[jostber]

Has anyone tried a DC offset unit like this from Kemp to handle transformer hum? I wondered to check if this would work for a 211 amp with some mechanical transformer hum I have.

http://www.kempelektroniks.nl/en/231...c-x-terminator

[Speedskater]

Does it hum 24 by 7 ? How about in other buildings? How old is the unit the transformer is in?
DC offset is well down my list of causes.

[jostber]

The amp hum is quite low through the speakers, but you can hear the transformer humming (like a low buzzing sound) when getting close to it. This amplifier is about 5 years old and  is working great except this. The transformer is quite massive for this amp.

I also have two Bob Carver 180 Monoblocks in the same location, no hum from these at all.

[timind]

I'll ask the obvious. Have you made sure the transformer's bolt is tight? Tightening the bolt worked for me once.

[jostber]

I will check that, but I believe this must come from the transformer itself.

[sfox7076]

Hum through the speakers would not be the same hum as the mechanical hum of the laminates.  I have a 300B amp that has some mechanical hum on the transformers, but no hum in any other form.  The DC offset hum or mechanical hum is the laminates in the transformer shaking. The hum through the speakers is a signal issue.

[WireNut]

If you or a friend like DIY there are a lot of options for adding / building your own DC Blocker.
If your not into DIY then Audio by Van Alstine offers a pre-built unit "The Humdinger" and ATL HI-FI also has a pre-built unit.

http://www.avahifi.com/products/humdinger-dc-line-blocker   
 
http://www.atlhifi.com/shop/fully-assembled-devices/dc-blocker-trap-filter-assembled-in-case/



For pre-build DIY units to add to your amp or for just the circuit boards with build instructions look here:

http://sjostromaudio.net/shop/mains-circuits/60-dct02-dc-filter-for-toroidal-transformers-built-unit.html

http://www.atlhifi.com/shop/populated-pcb/fully-populated-dc-blocker-pcb/

[jostber]

Thanks for the feedback, I will check more this weekend and report back.