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Marshall JTM50 simulation

Chiguete

Experienced
So I just recently learn that the main amp the Angus Young has used most part of his career is the not so common Marshall JTM50 and since Fractal doeant have ut maybe someone here can tray to sumulate the tone sing the JTM45 and modding its values?
 

scorch

Experienced
I've got one that I built years ago. Basically a Brit JTM45 jumped with EL34 tubes and a Plexi tonestack.

I've since modified that and use KT77 tubes and a Friedman Smallbox tonestack just because I think it sounds better.

The front end is still JTM45 so you'll have to roll back the bass to keep it from being too boomy. But it has more crunch than a JTM but smoother and cleans up better than a Plexi.

I also use the 4x12 Basketweave speaker impedance curve with pre-Rola greenback speaker impulses.

It's just a ballpark attempt but I really like it and have used it for years.
 

mr_fender

Fractal Fanatic
Like most early Marshalls they vary a bit too. Some had tube rectifiers while others had solid state rectifiers. The solid state models would likely have a little less sag and have slightly higher B+ voltages. I believe they also had less negative feedback in the power amp than the JTM45 as well.
 

Joe Bfstplk

Fractal Fanatic
Like most early Marshalls they vary a bit too. Some had tube rectifiers while others had solid state rectifiers. The solid state models would likely have a little less sag and have slightly higher B+ voltages. I believe they also had less negative feedback in the power amp than the JTM45 as well.
JTM45 had a lot of negative feedback around the output section, if memory serves - a 27k resistor off the 16 ohm tap, basically copying the 5F6A Fender Bassman resistor value that was coming from a 2 ohm output, so figure 2.828 times the voltage being fed back.
 

Joe Bfstplk

Fractal Fanatic
Yeah, the JTM50 used 27k feedback resistor as well, but off the 8 ohm tap.
Yeah, they were already starting to untighten the output section at that point, I guess. Dropping from 2.828 times to only double the amount of feedback in the Bassman. :) Later circuits loosened up even more, and had a somewhat easier/softer transition to distortion.
 

mr_fender

Fractal Fanatic
You could also try starting with the 1987x, change the tone stack to Brit45, turning off the bright cap, and turn up the negative feedback a fair amount.
 

Brian Coonan

Power User
I've got one that I built years ago. Basically a Brit JTM45 jumped with EL34 tubes and a Plexi tonestack.

I've since modified that and use KT77 tubes and a Friedman Smallbox tonestack just because I think it sounds better.

The front end is still JTM45 so you'll have to roll back the bass to keep it from being too boomy. But it has more crunch than a JTM but smoother and cleans up better than a Plexi.

I also use the 4x12 Basketweave speaker impedance curve with pre-Rola greenback speaker impulses.

It's just a ballpark attempt but I really like it and have used it for years.
I messed around with the settings you provided - got a pretty good sounding amp. Thanks for the info!
 

Raab90

Inspired
So I just recently learn that the main amp the Angus Young has used most part of his career is the not so common Marshall JTM50 and since Fractal doeant have ut maybe someone here can tray to sumulate the tone sing the JTM45 and modding its values?

Makes sense.
This is the one and only amp I've actually heard sounds like Angus solos. Out of all his videos, the one where he uses the JTM50 are in my opinion the only ones where he actually nails perfectly the Angus tone. I could close my eyes and think it's Angus.

 
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