Power scaling

Marshall JCM900It is pretty complicated to get a nice overdriven amp sound at a moderate volume level.
Of course, there is the possibility to install a master volume but, in that case, you will only get a preamp distortion and no power amp overdrive.
And in the end this kind of sound has nothing to do with the beloved power amp overdrive.
Another possibility is to use an attenuator – but this also may have a negative influence on the tone and the dynamic.

Power scaling

Therefore, I would like to introduce the power scaling in this article.
Power scaling is, simply said, a way to adjust the voltage of the tube via a pot.
In this context, most guitarist think of Eddie Van Halen who used a Variac to reduce the power of his Marshall and thereby created the legendary “Brown Sound”.
In difference to Van Halens way of power reduction, the power scaling does not decrease the tube heating and therefore reduced the wear and tear of the tubes.
There are different ways of power scaling but for the reason, that inside of the amp you will find dangerously high voltage all of them should be realized by a proven expert.

Variac

If you lower the power of the whole amplifier by a power scaling, you will get the “Variac” or “Brown Sound” effect.
The tone will be darker and smoother and the sag of the attack of the strings will definitively have an influence on the way you play your guitar.
Although the tone loses a bit of its definition, this “sag” effect is perfect for certain styles of music.

Power amp scaling

I prefer the power amp power scaling (and, if existing, the phase inverter).
In this case the character of the amplifier is maintained, and the power amp can be driven to saturation.
In this case, the full utilization of the power amps capacity will lead to an overdriving preamp because it still receives the higher voltage.
Therefore, it might make sense to install a master volume by which you will be able to reduce the volume gradually until your sound reaches the level of overdrive you long for.
In this context, it is important to keep the master volume fully torqued initially to keep it out of the signal chain.

Recently, there are also some amplifiers which are equipped ex works with a power scaling.
And you can also find various DIY kits on the internet.
Besides London Power Scaling there are also versions of different license holders and you can even find cheap kits to install a power scaling into your amp.
But as I mentioned above: only experts should work inside of an amplifier because the voltage can be highly dangerous!