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Paging Speaker With Dull Hum

 
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Old 04-13-2019, 06:55 AM   #1
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Paging Speaker With Dull Hum


Hello all,

I have a customer with a paging system in their building.
Over the past few days it has been noticed that there is
a Dull Hum coming over the speakers. Some louder than others.

I am not necessarily a "sound guy" but, it is electronics low voltage.
I don't have the mfg. model at the moment but it could be a Bogen.

> Maybe a 250 Watt at 70 volt with (1) output.
> Speakers have various outputs off a transformer at each speaker.
> Tapped at maybe 1/4 to 3/4 watts.
> All are in hallways in a 4 story building for general announcements
off a phone system paging output.
> Has 3 used inputs
> Est. 20 years old

So far I have tried a little troubleshooting as follows.

> Power (twice) cycled for about 10 seconds. No change
> Removed each input one at a time. No change
> Removed all (3) inputs at same time. No change

I am guessing it is the amp going south.

But was wondering if there are other things that could cause
this Dull Hum on the speakers?? Needless to say if I had a
second Amp I could just swap it out and see if the problem
persist. However, that is not the case.

Any insight or suggestions would be appreciated.

Thanks,

Les
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Old 04-13-2019, 08:08 AM   #2
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Re: Paging Speaker With Dull Hum


Sounds like a bad filter cap in the power supply. Does anyone still do component-level repairs these days?

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Old 04-13-2019, 09:00 AM   #3
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Re: Paging Speaker With Dull Hum


From car audio, I know that a signal wire too close to a power wire can pick up noise.


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Old 04-13-2019, 11:40 PM   #4
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Re: Paging Speaker With Dull Hum


Unplug Every little Power supply that in plugged into any circuit on the main panel,, the ones on the same breaker first.

I had a bad 12VDC supply on my router/wireless modem that "poisoned" the 120 VAC circuit....

Run down the grounds to see they aren't loose or a little 'dry' high resistance...

Bad capacitor filter on amp power supply?
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Old 04-14-2019, 12:08 AM   #5
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Re: Paging Speaker With Dull Hum


Plenty of maybes.

Start at the speaker where it is loudest and work back. AV voltage checks with no input signal to the amp.

First guess that could explain it being louder on some than others is you're getting AC fed in on one of the branches.
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Old 04-14-2019, 11:41 AM   #6
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Re: Paging Speaker With Dull Hum


Thanks for the input on this issue.

At this point I need to do some more diagnostic troubleshooting.

Need to get the Mfg. and Model number off the Amp.

Actually more work that I didn't need at this time.

Thanks again.

Les
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Old 04-14-2019, 12:09 PM   #7
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Re: Paging Speaker With Dull Hum


remove the outputs and test with a known good speaker
if good then reinstall outputs one at a time- my be a grounded speaker line
also test with known good mic or switch to aux or radio

I used to repair those in schools a while ago but forgot more than I remembered about Bogen and Soundolier
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Old 04-14-2019, 02:48 PM   #8
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Re: Paging Speaker With Dull Hum


Quote:
Originally Posted by rrk View Post
remove the outputs and test with a known good speaker
That is on my list to see what happens and then go from there.

Thanks,

Les
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Old 04-14-2019, 03:31 PM   #9
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Re: Paging Speaker With Dull Hum


Quote:
Originally Posted by ABLE1 View Post
That is on my list to see what happens and then go from there.

Thanks,

Les
Always have to go back to square 1 and start fresh, you have idea who was messing around with it.

I once was working on a F/A in a big school and found that for several years nothing was wired to it on the detection side except 1 pull station where they conducted the monthly fire drills from. Over the years someone played with the wiring to get it out of trouble condition. They had to have firemen stationed in the hallways until it was repaired.
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Old 04-14-2019, 03:36 PM   #10
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Re: Paging Speaker With Dull Hum


If you disconnect all inputs and it still hums try a ground cheater. If the hum stops you have a couple options.

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Old 04-14-2019, 04:06 PM   #11
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Re: Paging Speaker With Dull Hum


Quote:
Originally Posted by Inner10 View Post
If you disconnect all inputs and it still hums try a ground cheater. If the hum stops you have a couple options.

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Hi Inner,

As typed in the first post I unplugged each and all inputs and no change.

As for the "Ground Cheater", are referring to one of those plugs that
just has the male hot and neutral on one side and female hot neutral and ground on the other??

If yes, and if I can find one somewhere in my shop and if the hum goes away what are my "Couple of Options."

Maybe??
Option 1 -- Leave alone and walk away. Nooooo!!
Option 2 -- Please fill me in..........................

Thanks!!

Les
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Old 04-14-2019, 04:14 PM   #12
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Re: Paging Speaker With Dull Hum


Quote:
Originally Posted by ABLE1 View Post
Hi Inner,



As typed in the first post I unplugged each and all inputs and no change.



As for the "Ground Cheater", are referring to one of those plugs that

just has the male hot and neutral on one side and female hot neutral and ground on the other??



If yes, and if I can find one somewhere in my shop and if the hum goes away what are my "Couple of Options."



Maybe??

Option 1 -- Leave alone and walk away. Nooooo!!

Option 2 -- Please fill me in..........................



