Don’t want to hijack the thread or anything, but this may help also with the edification angle a bit. I apologize in advance for the stoopidly long post.
There are generally two different possible reasons for voltage instability: one originating from outside the home and the other coming from inside.
From outside, it usually means the local utility is having problems keeping up with demand during peak hours of the day and they dial back the voltage just a bit during those times as one of the ways to help alleviate the problem for themselves. But it can lead to voltage irregularities at certain times. This general pattern may wax and wane seasonally (if the utility is regularly stressed), possibly only becoming noticeable in summer and winter months, depending on your climate in the part of the country you live in. It basically can be thought of as a climate-vs-usage thing.
From inside, it’s caused by a mismatch of either (or both) of your electrical consumption patterns on a daily, weekly or monthly basis or also by a mismatch in your usage vs the particular branches of circuits from your breaker box.
Let’s start with the electrical consumption based on time frames first. If there’s anything that routinely happens in your household that can be thought of as an out-of-the-ordinary change in consumption patterns that involves a large voltage pattern swing, that could be an indicator of a basis for voltage instability. Like, for example, say, your HVAC turns ON and OFF throughout the day/night - that would be considered a normal usage pattern...no problem there. But, if, say, you’re somebody who lives alone and is under the impression that turning OFF all or most of the circuit breakers at night is a good idea (either in an effort to reduce EMI/RFI in the home, or to just to save on the monthly bill), then that may constitute more of a ’shock to the system’ for the home. That’s just a more dynamic swing of the total usage pattern: ON during the day vs OFF at night - that’s a bit more out of the ordinary as far as the home’s electrical system is concerned. Or, if the owner is out of town frequently and leaves the home with the main breaker OFF for days or a week or more at a time - another such situation that will lead to voltage instability from inside.
Now we look at mismatches in the individual circuits from the breaker box. Ideally, for optimal voltage stability within the home, it would be great if every circuit was operating at about 80-85% of maximum circuit rating and all circuits stayed that way 24/7....and nothing was ever turned OFF or ON and the load remained constant. If, say, you had a 15A circuit, then the ideal load here (mainly for industry safety reasons) should, in this theoretical model here, be as close to a steady 12A or so as possible...and remain that way indefinitely. Having treated all circuits this way and after 3 or so weeks of this condition, and indeed from thereafter, we could expect virtually zero voltage instability from within the home.
In your own breaker box, look for circuits that continually are going unused (more commonplace in larger homes). Active breakers - especially those with higher amperage ratings - that never have, or seldom have, any load can be the culprits in voltage irregularities within the home! Perhaps especially if most of them are located on one phase (vertical stack of breakers inside the box). If you find Any such circuits, the best and simplest solution from an audio standpoint here is to simply plug something in at the wall to this circuit leg that will present more of a stable load for the circuit. It might be nice for it to be 80-85% of max, but really anything would be better than nothing. You can take some devices from other breaker circuits that are perhaps a bit "full up" at the moment and redistribute the electrical load a bit better throughout the home. Over time (see paragraph below) your AV system will thank you for it!
Note from the above that in real life, All homes can expect to experience at least Some (nominal for our audio considerations) level of voltage instability from time to time simply because we deviate a bit from that continuous ideal. But, it’s maybe interesting to note that our routine deviations typically do not cause us to experience wild or rapid voltage fluctuations in everyday life. Even when our usage patterns can start or stop with certain devices or appliances all during the day...and then slow down at night. That doesn’t seem to us to cause wild fluctuations in voltage, but that is because the effects of the ON/OFF cycle, or "shocks to the electrical system" (sudden changes in load), do not all onset immediately (with the exception of the voltage drop itself, which is instantaneous), but its after effects actually take days and even weeks to settle out in the home’s entire electrical circuit. This process is ongoing in slow motion as it were for every device being turned ON or OFF home-wide, and the overall voltage stability of the house (in this case for the moment we’ll consider it separate here from the voltage condition from outside the home), at any given time, can be thought of as the amalgamation of all the electrical activity or inactivity in the home over the past few weeks. So just because you turned OFF your main breaker last night and flipped it on again this morning, doesn’t mean that your audio system will necessarily fully experience all the voltage instabilities from that - Today - (again, the two, immediate voltage drops here notwithstanding).
Remember also, of course, that it’s possible for a home to be experiencing voltage instabilities coming from both the inside and outside at the same time.
Returning you to your regularly scheduled programming.
