I took delivery of my studio monitors today and I had ordered some jack-jack speaker cables to go with them.

The Speakers are ESI nEAR 05 which from the reviews I read are pretty good.

When I plugged the speakers in and connected them up to my mixing desk I got a nasty hum if the main output slider was past half way. I looked at the writing on the speaker cables I bought and the writing says 'OFC High-Quality Digital Signal Microphone Cable'.

Firstly, I'm sure I know the answer already but can Microphone cable be used for Speaker leads?

Is the fact that the cable is 'Microphone Cable' be the reason I'm getting a hum?

Should I contact the retailer (who actually made these leads) and complain? The description on their site says "The Unbalanced Jack Cable can be used for many speakers with a 1/4" jack connection."

Digital signal microphone cable, lol!

I think you have a few things confused. To explain the above, as far as I'm aware, there's no such thing as a digital mic cable! Microphones output an ANALOG signal. So don't really know what's going on there.

Next up... SPEAKER LEADS/CABLES refers to cables that carry low impedance signals from amplifiers. Where the confusion is, is your amplifier is built in to your speaker. So you don't need 'speaker cable'.

So it goes (usually) Output of interface/mixing desk at LINE level --> into an amp which amplifies and outputs SPEAKER level --> SPEAKER cable goes into a passive speaker.

Now your speakers are active. So the amp into speaker part is done inside. So as you can figure out, you need a cable the carries line level.

Another note, your inputs on your speakers are balanced. And as you've said, your cables are not. Unbalanced cables are more susceptible to hum especially when bundled up with mains cables (such as stuffed behind all your equipment and speakers...), and over long distances. So providing your interface/mixer has balanced outputs, you need balanced cables.

Here's where it gets confusing. Mic cable IS usually balanced, as mics have 3 pins. Positive, negative and ground. So a balanced cable for line level signals (which you need), will also have 3 cores inside (and yes mic cable is fine to use for this). However it can be wired without one of them to unbalanced connections. The jack plugs, ones with one black ring, unbalanced. Two black rings, balanced. Usually. However with headphone cables for example, rather than balanced it's TWO unbalanced. Hence stereo signal in one cable!

Mic cable is NOT suitable for speaker cable. Remember, you don't need speaker cable! A cable that goes to your speaker, doesn't make it a speaker cable! Confusing right? Just remember, speaker cables go from an amp, to a passive speaker. You just need to transfer the line level signal...

So not only does it say you have a digital microphone cable, it also says it's suitable for many speakers. This is bad terminology, it could mean from amp to speaker in the conventional sense of speaker cable, or from mixer to active speaker in the sense of, 'a cable for a speaker'.

My advise would be send them back and exchange for a BALANCED cable. Note your speakers can receive an XLR input too. So if you're interface/mixer has XLR outs, you can use a standard balanced XLR-XLR cable.

Christian.

First of all Dafrom,..."'OFC High-Quality Digital Signal Microphone Cable'."

Is b*ll*x. There is "digital" cable and there is mic (balanced line) cable, not both (there is but one(?) digital microphone system about AFAIK and you don't got it!

So, what HAVE you got? If it is stereo jack to jack it should work perfectly well to link a mixer to those active monitors (of which PW said nice things)but a jack to jack lead is NOT a mic lead! If it is in fact XLR to XLR that is a mic lead and once again you should have no hum troubles.

If it is in fact a MONO jack lead, a guitar lead in principle, ship it back because "they" should have known better, even if you specified it I would have expected them to advise? Even so even an unbalanced cable should be fairly quiet. Your best plan would be to check the connections with a test meter and if you do not have one and don't know how this is a headsup to getting one and finding out!
Such problems will dog you all the way thru' a recording lifetime!
And if it IS balanced and it DOES test out ok you probably have a hum loop, but we have to progress systematically.

Dave. Sorry Christian, we crossed qwerties. Jeeps you youngsters can type quick!

Edited by ef37a (08/11/11 12:18 AM)

Hi Christian,

Thanks for your reply. It confused me saying 'Digital Microphone Cable' too.

