Humming through XLRs

[Mark Dunlop]

I recently bought an Audiolab combo - the 8300CDQ & 8300 XP and decided to try the XLR ouputs for a wee change. I then bought replacement speakers - B&W DM602 S3s out, ATC SCM 11s in.
There's a hum from the speakers when I select the XLR output on the 8300XP which is not present when I select the RCA outputs. I don't think the B&W speakers hummed, but I've sold them and now can't be sure. XLR leads are new from Designacable. RCA leads are home-mades.
Wasn't expecting XLRs to hum, and certainly not when RCAs don't... anyone got any clues?
Cheers
m.d.

 

[abacus]

Could be a faulty unit, also the XLR are at both ends and not going from XLR to RCA.
To be honest, for such a short length there is no advantage to XLR over RCA.

Bill

 

[Mark Dunlop]

Could be a faulty unit, also the XLR are at both ends and not going from XLR to RCA.
To be honest, for such a short length there is no advantage to XLR over RCA.

Bill

Cheers, Bill. I only decided to use XLRs for the s & giggles, really. I would say the sound is a little louder through them than the RCAs and the hum isn't apparent when listening.
I had a hum from a Rotel cd player once that I fixed by using a different power cable, but this is a different kettle of fish.
m.d.

 

[daytona600]

XLR wil be almost twice as Loud +6db on Balanced outputs compared to RCA
Should be no Hum even with hundreds of feet of cables unless 50hz picking up mains frequency from power cables

 

[Gray]

XLR leads are new from Designacable.

.....so they're probably ok.
But, if you've got a multimeter, you may as well check to confirm all is well.

You'll see the XLR pins are numbered 1,2,3 (printed on the plastic close to holes and pins).
Use continuity test to confirm all go to the corresponding numbers, plugs to sockets.
Pin 1 is the screen.
Will (should) have been tested prior to sale, but no harm in checking.

 

[Mark Dunlop]

UPDATE
Now this is really weird... If anyone can offer an explanation, be my guest.

I took the XLR leads out, switched back to the RCAs and I put on "Leave" by REM while I was doing some other things. It's a song I know like the back of my hand so, a minute into the track when the lead guitar is supposed to come in and DOESN'T, my ears went "Wait a sec... where's the guitar?" The lead guitar was almost inaudible. Further investigation ensued...

I had decided to bi-wire the new ATC speakers when I got them, again just for the s&g and because I had some spare speaker cable knocking about. I removed the second wires and re-bridged the terminals and, lo and behold, no hum from the speakers! I then re-attached the XLR leads and, lo and behold, still no hum from the speakers! I now think the hum was something to do with the bi-wired speakers, rather than the power amp, because there's no hum now and every instrument's at the level it ought to be.

So, now I'm wondering 2 things. 1. Why were the speakers humming when bi-wired, but only via the XLRs and not via the RCAs? 2. Why were the speakers only playing certain things (like the lead guitar) at an almost imperceptible level when bi-wired, but playing everything when single-wired and properly bridged at the terminals?

This is very odd. I've never been bothered about bi-wiring before and I only tried it for the crack. Based on my limited experiences, I'd say "Bi-wiring is a crock!"

m.d.

 

[Messiah]

Perhaps they were not wired correctly and were out of phase?

 

[Gray]

UPDATE
...."Bi-wiring is a crock!"

Plenty of people would've told you that for nothing 😁

But, whatever else, buzzing couldn't be the result of correctly done bi-wiring.

 

[Mark Dunlop]

Perhaps they were not wired correctly and were out of phase?

It's not beyond the realm of possibility that I'd have cocked it up, but I'd have thought the speakers would either 'work' or they wouldn't. Also, why only humming through XLR if they weren't set up right? Very odd...
m.d.