Plexi 1

merlin17

merlin17

Power User
Hi!

Is really anybody using this one in 9.0.2 with the bright switch on (default)?
It has soooo much gain then even with the drive at 0...

I have a Tube Amp Doctor Plexi here at the moment (Hi, Marco!) which is said to be true to old Marshall Plexis and it is really different... It is not my favourite amp, but I tried to recreate it in the Axe. I'm somewhat close (there's a directness in the mids that I don't quite get with the model), but I have to use totally different settings (at first turning the bright switch off)...
 
I've always wondered why Plexi1 had SO much gain. I don't really have anything to compare it to and only plugged into a real Plexi once back when I was too young and stupid to know how cool it was. But I expected that model to be cleaner with the drive down low.
 
I think the manual states that the Plexi 2 is a more faithful reproduction of the original. As an exercise in learning how to adjust the AxeFx, I suppose trying to exactly match something else could be a good thing. However, personally, I just try to get close to what I think it should sound like and not really do a direct comparison. In reality, you could probably get another amp like you have and set them side-by-side and they wouldn't sound exactly the same. Or, change the speaker cab, a tube, etc. and it will sound different.
 
It was a test out of curiousity, I normally dial in what to me sounds and feels right and I don't care what model it is.

Jay: Maybe you're right, but in this case I get much closer with Damping at 0...
 
If you find it too gainy, you can also adjust the bright cap value in the advanced parameters. A lot of the gain in Plexi 1 is from the bright cap. Individuals prefer a lot of different bright cap values for different reasons. Changing that value can drastically change the character of a plexi. If my memory is correct (it rarely is), that's one of the main differences between the Plexi 1 and 2 sims. The bright cap value wasn't selectable when Plexi 2 was added.

D
 
The "problem" here is the Bright Cap Value, it's set on 5uF in default! That's far too high! Put it on 0.68 to get a better result!

greetings
Paco
 
Mr.PC said:
The "problem" here is the Bright Cap Value, it's set on 5uF in default! That's far too high! Put it on 0.68 to get a better result!

greetings
Paco
Click to expand...
Ahh, thanks! I'm not completely ignorant to the basics of tube amps but that kind of stuff is deeper than my understanding goes.
 
Mr.PC said:
The "problem" here is the Bright Cap Value, it's set on 5uF in default! That's far too high! Put it on 0.68 to get a better result!

greetings
Paco
Click to expand...

Actually 5nf. Your "u" is upside down. That would be a ginormous bright cap. 5nf is pretty big for a bright cap too. I agree, .68 is a much better place to be.
 
The value of the bright cap varied in plexis from a low of 220 pF to a high of 5 nF. If you want that VH1 sound you want 5 nF to get that midrange knock.

The Plexi 2 model has a 220 pF bright cap and is very similar to the Plexi 1 model otherwise.
 
@ kev and Cliff: Yeah you're right... :oops: we talking about the bright cap not the cathode cap (which has a different influence here anyway, maybe it was too late yesterday).

my fault
 
Mr.PC said:
@ kev and Cliff: Yeah you're right... :oops: we talking about the bright cap not the cathode cap (which has a different influence here anyway, maybe it was too late yesterday).

my fault
Click to expand...

I would LOVE to be able to access a "super secret" menu and play with the cathode bypass resistor/cap values and post phase inverter coupling caps. I've fine tuned my home brew amps this way and really tightened things up. Being able to do this for each type of guitar would be awesome. About the only thing left would be to have different tubes and transformers modelled and interchangeable.....and then I woke up. :cry:
 
FractalAudio said:
The value of the bright cap varied in plexis from a low of 220 pF to a high of 5 nF. If you want that VH1 sound you want 5 nF to get that midrange knock.

The Plexi 2 model has a 220 pF bright cap and is very similar to the Plexi 1 model otherwise.
Click to expand...

EVH classic Marshall actuallt had a 250 pF cap.
 
Guys, help a leaner out here please. Is there a big difference between changing the bright cap settings and simply increasing/decreasing the drive dial? I know the answer is 'try it and see' but I can't at the moment. I'd also like to understand what is going on 'under the lid' a bit more!

Cheers
 
Nic said:
Guys, help a leaner out here please. Is there a big difference between changing the bright cap settings and simply increasing/decreasing the drive dial? I know the answer is 'try it and see' but I can't at the moment. I'd also like to understand what is going on 'under the lid' a bit more!

Cheers
Click to expand...
The bright cap is soldered across the volume knob. It lets higher frequencies pass when the volume knob is turned down. The larger the cap, the lower the cutoff or blocking of the lower frequencies so you get more frequencies, or gain. As you turn the volume up, it's effect is lessened because the volume pot starts to let everything through and the cap becomes closer to being shorted out. Choosing a smaller value cap lets less lower frequencies to pass, therefore less gain. It's called a bright cap because it's there to pass higher frequencies at lower volumes to give the signal more presence at low volumes. Confused yet? :?
 
The Drive doesn't go all the way to zero. The control is linear-in-dB with 0 being -50 dB.
 
kev said:
I would LOVE to be able to access a "super secret" menu and play with the cathode bypass resistor/cap values and post phase inverter coupling caps.
Click to expand...

Psst! Don't tell the "I don't want more buttons" guys...
 
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