So is the fact that it's unbalanced the likely cause of the hum? I've had a look on this particular retailers website but I can't find any jack to jack cables that specifically say 'balanced' cable so I'm wondering whether Jack to XLR would be a safer bet (my desk doesn't have XLR outputs unfortunately).

Quote dafron:

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Hi Christian,

Thanks for your reply. It confused me saying 'Digital Microphone Cable' too.

So is the fact that it's unbalanced the likely cause of the hum? I've had a look on this particular retailers website but I can't find any jack to jack cables that specifically say 'balanced' cable so I'm wondering whether Jack to XLR would be a safer bet (my desk doesn't have XLR outputs unfortunately).

---

You just need two of these:
http://www.maplin.co.uk/stereo-quarterin-jack-leads-224831?ordercode=N44FY

Dave.

Quote ef37a:

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First of all Dafrom,..."'OFC High-Quality Digital Signal Microphone Cable'."

Is b*ll*x. There is "digital" cable and there is mic (balanced line) cable, not both (there is but one(?) digital microphone system about AFAIK and you don't got it!

---

I'm only quoting what it says on the casing of the cable.

Quote ef37a:

---

So, what HAVE you got? If it is stereo jack to jack it should work perfectly well to link a mixer to those active monitors (of which PW said nice things)but a jack to jack lead is NOT a mic lead! If it is in fact XLR to XLR that is a mic lead and once again you should have no hum troubles.

If it is in fact a MONO jack lead, a guitar lead in principle, ship it back because "they" should have known better, even if you specified it I would have expected them to advise? Even so even an unbalanced cable should be fairly quiet. Your best plan would be to check the connections with a test meter and if you do not have one and don't know how this is a headsup to getting one and finding out!
Such problems will dog you all the way thru' a recording lifetime!
And if it IS balanced and it DOES test out ok you probably have a hum loop, but we have to progress systematically.

Dave. Sorry Christian, we crossed qwerties. Jeeps you youngsters can type quick!

---

As I said, I'm only quoting what the cable says on it. I didn't call it a Mic lead, I said it was 'Microphone Cable'.

Going by what Christian said, it's unbalanced cable as the connectors only have one ring so I will be getting them changed for balanced cables.

Thanks for your reply

Hey! Not blaming you at all!
It is them as made the cable that marked it wrongly!

Yes, an unbalanced "system" is more prone to hum than a balanced one but is rarely a problem at line level signals so you either have a faulty lead (unlikely both are borked. Is the hum in both channels?) or, and I suspect more likely, you have an earth loop problem.

But DO get yourself a testmeter, in a month you will wonder how you ever managed without one.

Dave.

Quote ef37a:

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Hey! Not blaming you at all!
It is them as made the cable that marked it wrongly!

Yes, an unbalanced "system" is more prone to hum than a balanced one but is rarely a problem at line level signals so you either have a faulty lead (unlikely both are borked. Is the hum in both channels?) or, and I suspect more likely, you have an earth loop problem.

But DO get yourself a testmeter, in a month you will wonder how you ever managed without one.

Dave.

---

Thanks Dave.

The hum is in both channels. I've tried both leads and actual guitar leads and get the same issue which is what led me to think it's the fact that they cables are 'unbalanced'. If I have nothing going through the desk but push the main output fader to '0' I get a hum. As soon as I unplug the lead, the hum goes. If I turn the fader down to about '-4' the hum goes.

I also tried just taking a line out from my Saffire Pro 40's headphone outputs but that got the same hum.

I just want to try and establish whether to complain about possible faulty cables or faulty speakers.

Will definately get a testmeter though.

I just had another play with the cables, etc and noticed the following:

1. The speakers connected to the desk, main output fader at minimum, using the unbalanced cables had a fairly loud hum. The higher I pushed the main output fader, the louder the hum got.

2. The speakers connected to the desk, main output fader at minimum, using a stereo cable still had a fairly loud hum (although the cable is an old 'budget' cable). The higher I pushed the main output fader, the louder the hum got.

3. The speakers connected to my Saffire Pro 40, using the unbalanced cable had a slight hum with the volume control above around 80%.

4. The speakers connected to my Saffire Pro 40, using the stereo cable had no hum whatsoever.

Any recommendations as to what I can try next?

