Transformer Noise


I have an old Krell KAV-2250 that sounds pretty nice, except for the transformer hum.  The hum is noticeable when the volume is at zero and slightly audible at lower levels.  The amp has been unplugged for a few years.  Is there anything I can do to eliminate the hum or does that just something I have to live with due to the high power transformer?  I was going to send this to my son, but I think it might really bug him (it's bugging me too!)
thegoldengoose
If it's mechanical, it may indicate you have DC on the line, often caused by light dimmers or PC power supplies.

If it's coming through the speakers, check out my blog page:

http://pqltd.blogspot.com/2016/11/quick-safe-and-easy-fixes-for-ground.html
Erik, you are magic! I unplugged a small transformer that was next to where my amp was plugged in and the noise stopped immediately. The offender was a small "wall wart" that charges my Chord DAC.

I had another amp plugged into the same location (with a different power cord) and I didn't have that problem.

Thanks for this post & all your other posts!
That is also a symptom of a filter cap gone bad. Try using a cheater plug -- if the hum is reduced it's most likely ground loop, If it stays the same, probably a capacitor. 
Most welcome!

Erik
I unplugged a small transformer that was next to where my amp was plugged in and the noise stopped immediately.
I’d lay odds on it that wall wart, was a smp (switch mode) one, the pita for audiophiles, and it’s getting harder to get linear ones. Same goes for many desk top computer power supplies, as they are also smp.
You can see/hear just how much noise they put out if you tune a portable am radio to am band down around 700-800khz off station (not muted) so your can still hear the hiss, and then go near the wall wart with it, it’s a real ear opener, the noise they put into the air, and into the mains.

Cheers George
I emailed Chord.  Perhaps they can verify if the wall wart is switch mode or not.  I directed them to this thread.

Much thanks for all your comments.
If it feels light in your hand it's usually smp, if it's got nice weighty feel to it it's usually linear.

I only recommend linear wall warts to be used with my Lightspeed Attenuators. Even though quality smp seem to work and sound fine, but the proof is in the test bench measurements linear wall warts are quieter than even quality smp ones. Even though the Lightspeed has a secondary well regulated filtered supply within it.  
 
Cheers George