Modeling Questions

[yek]

Is the Master Volume of the amp model compensated?

No interaction between MV en Amp Level.

And in current Cygnus firmware the MV tapers are the same as on the original amps, with some exceptions.

"In the vast majority of models the knobs behave the same as the amp. There are a handful of models where I've taken artistic license and changed the tapers to give a more useable response. For example the Master Volume in a Blues Jr. is linear taper. This is ridiculous as it makes it very difficult to find the sweet spot. The model uses an audio taper instead which makes finding the sweet spot easier. (..) and now Cygnus firmwares have authentic behavior for most models except in a handful of cases where the manufacturer's choice of taper is dumb."

 

[James Freeman]

I personally prefer when the tapers match the real amp,

Same.
Since I will be running my Axe Fx through a power amp and a cab most of the time I would like the most authentic experience as possible.
BUT, specifically for the master volume I prefer a slow log (log10) or audio taper because this gives more useable range before the PI turns everything to shit, especially in high gain amps.

Edit:
For Presence, Tonestack, EQ, etc... all authentic please.
This again is related to the topic that people have no idea that some knobs are 'fixed' in the Fractal, the 5150 Presence is a good example.

This:
https://forum.fractalaudio.com/threads/presence-taper-that-matches-the-real-amp.187775/
https://forum.fractalaudio.com/threads/authentic-mark-graphic-eq.199317/

 

[IronSean]

Is the Master Volume of the amp model compensated?

I’m curious about this too - I do find I have to compensate with the output control quite a lot because I typically run the poweramps with lots of headroom.

AFAIK, some amps have more “sensible”/different MV tapers to the real amps, and a lot of the time the feel of adjusting the MV seems a bit different to the real thing even if they can produce the same sounds. I personally prefer when the tapers match the real amp, because I can use familiarity of the real thing as a reference point for dialling it in. I can understand why tapers have been changed to give them a smoother transition between tones but it obviously means you can’t rely on the experience you’ve had with the real thing as much.

The other weird caveat to this is amps that have multiple cascading volumes. i.e. anything with a Channel output volume/post-gain/master, and a global master. See: most multi-channel amps. JVM, Mark IV, Mark V, Rectifiers, etc. The Axe only exposes one master because having two would be redundant. But how do you make an "authentic" taper when the real amp has two controls at different parts of the circuit. The truly "authentic" answer is to keep both, except that the difference between high channel master and low global master vs low channel master and high global master is essentially none and would just cause confusion.

 

[James Freeman]

Why are the Plexi and Plexi100W tonestacks are so different, they supposedly have the same 500p+33k component values?
Plexi and JCM800 tonestacks sound identical, what's going on with the super dark Plexi100W tonestack?

I thought that a 70s 100W 1959 Super Lead has the standard 500p+33k configuration.
Not even the JTM45 tonestack with 250p+56k configuration sounds that dark.....

This leads me to believe there is a bug in the Plexi 100W tonestack.

 

[FractalAudio]

Why are the Plexi and Plexi100W tonestacks are so different, they supposedly have the same 500p+33k component values?
Plexi and JCM800 tonestacks sound identical, what's going on with the super dark Plexi100W tonestack?

I thought that a 70s 100W 1959 Super Lead has the standard 500p+33k configuration.
Not even the JTM45 tonestack with 250p+56k configuration sounds that dark.....

This leads me to believe there is a bug in the Plexi 100W tonestack.

Our reference amp has a 560p treble cap and a 10A treble pot taper. Both components appear to be original.

The tech who checked it out after I bought it said it was one of the best sounding 100W Plexis he'd ever heard. That tech just happens to be Alan Phillips of Carol-Ann Amps. So I modeled it to agree with the reference amp.

 

[James Freeman]

I see, both Mid and Treble pots in the Plexi100W tonestack are Logarithmic, very not typical, definitely not in a 70s Super Lead or a modern 1959SLP reissue which specifically calls for Linear tapers for Treble and Mid controls.
It was immediately noticeable when I was experimenting with Jose mods at lower master volumes, it makes all the 100W Plexi's in the Axe Fx super dark at 5,5,5.

Is there a way to overwrite model defaults?

 

[FractalAudio]

I see, both Mid and Treble pots in the Plexi100W tonestack are Logarithmic, very not typical, definitely not in a 70s Super Lead or a modern 1959SLP reissue which specifically calls for Linear tapers for Treble and Mid controls.
It was immediately noticeable when I was experimenting with Jose mods at lower master volumes, it makes all the 100W Plexi's in the Axe Fx super dark at 5,5,5.

Is there a way to overwrite model defaults?

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.

