qsa black red Well warm is not high harmonics
your ear is excellent find this problem.
it can be easy solved
mainly due to the interaction between ac transformer and fuse,so align the magnet field and e-field for the qsa fuse in right Clock location,sound become.much better.
just like turning the radio in right position
and longer burn in time over250hours,
to get better sound quality.
method
if you put the fuse and see the qsa arrow at 3o clock
position.at A marking
and then take off re install in differen clock postion, total 12position.
one of the clock prosition is very good sound.
if saving time ,3 , 6, 9 ,12 o'clock position
one of them is the best.
after turning in right position, richer harmonics.
it is A free of charge method,but need to waste of the time to do,but it is A funny job.