You could try attaching a bit of speaker wire as an earth strap between the chassis of the amp and pre-amp and see if that helps.
Amp Hum
I know there are several posts regarding amp 'hum' but I wanted to start a new thread regardless.
Have an Audio Research D 90 and SP 12 Pre that I've had for many years. Recently, I've noticed a significant hum coming through the mid's on my speakers. The amp itself has a similar hum from the large transformers and appears to be transferred to the speakers.
I have a dedicated power line and circuit direct to my main fuse box that's less than 10 feet away so I can't think of any interference from outside sources. I also use a PS Audio power port for the outlet.
The hum doesn't fluctuate and is always there. Checked connections and so forth but my set-up is pretty straight forward. I do use a basic Belkin power strip between the amp and pre so I can power up a cooling fan during use. I disconnected the fan and the hum remains.
Any ideas or help would be appreciated.
Have an Audio Research D 90 and SP 12 Pre that I've had for many years. Recently, I've noticed a significant hum coming through the mid's on my speakers. The amp itself has a similar hum from the large transformers and appears to be transferred to the speakers.
I have a dedicated power line and circuit direct to my main fuse box that's less than 10 feet away so I can't think of any interference from outside sources. I also use a PS Audio power port for the outlet.
The hum doesn't fluctuate and is always there. Checked connections and so forth but my set-up is pretty straight forward. I do use a basic Belkin power strip between the amp and pre so I can power up a cooling fan during use. I disconnected the fan and the hum remains.
Any ideas or help would be appreciated.