Fractal Audio AMP models: Brit 800 and Brit 800 Mod (Marshall JCM 800)

[sumitagarwal]

Use a plexi model for the low input... should be close.

Tried that today... doesn't have the glassiness or wider frequency bandwidth that I seem to be getting from the Brit 800 model.

Been reading a lot of good things about the real 2204's Lo input... less bright than the Hi input. Many even think it is Fenderish, especially with 6550 tubes

 

[iaresee]

Tried that today... doesn't have the glassiness or wider frequency bandwidth that I seem to be getting from the Brit 800 model.

Been reading a lot of good things about the real 2204's Lo input... less bright than the Hi input. Many even think it is Fenderish, especially with 6550 tubes

So you want "glassiness or wider frequency bandwidth" (high frequency content) or you want "less bright" (less high frequency, ergo less frequency bandwidth)? Those statements are at odds with each other.

I'll give you some solid advice: follow your ears. Don't worry so much about matching exact physical characteristics. Just listen and turn knobs until you're hearing what you want to hear.

 

[sumitagarwal]

Well, I think that considering this is a thread about the Brit 800 model its appropriate to discuss how to access or simulate the different hardware features of the amp its based on.

Anyways, did some more tinkering. I took the Plexi 50w Hi 1 model and went through all the component values and lined them up with the values from the Brit 800. I think the only parameter differing between the two that I left as-in was Preamp Crunch, which was higher on the 800. After doing this the Plexi and the 800 are sounding nearly indistinguishable to me when the MV is dimed and the preamp gain is very low, which I guess makes sense since the low preamp gain should be eliminating the effect of the cascaded first gain stage of the 800. My reading has confirmed that the JCM800 2204 Lo input bypasses the first gain stage, making it more similar to a Plexi, but does anyone know if the Lo input of the JCM800 2204 also reduces input sensitivity? I'm no good at reading schematics.

This exercise has also made me wonder: JMP MV models are often requested for the Axe-FX. But if the JMP 2204 and the JCM 2204 are identical circuit topology, with perhaps a few component value changes, shouldn't we be able to apply the correct JMP 2204 component values to the Brit 800 model? I'd wonder what those are. Of all the things i changed to make the Plexi 50w Hi 1 be voiced like the Brit 800, the Bright Cap value made the most difference by far.

 

[iaresee]

Well, I think that considering this is a thread about the Brit 800 model its appropriate to discuss how to access or simulate the different hardware features of the amp its based on

I totally missed that this discussion was in the model thread. Sorry about that. Perils of always coming to the site through the new posts link.

 

[sumitagarwal]

I totally missed that this discussion was in the model thread. Sorry about that. Perils of always coming to the site through the new posts link.

No worries.

Bringing the Brit 800 component values over to the Plexi 50w Hi 1 has been a really interesting way to get to know both amps better and where they get their sound from (bright cap values, negative feedback, etc). Its coming together as a helluva sort of "channel switcher" amp where the shift from one tone to another comes across as totally organic and natural, rather than sounding like two different guitarists/rigs. Looking forward to playing around with this some more, and really would welcome some more thoughts.

For reference, here are the schematics I found. I think they're the right ones (correct me if I'm wrong!) and maybe others can read them better than I can:

2204 (Brit 800):

1987 (Plexi 50w):

 

[sumitagarwal]

I may be the only person interested in this, but since I continue to read glowing reviews of the 2204 low input ("gorgeous cleans", "perfect pedal platform", "its like a Hiwatt") I thought I'd do some more research into this.

I'm terrible at reading schematics, but I think this site helped me better understand these amps: https://robrobinette.com/How_the_Marshall_JCM800_Works.htm

My understanding is that the signal path of the 2204 and and 1987 look like this:
2204 High:
V1B Gain w/ .68uF bypass --> Bright cap --> Volume --> V1A Cold Clipper Gain --> Bright cap --> V2A Warm Gain --> V2B Cathode Follower --> Tone --> Master Volume --> PI --> Power Tubes

2204 Low:
Bright cap --> Volume --> V1A Cold Clipper Gain --> Bright cap --> V2A Warm Gain --> V2B Cathode Follower --> Tone --> Master Volume --> PI --> Power Tubes

1987 High:
V1B Gain w/ .68uF bypass --> Volume --> Bright cap --> V2A Gain --> V2B Cathode Follower --> Tone --> Master Volume --> PI --> Power Tubes

As far as I can tell, most of the component values, especially those in the tone circuit and power circuit, are identical across. the 2204 and 1987. Ultimately, the 2204 Low is very similar to the 1987 High with a couple of important differences:

1. The Preamp Volume is in the "wrong" place... its at the very front of the circuit, before the first gain stage. This *would* mean that the the 2204 Low Preamp Volume is the same as the Axe-FX Input Trim except that the Input Trim doesn't increase brightness as it rolls down, and the Input Trim only goes down to 0.100.
2. The 2204 has a cold-biased V1A followed by a warm-biased V2A, whereas the 1987 has normally biased stages. This should give the 2204 a smoother overall character
3. You've got a Master Volume available to use

From the above, the 2204 Low does look like its its own interesting thing. The Input Trim "set to .5" way to select the low input in the Axe-FX is designed with Fender circuits in mind, which do attenuate by half for the low input. However, it doesn't really work for the 2204 because the low input has one less gain stage and loses the bright bypass of that gain stage, so it should be much warmer than the result achieved by using the Input Trim.

I could be very wrong.

 

[marshall2553]

I may be the only person interested in this, but since I continue to read glowing reviews of the 2204 low input ("gorgeous cleans", "perfect pedal platform", "its like a Hiwatt") I thought I'd do some more research into this.

I'm terrible at reading schematics, but I think this site helped me better understand these amps: https://robrobinette.com/How_the_Marshall_JCM800_Works.htm

My understanding is that the signal path of the 2204 and and 1987 look like this:
2204 High:
V1B Gain w/ .68uF bypass --> Bright cap --> Volume --> V1A Cold Clipper Gain --> Bright cap --> V2A Warm Gain --> V2B Cathode Follower --> Tone --> Master Volume --> PI --> Power Tubes

2204 Low:
Bright cap --> Volume --> V1A Cold Clipper Gain --> Bright cap --> V2A Warm Gain --> V2B Cathode Follower --> Tone --> Master Volume --> PI --> Power Tubes

1987 High:
V1B Gain w/ .68uF bypass --> Volume --> Bright cap --> V2A Gain --> V2B Cathode Follower --> Tone --> Master Volume --> PI --> Power Tubes

As far as I can tell, most of the component values, especially those in the tone circuit and power circuit, are identical across. the 2204 and 1987. Ultimately, the 2204 Low is very similar to the 1987 High with a couple of important differences:

1. The Preamp Volume is in the "wrong" place... its at the very front of the circuit, before the first gain stage. This *would* mean that the the 2204 Low Preamp Volume is the same as the Axe-FX Input Trim except that the Input Trim doesn't increase brightness as it rolls down, and the Input Trim only goes down to 0.100.
2. The 2204 has a cold-biased V1A followed by a warm-biased V2A, whereas the 1987 has normally biased stages. This should give the 2204 a smoother overall character
3. You've got a Master Volume available to use

From the above, the 2204 Low does look like its its own interesting thing. The Input Trim "set to .5" way to select the low input in the Axe-FX is designed with Fender circuits in mind, which do attenuate by half for the low input. However, it doesn't really work for the 2204 because the low input has one less gain stage and loses the bright bypass of that gain stage, so it should be much warmer than the result achieved by using the Input Trim.

I could be very wrong.

I have absolutely no idea about the technical stuff, but I've had trouble getting the same tones out of the Brit 800 as I did my 2203 on the low input. Not sure if it warrants a separate model or if it can be achieved by tweaking the existing one.

 

[sumitagarwal]

I have absolutely no idea about the technical stuff, but I've had trouble getting the same tones out of the Brit 800 as I did my 2203 on the low input. Not sure if it warrants a separate model or if it can be achieved by tweaking the existing one.

And, having a 2203 and an Axe, would you say the 2203 Low would be worth figuring out and simulating?

 

[marshall2553]

And, having a 2203 and an Axe, would you say the 2203 Low would be worth figuring out and simulating?

I don't know. I sold the 2203 several years ago, it was the loudest amp I've ever owned with a master that was not conducive to civilized volumes. I liked playing through the low input, you could get some great clean and just breaking up tones, but it isn't exactly what that amp is known for.

 

[sumitagarwal]

I don't know. I sold the 2203 several years ago, it was the loudest amp I've ever owned with a master that was not conducive to civilized volumes. I liked playing through the low input, you could get some great clean and just breaking up tones, but it isn't exactly what that amp is known for.

The 100-watters are pretty nuts...

 

[Pwrmac7600]

Curious why we don't have a proper model of the 2203 in the axe?

 

[sumitagarwal]

Curious why we don't have a proper model of the 2203 in the axe?

Like most things Axe, it basically comes down to Cliff's preferences. In this case its because he tied out a bunch of 2203's and 2204's and found that the best-sounding one happened to be a 2204, specifically a Canadian one (if memory serves correct, Canadian ones came with different tubes than US).

