Marshall Mods - What are your Favourite Mods?

[cluster]

Hey Guys,

I built a platform amp based on a JTM45 (KT66) and now I want to experiment with Mods to shape the tone of the amp. More like "Voicing" Mods. I'm curious as to what are your favourite mods. So far I've split the cathode at V1 to make it more plexi like. 0.1µf coupling caps at the output to fatten the tone a bit. 50/50µf power cap and solid state rectifier to tighten the feel. 32/32µf PI and 16µf preamp power cap. 500pf/33k at the tone stack. Put an 12AT7 at PI to tame the harshness. Not really interested in a PPIMV or Cascading the preamp. This amp has more than enough gain for what I do (70's Classic Rock). I looked at the Friedman mods he's done, like the C45 mod (works best with the extra preamp tube HBE). Not sure if it will work with this amp which doesn't have the extra gain stage and isn't cascaded? The Sat mod never sounded good to me. His Fat switch is nice for single coils (easy to do). The one I'm interested in is his structure switch mod. Does any know what that does?

Mods I'm considering ATM:

1) Cathode switch at V2 with different Resistor/Bypass Cap combos
2) Some kind of presence feedback mod on a switch.
3) ??

So, I'm pretty slim on ideas. Can anyone chime in on other ideas on ways to voice the amp?

Thx..

[Helmholtz]

What sound are you after?

A JTM 45 sound or rather a "Plexi" (JMP 50/1987) sound?

[cluster]

What sound are you after?

A JTM 45 sound or rather a "Plexi" (JMP 50/1987) sound?

JMP 50/1987

[Helmholtz]

JMP 50/1987

Then you should use EL34s instead of the KT66s.

What is the primary impedance of your OT?
And what is your speaker impedance?

[vintagekiki]

https://schematichell.com/mods/
Marshall Mods

[Chuck H]

Well... You don't want extra gain. You seem yo be interested in opening up the tone stack. Maybe you could modify it by trading it in for a Fender BF type amp!?!

But seriously. Since you're not interested in extra gain and the models in question are well known and revered I'd say that you should simply experiment with speakers and guitars and just use the amp as built to a 1987 JMP 50.

I use to play through one of those for gigs. It wasn't my favorite to be perfectly honest, BUT... I got more compliments on my tone using that amp than any other. I actually had a pair of them (in case one went down on short notice). One was a little harsher than the other, but no one ever seemed to notice but me

[dumbassbob]

what filter caps are you using 50-50 ect I lowered the filter caps And it warmed up my 45 Made it sound like Clapton in 1966.Marshall started Over filtering I did the same with my bandmaster Kendricks likes to turn everything into a Twin Reverb Made my Bandmaster too clean Skip Simmons lowered it back to stock It came back to life.All these Mods I hear on You Tube 90% sound like a DS1 in front of a noisy amp

[R ski]

My first favourite mod is on the input stage triode: remove cathode resistor and by pass capacitor if installed, replace that with a red LED with the cathode connecting to ground and the anode connecting to first tube stage cathode. If that LED is right polarity, then the Led lights up, dull. This mod really makes swapping 12AX7 to 12AY7 or 12AT7 on first stage beneficial, clean head room, plenty of drive

[EL-34/JMP]

Personal favorite.

[Chuck H]

I can honestly say that the Friedman clones I've heard all sound like "good" Marshalls. You know the tone. When you hear a Marshall sounding that way you say "That's a good one". Though I've never been crazy about adding effects loops to vintage designs I think if anyone could keep to the original tonal integrity it might be Friedman.

Unfortunately we get no specifics about the mods done to this amp. Which is the point of this thread. So... Thanks for nothin'?

[EL-34/JMP]

"I think if anyone could keep to the original tonal integrity it might be Friedman."

Unfortunately we get no specifics about the mods done to this amp. Which is the point of this thread. So... Thanks for nothin'?

Yep thats why i had him build me this amp to my spec's in 2011 which was before he had his own amps & gizmo line.
Course you can email Dave yourself @ racksystems@yahoo.com.
No real clone has the harmonic overtones of a real JMP IMO.

https://www.youtube.com/watch?v=wZ6INe1qZj8

[The Dude]

You need a few more pedals.

[Chuck H]

I may have already mentioned this?... I "selected" one of my JMP 50's at a boutiquey shop in the Bay area, Ca. that specialized in vintage Marshalls. As a result I probably paid a hundy more for it than I might have buying privately. But there's a premium on already vetted gear with a Marshall logo. It seemed like a fair trade.

I walked into that shop and plugged into all six of the JMP 50's they had on display. One of the clerks came over and said "I've never heard THAT amp sound so good." Maybe it was placating (?) but his reaction seemed genuine. All I did was crank it proper and adjust the controls for the guitar I was plugging in. It did sound "right" though not the holy grail. What I realized then was that even in a place like that there weren't many players coming in that "got it" as far as playing to an amps strengths. It probably didn't hurt that I already owned one of this model and was intentionally shopping for a backup. So I knew how to get the most out of it going in... It was a fun moment. I actually got to meet Rick Emmet in that store on a subsequent visit, but that's another story Anyway...

My tone at that time was based on the JMP50 with a boost pedal in front. I was using a delay to simulate some reverb effects and a phase shifter for some schmooze but that's about it. And what else does one need? I never found my own ideal tone before I started building my own amps but this rig may have been as close as I ever got before that.

[EL-34/JMP]

You need a few more pedals.

Already have a few more ...

[Helmholtz]

... I "selected" one of my JMP 50's at a boutiquey shop in the Bay area,....

First of all we should clarify which "JMP 50" we're speaking of, as the JMP series started in 1967 and comprises a number of different models.
Including the very different 1987 and 2203 circuits.
Marshall did some own mods over the years and even the 2203 could be seen as a modded 1987.

Now as you're familiar with Marshalls and know how to design tone, the question could be: What would you have done to your Marshalls using your present day experience?