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8020a hum

tenzan, modified 12 Years ago.

8020a hum

Youngling Posts: 6 Join Date: 5/20/10 Recent Posts
Hi all,

I'm having a problem with one of my 8020s. One speaker is emitting a very loud hum when I connect an unbalanced cable (I've tried an XLR to RCA lead and an XLR to jack lead). However, there is no hum with a balanced XLR to XLR cable. It's only happening on one speaker - the other is fine with the same cables, so I'm guessing that something is wrong.

In addition, the xlr to rca cable works fine when connected to the pre-outs of an Arcam AV9, but not with the RCA outs on my mackie 1202 (tape outs). As soon as I disconnect from the AV9 the hum appears - back into the pre-out no hum. The speaker sounds fine when used with the AV9.

I have also tried daisy chaining the speaker with the female xlr out to the male and no problems, so it seems to be something to do with the unbalanced cable.

When I say hum, I really mean hum, not just a little interference.

Any ideas would be appreciated.

Cheers,

Tenzan
tenzan, modified 12 Years ago.

Re: 8020a hum

Youngling Posts: 6 Join Date: 5/20/10 Recent Posts
also, just to restate

I've tried my xlr to rca and xlr to jack cables on the other speaker and there's no problem at all, so I guess it's not the cables.

And, when there is no cable in the speaker and it's turned on there is no hum at all.

Cheers,

Tenzan
andreas, modified 12 Years ago.

Re: 8020a hum

Padawan Posts: 61 Join Date: 4/8/09 Recent Posts
Lools like you answered it yourself. The Arcam test speaks against the Mackie. If more sources directly connected sound ok, then something is wrong with the Mackie or something connected to it (ground loop e.g).
tenzan, modified 12 Years ago.

Re: 8020a hum

Youngling Posts: 6 Join Date: 5/20/10 Recent Posts
Thanks for this - you see, I'd agree but...

...I don't have a problem with the Mackie on anything else, and even if it's not switched on, I'll still get the hum from the speaker.

However the AV9 stops the hum switched on or not.

Unbalanced cables not connected to anything but the genelec still make the speaker hum like mad, and it happens on only one speaker. Put a balanced cable in, and not connected to anything either absolutely fine. And when I say hum, it's not that hum you get when you touch to end of an unconnected cable, it's constant and loud.

I did try the speaker on the pre-outs of another arcam amp, and I got the hum - I'm not too sure why the AV9 stops the humming, but wondering whether it's a grounding issue in the Genelec, and the AV9 provides this.

Cheers for the reply, would appreciate any other thoughts you might have,

Tenzan
andreas, modified 12 Years ago.

Re: 8020a hum

Padawan Posts: 61 Join Date: 4/8/09 Recent Posts
I did try the speaker on the pre-outs of another arcam amp, and I got the hum


Well, first of all, when you take a pure seperate source, like a standalone CD player, only connect that via these unbalanced cables to XLR to the 8020s and you get no hum, then the speakers are just fine. That would my personal conclusion, espcially when you swapped power and signal cables among them with that one source.

However, usually players will have a different grounding method, with no third grounding wire connected in the power plugs (often just the small power plug). I do not know what the Arcam AV9 does, but some modern Home Theater units, although they show a third "nose" in the power plugs for gounding, do not have that one connected in their sockets in the back of the unit. I noticed this on some Pioneer receivers I had some time ago, big 3 pin sockets in the back, but showing only two pins. Ground loops are quite common in the home cinema world, as so many different sources meet in one point and I assume it is not mandatory anymore to have all 3 pins to get all certficiations. Internal wiring in the Arcam can also be just different to the outputs. I'm not sure, if a difference in resistance on the outputs play a role too.
tenzan, modified 12 Years ago.

Re: 8020a hum

Youngling Posts: 6 Join Date: 5/20/10 Recent Posts
Thanks Andreas - it helps clarify the issue.