 

[James Freeman]

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

The reference 70s 100W Super Lead and 1959SLP Reissue are also like that?
That amounts to zero stock 100W Super Leads in the Fractal, at least by default.

A few more questions;
What would be the correct "Presence Frequency" value to emulate a 0.68uF presence cap in a 1987 & 1959 MKII Super Lead?
Is the coupling cap on the Treble channel 0.0022uF (2.2n)?

 

[FractalAudio]

The reference 70s 100W Super Lead and 1959SLP Reissue are also like that?
That amounts to zero stock 100W Super Leads in the Fractal, at least not by default.

A few more questions;
What would be the correct "Presence Frequency" value to emulate a 0.68uF presence cap in a 1987 & 1959 MKII Super Lead?
Is the coupling cap on the Treble channel 0.0022uF (2.2n)?

That's a mistake. I've fixed that for the next release.

To simulate a 68nF presence cap set the Presence Frequency to 0.68 (I'm assuming you meant 68nF and no 680nF).

The coupling cap is 2.2nF.

FWIW, our reference 50W Plexi has a 68nF presence cap and the presence network is JCM800-style.

 

[FractalAudio]

Oh, and our reference 100W is a late 60s. I think it's a '67 IIRC.

I was puzzled by the pot tapers but they all look original. I then thought about it a bit and wondered if that's why Bogner uses log pots for his amps. His stuff is definitely Plexi-inspired.

Or maybe all Marshall could find at the surplus electronics store that week was log pots. Who knows.

 

[James Freeman]

Thank you!

I meant a 680nF, 0.68uF, the MKII Super Lead had huge Presence caps.

 

[Liam Thompson]

The reference 70s 100W Super Lead and 1959SLP Reissue are also like that?
That amounts to zero stock 100W Super Leads in the Fractal, at least by default.

A few more questions;
What would be the correct "Presence Frequency" value to emulate a 0.68uF presence cap in a 1987 & 1959 MKII Super Lead?
Is the coupling cap on the Treble channel 0.0022uF (2.2n)?

Someone get this guy on the beta testing program!

I'm on with building myself a '69 plexi replica, I love the in depth talk about circuits on the forum at the minute there has been a lot of interesting reading lately.

 

[James Freeman]

Oh, and our reference 100W is a late 60s. I think it's a '67 IIRC.

That's a very rare beast.
Some of these even had the old 250p+56k tonestack, maybe even a shared cathode.
These are 'transitional Plexi's' very rare.

 

[FractalAudio]

Thank you!

I meant a 680nF, 0.68uF, the MKII Super Lead had huge Presence caps.

Set it to 1/6.8 = 0.147.

 

[FractalAudio]

That's a very rare beast.
Some of these even had the old 250p+56k tonestack, maybe even a shared cathode.
These are 'transitional Plexi's' very rare.

Yup, wasn't cheap either.

 

[∞Fractals]

Thank you!

I meant a 680nF, 0.68uF, the MKII Super Lead had huge Presence caps.

Slightly off topic… Just curious James, where does your deep Marshall knowledge come from?

Super fascinating discussion to follow

 

[ccc118]

Oh, and our reference 100W is a late 60s. I think it's a '67 IIRC.

I was puzzled by the pot tapers but they all look original. I then thought about it a bit and wondered if that's why Bogner uses log pots for his amps. His stuff is definitely Plexi-inspired.

Or maybe all Marshall could find at the surplus electronics store that week was log pots. Who knows.

I remember at one point the 100w was based on a 1969. I looked it up and found this: https://forum.fractalaudio.com/threads/nothing-like-a-real-plexi.64593/post-801933

Did the reference amp change when Cygnus was added? That's the amp I use the most, so I'm just curious about it.

 

[FractalAudio]

I remember at one point the 100w was based on a 1969. I looked it up and found this: https://forum.fractalaudio.com/threads/nothing-like-a-real-plexi.64593/post-801933

Did the reference amp change when Cygnus was added? That's the amp I use the most, so I'm just curious about it.

That's the amp. So, yes, it's a '69. The 50W might be a '67. Hard to keep track of it all. I must have at least a dozen Marshalls now.

 

[James Freeman]

Slightly off topic… Just curious James, where does your deep Marshall knowledge come from?

The Internet, analog electronics is my hobby and true passion.

Set it to 1/6.8 = 0.147.

Thank you.
The 680n pres cap is typical to a lot of 70s MKII Super Leads (Metal Panel), the ones with low NFB 100k from the 4ohm tap.

The 1959SLP Reissue has the MK1 configuration, 47k from 8ohm tap and 5k+0.1u presence network.
Both should have the standard 500p+33k tonestack with Linear Mid and Treble.

 

[yek]

Hard to keep track of it all.

cough wiki cough