If the hum gets louder with the main fader then either the mixer is introducing the hum, perhaps due to an earth loop with the speakers, or something else that is plugged into the mixer is introducing it - have you tried with just the speakers and mixer with nothing at all plugged in? Speakers and mixer go to the same mains socket?

If you plug the mixer outputs into your soundcard inputs can you get a hum from that combination?

--------------------
* Soundcloud *
* Bandcamp *

"4. The speakers connected to my Saffire Pro 40, using the stereo cable had no hum whatsoever."

This ^ indicates that you have a hum loop, 99% certainty, assuming the Pro 40 makes sounds?!

The quickest solution is a 1:1 transformer isolator between mixer and speakers, The Art Cleanbox 2 is the default recommendation but also check out Orchid Electronics.

A better solution IMO would be to use stereo|("balanced") leads but break the shield connection (in both) one end but this requires some DIY cable making skill and soldering experience (plus the kit of course!).

Dave.

Quote christianmurphy:

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Digital signal microphone cable, lol!

---

Actually it isn't totally ludicrous...

If the cable is two core and screen and has a characteristic impedance of 110 ohms then it could also be used for AES/EBU digital signals. Quite a few larger studios are cabled with Belden 1800 cable which can be used for both analogue and digital signals.

James.

--------------------
JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Thanks for all the replies.

I had a bit of a play before I went to bed. I tried the speakers in every 'jack' output (including the aux sends, etc) The hum remained in every output apart from the headphone output. When connected to the headphone output, even with the volume on maximum, I didn't get any hum whatsoever.

I unplugged every cable from the desk apart from a single line cable to the monitor, kept the line cable well away from any mains cable (all mains cables under desk, line cable above the desk), still got the hum on every output.

I've noticed that hidden on the back of the desk, there's 2 XLR connected clearly marked 'Balanced Main Outputs', so as I've got some new Mic cables coming today I'll give them a go.

Semantics James, with great respect, semantics.

An AES 110Ohm cable is no more "digital" than a TRS lead is "balanced" To turn this on its head, you could describe CATx ftp LAN cable as "balanced audio multicore", a job it does extremely well, but nobody does!

The vendors are simply cashing in on the term "digital" to pimp the product, like "high definition", it means nothing and just serves to confuse the noob.

Dave.

Quote christianmurphy:

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... as far as I'm aware, there's no such thing as a digital mic cable!

---

Actually there is... because there are now digital mics which use the AES42 interface format (a modified form of AES3) and these require proper, 110 ohm low-capacitance cables optimised for data rates in the 3-10MHz region. Rather different requirements to standard analogue mic cable.

...but whether these specific cables really are AES42 compliaint or just marketing BS is anyone's guess!

As you say, it is important to realise that the type of cable is not necessarily directly related to the equipment it connects to.

Speaker cable is designed to carry high currents between a power amp and a passive speaker or drive unit. It will have two (or sometimes more) cores and no screen.

A balanced audio cable is designed to connect line level equipment or analogue microphones. It will have two cores and a screen, and is usually terminated with XLRs or TRS plugs.

The OP has active speakers with a balanced line level input, so requires standard balanced cables to connect them.... as has been stated.

The hum that is present is almost cetrainly due to the use of unbalanced connections resulting in ground loops, and the lack of a screen, which may be allowing RF interference in. The use of balanced cables would almost certainly cure the problem. Look for TRS-TRS (balanced) jack leads, or balanced TRS jack to male XLR. Either would do.

hugh

--------------------
Technical Editor, Sound On Sound

Quote Hugh Robjohns:

---

Quote christianmurphy:

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... as far as I'm aware, there's no such thing as a digital mic cable!

---

Actually there is... because there are now digital mics which use the AES42 interface format (a modified form of AES3) and these require proper, 110 ohm low-capacitance cables optimised for data rates in the 3-10MHz region. Rather different requirements to standard analogue mic cable.
hugh

---

Cheers Hugh. When typing that originally it came out as - There's no such thing. Then I remembered reading about a digital neumann mic. So went back and added as far as I'm aware . I'm guessing it's generally high end business? I wonder if all this digital mic crazyness means we'll be able to end up with wireless studios Now that I would go for!

