Plexi 1987x info

lastcaress83

lastcaress83

Inspired
I just received my Axe FX III mk2 Turbo today and have been working to match tones with my real amp, a 2020 Marshall 1987x. Working with the 1987x Treble model, the first glaring difference between the two that I noticed was a drastic decrease in gain in the model vs the real amp. After messing about with the input drive I was able to get the gain levels closer but at the expense of some clarity. After mucking about for quite a long time, giving up, then just playing with random presets I happened upon the Plexi 50w Treble High 1 amp model and it was a revelation. All the glassy bite, hair, and gain were right where they belong and it's MUCH closer to my 1987x in the high gain treble input.

My question is, does anyone know which inputs were used for the 1987x amp model? Based solely on my observations, I'd have to assume it was made using the lower gain inputs. It seems odd that Fractal didn't clarify this for the 1987x but did for the 1972 50w Plexi.
 
The 1987x in the axe is I believe a 90's re-issue. I'm not sure if the newer ones have a different circuit or not, but maybe in later years they made it closer to the original plexi and that's why the plexi 50 watt sounds closer for you?

According to Yek's write-up on it, it was darker than the original plexis. It might also be related to the fact that the Fractal reference didn't have a bright cap installed. Maybe the 2020 did? That would certainly explain a gain difference at lower volumes.

https://forum.fractalaudio.com/thre...-1987x-marshall-1987-vintage-re-issue.111362/

I'd say just use the 50 plexi if it has what you are looking for, it's definitely badass.
 
Try turning the bright switch on and see if it gets you closer. Normally the amp has a bright cap, but Cliff said a while back that his came from the factory without one, so the model defaults with it off. That should make a big difference.
 
Thanks everyone for the help! I’ll try the bright switch. I’ll also crack my head open to see if that cap which was missing from Cliff’s amp is present in mine.

Still confused about the inputs though since the 1972 50w specifies whether high gain or low gain was used while the reissue does not. Will report back tomorrow!
 
lastcaress83 said:
Thanks everyone for the help! I’ll try the bright switch. I’ll also crack my head open to see if that cap which was missing from Cliff’s amp is present in mine.

Still confused about the inputs though since the 1972 50w specifies whether high gain or low gain was used while the reissue does not. Will report back tomorrow!
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Often amps that have a high/low gain input are modeled with the high gain input and the low gain can be simulated by lowering Input Trim to .500.
 
unix-guy said:
Often amps that have a high/low gain input are modeled with the high gain input and the low gain can be simulated by lowering Input Trim to .500.
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Thanks for the explanation. If that’s the case, I can only assume its the missing cap(s?) to blame for the disparity.
 
lastcaress83 said:
Thanks for the explanation. If that’s the case, I can only assume its the missing cap(s?) to blame for the disparity.
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Possible... Or maybe component tolerances (if you read the link I shared?).

Or maybe the Speaker Impedance Curve affecting things.

Did you try to disable power amp modeling and run the Axe Fx into the effects return of your real amp to compare the Preamp sections directly?
 
unix-guy said:
Possible... Or maybe component tolerances (if you read the link I shared?).

Or maybe the Speaker Impedance Curve affecting things.

Did you try to disable power amp modeling and run the Axe Fx into the effects return of your real amp to compare the Preamp sections directly?
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I would be very surprised if it were tolerances given how big the difference is, especially considering how close the 1972 sounds.
I matched the impedance curves as best I could. The Boss TAE has selectable loads with recommended settings to emulate different cab/speakers. I used the 4x12 greenback setting for the real amps load then a greenback impedance curve for the model. I also set speaker distortion to “Hard”, which helped a bit.

I haven’t tried running the model’s preamp into the real amps power amp as activating the effects loop on the real amp decreases gain a bit. I may try that tomorrow just to see how it sounds.
 
Chuck P said:
That's a pretty extreme step, even if you have good health insurance. Maybe just use the 50w.
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Thanks for your concern! I was an avionics tech in my past life and have built and rebuilt amps for fun so I’m pretty comfortable with this kind of work.

That being said, it sounds so ridiculously close already that there’s not much point other than to satisfy my curiosity.
 
lastcaress83 said:
Thanks for the explanation. If that’s the case, I can only assume its the missing cap(s?) to blame for the disparity.
Click to expand...

Most likely. The very high bright cap value in many Plexi style amps lets A LOT of signal through the volume control. The common 4700 pF value in many Plexi's puts the filter cutoff below most midrange frequencies, so you get a noticeable gain boost in addition to the added brightness. In contrast, the bright cap used in Blackface Fenders is usually around 120 pF.
 
You should read this too: forum.fractalaudio.com/threads/plexi-models-sound-dark-a-different-perspective-i-tried-everything.189249/post-2423806
 
lastcaress83 said:
You nailed it, that’s the real one. I must need better speakers, on my iphone and in my truck they sound VERY close
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They are very close indeed, just not as close maybe as my similar JP-2C test. But still close enough that I would probably sell the amp if I wasn't especially attached to it.
The difference could easily be due to you setting everything to 5 instead of tweaking the amp model as close to the real amp as possible, or even more likely the fact that there might be slight or even major circuit differences between your and the modeled amp.
In any case, both tones sound great and they just ooze Plexi. Would you be so kind to share the preset (if it has anything other than the model at 5 between all controls)? I'd be happy to give it a go.
 
lastcaress83 said:
Here’s a quick comparison between my 2020 1987x and the Plexi 50w High 1 amp model. Settings were exactly the same: Everything on 5.
I put them both into my tube amp expander and recorded out of my 1960A with Celestion G12T-75’s using my iphone mic.

I think it might be time to sell an amp!

Amp 1

Amp 2
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Nice job getting them to sound really similar. I think I preferred the 1st one. The 2nd one has a lot of pick attach chirp happening that is kind of annoying in isolation.
 
axes said:
They are very close indeed, just not as close maybe as my similar JP-2C test. But still close enough that I would probably sell the amp if I wasn't especially attached to it.
The difference could easily be due to you setting everything to 5 instead of tweaking the amp model as close to the real amp as possible, or even more likely the fact that there might be slight or even major circuit differences between your and the modeled amp.
In any case, both tones sound great and they just ooze Plexi. Would you be so kind to share the preset (if it has anything other than the model at 5 between all controls)? I'd be happy to give it a go.
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Its just the amp with everything at 5. I may have adjusted transformer match and increased bias to 70% to match the reissue amp, not sure if I was aware of those settings at this point. Listening back to this what I mostly hear is a difference in response. The real amps response has more
give, model sounds more stiff. Also, there’s a sizzle in the distortion not as prevalent in the model. Of course, this could all be difference in tube hardness, matching, loads/SIC, etc. I need a fractal Load Box for future comparisons but they were out of stock last I checked
 
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