• We would like to remind our members that this is a privately owned, run and supported forum. You are here at the invitation and discretion of the owners. As such, rules and standards of conduct will be applied that help keep this forum functioning as the owners desire. These include, but are not limited to, removing content and even access to the forum.

    Please give yourself a refresher on the forum rules you agreed to follow when you signed up.

Power Amp Hardness

bshaw92

Inspired
So, I have been on a mission to try and tonematch my amp (DI) recently and not having good luck. I finally gave up and just decided to play with knobs....(I hate spending time playing with knobs rather than just playing, but I'm already at the point so no turning back.). I wish I was more knowledgeable about what does exactly what (amp builder level), but I'm not there. I plug my amp into my 2 Notes load box and run into the Input 2 of my Axe 3. On Input 1 I have my guitar into the amp block into the shared cabinet from Input 2 with an ABY switch. I'm going to do this by ear! I was playing with different knobs that I normally do and was not getting there. The tube amp has a more rounded smooth distortion. I could get close with the eq. etc., but the distortion characteristic was not a rounded and bouncy as the amp. This is the part that is always missing IMO in the YouTube videos I've seen. I move to the power amp hardness and give it a shot. I reduce it from 5.5/5.0 (EL34) to 2.5 and that was the ticket. Now, maybe this isn't going to be required for every amp, but on the Tweed Twin 3rd Power Dual Citizen it moved it from being in the ball park to being rather indistinguishable. I plan to try this at different settings and then move on, but wanted to make mention of this result in case anyone else hasn't tried it yet.

I have been playing with the Fat Switch and Xfromer match in an effort to get a little more girth and roundness to the distortion characteristic, but they did not achieve what the adjustment to the power amp hardness did.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
There are a two things that determine the smoothness of the power amp distortion:
1. Power Amp Hardness. As you've discovered turning it down makes it smoother (obviously). The value controls the "kvb" of the tube model.
2. Negative Feedback. Negative feedback linearizes the power amp. At some point, though, the power amp then runs out of headroom and goes into clipping. The more negative feedback the more linear the response and the more abrupt the clipping. Less negative feedback, smoother clipping.

I often turn P.A. Hardness down, usually between 3-4, because I like the smoother sound.
 

maxolla

Inspired
There are a two things that determine the smoothness of the power amp distortion:
1. Power Amp Hardness. As you've discovered turning it down makes it smoother (obviously). The value controls the "kvb" of the tube model.
2. Negative Feedback. Negative feedback linearizes the power amp. At some point, though, the power amp then runs out of headroom and goes into clipping. The more negative feedback the more linear the response and the more abrupt the clipping. Less negative feedback, smoother clipping.

I often turn P.A. Hardness down, usually between 3-4, because I like the smoother sound.
What is a good way to get sag? I want to play with creating some bounce to the tone (recto sponge switch)
 

Rex

Legend!
There are a two things that determine the smoothness of the power amp distortion:
1. Power Amp Hardness. As you've discovered turning it down makes it smoother (obviously). The value controls the "kvb" of the tube model.
2. Negative Feedback. Negative feedback linearizes the power amp. At some point, though, the power amp then runs out of headroom and goes into clipping. The more negative feedback the more linear the response and the more abrupt the clipping. Less negative feedback, smoother clipping.

I often turn P.A. Hardness down, usually between 3-4, because I like the smoother sound.
KVB? Teach me.
 

200man

Experienced
...it’s the cut-in voltage where forward conduction begins.
I assume it’s ~.7 for silicon, maybe .3 for germanium?, for tubes...i dunno offhand
 
  • Like
Reactions: Rex

Rex

Legend!
...it’s the cut-in voltage where forward conduction begins.
I assume it’s ~.7 for silicon, maybe .3 for germanium?, for tubes...i dunno offhand
You mean the grid voltage that just barely blocks plate current?
 

200man

Experienced
It's the "knee voltage" for the plate. The formula for plate current is Ip = f(Vg1, Vg2) atan(Vp/kvb). The lower kvb the more abrupt the transition into clipping. Power Amp Hardness is the inverse of this normalized to the plate voltage.
excellent! thank you!
 
Top Bottom