I think getting your cable understanding sorted is one of the biggest jumps early on when it comes to music tech. I bought a shed load of cables a few years back trying to interconnect mixers with soundcards and so on. Kind of learnt the hardway, but still use some of them cables today aha!

Xlr leads finally arrived today so all excited (like a child) I plugged them in, switched everything on and still get the same hum.

Ive moved the power supply away from the desk and made sure the xlr cables and power cables are as far apart as possible but mad no difference.

Any advice would be very much appreciated.

Is it likely that the desk is faulty?

1. Are all of your mains cables connected to one common point?

2. What do the speakers sound like with no signal source nor cable connected? Hiss, hum, both, nothing?

3. Can you try shorting the speaker inputs to ground at the speaker?

Quote Jeraldo:

---

1. Are all of your mains cables connected to one common point?

2. What do the speakers sound like with no signal source nor cable connected? Hiss, hum, both, nothing?

3. Can you try shorting the speaker inputs to ground at the speaker?

---

1. Yes but have also tried using a different wall socket for the mixers psu.

2. As soon as I unplug the cables from the desk, the hum stops (even with the cables still connected to the speakers)

3. How do I do that?

Thanks so much for the post.

Morning Dafron.
I am sorry to say that I am 99% certain that you have a classic hum(ground) loop problem and the only practical, safe course of action now is to modify those XLR leads.

Fitting balanced cables can often cure hum troubles, even hum loops, but strictly speaking, "balancing" cannot remove a hum loop, sometimes it does, but if the equipments' internal earthing regime is wrong,as is unfortunately still much the case, it can't.

So, with just one XLR lead connected you still get hum? (I would expect that to be the case). You must now take ONE XLR connector apart, I suggest the male connector and dissconnect the shield wire from pin 1. You could just cut this back but better to unsolder it and insulate with tape(I use paper decorators tape, does not go sticky)but if unsoldering, plug it into a female end to both heatshunt the pin and keep it aligned, some XLR substrates MELT these days! If this solves the hum trouble try the other lead, almost certainly the hum will return so repeat the process.

Lastly, MARK the lead ends as being "PIN ONE DISS'ED" or similar.

Dave.

Hi Dave. Thanks for your excellent post. I went ahead and tried what you suggested (unsoldered the shield from the Male XLR plug) but still get the hum.

Quote dafron:

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Hi Dave. Thanks for your excellent post. I went ahead and tried what you suggested (unsoldered the shield from the Male XLR plug) but still get the hum.

---

And you only have that one XLR lead connected? I am sorry then but I am out of ideas! I shall keep thinking tho!

Dave.

Quote ef37a:

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Quote dafron:

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Hi Dave. Thanks for your excellent post. I went ahead and tried what you suggested (unsoldered the shield from the Male XLR plug) but still get the hum.

---

And you only have that one XLR lead connected? I am sorry then but I am out of ideas! I shall keep thinking tho!

Dave.

---

Yep

If I turn the volume control down to barely 'on' I get very minimal hum (to the point where it's usable) and still get a good amount of volume but admittidly that doesnt necessarily solve the problem.

Made some progress.

I'd left one jack plug from an 8 way loom plugged in at the back my mistake. Took that out and the hum stopped with the modified XLR cable.

So that's the good news. Now, why is it that I get the hum again with the multicore connected? The multicore is an 8 way Jack to Jack MONO loom.

Thanks again for all the help. I really appreciate it.

EDIT: The multicore is going from the outputs of the audio interface to the line inputs on the desk.

The thot plickens!

Of course the Pro 40 is mains powered and earthed! So, presumably you are running the 8 pro outs back to the mixer and mixing "out of the box"?
What is the mixer? I don't suppose we could be lucky and find it runs on an external single rail supply? If so you see we might be able to find a supply that did not pass mains earth through, a common laptop PSU problem.

Do you still get the hum with everything plugged up but with the FireWire lead diss'ed? Not that there is a lot you can do about that AFAIK! Your only recourse might be to "earth free" all of the returns in the loom....Sorry! That or a bank of traffs!

Dave.

Quote ef37a:

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The thot plickens!

