2. misc-audio
  3. 181882-152262

Weirdly Specific HUM issue

I have a pair of KEF LS50 Meta's driven by (2) Schiit Audio Lidar amps configured as monoblocks, coming through a Schiit Freya+ preamp. I use an Ompower EM1100 conditioner and Audioquest shielded power and interconnect cables.

I get a slight but noticeable hum in the Left speaker only (farthest from the preamp), but ONLY under these conditions:

Plugged into (powered on) power amp only (no source connection) - NO HUM
Preamp connected (balanced XLR) and powered ON - HUM
Preamp connected (balanced XLR) and powered OFF - HUM persists
Hum only stops when I physically disconnect the input from the preamp (same with both preamp output channels)
Thoughts? Why would the hum persist even with the preamp powered down?

Thanks in advance.

Ag insider logo xs@2xgwilmot
erik_squires
16,119 posts
 

That actually makes sense.  Now disconnect all the inputs to the preamp. :)

Ground loops are caused by alternate current PATHS not sources.  Are your monoblocks plugged into the same outlet?

fuzztone's avatar
fuzztone
5,624 posts
 

Try a HumX or a cheater on the Freya.

Ag insider logo xs@2x
gwilmot OP
6 posts
 

Thanks for the replies - I forgot to mention I am testing with no inputs currently connected to the preamp. Also, the monos are not plugged into the same receptacle (in fact the right channel is disconnected completely).

 

I do have an iPurifier plugged into the same receptacle as the power amp, I’ll try switching it to the preamp receptacle.

More to discover