Krell KAS amplifier hum

Al, as for the Jensen transformers you mentioned the XRL cables the OP is using are 6m long.

Any RF (buzzing) issues using a 6m XRL cable on the OP’s Krell amps?

Jim, as you may have seen the length of the cable on the input side of the transformer is not critical, from the transformer’s perspective. What matters from its perspective is just the capacitance it sees on its output side, which for a given cable type is of course proportional to length.

The constraint on the length of the 6 meter cable is that its capacitance should support ARC’s usual recommendation for most of their preamps and line stages of load capacitance of 2000 pf max. For a 6 meter cable that corresponds to around 100 pf/foot. Any decent cable should meet that requirement with a good deal of room to spare, which in turn would almost certainly allow more than enough margin for the unknown and most likely unspecified input capacitance of the amp, that would be "reflected" through the transformer and that is probably small compared to the capacitance of the 6 meter cable.

As far as RF which may be picked up by that cable is concerned, the transformer’s 50 kHz 3 db bandwidth limitation can only help.

Best regards,
-- Al

jg2077 OP47 posts

12-13-2019
11:43am


It would be easy to plug the 5.0 into one of the unused 20A outlet, as would be to move the Pre. Having to Move everything would require MUCH work. Could I use a long heavy-duty power cord plugged into one of the 20A outlet to power the 5.0 distributor where it sits without moving it?

How long is the heavy duty power cord?
25ft or less? If yes that would be fine. Just don’t coil up any excess cord.

Update:

1.  All was left as initially, I only powered up the amp; very low hum from the speakers (ear against the speaker).  Could not be heard from 1 ft. away. 

2.  Unplugged pre from back of distributor and turned ON the distributor.  No change from above. 

3.  Plugged in Pre, the hum increased significantly. 

4.  Unplugged distributor from common 15A outlet.   Ran a 10ft cord from unused 20A dedicated outlet to the distributor  and powered on.  Same outcome as noted above; maybe...slightly less hum.

I will try another Pre and report back.   I have to take my son to pitching lessons. 😀

Regards, 
Jose 

Update:

I replaced the 6L6 tube and left all else the same; the hum can only be heard from 18inches away, without any music. Also, the hum is of a lower frequency.   I can tolerate this for the time being. 

I am going to replace the ARC Ref3.  I haven't made up my mind as to my next preamp choice. 

Thank you all for helping. 

Happy Holidays, 
Jose