Of course the Pro 40 is mains powered and earthed! So, presumably you are running the 8 pro outs back to the mixer and mixing "out of the box"?
What is the mixer? I don't suppose we could be lucky and find it runs on an external single rail supply? If so you see we might be able to find a supply that did not pass mains earth through, a common laptop PSU problem.

Do you still get the hum with everything plugged up but with the FireWire lead diss'ed? Not that there is a lot you can do about that AFAIK! Your only recourse might be to "earth free" all of the returns in the loom....Sorry! That or a bank of traffs!

Dave.

---

Yeah I'm mixing out of the box.

The mixer is a Behringer MX8000. It uses an external power supply but I don't know much about electronics.

I tried with an iPhone connected with a 2 phono to mini Jack lead (and 2 phono to jack connectors) and that worked ok. I haven't yet but will try with an XLR cable connected to a Microphone now.

How would I earth free all the returns in the loom? The jack plugs are moulded. Sorry if I sound dumb but what's a bank of traffs?

Thanks again Dave.

http://www.studiospares.com/signal-interfaces/art-t8-8-channel-transformer isolator/invt/325660/

^ Bank of traffs!
To earth free that loom you would have to chop each plug off one end and replace with a new one but with no shield connection. Personally I would not commit such butchery and would make up a box with jacks in it with earths dissed (but with RF bypass capacitors. Not hard to make, you obviously can solder...Simples!)

But this all should not be happening! Surely Presonus considered peeps would want to run 8 outs to a desk and interface a pc and monitors???

Dave.

Quote ef37a:

---

http://www.studiospares.com/signal-interfaces/art-t8-8-channel-transformer isolator/invt/325660/

^ Bank of traffs!
To earth free that loom you would have to chop each plug off one end and replace with a new one but with no shield connection. Personally I would not commit such butchery and would make up a box with jacks in it with earths dissed (but with RF bypass capacitors. Not hard to make, you obviously can solder...Simples!)

But this all should not be happening! Surely Presonus considered peeps would want to run 8 outs to a desk and interface a pc and monitors???

Dave.

---

Thanks Dave. Have now tried with a couple of microphones and all worked great.

So it's just the Pro 40 to the desk that's the issue but as you said, this shouldn't be happening. I mean, I can't really need to rewire every cable I want to use surely. There's gotta be a cause but it's just finding out what that cause is lol.

Also am I likely to get a hum going from direct outs to the inputs of the Pro 40 using the same loom?

Another thought, even though the wiring in the house was tested for safety, is it likely to be something to do with the wiring in the house that's causing these problems? It is a pretty old house with possibly original wiring (plug sockets don't have switches, etc). Will go and get a cheap mains tester as well.

Is it worth trying the mixer/speaker/fw combo in another room?

any thoughts guys?

Right, have made some further progress with this.

Running my 8 way jack to jack looms from the outputs on the Saffire Pro 40 to inputs on the mixing desk produce a hum that gets louder as I increase the channel faders.

Running individual jack to jack cables from the outputs on the Saffire Pro 40 to inputs on the mixing desk produce the same hum.

Running STEREO jack to jack cables from the outputs on the Saffire Pro 40 to inputs on the mixing desk produce a VERY VERY faint hum but DOESN'T get louder as I increase the channel faders.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Running the 8 way jack to jack loom from the Direct Outs on the desk to the inputs on the Saffire Pro 40 work no problem at all and produce no hum on the recorded track.

Therefore, I think my solution would be to buy stereo jack to jack cables to go from the outputs of the Saffire Pro to the desk and keep the 8 way looms for recording.

Does that make sense?

Does it make sense? Yes in as much as all electronic circuitry must obey physical laws tho' it is sometimes very hard to see quite how! (this is in contrast to computer programs which are often not sensible or "logical" except to the person that wrote it perhaps).

The fact that the direct outs on that mixer do not induce the hum suggests to me that Behringers have a slightly different internal grounding regime for certain sockets. It could very well be that you will have to resort to a "worked around" setup to keep everything quiet using a collection of modified (and marked up FCS!)dedicated cables. You have a fair investment in cash terms in that mixer, AI etc perhaps that bank of traffs is worth thinking about?! Paul White reviewed them and had good things to say.

