Hum with balanced cables

pkquat

I recently got a set of balanced cables for my Parasound P5 to A23 interconnect. Speakers are SRS 2.3 with interconnect cable. I figured balanced should be quieter or better, or at least see if I hear a difference. When I first hooked them up, no matter what, or what length (one set was still coiled) I got a strong hum. I am guessing it was a ground loop. The switch was properly set to unbalanced on the A23. I tried lifting the ground, and disconnected the DC trigger. Nothing fixed it. Unbalanced cables had no hum compared to balanced. With unbslanced cables and the ground lifted, I get the least minor hum. I even borrowed a set of balanced cables and it was still there. I changed nothing that I know of and now everything is fine. Balanced cables have even less bare audible hum.

Any ideas for a cause, or something to look for or check?

sgmsmg

Was this with the cables I just sold you? Based on your description it happened with both sets and a different set you borrowed?
Reading the end of your post indicates the current state is using balanced cables and the hum is gone/minimized?
This seems very strange. Are you using balanced cables between Source>Pre-Amp>Amp?
Have you tried all sets of cables again to see if the hum comes back?
Maybe the balance/unbalanced switch on the A23 wasn't toggled fully?
Let me know if you isolate it to one of the sets I sold you. I never had an issue with them but they were only used for my subwoofers.

CoolJazz

If you running balanced cable between balanced connections, then why would you say that you 'properly' set the amp end to unbalanced? Likely that bal/unbalanced switch would be doing the same as tying pin 3 to pin 1 of the XLR.

Without a schematic, it's guessing but I would wonder if you had one leg of the balanced connected to ground (via that switch) causing really heavy load on the preamp output. Shorting an active output can blow it, cause very high distortion if it has enough output resistance built in to survive or cause various audio problems due to the pre's output stage trying to blow. Normally I wouldn't think a buzz/hum would be the description, but might show up that way.

If Parasound does the XLR pin 3 right and doesn't share grounding between the chassis, then the ground lift should be able to be closed on the amp and both the pre and the amp share a hopefully common ground reference from the power ground. Using the same power source is important in most cases. Depending on other components hooked to the pre, things could change for grounding though so ungrounding the amp might be necessary (hence the ungrounding switch).

Balance has a number of positives and should not be going in the direction of any kind of increased buzzing or hum.

CJ

voltz

When I bought my ModWright amplifier.. to go with my Modwright preamp.. I first hooked it up with some Acoustic ZEN balanced cables and it sounded so right

then when I switched to RCA cables/Unbalance the hum was crazy.. using the same brand of cables/Acoustics ZEN's and with balanced it was so quiet it was scary

This is the stuff about audio that can drive you crazy!

good luck hope you can solve the problem!

pkquat

TY for the responses.

Sorry for the goof and confusion in the original post. "The switch was properly set to balanced" is what it should have said.

To be clear, I am using balanced cables and everything is now fine with any balanced cable or unbalanced cable, the balanced input switch or ground lift switch in either position.

When I first hooked up any balaced cable, I got the hum. I flipped all the switches multiple times, both pre-amp and amp were powered on and off multiple times, and inputs were switched. Balanced yeilded hum, and unbalanced did not. Everything was powered off overnight. The next day when I tried balanced cables there was no hum per se. I tried to see if I could flip some switch to find a cause, but nothing caused any highly audible hum. I even laid coiled cable over one of the power cables. It has been fine for the past few days.

I am curious what could cause it for future reference.

pkquat

I may have found the cause. I have two laptop power supplies. One is an older big brick, and the other is a newer smaller design. I brought the big brick out to power a work laptop. If my laptop is plugged into the big brick, and a haupage video converter is plugged into the laptop via usb, and both are on the same circuit as my audio gear strange things happen with balanced cables. If the haupage is on, I get modem like sounds. If the haupage is off, I get hum. If I use unbalanced cables there are no other sounds or hum. If I use the smaller PS, or the usb is not plugged in there are no sounds or hum.

Crazy

mantis

I never ever got a hum with any balanced cables in my entire life . By Design Balanced cables have the lowest noise floor compared to unbalanced. It is not physically possible for a un balanced cable to have a lower noise floor by design.
You have noise in your power I feel. Something is injecting a EMI signal into your system. It's not the cables it's absolutely something else unless you purchased bad cables.

pkquat

The cables are fine. I agree it is noise getting injected into the power... but under a weird combination of connections / conditions. I have no idea why it does not show up with unbalanced cables. All I can guess is some type of ground loop or ground noise related issue with the right combination of laptop connections. It was a mystery until I stumbled on it again.

BlueFox

Your next step is to get multiple dedicated AC circuits. One for the preamp, CDP, etc., and one for each amp. And don’t plug non-audio junk into an audio AC line.