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The Joy of (Less) Variac

StickMan

Experienced
To be honest, I saw this in a video on Reddit or Facebook, but it got me trying stuff out.

On the "Power Supply" tab of the Amp block, there is "Variac". It's a percentage, with 100% being the mid-point and the default. My understanding is that it controls the AC power supply value, with 100% being 120V (or thereabouts). Essentially, lowering the voltage reduces the clean headroom of the amp resulting in earlier breakup. Increasing it does the opposite.

The big thing I've noticed is that changing the Variac also changes the nature of the distortion. I'd say that the distortion with lower Variac is a lot "looser" and warmer. Raising the Variac can make the distortion a bit tighter, harsh and brighter. If you drop the Variac all the way down to the minimum (50% I think), the distortion is really wooly and wild.

It feels a lot to me have some of the same effect as adjusting Negative Feedback. Increasing NF results in less distortion and tightens it up, dropping it does the reverse. But it's not the same result.

To my ears, a lot of the models sound a lot better with the Variac dropped just a bit, somewhere in the 92%-96% zone. YMMV, but it's worth messing with if you're looking to dial in that perfect tone.
 

dr bonkers

Fractal Fanatic
Vendor
I am addicted to the Variac.

A lot of amps that are not in the Fractal can have their sounds simulated by picking a similar amp and messing with the Variac to hand tune the breakup by ear.
 

Deaj

Experienced
I'm going to have to revisit this parameter. The amp models have become so easy to dial in that I haven't used the advanced parameters for some time now.
 

StickMan

Experienced
I'm going to have to revisit this parameter. The amp models have become so easy to dial in that I haven't used the advanced parameters for some time now.
That's really why I started this thread. It's a parameter off the first tab that has a pretty dramatic impact on the sound, and can make a good patch a great patch.
 

joegold

Fractal Fanatic
FWIW
I was told once here, by Cliff I think, that lowering this parameter to 90% was the best way to simulate the Tweed switch on my Simul-Satellite.
 

Veloso1978

Inspired
To be honest, I saw this in a video on Reddit or Facebook, but it got me trying stuff out.

On the "Power Supply" tab of the Amp block, there is "Variac". It's a percentage, with 100% being the mid-point and the default. My understanding is that it controls the AC power supply value, with 100% being 120V (or thereabouts). Essentially, lowering the voltage reduces the clean headroom of the amp resulting in earlier breakup. Increasing it does the opposite.

The big thing I've noticed is that changing the Variac also changes the nature of the distortion. I'd say that the distortion with lower Variac is a lot "looser" and warmer. Raising the Variac can make the distortion a bit tighter, harsh and brighter. If you drop the Variac all the way down to the minimum (50% I think), the distortion is really wooly and wild.

It feels a lot to me have some of the same effect as adjusting Negative Feedback. Increasing NF results in less distortion and tightens it up, dropping it does the reverse. But it's not the same result.

To my ears, a lot of the models sound a lot better with the Variac dropped just a bit, somewhere in the 92%-96% zone. YMMV, but it's worth messing with if you're looking to dial in that perfect tone.
Let increase the Variac to distortion rise from the dead?
 

Tahoebrian5

Fractal Fanatic
I’m not sure if this is important in the Axe, but I remember reading somewhere that you should take a look at rebiassing your tubes when using lower supply voltage. Might be worth checking out
 
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