I personally wish that the Axe-FX had fewer amps, but had each amp modeled from top to bottom. Instead you'll generally find that Cliff has left the clean channels or low inputs out because per his taste you'd be using the wrong amp for a clean tone.

FWIW, I trust his call on that 2204 sounding the best, but I really would be curious to compare against a 2203 model. I'd expect the 2203 to have more headroom and hit harder at the expense of saturation.

 

[yek]

Curious why we don't have a proper model of the 2203 in the axe?

We do: BRIT AFS100 1.

 

[sumitagarwal]

We do: BRIT AFS100 1.

But that's a significantly modified 2203, of which we have several in the box

 

[Brownmatthall]

Like most things Axe, it basically comes down to Cliff's preferences. In this case its because he tied out a bunch of 2203's and 2204's and found that the best-sounding one happened to be a 2204, specifically a Canadian one (if memory serves correct, Canadian ones came with different tubes than US).

I personally wish that the Axe-FX had fewer amps, but had each amp modeled from top to bottom. Instead you'll generally find that Cliff has left the clean channels or low inputs out because per his taste you'd be using the wrong amp for a clean tone.

FWIW, I trust his call on that 2204 sounding the best, but I really would be curious to compare against a 2203 model. I'd expect the 2203 to have more headroom and hit harder at the expense of saturation.

Clean channels aren't modeled not because cliff thinks he knows best for you, but because the channel is usually a copy of a model we already have (usually not as good as the model either), low inputs are just the input trim set to .5 as well.

 

[Pwrmac7600]

We do: BRIT AFS100 1.

I messed around with that the other day, but it's voiced pretty differently than the standard jcm800. Now any tricks to get it to more closely resemble a stock 800 2203?

 

[sumitagarwal]

Clean channels aren't modeled not because cliff thinks he knows best for you, but because the channel is usually a copy of a model we already have (usually not as good as the model either), low inputs are just the input trim set to .5 as well.

Not always true. On some models, like the JCM800 we're discussing, low input omits a gain stage and some of the treble peaking, making it very different.

 

[Stratoblaster]

On some models, like the JCM800 we're discussing, low input omits a gain stage and some of the treble peaking, making it very different.

As well, when you use the Lo input on the 2204 you also have a treble peaking parallel resistor/capacitor network in series with the bright cap/input pot and wired to the grid input that has no grid stop resistor; this is a very different input stage vs the conventional input circuits you see 99% of the time. That may have a bit of an effect on pickup loading, etc., but the Lo input stage is a bit of an oddball on the 2204.

Also, the Lo input stage has a high resistance cathode resistor (Rk = 10K) which is called a 'cold cathode' stage; it's cold biased much closer to cutoff and the tone is grittier/grainier, imparting different tone/harmonics vs a 'regular' tube preamp stage. On both of my 2204 Marshalls I changed that resistor to either 4.7k or 5.6k (can't remember exactly); it added more gain and warmth which I prefer vs the stock value.

I'm not sure you could really remove the effect of the Hi input stage on a 2204 in the various JCM-800 models in the AFX. I guess you could lower the Input Trim and use a inverse EQ to negate the effect of the highs getting boosted in the Hi stage (there are online calculators that can show you the gain, corner frequency, rolloff slope, etc., for a given Ra/Rk/Ck; the values are Rk = 2.7k and Ck = .68uF with the anode resistor Ra = 100k in the 2204) but I'd think the effort wouldn't be worth it...YMMV.

https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/
http://www.it11audio.com/nowp/triodecalc

 

[dr bonkers]

It would be really nice if someone with component-level knowledge of different amps' clean channels would share which models' cleans with particular parameter modifications are equivalent to other amps' un-modelled clean channels.

I would pay $25 easily just for the info without even needing any presets built.

In the past people would say just do a Google search, but that doesn't work for most people including me because many of the results served up have nothing to do with what the differences between the JTM-45 and Sunn Model-T are and how to program those differences into the Fractal to get one model to behave like the other with basic controls, just as one example.

 

[sumitagarwal]

It would be really nice if someone with component-level knowledge of different amps' clean channels would share which models' cleans with particular parameter modifications are equivalent to other amps' un-modelled clean channels.

I would pay $25 easily just for the info without even needing any presets built.

In the past people would say just do a Google search, but that doesn't work for most people including me because many of the results served up have nothing to do with what the differences between the JTM-45 and Sunn Model-T are and how to program those differences into the Fractal to get one model to behave like the other with basic controls, just as one example.

Goddamn would I love a write-up on what to change on the JTM-45 to get a Sunn...