electrical hum

Hi,

When I have my mpc2000xl plugged into my mixer, I get a strange electrical hum which increases when I turn up to volume. I've eliminated the usual culprits e.g. faulty cables, inputs etc. I have also run the signal from the headphone jack to a mono channel and the sound is clean. In addition I have another sound controller connected to the desk and the sound is also perfect.

Not sure what the deal is here. Suggestions?

Do you have the 8-outs? Do you have a card reader? If you do, What kind?

Bumping for interest

Since nobody's replied yet, I thought a bit of extra info might be at hand.

Basically, I was using the mpc in a different place, through a different desk. New desk kinda shitty but it does the job. I know this because I'm running another sound module through it and it us more or less crystal. However, the ground him I've got is just horrible. I'm thinking for some reason that perhaps the electrical impedance of both components is not matched but I can't see how. Secondly, it occurred to me to maybe try using balanced cables. It doesn't quite seem to be the right answer though as I have always used unbalanced cables on samplers. Can anyone give me a heads-up on this before I splurge more cheddar on cables? The third and only other thing I can think of is DIing the mpc to the desk. Not sure why I would really want or need to do that but maybe it'd work.

Finally, there is of course like most studios, a lot of cables but they're reasonably separate, I mean, the electrical and audio cables are kept apart and besides, I'm not getting any horrible sounds from anywhere else.

What do you guys think?

JUKE 179r wrote:Do you have the 8-outs? Do you have a card reader? If you do, What kind?

Hey man, thanks for the reply. Nah man, no 8-outs. It's fully expanded though and it has the addonics non-hot swappable card reader.

Another thing that has just occurred to me. What if I unseated the expandable memory card and gave them a clean? Can't see how that would make a difference though.

It really sounds like electrical interference to me so, I've been considering the poss. of getting some better cables or something.

You guys are always on point though and I'm sure someone knows the answer.

Since you got it open, (carefully) tighten down all the mount screws and ensure all the ribbon cables/wire connectors are firmly pushed into position onto the circuit boards.

We're good there but still no joy.

Just noticed that the impendance on the outs of mpc is 100 ohms and the input on the desk 10k ohms but not sure what this means if anything.

UPDATE: Ok bros, I've made a decision. I'm going to DI that shit. I'll keep y'all posted.

Ok so here's what went down:

1.) Did what Juke suggested, tightened a few screws, unseated and reseated the card reader, SIMMS etc., sprayed a bit of compressed air here and there, put the lid back on, tightened it down good. TBH, looking pretty tight in there. Apart from a bit debris, under the pads etc. no sign of anything gone awry in particular.

2.) Switched the thing back on. No noticeable difference , maybe the 60Hz hum a bit quieter, probably just my imagination but still unacceptable.

3.) Due to only having one Behringer D100 DI box at hand, hooked the L out on MPC up and into a channel on the desk. Both attenuators compressed, ground lift off. Noticeable reduction in hum, not perfect as there is still a faint, faint hum but acceptable. We're good to go.

Here's what really gets me. Messing around to compare the difference. Got R out directly plugged into desk, horrible result, L out clearly much, much improved in terms of noise. Unplug the R cable and plug it into headphones out to see how the DIed channel sounds in comparison... L is now completely and utterly perfect - there is no noise present whatsoever. This applies to the DIed channel regardless of the fact that the headphones channel isn't even on!

To sum up, much improved through DI. But completely clean when DIed and headphone out plugged into a channel on mixer (depsite not being on). Can anyone explain?

So, from a personal point of view, I don't think anything is wrong with the machine. It was (to my knowledge) working perfectly through another desk, so, in my opinion, it must be the desk. Admittedly, a 8-track Behringer Eurorack is a piece of crap, but it works ok with my other equipment and does the job for me at the present moment. The line-ins are balanced etc. To sum up, it might not be the best, but it'll do.

Another problem could be the electrics in the studio that I'm using. However, apart from the usual 'airy' noise on my guitar amp which isn't really a problem, no other equipment has been affected. Obviously, I'm working on making sure all my cables are the right length, the best quality and whatnot and in any case everything has been neatly separated and tied back. Current and audio cables do not run parallel etc.

So, the headphones thing really gets me. At this point, I'd really be interested in hearing what you guys proffer opinion-wise as I'm stumped. I'm happy as things are, will buy another DI, some better cables, eventually a new desk or audio interface. But in anycase, I'll leave it to you. It's gotta be the desk, right?

Hey man, thanks for the reply. I've got everything connected to one outlet. I've got one 4 socket power bar (w/surge protection) with another 4 socket power bar connected. So it's like two connected together but going into one outlet. It's essentially the same thing, isn't it?

Do you have a DI-box? You can stop the hum by using the ground-lift of the DI-box. It is probably easier than figuring out, which piece of your hw is responsible...

Hey Wal Martian, no nothing of the sort - just one of those really bright industrial light fixtures overhead.

vdd wrote:Do you have a DI-box? You can stop the hum by using the ground-lift of the DI-box. It is probably easier than figuring out, which piece of your hw is responsible...

Check my last full post. I used a DI box which all but eliminated the problem but not completely. The problem only completely went away when I connected the headphone output of the mpc to a channel on the mixer. Strange thing was that the channel wasn't even active and I'm not sure why this would even the problem out.

I read this post, thought it was interesting:

viewtopic.php?f=1&t=157071

However, no concrete answers to the problem. I'm going to get shorter cables and balanced ones at that and balance the signal coming from the MPC using DI. That should fix the problem. This could count as part of a drive to improving the whole studio environment and I sure have learned a shit ton in the process.

However, I have a sneaking suspicion it might be the desk.

Any more suggestions / thoughts would be kindly appreciated.

Sounds like a grounding issue to me. If it is, easy fix.... you need need an ground loop isolator.
You can buy them cheap. If it doesn't work, who cares, at least you've ruled it out.

http://www.ebay.com.au/itm/CAR-AUDIO-ST ... xy--NRrwgx

MrDismal wrote:Sounds like a grounding issue to me. If it is, easy fix.... you need need an ground loop isolator.
You can buy them cheap. If it doesn't work, who cares, at least you've ruled it out.

http://www.ebay.com.au/itm/CAR-AUDIO-ST ... xy--NRrwgx

Isn't a ground loop isolator the same thing that's in a DI box or is it something different? Where and how would I place one on the signal chain? It looks like an RCA connection to me.