We have uncovered a possible issue with the Zkit60 that can produce a louder than normal amount of power line hum / buzz.  In the USA it will be 120hz and in Europe it will be 100 hz.  Once corrected, there will still be some audible high frequency "hash" if you listen for it right at the speakers, but the 120 hz/100hz power line noise should be all but gone.

If you are in doubt about whether you have this problem, you can search on line for a tone generator that will play 120hz or 100 hz tone for you.  If this frequency is the same as what you are hearing from your speakers (amp on, no input) then you have this problem and you can fix it.

To correct the problem, open up the Zkit60, loosen the transformer bolt, and rotate the transformer until the noise is minimized.  Then tighten the transformer bolt, and re-assemble.  If you have a scope and dummy load the process is easy.  If you don't, you will have to have the amp in system as you rotate the transformer so you can listen for the quietest position.  In any event, if you undertake this adjustment, be prepared to extend some transformer lead wires that may have been cut too short to allow 180 degrees of transformer rotation.

As always, be safe.  The power input always seems to find me when I'm working on a live amp.  Perhaps a thin pair of gloves is a good idea.

Dan

I did some YouTube research it seems like my buzz sounds like a ground loop buzz. But it's still there when there's no source plugged into the amp, the amp is plugged directly into the wall, and all electronics around it are unplugged.


The Zkit60 is replacing an SE84C, which was connected the same way, and the SE84C didn't have this problem.