Then, although I can see it makes much of the mixer redundant, perhaps you should consider mixing in the box? I am not one of those that mindlessly berate Behringer products but running your signals back and forth though a less than stellar mixer is probably not doing them any favours.

Dave.

Quote dafron:

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The mixer is a Behringer MX8000.

---

There's your fault right there!

Take the MX8000 and throw it in the bin. You will find that doing this will cause the hum to stop right away.

I'm not joking BTW, these things are built faulty and have totally undersized PSUs, so humming is what they do best. The grounding is feeble, the meter bridge causes hum all by itself and the PSU has part of the circuitry inside the body of the mixer, which causes more problems. Occasionally, when the diode bridge overheats, they go up in flames, after smoking for a while.

Are you sure you have the right model mixer Red?

I am no defender of Behringer for several reasons but we must be accurate.

The picture of the MX8000 I find has no meter bridge and it is supplied from a 19" Rack power supply rated at 400watts and weighing in at 8.3kgs!

Then the power connector shows +and - 18V, +48,+12 and +5V so I can see no requirement for further onboard regulation?

The fact that the OP CAN get clean sounds thru the mixer also rather discounts it as a prime cause.

Behringer are in fact not alone with PSU troubles. There was a range of Soundcraft mixers I understand that were a bit feeble in this department?

Dave.

http://cellsonik.com/equipment-detail.php?id=32 This MX8000 has the meter bridge as did some other photos that came up.

--------------------
http://soundcloud.com/richie-royale
http://www.mixcrate.com/richieroyale

Quote Richie Royale:

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http://cellsonik.com/equipment-detail.php?id=32 This MX8000 has the meter bridge as did some other photos that came up.

---

Fair enough, meter bridge is optional! But what about the 18pound power supply? Behrries might be a bit odd but I can't see them building a wall rat rated supply then puttting it in a rack with some rocks as ballast?

Yep, the one that is the exact copy of the Mackie 24.

And yes, there was a meter bridge (optional) and it buzzed.

Behringer is notorious for bodging their PSUs and that would be my first port of call. They went from transformer and diodes and caps (the way God intended) to one of those universal thyristory things. Come to think of it, I was wrong in stating that they had some of the regulation inside the thing, that was the Euro series.

But the first thing would be to slap an Oscar on the power rails and see if they are clean.

But many manufacturers seem to like to save on the PSUs and I have seen rubbish work from SSL, Amek, Soundscraft and even AMS-Neve. Usually, it is because they lovingly build a desk and then go shopping for the cheapest power supply out there.

As for our OP, it looks as if the poor bloke has already swapped everything around, except the desk, so . . .

Thanks for all the replies guys.

At the moment, replacing the mixing desk isn't an option. I fully appreciate that the PSU may be the cause of the problems but the funds simply aren't there to warrant a new desk and I don't really like the idea of mixing 'In The Box' at the moment.

I did look into the option of the ART T8 'bank of traffs' but for what I need, I'd need two of them, plus an additional 2 8 way looms so I'd be looking at in excess of £300 - almost the cost of an Allen & Heath Zed 24.

@The Red Bladder - Throwing the MX8000 in the bin simply isn't an option I'm afraid - especially if there are sufficient 'work arounds'.

As I said, with the right cable combination, the mixing desk is quite usable. I've just ordered a stereo 8 way loom to see if that works (if not, I can return it) but at £23, that's the better option until I can afford a new desk

Adimittadly I haven't read every post, but browsed over most of them, would one of these before the monitors not sort it?

If the cables you are using between the Saffire and the desk are all balanced you might solve your problems by snipping the screen of each cable at one end. Hopefully the loom you have bought doesn't have moulded plugs - if it does it will make it difficult to do this.

James.

--------------------
JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

I do understand that you can't go replacing desks on the say-so of some geezer on a forum, so here are the steps I would go through (speaking as a former repair guy) before spending any money on anything -

1. Make sure that the desk is earthed. The resistance between a metal part of the desk and the house earth wire has to be absolutely zero. Your £5 multimeter from Maplins here is your friend.

