Hum on mixer...

  • Thread starter Thread starter WykedPT
  • Start date Start date
WykedPT

WykedPT

Member
Not sure if this is the right place for my question. If not please let me know. I'm having a problem with hooking up my ADAT to a Mackie console. When they are connected there is a hum on the mixer that goes away when I turn off the ADAT. I can plug anything else in (mic ,instrument, my zoom recorder etc.) and they produce no hum. Likewise I can connect the ADAT to the zoom or a amplifier and no hum there either. Also plugged them into different outlets on different circuits and that did not help...Any Ideas? Thanks..
 
Yes there is a ground loop of some sort between the Mackie and Adat - I’d check the ADAT out to see if there is a open cirucit or some such thing - or I may just lift the ground on the Mackie and see what happens.
 
Thanks for the reply..I plugged the ADAT into the outlet using a ungrounded to grounded adaptor and that took care of the problem. So guess I'll whip up a ground lift box.....Thanks Papanate..
 
If the connection is balanced, lifting the audio ground(s) might solve it. Lifting power ground as a diagnostic test is okay, but it's technically not the correct solution.
 
In the UK, with our 240V power, lifting grounds is a frequent solution and one that guarantees a big red sticker when you have your equipment safety tested, as we do in non-domestic situations, and of course, while grounded via the cables in one situation, it won't be, when you move the kit around, and your body becomes the safety link between them when you unplug the cable doing the grounding!

ask yourself a question. Is the mackie designed to cause this problem keeping in mind the number out there, or is the ADAT the problem, the disconnected ground on the mackie is solving. It seems one piece of kit is faulty (both being proven designs). You have not cured it, just removed a safety component to kill the symptom. You've proved there was AC on the ground, flowing to the safety ground - and the hum was evidence. If you are brave, you could get a piece of wire and go from the Adat or Mackie ground and touch it to a radiator, or water pipe. The hum will come back, but maybe there will be a spark. Probably a teeny-weeny one. Or a much bigger, noisier one. If that is the case - you would not want to try it with your fingers, which could easily happen in a studio when you lean over things.

This sounds over cautious and daft, but over the years I gained a healthy wariness for ground removal after getting many shocks. The worst being on an electric guitar amp with lifted ground. The guitar was live, via a failed capacitor - luckily with fairly low current available. The microphone was a Shure 55. I got the shock through my lips!
 
I am going to wade in with Rob here...NEVER LIFT MAINS SAFETY GROUNDS!! Not even in my view as a diagnostic.
Take a bit of time to make up some special "braid breaker" cables. An XLR-XLR with no connection to screen (p1) ONE end and mark the cable up. TS and TRS jack to jack the same, screen diss'ed ONE end only. You can also buy isolating transformers e.g. the Art Cleanbox ll.

115V is only SLIGHTLY lethal than 230V.

Not having a complete 'thru' screen can, in rare cases, lead to the intrusion of RF I interference but there are fixes for that.

I am not totally with Rob when he says "the ADAT unit is faulty". The problems of ground loops are often complex and not really down to poor equipment. Yes, there are ways to avoid loops at the design stage but unless EVERYONE uses that design criteria AND has always done so, we will find equipment combinations that hum!

In fact, "Class ll" double insulated, earth free equipment is becoming ever more common. Many smaller but very high Q active monitors now use a bi-pin mains connector. This can result in a totally "not earthed" studio that hums!

Dave.
 
I don’t worry about lifting a ground to see if the unit is the problem - keeping it lifted has the possibility of being hazardous - but not really - in the case of @rob aylestone ’s spark that is different - in that case there is an open circuit and the unit is faulty - in the case of the op @WykedPT
- what would you do? The unit doesn’t seem like it has a problem - just a grounding scheme that doesn’t work with the ADAT - how would you fix it?
 
Thanks for all the replies. I wasn't going to leave anything without a ground. I plan to take it to a tech in the next couple days. I've been buzzed a couple times also. Really can't figure out why the Mackie is the only thing I plug it into that creates the hum..
 
Ok. Been snowed in today so was checking a few things out on the hum. Checked out the house wiring and found everything is good there. Narrowed a couple things down. The hum doesn't seem to be power related. So next I checked all connecting cables. Nothing there. Don't know why I didn't catch this before but it seems to be the outs on the ADAT. No hum from the inputs. Hit record on the ADAT and raised the sliders and nothing showed up on the ADAT.
 
WykedPT said:
Ok. Been snowed in today so was checking a few things out on the hum. Checked out the house wiring and found everything is good there. Narrowed a couple things down. The hum doesn't seem to be power related. So next I checked all connecting cables. Nothing there. Don't know why I didn't catch this before but it seems to be the outs on the ADAT. No hum from the inputs. Hit record on the ADAT and raised the sliders and nothing showed up on the ADAT.
Click to expand...
I am 99% sure you have a ground (aka "earth" aka "hum") loop problem and that is caused by the Mackie and the ADAT devices both having mains earths. You don't say how you are hearing the hum? Active monitors? If so and they have a ground connection, they could be the route cause. You also don't say what the exact make and model of ADAT you have so we don't know the audio connectors but if we assume jacks, make up as I said earlier in the thread some cables with the screens disconnected one end.