Thanks!!



Les
First does the amp use a 3 pin cord with ground or a polarized double insulated? If it's the latter then get a new amp. If it's the former and it's and IEC then snap off the ground with a pair of pliers to test. If it's built in then make your own ground cheater or buy one.

If the ground cheater works, stops the hum, and when removed it hums with no other possible devices connected that could be making a ground loop....tell your client they can put the cheater on themselves or you will have it repaired/replaced.

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Old 04-14-2019, 04:27 PM   #13
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Re: Paging Speaker With Dull Hum


Well it has a ground on the plug. I will at least give the a quick test.
I know I have a "Ground Cheater" somewhere.

Thanks for the tip.

I have a 70 volt ceiling speaker that I am going to connect
to the output to see if the speaker wiring could be the problem.

Will know more later.

Thanks,

Les
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Old 04-15-2019, 05:07 PM   #14
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Re: Paging Speaker With Dull Hum


OK, as a follow up on this Amp challenge the following is
new information.

> Found Date of Install >>1991<< that makes it 28 years old.
> Amp is a University Sound Model# 1110 100 Watt Amp
> Temporarily installed a Ground Lift Adapter at power plug. No Change
> Removed output leads and connected a single speaker No Change

At this point I think it is safe to say that the Amp and/or Caps in the
Amp are defective. It matters not, since a new replacement is the
obvious next course of action. On either end on the heatsink there are
a couple of transistors 2N5881. The Caps are not visible, so it would
need to be disassembled. I will do so after I remove and before I place
in the nearest dumpster at the recycle center.

That is unless someone want to pay for shipping and you can
play with it. Otherwise it had a good life.

The next question is other than the added co$t is there a benefit to
installing a larger wattage amp?? Meaning that it will work with less power and will last longer and if necessary adding additional load will not be a huge challenge. Thoughts??

Thanks to all of those that assisted with good help and insight.
All is appreciated.

Have a good rest of your week.

Les
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Old 04-15-2019, 05:50 PM   #15
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Re: Paging Speaker With Dull Hum


Quote:
Originally Posted by ABLE1 View Post
OK, as a follow up on this Amp challenge the following is

new information.



> Found Date of Install >>1991<< that makes it 28 years old.

> Amp is a University Sound Model# 1110 100 Watt Amp

> Temporarily installed a Ground Lift Adapter at power plug. No Change

> Removed output leads and connected a single speaker No Change



At this point I think it is safe to say that the Amp and/or Caps in the

Amp are defective. It matters not, since a new replacement is the

obvious next course of action. On either end on the heatsink there are

a couple of transistors 2N5881. The Caps are not visible, so it would

need to be disassembled. I will do so after I remove and before I place

in the nearest dumpster at the recycle center.



That is unless someone want to pay for shipping and you can

play with it. Otherwise it had a good life.



The next question is other than the added co$t is there a benefit to

installing a larger wattage amp?? Meaning that it will work with less power and will last longer and if necessary adding additional load will not be a huge challenge. Thoughts??



Thanks to all of those that assisted with good help and insight.

All is appreciated.



Have a good rest of your week.



Les
You can't put in too big of an amp, and that's a little guy to begin with. Just grab whatever you can source locally, you are spoiled for choice and that type of amp is reliable as all hell....and they are pretty cheap.

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Old 04-15-2019, 06:33 PM   #16
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Re: Paging Speaker With Dull Hum


If you can even find a bench tech above board-jerking level to repair it with a $1.19 component, the labor charge will likely be multiples of what a replacement will cost. So yeah, RIP.

Whether to go with a heftier replacement depends on the likelihood of increased load in the future. Unlikely this one failed from working too hard; its time was just up. I've seen electrolytics dry up way quicker than three decades.
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Old 04-15-2019, 06:51 PM   #17
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Re: Paging Speaker With Dull Hum


Quote:
Originally Posted by Tinstaafl View Post
If you can even find a bench tech above board-jerking level to repair it with a $1.19 component, the labor charge will likely be multiples of what a replacement will cost. So yeah, RIP.

Whether to go with a heftier replacement depends on the likelihood of increased load in the future. Unlikely this one failed from working too hard; its time was just up. I've seen electrolytics dry up way quicker than three decades.

Hi Jerry,

I am quite sure a cheap repair can be made. Would not even know
what the actual value of the Cap would be or how long it would take
to get it. Much easier to swap in a new unit.

Since it has lasted 28 years it was not undersized.

IF I had time............... It might interesting to see what
someone would pay on a eBay auction.

Have a good week.
So far my score is just one Monday this week.

Les
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Old 04-15-2019, 07:00 PM   #18
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Re: Paging Speaker With Dull Hum


After 28 years it's time was up
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Old 04-15-2019, 07:10 PM   #19
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Re: Paging Speaker With Dull Hum


Quote:
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After 28 years it's time was up
Actually it is still working quite well on a daily basis.

Pages come over very well when made. It is just this
continuous drone or dull hum that is the first sign of
a inevitable demise.

Maybe it is the sound of death..........................
Scary........................
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Old 04-15-2019, 07:17 PM   #20
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Re: Paging Speaker With Dull Hum


Probably take 25 minutes to fix it.

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