2. Take a look at the power coming from the PSU. I would use an Oscar (oscilloscope) to see if the power has any 50Hz wave form or other gremlin lurking. Often a rectifier bridge will lose a 'leg' or just not work properly as a result of overheating and the outcome is buzzing that varies, depending on where, when and how you use the thing and how much current the desk is drawing and where you are getting your signal from. A dodgy PSU will effect the main busses before it effects the direct-outs and similar things as these should have additional smoothing caps on them. Capacitors that are feeling old and tired produce much the same symptoms.

3. Now you can start looking for other things, like LEDs that interfere and that sort of thing.

Thanks guys.

If the loom I've ordered doesn't work I will be able to return it (I spoke to the company first to explain the problem, etc) but I bought it over separate cables because it came down to price really (the loom cost £23 whereas 8 individual cables would've cost about double).

Thanks for your post Red. To be honest, I think it is a mixture of the desk being some 12 years old and being a Behringer that's the issue. I'm kicking myself for buying it but I hoped it'd last me at least a year, but I guess there's not much I can do if the desk is dying.

Is it worth pursuing with modified cables for the time being? I guess that at least if I unsolder shields on cables, I can always solder them back when I get a new desk.

Don't give up on this desk! Fix it.

The 24-8 is actually quite a good desk, as it is a one-to-one copy of the Mackie 24-8, even down to the board layout. Uli Behringer asked some students on work experience (so the story goes) to copy the Mackie after getting hold of the service docs. (Greg Mackie sued him successfully!) As it is as old as it is, it will have the 'real' PSU with trafo and all that stuff, so (if the PSU is bust) fixing it is child's play. Anyone with a basic knowledge of electronics and armed with an oscilloscope can find out where that buzz is coming from. Things like capacitors and rectifiers cost very little indeed - pennies.

I've actually just noticed that the PSU says 'MX8000A Power Supply' so it looks like the original PSU died and has been replaced.

I just found out there's a Pro Audio company in the next street to where I live so I'll go and have a word with them to see if they could take a look.

I just spoke to a Tech about my problems with this desk to see if they could take a look at the desk.

He offered pretty much the same solutions as here (disconnecting shield on one end of each mutlicore connection channel) but also suggested it could be an earth loop because of the interface being powered. He suggested removing the earth from the interface's plug but is this safe to do? He did say not to use it on its own with the earth removed but he said as the desk will be providing earth it should be ok with the desk.

He did also recommend a DI box with an earth drop switch on it but as I need 16 channels it's a bit unfeasable at the moment.

Any thoughts before I give this a go?

Removing the mains safety earth from any device which is designed to employ one is (a) potentially lethal and (b) may invalidate any life/house/business insurance you may have.

In short, don't do it. Ever.

Relying on mains fault saftey earth connections through the audio wiring is just stupidly stupid, and most definitely NOT recommended or approved by any competent and reasonably sane person.

There are much safer and better ways of solving your problem... but first you need to definitely identify whether the problem is a ground loop issue or a dodgy console PSU.

Hugh

--------------------
Technical Editor, Sound On Sound

Just on the strength of that suggestion, I would ignore ANYTHING that so called 'tech' has to say, gods be, you would think that anyone describing themselves as a technician would know better.

Lifting screens can work, but there is actually another trick, you can go the other way, and run a fairly heavy cable between the case of the interface and the case of the desk in parallel with the snake (and as close to it as possible (Tape it to the snake)), this will often push the hum down to an acceptable level by providing an alternative low Z path for the circulating current.
It does not solve the problem, but can often get it down to the a level that can be lived with.

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!

Thanks guys, it didn't strike me as a safe thing to try to be honest.

However, this whole thing is really starting to do my head in.

My stereo loom arrived today, still got a hum, hacked off one of the jack plugs, soldered a new plug on leaving the shield unsoldered, still got a hum. Joined the the two sheilds together and the hum was still there but very faint...what's going on???

It does appear that this is an earth loop from what I can gather because it only happens when the power is connected to the audio interface.

Anymore ideas?

Is it worth trying a DI box? If so, which sort? Would a Behringer DI800 work even though in itself is powered and not passive or would I need a passive DI box?