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Power Level AC-20

Jbmetal

Inspired
So, I was messing around with the Morgan AC-20 DLX model and I like using the controls on the physical amp first, so I was checking it out. That sparked a question about the Power Level control on the real amp. Clearly, the only thing this does is makes the power section break up sooner, so to simulate this, would you just increase the Master Vol Trim? But to what extent would it be accurate before going beyond the scope of the original control? Thanks!
 

guitardoc

Experienced
Iirc, Cliff stated once that the modelled knobs match the ones on the real counterpart 'accurately'. So in order to achieve what you would like to get you would not need to change the master trim in any way since 1.0 matches the real amp. I do not own this amp so I don't know how accurate the model is though. When comparing the models to the amps I own they come really really close. So close you can't tell which is which at some time.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Iirc, Cliff stated once that the modelled knobs match the ones on the real counterpart 'accurately'. So in order to achieve what you would like to get you would not need to change the master trim in any way since 1.0 matches the real amp. I do not own this amp so I don't know how accurate the model is though. When comparing the models to the amps I own they come really really close. So close you can't tell which is which at some time.
The AC-20 has power scaling. The Axe-Fx II does not model the power scaling circuit as there is no point in that.
 

javajunkie

Moderator
Moderator
Right, the point of power scaling is to get a cranked master volume tone at lower volume. All we need to do on the Axe-fx to get that is lower the Amp level.
 

Jbmetal

Inspired
So it doesn't do anything but make it quieter? Because I've had and played amps that had this feature and it seemed to change the breakup characteristics, i.e. breaking up sooner, of the power amp. Could be totally wrong.

Enlighten me, oh mighty Cliff.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
So it doesn't do anything but make it quieter? Because I've had and played amps that had this feature and it seemed to change the breakup characteristics, i.e. breaking up sooner, of the power amp. Could be totally wrong.

Enlighten me, oh mighty Cliff.
It's not SUPPOSED to do anything but make it quieter but none of the implementations are perfect. They all suffer various imperfections that alter the tone and breakup characteristics as the power level is decreased. The AC-20 model is based on the amp with the power scaling at maximum power which effectively disables it (and sounds best IMO).
 

Jbmetal

Inspired
Awesome. Thank you very much! Clears up a lot. That's another reason why I tell every guitarist I know to buy an Axe-Fx; such good support and help from the master himself.

On the other hand, I increased the Master Volume Trim and it sounded fantastic. It kind of smoothed out some of the rougher overdrive.
 

Scary

Experienced
All amps have a sweet spot, and it's nice to know how this amp was modeled. I also appreciate the posts from FractalAudio and staff. Makes this tone quest that much more fun!
 
Power Scaling (as originally developed by London Power -- can't say what the Morgan does) lowers the plate, screen, and bias voltages of the power tubes, causing them to break up earlier. If you want to keep the same amount of distortion as before, you need to reduce the drive to the power stage. You could scale the whole amp (except the heater voltages), but then you'd have to reduce the guitar volume accordingly, to have the same amount of overdrive.

But as Cliff says, there's no need for Power Scaling in the AxeFx -- just turn down the output volume, problem solved.
 
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