Almost every guitarist knows this phenomenon: in the rehearsal room the sound of the guitar was absolutely perfect, and the amp has been situated right in the sweet spot. But live on stage, the magic has disappeared.
Surely, there are several parameters that effect on the sound. Mainly the altered kind of room with its different types of reflection is an important aspect.
But another, also considerable factor that affects the sound of a e-guitar is the electricity.
It should be recalled that the “e” represents the word electric.
Power fluctuations can vary depending on their localization. Until 1987 the mains voltage in Germany was about 220V with a tolerance of 10% and since then is about 230V. The mains voltage in the USA was about 110V and now is about 120V.
Regarding the accepted tolerance, the mains voltage in Germany can vary between 207 and 253V.
If you keep in mind, how exactly the bias can be measured and adjusted, you may can imagine, how the sound can vary if the power socket provides 50V more or less. Accordingly, the bias of an amplifier has actually been adjusted for the one power socket that provided the power while the amp has been calibrated.
The bias varies depending on the prevailing voltage and therefore, the amp will sound different.
An amplifier with a hot bias can be driven into saturation quite easily and will emphasize the mids while a cold bias will lead to a cleaner, almost sterile sound.
Because of this fact, the sound of the Fender export amps varies from the sound of the American amps with a transformer. The frequency of the US electricity grid is about 60Hz while the frequency of the European is about 50Hz. The frequency of the polarity will in fact also effect on the sound.
An expensive, but maybe interesting solution could be a so-called power conditioner. To those who love 80s hair metal: no, a power conditioner cannot be used for hair styling but to stabilize the voltage. This device, which is used between the amp and the power socket, enable you to adjust the output voltage so the amp will always sound the same.
If your live sound varies from expectations it`s not always the sound engineers’ fault. You ought to measure the voltage and maybe re-adjust the bias of your amp before you fire your sound engineer. Or you get yourself a power conditioner.