How much home AC voltage variance is too much?


I have been measuring my AC voltage of my dedicated circuits for my audio system. During the past 24 hours, the voltage has ranged from 121.5 to 122.3 volts. Is this too much variance? Is this too much voltage, given our target is 120? What is an acceptable voltage variation for most high end amps and pre-amps?

I am also wondering whether or not to pursue an AC voltage regulator or regenerator. Additionally, I am considering a balanced power conditioner, such as the BPT 3.5.

Any thoughts would be helpful. Thanks.
banpuku
The National Grid my electric company states within +/- 10% of 208/230Vac residendial and 480Vac commercial. Not responcable for 120 as it is part of 208/230Vac. Brown outs and spikes have to do with condition and load of the system as a whole and have no control over.
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Two Exact Power EP15A's, one for each channel (amp), has solved the problem for now.