed a rebuild thingy... Kind of oddball specs at that.

Yeah, I would definitely agree about a pre-amp re-do. Looks like a 2 watt Iskra 2.7K there on V1.

Hey shanti, which JTM-45 Opt Tran do you have as indicated by RS. A Radio Spares or is that a MM's RS Tone Clone?

ime, the basic specs are not any more important than the individual bias' on all the tubes or the filter values, or the overall voltages throughout the amp. All that stuff is what puts the even odd order harmonic structure together and is what forms the overdrive characteristics as much or more than what v1 or v2 caps are or mixers etc.....he should provide a voltage chart for that amp......as far as filters, sounds like preamp is 16, and i'd guess the rest is similarly stock and low, and if they are original, remember they likely are not filtering even their full rating so i suspect an overall low filter is also what makes this sound what it is.....

There's truth in all you say about the voltages and filtering as they also relate to the sag and feel of the amp but the other stuff is relevant, IMO, as they affect the overall frequency slope/shape. Key stuff as they relate to how much gain the amp has as well. Just my .02.

The amp was very modified when I got it so it is more of a rebuilt than an restoration. Its not stock!!! (Not trying to pass it as anything else! Got a pile of modified marshalls from an estate in various stages of disaster assemble and dissasembeled and I am restoring them/rebuild them as best I can but with a focus on sound, since they are not virgins as to speak...

This one was the first I started with as a plattform testing various preferred features I like in my old marshalls and it ended up like this. Its the "Be(a)st of feature" plexi in my mind...

Ill try to answer any questions

Johan S got very found of this amp and will release a 15 min clip of it soon.

plexi

Ill tried to mod a layout from the forum to put the specs in, I might have to make a revision (I did it kind of fast ) and with your eyes I know we find something...

that's pretty much a stock 67/8 amp in terms of basic circuit and real world listening. there's a few changes but nothing that would add up to why it's 'special'. the mixer's being half is not contributing to the tone, the lack of bright cap is common. the tone network is metal panel stock. good enough. It's a stock 2 stage plexi with no gain mods. What you are discussing is originality. yes the amp is not original but it is basically stock.

If you put these exact specs in another amp with different tubes and trannies, it will sound different. When marshalls become 'special' is when it all jives together. It must in this amp, it's that simple. There is no special circuit variation that creates 'that tone'. It's basically that same stock circuit but slightly changed from amp to amp due to tubes and trannies. You'd explain more about why this amp sounds good by noting off spec resistors and preamp voltages. And take a look at it on a scope and you'll see what you hear

what about tubes?

Sorry I don't have a working scope at the moment...had an old one from my old highschool but it broke down... See if I can bring it to a friend and measure it.

Power tubes are old EL34 philips (mullards), preamp are Brimas ecc83... But I have put in other tubes and it still sounds awesome. The Mullards add an extra edge however...

I think its one of those special Output transformers in a combo of the "right" variations of the smaller parts, electrolytes, mustards and resistors. I got a few plexis with the same OT (they all sound good) but my 12000 series is also one of the special ones that stands out. Had a friend that cloned that one using an old 71 with old parts right filtering and all. It a good amp, you can hear the heritage, but it still sound different from my 12257.

plexi