I can add a little here.  I'm an engineer with a power company that
works with the distribution system (the lines that run up and down
the alleys and to houses).

There is a large variation in the capacities and impedance involving
electrical services into houses.  Most relevant to whether or not the
lights dim perceptively when the refrigerator comes on or the
Pianocorder hits a big chord is the distance the house is from the
transformer that provides the voltage used in the house, and the size
of the wire running between the house and the transformer.

This stuff in older neighborhoods was designed to handle houses that,
at the time, had only a few lights, a radio, a refrigerator and very
few appliances.  It usually doesn't get upgraded until people add
enough new electrical load that voltage dips which cause the lights
to dim start becoming a problem.  There's still a lot of places where
there's been little change in the electrical system for 20 or 30 years.

Newer areas, where the houses have refrigerated air conditioning,
maybe electric heat, and a ton of appliances, usually have very strong
electrical hook-ups and a Pianocorder could not cause any perceptible
blink.  You'll probably see some blink when the 4- or 5-horsepower
refrigerated air conditioner compressor motor kicks in.  An electric
motor typically pulls 4 to 6 times as much current when it starts as
when it's running.

Before I upgraded the electrical service to my old place, the lamp
beside the Pianocorder could be seen merrily keeping time with the
music.  After I got things beefed up doing a remodel, it didn't do
that anymore.

Regards,

Dick Merchant
Carlsbad, NM