Modeling Questions

FractalAudio said:
Yup, all the pots are log pots in our reference amp.

The "classic" Plexi tonestack is #4 (Plexi). In the advanced menu you can choose from all the different tonestacks via the Tonestack Type parameter.
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It's important to note that Marshall back in the day anyways, did not strictly follow their published schematics, and instead shipped amps out with a variety of parts that they had on hand at the time, especially note worthy for variation were pot tapers and bright caps IME.
 
DJD100 said:
It's important to note that Marshall back in the day anyways, did not strictly follow their published schematics, and instead shipped amps out with a variety of parts that they had on hand at the time, especially note worthy for variation were pot tapers and bright caps IME.
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I'm pretty sure he knows ;)

FractalAudio said:
Or maybe all Marshall could find at the surplus electronics store that week was log pots. Who knows.
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unix-guy said:
I'm pretty sure he knows ;)
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I thought this was more for @James Freeman. I was going to add this comment as well for James' benefit. I waffled on if he was aware there is a lot of variances due to parts availability or if he was focused mostly on the "official specs". James, the specs are well documented but there is a lot of variances. Very rare for two Marshalls from that era to sound exactly the same.
 
I have to say, I also really enjoy reading about these details and seeing the engaged interaction from @FractalAudio with the people who use the gear.

It shows receptiveness to user feedback, competence in the modeling processes, and also makes me confident that Fractal is focused on having the best models out there instead of telling people it’s the best and expecting them to take their word for it.
 
Regarding the 1970 100W Plexi;

Wiki says:
"1970 Marshall 1959SLP 100 has a darker, smoother sound than earlier Plexis."
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I really don't think this is true, especially now with the correct "plexi" tonestack, and much lower NFB.
It's almost a MKII "metal panel" Super Lead which was the most common NMV Marshall in the 70s, it's bright and aggressive.
100W 1959 MKII had 100k from 4ohm tap NFB network, and a 0.68u+5k presence pot in parallel with the 4.7k tail resistor.

Here's the correct 70s MKII Super Lead presence network;

MKII Presence.jpg

MKII Presence 2.jpg

EDIT: In a digital model this parallel network is not actually needed because there is no DC noises, the regular 5k pot + 0.68u Plexi configuration will do and have a smoother taper.

What I'm saying is, the current 1970 100W Plexi model can turn into a really nice MKII Super Lead with a small presence cap change.
Also, why isn't there a separate Treble and Normal channels? This amp model deserves more love.

I have a ‘73 50 watt that has the .68/4.7k presence setup on a 5k pot. I also have a ‘77 2203 with the same setup. I’m not sure when the 25k pot came along, but neither of my amps have it.
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source
 
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aens said:
@James Freeman @FractalAudio could you do a guitar amp podcast together? I’m learning so much new stuff here. This is like Einstein and Tesla having a nice little chat about guitar amps.
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You know It will never happen but I would love to see Cliff on Tone Talk w Mark and Dave , I think it would be super interesting to many people , I know how Dave feels about modelling and obviously his designs but maybe he would learn more and be a bit more open minded if he saw the amount of detail and work FAS does

The other concern maybe competition but that kind of hypocritical considering they have the Headfirst guy on who is basically building BE and JJ circuits
 
What's the reason for the 2203/2204 high/low modes? I thought the only difference between those would be something you can account with the Input trim?
 
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