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Not a ground loop hum???

I thought I had a ground loop hum, given that with my pre, cdp and amp all on, without any music playing, there is a hum emanating from my speakers. Following the advice seen here and elsewhere, I went out and got some cheater plugs to try and hunt down this annoying and, at times, distracting hum.

My system comprises: Anthem CD-1 (with DH-Labs power cord), Blue Circle BC21.1 tube pre (with BC62 pc), BC22 amp (Zu Cable BoK pc), Rune loudspeakers by Zu Cable (hooked up with Zu Cable Libtec speaker cable), Blue Circle MR1200 balanced power line conditioner/distributor (Zu Cable BoK pc), and van den Hul D102 MKIII interconnents.

Well, with the three components' power cord fitted with a cheater plug and all plugged into the power conditioner, the hum was still present, same intensity, volume, etc. Removing the cheater plugs one by one starting with the cdp, then pre, then amp, there was no reduction in the hum. In fact, I think I may have heard it get worse at one point.

Any ideas out there as to the cause of the hum? Maybe the tubes in the system are the culprit. There is a pair of Siemens CCa (6922 type) with Pearl tube coolers installed in the pre, and the tube in the cdp is a Telefunken CCa with a tube cooler.
mghcanuck
mghcanuck OP
116 posts
 
Completely forgot to provide an update on the situation with my MR1200. Well, after trying it out in our new house and hearing the same level of noise, I sent the power conditioner back to Blue Circle, paid for shipping and about $60 for the filter add-on. They also checked it for mechanical and QC issues. Once I had it back home and inserted into the audio system, no more noise/hum from the unit!

Now I have two other noise isses to resolve. One is hum from the speakers, which increases in intensity as the volume is turned up. Could this be the inherent noise from the tubes in the preamp and or CD player? I've read in a couple of places about the noise from high gain preamps being audible through high-efficiency speakers? My speakers have a rated sensitivity of 101dB.

The other noise I recently discovered when I tapped the chassis of my preamp by accident. I gave the middle of the face plate a a light rap and heard distortion out of the left channel speaker. Any ideas?

Thanks again for any advice and suggestions.

Max
newbee
4,767 posts
 
Your hum could easily be residual hum from the tube pre-amp, although in my system it sounds more like tube rush/hiss. Do I assume correctly that this hum is well below the level of the sound of the music you are playing? Tapping the chassis, probably a microphonic tube in the left channel.
mghcanuck OP
116 posts
 
Hi Newbee,

Thanks for your response. That's correct, the hum is not audible when music is playing.

Damn that tube! I don't know a lot about tubes, but I should have thought about the possibility of it being microphonic. Time for a new pair I guess.

Regards.

Max
sean
6,231 posts
 
Mgh: Did you ever resolve the problem that you were having with the left channel? What about the hum in your speakers that was volume sensitive? Sean
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