I tried connecting the 8020 to a CD player's outs and no problem either on or off - I thought I'd check the Mackie with the same power lead, and with the RCA tape outs to the 8020, switched off - loud hum, switched on - fairly loud hum and not really workable (it's fine on the other speaker as a matter of interest, on or off).

Lastly I tried an RCA to jack adapter to link up the jack outs of a Pro Tools MBox. Very, very slight hum with this, but not noticeable when monitoring. (Mind you pull the jack connection out, very loud hum...)

I think it has to be some grounding issue, - the only odd thing is that it's only on one speaker, which I guess is why I starting thinking there was a problem.

But it's saved me a trip to the shop. Cheers, Andreas!

Best,

Tenzan
andreas, modified 12 Years ago.

Re: 8020a hum

Padawan Posts: 61 Join Date: 4/8/09 Recent Posts
Would be interesting to know what happens when you disconnect both speakers, signal and power cables, but leave the wires where they are and you just physically move the bare one speaker to the place of the other and via versa. So that only both speakers are trading places nacked. Will the hum move as well or stay in the left channel....so to say ?
tenzan, modified 12 Years ago.

Re: 8020a hum

Youngling Posts: 6 Join Date: 5/20/10 Recent Posts
Hi Andreas,

Well, this is pretty weird, so maybe there's something not quite right with the speaker: after keeping all the cables the same but just moving the speakers around the hum moves and still remains with the 'faulty' speaker.

Or maybe it's the other way - the quiet speaker is faulty, and it should make a hum if using unbalanced cables not plugged into anything. Would be great if a Genelec technician could shed some light on the subject... :idea:

Cheers,

Tenzan
andreas, modified 12 Years ago.

Re: 8020a hum

Padawan Posts: 61 Join Date: 4/8/09 Recent Posts
Hi Tenzan,

I'm not convinced it is the speakers ;)

I once had the most tricky ground loop that I searched for some endless time with endless swaps between cables, sources, etc. In the end it was the 230V inwall power sockets in the rear wall having an old wiring method and a wrong connection. I assume electricly there can be certain "variances" that lead to "electric potentials".

If you manage to connect a spare standalone source with the cinch to XLR cables, and you find a another source with XLR outputs and a pure XLR connection and you find in both ways nothing, it is a proof the speakers are ok. Whether it is your cables or power sockets/power wiring, or the Mackie, is then a matter of time to find. You can also try as a test, not forever as it can be dangerous, to ground lift the Mackie e.g. with tape on the ground pin of it's power plug. Some manage to measure their way through with a voltage tester measuring between ground pin and housings.

However, you are right, maybe Ilkka can advice better and more precise.
andreas, modified 12 Years ago.

Re: 8020a hum

Padawan Posts: 61 Join Date: 4/8/09 Recent Posts
What you can also test, is if you swap the naked speakers as said, but only use one channel of the Mackie for the test, so you only connect one speaker at a time to that same set of cables/same channel. If on that one channel, both speakers after each other have a hum or both have no hum will show that maybe both speakers are fine. Maybe then, just both speakers at the same time on the Mackie lead to an increased electric potential and hum. Then it can be the Mackie, power wiring or else.
ilkka-rissanen, modified 12 Years ago.

Re: 8020a hum

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts

However, you are right, maybe Ilkka can advice better and more precise.

You guys have pretty much debugged the problem just as I would have. :) He should try the test you suggested in your latest message. If only the other speakers hums when connected to the same channel and power, then we can conclude that the speaker needs service.
tenzan, modified 12 Years ago.

Re: 8020a hum

Youngling Posts: 6 Join Date: 5/20/10 Recent Posts
Hi again Andreas, and cheers for the response Ilkka,

Have tried what you suggested, and I'm afraid to say that it's still just this one speaker that hums. It's certainly workable when using P T Mbox, but something isn't right, so will get it serviced.

Thanks again for your suggestions.

Bye for now,

Tenzan