Suggestions to modify the plexi 1987 model to a plexi 1986 model

Change the tone stack to the jtm45. Probably increase feedback. The coupling caps in the 1987 for the output tubes are .022 and in the 1986 they are .1. The .1 uf caps will allow more bass to come through...so you might increase the depth, or low cut, or definition. My guess is you will probably have plenty of bass without adjusting anything.

Why would you want to do this?
 
Change the tone stack to the jtm45. Probably increase feedback. The coupling caps in the 1987 for the output tubes are .022 and in the 1986 they are .1. The .1 uf caps will allow more bass to come through...so you might increase the depth, or low cut, or definition. My guess is you will probably have plenty of bass without adjusting anything.

Why would you want to do this?
I have several vintage Marshall amps. I have a JTM45, a Model 1987 50W Plexi, a Model 1986 50W Plexi, and several later 50W amps from the mid-1970’s. I also have a couple of the last higher-powered tweed Fenders. The other similar amp I have is a very early 1964 YBA-1 Traynor that is tube rectified. All of these amps can produce beautiful leads, but the 1986 wins. I wouldn’t call it more bass. It’s more like a singing honk An elusive character. It just is what it is.

I would love its sound in my AF gear. I can’t nail it. I’ve screwed with drive settings. Since I service and repair my own amps, I’ve tried tweaking parameters. While the modeling software allows quite a lot of factors to customize, the variables aren’t down to the schematic level (nor should they be). I just can’t get that sound. So I thought I’d ask. One thing you’ve mentioned I haven’t tried. I haven’t started with a JTM45. Physically, it takes more effort to convert an actual JTM45 into a 1986, than it does starting with a 1987. But I can give it a go, so thanks for the idea.
 
I would love to see this bass circuit or amp added. And it has been requested several times in the past... I have tried to replicate my original ‘71 super bass and the closest I was able to get was using a tone match through my ultimate attenuator. You can also try the suggestions from this old thread:

https://forum.fractalaudio.com/threads/cliff-slope-resistor.78029/

I wish we could alter the tone stack values a little more to tweak.

And I may revisit this again after I get my III delivered tomorrow :)
 
Hey, good for you! Welcome to the land of III!

Yeah, the 1986 was a great circuit. Strange omission. Same with the Traynor, which was a great Canadian amp.

But I’m partly to blame, as I’ve tried and have not able to duplicate the 1986 with my limited experience working on Fractal hardware.
 
I am saying use the 1987 model, but change the tone stack to a jtm45. The 1986 has the same tone stack as a jtm45. Those old marshalls just sound so different even with in the same model and year. If it sounds good, it sounds good! Sounds like you've got a nice collection of amps!
 
Thanks. I have the Fryette PS 2, but I don’t feel like lugging amps around anymore.

Maybe this is a simple question, but how do I tell the AF3 to use one amp model and another amp’s tonestack?
 
Maybe this is a simple question, but how do I tell the AF3 to use one amp model and another amp’s tonestack?
Tone Stack is one of the parameters in the Amp block. Just choose the tone stack you want.
 
FWIW I have a JTM 45 1965 all original - It's one of those items that I will never sell... I cant replace it.
I have a IIXL (Im on the wait list for the III) In the past I tried to recreate the sound/tone and feel (feel is of major importance to me) The short of it is - I got close, close enough to get a smile (and that's important too ;))
The long of it is - It took an unbelievable amount of tampering A/B ing and lots of F***s & other expletives to get there, and many hours - Jeeze many hours. Its long gone now (the preset) But from memory I recall the IR being not so important, there were at least 3 or 4 factory cab options in the XL which worked well, I always use a PEQ block after the cab for any final tone shaping anyway, I sometimes also use one before the cab block too.
The real amp even in non jumper-ed mode has sooooo much bass and thud I usually need to turn this down to around 2.5, then almost max out mids and treble (a smidgen before full - or the magic is gone) Copying this in the axe did not have the desired effect. Im pretty confident in saying the bass needed to be absolute zero and the mids & treb needed to be maxed. So dont be afraid of maxing or minimizing the basic controls some models need it.
The output tubes where KT66's and I remember this being very important to change too.
Also in the dynamics page I needed to play with Dyn Presence, Dyn Depth, Preamp Dyn. Cant remember how, but basically the real amp has this glorious mids chirp to it when you dig in - The sound sonicaly laden with just the right frequencies which just jump off the fret board at will... This was very difficult to achieve but I got close. Supply sag also had a role to play (think that needed turning up from default) There were many other tiny tweeks to the deep parameters I think there was a Q value somewhere which needed adjusting (sorry I'm not in front of axe edit right now)
Overall I would say I got 80% there in terms of tone and 65% in terms of feel. I found you could get closer on tone but lost out in feel, or tweek to get closer on feel, but then lose out on tone.
It's a tough journey which can be fun or frustrating - Never in between for me, always one or the other each time I go after a sound.
One thing I had to bear in mind is that the amp that was modeled was not my actual amp to start with - so it was never going to sound like mine anyway.
From what I read and hear the Axe II had limitations and compromises needed to made in terms of amp modelling but the III has almost eradicated that problem, so hopefully you can get even closer. Im looking forward to getting my hands on the III and I'm going to try again.
Final shout - beware the firmware updates. If you do go deep into the parameter pages and tweek, and then finally find the sound you are going after, there is then a very, very good chance all your efforts will be gone in the blink of an eye, because the firmware will take that away and you need to start over. I've had my fingers burned too many times. And its the reason I dont have the preset now. Sometimes you cant really stay on the firmware because there may be a bug fix which you need, so you have to upgrade..
 
Thanks for your description. In a way, it's funny, that I could build the cabinet head, tolex and dress it, wire the chassis, and then button everything up in less time and with perhaps less effort, lol.

I was able to find the JTM45 tone stack parameter under the Advanced page editing the Amp block. I thought to try a different path. I decided to start with the JTM45 amp, and simply change the power tubes to EL34 and the rectifier to solid-state. But the JTM45 model already uses the EL34 selection (a bit of a surprise). I need to look closer, and it's probably there, but I haven't found the parameter for tube vs solid-state rectification.
 
That’s most of it, yes. I’m still noodling with the patch.

I could try the tone-match thing with my real amp. But I’m less sure - never been compelled to try it before.

Since the subject of amp models and the Traynor came up, I’m surprised that nobody mentioned it. The YBA-1 is a flipping miracle.

Ok, back to the parameter-editing grindstone...
 
Back
Top Bottom