Dedicated mains supply unexpected result

I assume that the work done was more than just a wire replacement but that you also had a new panel installed?

Get something like the Quille plug in voltage tester (9 pounds) on Amazon and watch it while playing music.  Pay attention to the Neutral to Earth as well as the Neutral to Hot voltages.

It could very well be a noise issue caused internally.  Try turning off every other circuit in the home to attempt to localize the problem.

Send pictures of your mains box open so I can see how its landed/wired

Per Eric, did they change the mains box.

Did they change your main breaker or add a AFCI.

If we are talking about a tube amp, check/reset the bias. 

Thank you for the responses, I have not replied untill now  so I had a chance to carry out some of the suggestions from posts to the thread (some of which seem to have disappeared?) and get the electrican back.

Anyway cleaned all the connections with contact cleaner, checked tightness of connections and the electrician checked continuity and impedence. Also the dedicated circuit is  now directly connected to the incoming mains supply. Ran the system for a couple of days and things did improve.

As a final possible improvement I replaced the house main fuse (the end caps were quite tarnished) and cleaned the fuse container/contacts. This seems to have brought about a noticable improvement over the original sound quality.

I don’t think it is my imagineation but some often played tracks have greater clarity and tighter bass.

Good to hear! It took my system couple of weeks to settle after the dedicated circuit was run. Cable break in and ears/brain getting used to new sound.