Finding a hum

BillESC

Well-Known Member
Joined
Aug 29, 2005
Location
Kilmarnock, VA
Back story.

Early in 2004 I installed a sound system in a 100 year old church. This included 8 EV recessed ceiling speakers and six wireless mics.

As time passed, we installed a sound system in the fellowship hall, teen center in the basement, etc.

Two years ago we replaced their 600 MHz wireless mics with Audio Technica ATW-1300 series systems.

Recently we received a service call to find a hum. Neal and I spent a total of 4 hours chasing down the problem.

Replacing cables, unplugging components, lifting grounds, removing power supplies, etc.

A Bogen tuner amplifier turned out to have a hum. It is shipping out for warranty repair since the Gold Series has a 3 year window.

Anyone else think Hums are hard?
 

Aaron Becker

Well-Known Member
Joined
Apr 27, 2016
Location
US - East Coast
I’ve chased my fair share of hums. It really depends how easy it is to physically bypass equipment or cabling to test for the problem segment.

Systems with complex DSPs where you can’t just plug in an XLR bypass and you have to start swapping Euro blocks and reprogramming at the same time to not run the wrong signal somewhere gets fun.

Sounds like you (kind of) had an advantage knowing the system too. As builts change. Settings change. This usually proves to be the hard part- figuring out where to look, especially in a system where you’re unfamiliar entirely.
 
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FMEng

Well-Known Member
Fight Leukemia
Joined
Mar 31, 2008
Location
Tacoma, WA
Yes, hums can be very difficult to find, especially in systems where there are any un-balanced interconnections. In broadcast engineering, I have the luxury of banning all equipment with un-balanced or psuedo balanced inputs or outputs.

The sound re-enforcement world is getting better, because analog consoles with un-balanced insert patch points and outboard processors are less common. Patch panels in installed systems is mostly a thing of the past, too. Getting the grounding right with patch panels is not easy.

There was a time when finding anything but mic inputs balanced was rare. We have the late Neil Muncy to thank for preaching to the industry back in the late 1980s to not only adopt more balanced I/Os, but to fix "the pin 1 problem," as he named it. There was a lot of really awful crap being made back then, and it all hummed. It took careful engineering to build large systems free of hum. I don't miss those days.
 

RonHebbard

Well-Known Member
Premium Member
Joined
Jun 12, 2004
Location
Waterdown, ON, CA
Back story.

Early in 2004 I installed a sound system in a 100 year old church. This included 8 EV recessed ceiling speakers and six wireless mics.

As time passed, we installed a sound system in the fellowship hall, teen center in the basement, etc.

Two years ago we replaced their 600 MHz wireless mics with Audio Technica ATW-1300 series systems.

Recently we received a service call to find a hum. Neal and I spent a total of 4 hours chasing down the problem.

Replacing cables, unplugging components, lifting grounds, removing power supplies, etc.

A Bogen tuner amplifier turned out to have a hum. It is shipping out for warranty repair since the Gold Series has a 3 year window.

Anyone else think Hums are hard?
@BillESC Nah. . . Finding hums is/are EASY, it's eradicating and exorcizing them that's the tuffy.
Toodleoo!
Ron Hebbard
 

RonHebbard

Well-Known Member
Premium Member
Joined
Jun 12, 2004
Location
Waterdown, ON, CA
Yes, hums can be very difficult to find, especially in systems where there are any un-balanced interconnections. In broadcast engineering, I have the luxury of banning all equipment with un-balanced or psuedo balanced inputs or outputs.

The sound re-enforcement world is getting better, because analog consoles with un-balanced insert patch points and outboard processors are less common. Patch panels in installed systems is mostly a thing of the past, too. Getting the grounding right with patch panels is not easy.

There was a time when finding anything but mic inputs balanced was rare. We have the late Neil Muncy to thank for preaching to the industry back in the late 1980s to not only adopt more balanced I/Os, but to fix "the pin 1 problem," as he named it. There was a lot of really awful crap being made back then, and it all hummed. It took careful engineering to build large systems free of hum. I don't miss those days.
@FMEng I too don't miss those days but I sure do miss Mister Muncy.
In another lifetime, I donated an Imperial butt load of 1960's commercial broadcast studio gear to Mr. Muncy for a proposed broadcast museum and delivered it directly to his home north of Toronto. It was a hot summer afternoon and in return Mr. Muncy ( Neil, just call me Neil) invited me into his basement for freshly squeezed orange juice with the Australian fellow behind Surgex, they were sitting in Mr. Muncy's air conditioned basement rehearsing a presentation on surge suppression they later gave at an AES conference in New York then repeated for the Toronto chapter.
Thanks for the memories and
Toodleoo!
Ron Hebbard
 

BCAP

Active Member
Joined
Jan 4, 2017
Location
Ohio
Anyone else think Hums are hard?
They certainly can be. I haven't been doing this as long as some folks but I've seen my share. The one I remember as surprising me the most was a bad rack power distribution piece (similar to Furman PL-8). I was only surprised because it was a permanent install in a studio and theoretically nothing was moved around at all. Also once had a bad input XLR jack on a mains EQ (input cable must have got yanked) and I pulled the unit apart to resolder the PCB jack onto the board then everything was fine. The ones I like most, to be honest are when you can solve an issue by supplying different AC power - easy, fun, problem fixed and everyone happy (some may even be mildly impressed).
 
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MNicolai

Well-Known Member
Fight Leukemia
Joined
Mar 30, 2008
Location
Sarasota, FL
Spelunking for hums is my favorite pastime. My favorite series of hums was at a university's roadhouse theater. They had gremlins in their PA system, intercom, and 70V systems. The PA was overhauled completely so whatever that problem was we addressed when all of the patchbays were replaced and the grounding and lifts were corrected. The intercom was on the fritz because the old cabling deteriorated in some of the wall stations and the foil shield came in contact with the conduit. The 70V was the best. Someone in the scene shop drilled into a CMU wall and tore a hole in a conduit with all the backstage 70V cabling in it. They turned it into a rat's nest and shorted everything out, walked away like nothing happened, and left it that way for several years until we traced out their entire 70v system to find the short.
 

Ben Stiegler

Well-Known Member
Joined
Aug 3, 2017
Location
Sf Bay Area
Spelunking for hums is my favorite pastime. My favorite series of hums was at a university's roadhouse theater. They had gremlins in their PA system, intercom, and 70V systems. The PA was overhauled completely so whatever that problem was we addressed when all of the patchbays were replaced and the grounding and lifts were corrected. The intercom was on the fritz because the old cabling deteriorated in some of the wall stations and the foil shield came in contact with the conduit. The 70V was the best. Someone in the scene shop drilled into a CMU wall and tore a hole in a conduit with all the backstage 70V cabling in it. They turned it into a rat's nest and shorted everything out, walked away like nothing happened, and left it that way for several years until we traced out their entire 70v system to find the short.
"Wasn't me, bossman, honest, I didn't see any sparks ..."
 
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