Wall Voltage Control

As you have probably noticed, the voltages coming out of the walls fluctuate, often from minute to minute, from venue to venue. At their worst, these fluctuations can, in some instances, harm your instruments (as with large fluctuations, or voltage spikes). At their best, the fluctuations can cause you to sound dramatically different from venue to venue, sometimes from hour to hour.

Options for dealing with wall voltage variations include:

Variacs
A variac is a multiplier, that you can set anywhere from zero to the limit for that particular model. A variac requires that you use a meter to monitor the output from the variac. When the output changes (because the input, or line voltage changes), you turn variac's dial to set the multiplier until the reading on your meter is back to where you want it to be. Variacs do not filter out high frequency noise.
Line Regulators
A good line regulator basically uses the input from the wall voltage to create a constant output voltage. An internal meter monitors the output voltage. When the reading on the meter changes (because the wall voltage is changing), the line regulator changes its internal multiplier to put the meter reading back to where you have the output voltage set. High end Line Regulators should filter out high frequency noise.
Surge Protectors
A surge protector won't protect your amp from routine fluctuations or high frequency noise, but a good strip will stop spikes from harming your amp.
Power Conditioners
A power conditioner will protect you from spikes and filter out high frequency noise.
The Maven Peal Sag Circuit
The Sag Circuit automatically protects your instruments from all of the above. You'll never have to worry about line voltage again.
To learn more about what the Sag Circuit can do for you, please visit: power supplies, wattage control and sag control.