Any time you have grounded equipment you have the potential for noise. This is due to the fact that there is always a tiny leakage current from the internal circuitry to ground, caused mainly by capacitive coupling of mains power to the chassis. Nothing you can do about that but there are good and bad practices in the construction of gear. Unfortunately the industry has only 'learned' about this fairly recently and good practice is not universal! So we have to resort to palliative measures such as transformers and chopping screens.

BTW those highly vaunted "High grade mains filter" mains distribution strips can sometimes worsen the problem depending on how they arrange the internal filter capacitors.

Dave.
 
Hi Dave . The ADAT I'm using is a blackface unit. I am listening thru headphones so so active monitors are not in the equation . The ADAT has TS cables . The mixer is a Mackie 24/8/2.
 
The connection may not behave well with the Mackie's input rings grounded. It should, but that doesn't mean that it does. What happens if you partially insert the plugs so the tips connect to the socket's rings?
 
Last edited:
WykedPT said:
Hi Dave . The ADAT I'm using is a blackface unit. I am listening thru headphones so so active monitors are not in the equation . The ADAT has TS cables . The mixer is a Mackie 24/8/2.
Click to expand...
I have found a user manual for 'a' Blackface ADAT unit and pp 12-13 actually go into the possibility of ground loops.
I can now see that you are running 8 cables to the mixer? That precludes transformers probably on cost grounds and having to mod 8 cables is a bit of a PITA but is I fear your only SAFE solution!

Dave.
 
bouldersoundguy said:
The connection may not behave well with the Mackie's input rings grounded. It should, but that doesn't mean that it does. What happens if you partially insert the plugs so the tips connects to the socket's rings?
Click to expand...
Hi...Tried that and the hum is still there. But I'm not sure that shows anything.
 
Ok , another interesting twist. When I just hook up the outputs from the Mackie there is no hum. I can go from my Zoom to the Mackie to the ADAT and no hum...:confused: But as soon as I plug another cable between the outs on the Mackie to the ins on the ADAT (having unplugged the outs from the Mackie) the hum returns. Same if I plug the outs back in. I am perplexed to say the least....
 
Last edited:
WykedPT said:
Hi...Tried that and the hum is still there. But I'm not sure that shows anything.
Click to expand...
N.B. You don't need to remove the screens to all 8 cables immediately, just do one then try that one. If you get clean signal on that channel, Bob's yer whatsit and get the rest done. Once done remember to mark them up.

Dave.
 
rob aylestone said:
lifting grounds is a frequent solution and one that guarantees a big red sticker
Click to expand...
While I'm in the US, I have to agree with Rob. I almost lost a bass player to a "lifted ground". A better idea (which I use in the states) is to find some bare metal on your equipment, and run a ground wire from/to each piece. AND KEEP the ground. If your equipment is anodized, you will need to scrape down to bare metal, (aluminum oxide is an insulator). I had this problem just this past weekend where I was getting a nasty hum and a whining sound out of my Zoom L-12. Turned out to be a bad ground from the Zoom to the rack.
 
I tried what Old Music Guy said about grounding from the ADAT to the mixer. It did lower the hum a bit but not to a usable level.
 
WykedPT said:
I tried what Old Music Guy said about grounding from the ADAT to the mixer. It did lower the hum a bit but not to a usable level.
Click to expand...
Yes, you can often reduce loop noise by "grounding the ****out of the system". Connecting heavy, Parallel Earth Cables* but this is at best a reduction in hum, not a fix, all you are doing is reducing the resistance the ground current is "sitting on". Zero resistance would give zero hum but then a balanced connection with an infinite common mode rejection ratio would do the same!

Breaking one earth path stops the current dead.

*Known as "PECs" in the network industry but optical cabling has largely rendered Copper redundant.

Dave.
 
I suppose we've lost the old system where chassis ground and electrical ground may or may not be connected to the audio ground. Tony Waldron, the designer of many house price Cadac audio mixers was frequently at odds with audio device manufacturers who routinely connected the audio ground inside a box to the chassis and electrical ground creating so many ground paths that fault finding was a total pain - and the faults were often one device where noise currents got bonded to the audio ground, and the piece of kit performed flawlessly, until another piece of kit with the same system was connected. Both devices were silent, but the combination produced severe noise elsewhere, with that bit of perfect equipment getting the blame!

It can be interesting if you have time to meter between a single piece of kit's chassis, power ground and audio ground on the connectors. Some have no connection others are joined all together.
 
You must log in or register to reply here.
Back
Top