Hum in my system due to Mackie 1202 - is this normal?

K

kirkhere

New member
I ask the question because it seems that my 1202 VLZ Pro is the cause of a hum problem. Or the main contributor. I'm stumped as to how to fix this one.

Here's the skinny:

I hook up an EV RE20 mic via balanced XLR to the 1202. When I monitor the audio with AKG K240 headphones, I hear a low level hum in the signal.

I changed cables (several times, all were wired correctly), changed mics (an SM58 then an EV 635a), borrowed a DI box, and had no luck and no change in the hum with any of them.

So I removed all in's and out's save for the phones, then listened to channel one alone. At max trim and max gain, there's quite a bit of air, and a low hum deep in there. (Is this typical in the 1202, due to the mic pre I guess, and does anyone else get this?)

Inserting a mic cable into the 1202, but not connecting a mic to the other end, does not appear to alter anything that I can tell (if it does, it's too subtle for me to detect).

When I connect a mic to the other end of the cable the hum springs to life. If I drop the trim and gain to about 2/3 to 3/4 (roughly where they need to be to send a good signal to the Gina card in my computer) the hum remains just loud enough to be noticeable. Overall, the hum does not overpower the sound picked up by the mic, but it's always present, and noticeable especially between phrases.

The 1202 is about a year old, and little used (all of it here, never on the road). Could it be faulty, or normal, and is something else at work here? How can I eliminate this?

Thank you for your time and help,

kirkhere
 
The hum is definately not normal. I had an original 1202 that developed an annoying hum after several years.

Do you get a hum through headphones with nothing else attached to the mackie? If so then you should probably take it in for repair.
 
According to the problem description the hum starts when the mic is attached. There can be basically two sources for this:

1. The mic itself. It may pic up RF from flourescens lights or a transformer or something.

2. The phantom power. If something breaks in the phantom power unit you may get phantom power that has a ripple on it, which will then cause the mic to hum.

If you can borrow another preamp with phantom power and connect it to a line in on the Mackie, you should be able to figure out if it's the mic or the Mackie phantom power. Also you might try turning *all* equipment off and removing all wall warts and turning off all lamps, so to only have the Mackie running and see if the hum is still there.
 
Regebro said:
If you can borrow another preamp with phantom power and connect it to a line in on the Mackie, you should be able to figure out if it's the mic or the Mackie phantom power. Also you might try turning *all* equipment off and removing all wall warts and turning off all lamps, so to only have the Mackie running and see if the hum is still there.
Click to expand...

Regebro is right. Try this. Also, try a "ground lift" ... this is just an adapter that "removes" the ground plug from the circuit. If you get one that doesn't have one leg larger than the other (you know, for those house outlets that only let you insert the plug one way) you will be able to turn the power cord over thus reversing the polarity.

If the hum just started recently (i.e., it's never done THAT before), you probably DO have a problem in the Mackie. Hope this helps.

One other tip ... UPS (uninterruptible power supply), the kind you buy to protect your computer from lightning strikes, some of them include some "power conditioning" to clean up your home current, which is notoriously "dirty".
 
Hey TexRoadkill, deadeye and Regebro, thanks for all your input.

I've killed all power in the house save for the one outlet, and the hum remains.

I have tried lifting the ground with a 3/2 adapter, and the hum remains.

In fact, I am using a hefty UPS from APC (Back UPS Pro 1000). I tried it both with and without it, and even tried it with the UPS and the power cable unplugged (forcing it to use its internal batteries). Still no change. I even tried the baby APC UPS from upstairs, a combo power strip/ups unit. Same results.

In that case, I guess it points me to the mixer, since I've changed mics, cables, and now power sources!

It's either voodoo RF all over my basement, or I guess the mixer.
Next call is to Mackie. Letcha know what they say...

...And here it is. The Mackie Tech believes I have a power issue with the AC in my circa 1950 home. Apparently this is not so uncommon. He thinks (but is not certain) that a line conditioner may solve the problem. He sounded more certain that an isolation transformer would do the job.

So I contact Furman (furman.com) and ETA Systems (etasys.com) and talk to sales guys. Actually, with Furman it's emails (no one returned my message by phone), and with ETA it's a salesman. The Furman guy apparently did not take EPSL (English and Punctuation as a Second Language) and writes very stream-of-consciousness emails. He also assumes I know and understand in greater detail what he's trying to say. Trouble is, I don't, and his writing style further convolutes his intended message. I don't want to decode messages, especially when the first line of his every reply IS WRITTEN IN ALL CAPS LIKE HE"S YELLING AT ME. Scratch Furman.

The ETA Systems guy was informative and friendly, sounded somewhat certain that a line conditioner would do the job, and suggested using one anyway "just cause it's only about $75" and would do more for my AC power than the APC UPS alone. But when I asked him three times how to hook it up (APC into the conditioner or conditioner into the APC? Does the order matter?) he answered with a stream of other information and I never got a straight answer. Among all that, I got some interesting data about how he believes their conditioners are better than Furman's, which sounded legit, but I never got the big question answered.

A visit to psaudio.com showed me some impressive looking power gear, which is also expensive. I don't mind expensive as long as it's a sure thing. But they too have not returned emails and phone calls yet, so I've no idea what the sure thing is.

I'm frustrated because this adventure has sent me into realms where the solution is unclear, and all the guides disagree on the solution--that is, when I can understand what they're telling me!

It should be simple, but it's not, apparently.

Anyone else got an idea?

k
 
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Hey Kirkhere, [kewl name man, I leik]
I have a mackie 1402 vlz that is very quite, have you checked that your outlets are all properly grounded? I get nasty ground loops when hooking up certan combos of gear, Etc.
sorry I couldn't be of more use.
peace,
Shreadzilla
 
Before you spend any more money take the 1202 and some headphones over to a friends house and see if the buzz remains. I doubt the ground in your house all of a sudden went bad but anything is possible.
 
You mentioned that the 1202 was "little used" - it's not real likely, but still possible that the filter capacitor for the phantom power could have dried out in that time. Electrolytic caps go bad faster when not powered up, but usually it takes more than a year.

It's also possible that your house wiring could have "gone bad", but just about as unlikely. You didn't mention (or I missed it) whether your wiring has been changed AT ALL since 1950. Do you have 3-prong outlets? If so, do they test OK with one of the little $10 outlet testers (the ones with the lights on them)?

Some older houses, before codes got tighter, were grounded to the water pipes (if at all) - I personally had an electric fence charger work for a year or so with its ground hooked to copper water pipe, then it quit (horses loved this, I didn't) - When I finally found the problem, it was due to the copper house plumbing being sweat soldered to the city's black iron pipe (just out of city limits, but connected to their supply) - anyway, when I started drawing current thru that connection, the electrolysis between the dissimilar metals caused the joint to increase in resistance, eventually causing the fence charger to quit working. When I drove a proper copper ground rod and hooked the charger ground to that, I became MORE happy and the horses were not pleased at all...

From my own experience, I would recommend taking TexRoadKill's advice first. That will narrow things down a lot - remember, troubleshooting = finding all the things it ISN'T... Steve
 
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