60Hz Hum Problem


#1

Hoping some resident audio experts can help me with a thorny 60Hz hum problem. I just bought a new Cary SLP-05 Pre-amp and balanced cables from my DS to the SLP-05 and from the SLP-05 to my BHK-250. The Cary has a cinema by-pass. In by-pass mode, I get a very loud 60HZ hum. Obviously tried disconnecting the by-pass cinema inputs. Hum goes away. Okay that’s a step. Odd because I use the device below to isolate the home theater input:

http://www.rdlnet.com/product.php?page=108

If I just plug in the RDL Hum Killer, with no home theater input to the RDL Hum Killer, the 60Hz hum comes back!! Taking the Hum Killer out and plugging the home theater directly into the the SLP-05 by-pass: the hum comes back. Basically anything with some kind of load plugged into the home theater by-pass causes a 60Hz hum only when using balanced cables. Going back to unbalanced, the hum goes away.

Couple other pieces of info:

Using unbalanced cables, I have to pull the ground pin on the BHK 250 to eliminate 60Hz hum in standard 2 channel mode. With the balanced cables, I can re-insert the ground pin and don't experience the 60Hz hum in standard 2 channel mode.

I also have a Music Hall 2 channel integrated that I use to drive outside deck speakers. I connect the input of the Music Hall to the Tape Out of the SLP-05 using unbalanced cables. With the balanced cables from DS to SLP-05 to BHK connected, when I turn out the Music Hall, I get a big thump that initiates the protection circuit in the BHK. With unbalanced cables connected from the DS to SLP-05 to BHK, the thump can barely be heard.

The Cary SLP-05 uses a pair of tubes as a balanced input buffer. I tried swapping the balanced input buffer tubes to eliminate the 60Hz hum to no avail.

I tried all the obvious things like disconnecting the cable TV connection, unplugging items on the home theater side one at a time. Unplugging the Music Hall integrated (both power and interconnects).

I have all the 2 channel equipment plugged into a P10. I tried the home theater plugged into the P10 and not. I also tried sine wave only on the P10. No solution.

I’m back in the music business with the unbalanced connectors but not happy about the investment I made in balanced interconnects. I can probably get them re-terminated as unbalanced but it does defeat one major reason for buying the SLP-05.

Hope I made the problem clear and thanks for slogging through it and attempting to help!!

P.S. Some pictures to help explain the situation.

IMG_6432-1.JPGIMG_6433-1.JPG


#2

I wouldn’t be so quick to get rid of the balanced cables because they’ll definitely sound better so you should hang in there.

I am confused about all this and part f the reason is the Cary. I am unfamiliar with what’s happening. I looked at the humbuster thing and it is a simple audio isolation transformer - something I would not suggest using since that will muck up the sound and there are better ways to break ground loops.

In my experience, it’s always best to take grounding problems one step at a time. Take a few moments to read through a couple of our How To tutorials and follow the steps carefully.

If these don’t work, can you give our customer service guys a shout?

http://www.psaudio.com/ps_how/how-to-practice-best-grounding/

http://www.psaudio.com/ps_how/how-to-find-and-fix-hum-extended/


#3

Thanks for taking the time to look Paul. I have a quick decision time on the cables - a return is required… Everything is playing well at the moment with unbalanced (ground pin pulled on BHK).

The odd thing is the hum occurs when only the hum buster is connected to the theater input: no input to the hum buster.

Only use the hum buster on the theater input. Don’t really care about the quality there. Won’t be using the hum buster anymore, doesn’t help.

I’ll call tech support. I’ve done a pretty good job of trying all the ground loop troubleshooting efforts. I’m suspecting something in the SLP-05: crap!


#4

No problem and good luck! We’re here to help in any way we can.


#5

FWIW I fixed the 60Hz hum problem. The SLP-05 pre-amp has an RCA and XLR Cinema input. The previous RDL isolation transformer (RCA in and out) did not eliminate the hum. This time I tried converting the RCA pre-ouput from the theater processor (inexpensive Yamaha theater receiver) to XLR using the device below:

http://whirlwindusa.com/catalog/black-boxes-effects-and-dis/direct-boxes/imp2

https://www.amazon.com/gp/product/B0002DUQ72/ref=oh_aui_detailpage_o02_s01?ie=UTF8&psc=1

It has a ground lift switch but enabling or disabling the ground lift doesn’t make a difference. This setup completely eliminates 60Hz hum from my system. The home theater audio is improved as well.

Jensen makes a better product but it’s more than twice the cost of the Whirlwind device and it’s only home theater. I just want it to sound reasonably good. Don’t care about home theater near as much as 2 channel music.

The only downside is a 20db attenuation in the front left and right channels (the channels utilizing the Whirlwind isolation device) output but that’s easily accounted for through the home theater settings.

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