Dull Hum Amp Sound Question

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Hello,

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



Re: Dull Hum Amp Sound Question
On Saturday, 13 April 2019 12:54:34 UTC+1, ABLE1  wrote:
Quoted text here. Click to load it

Main causes are:
loss of screen on an audio input
deteriorating cap/s in amp
deteriorating cap/s in something that feeds the amp
removed earth or chassis connection somewhere.

You can distinguish 2 from 1,3,4 by unplugging all inputs


NT

Re: Dull Hum Amp Sound Question
On Saturday, April 13, 2019 at 9:54:34 PM UTC+10, ABLE1 wrote:
Quoted text here. Click to load it

The noise is probably 50/60Hz mains frequency leaking into an audio input.

It could also be 100Hz power supply ripple.

NT has listed two ways in which mains hum can get into an audio system - lo
ss of screen (or screen connection to ground) on an audio input cable, or a
 lost earth/ground or chassis connection somewhere.

Grounding different bits of an audio system to ground at different places c
an introduce hum - it's not unusual for "ground" at one point to have a vol
t of so mains frequency potential when compared with another ground connect
ion. It shouldn't happen, which isn't to say it doesn't.

Deteriorating reservoir power capacitors in a mains to DC power supply some
where can increase ripple levels - usually 100/120Hz but it can also be 50/
60Hz.

Looking at the audio output with an oscilloscope can help - you can work ou
t the frequency of the hum, which often helps.

--  
Bill Sloman, Sydney


Re: Dull Hum Amp Sound Question
On Sat, 13 Apr 2019 05:29:56 -0700, bill.sloman wrote:

Quoted text here. Click to load it

If he has a scope, checking for ripple on the power supply rails is also  
worth a look.




--  
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
We've slightly trimmed the long signature. Click to see the full one.
Re: Dull Hum Amp Sound Question
On 13/04/2019 12:54, ABLE1 wrote:
Quoted text here. Click to load it

The hum being different in different speakers could be down to their  
different bass responses. It probably is power line 60Hz/120Hz where PA  
speakers have very poor sensitivity.

Your tests have established that it isn't coming through the inputs.  
That leaves the power and output wiring. Your guess that the amplifier  
is failing is probably correct, drying out power supply reservoir  
capacitors being one of the more likely.

You didn't mention checking the output wiring, it is imaginable that a  
poor connection lets in RFI but rather unlikely to cause a steady hum.  
There'd be no harm in checking the output connections even though it is  
only a slim chance.

Also check that the amplifier is actually grounded to a good ground.

My guess is the hum really is power line from an ageing power supply. If  
the power supply has some short hold up time (i.e. it will continue to  
produce an output for a fraction of a second after power off) then it  
may be possible to tell if the hum goes instantly power is cut or  
continues that very short hold-up time. That would help nail down the  
source to the amplifier's power source vs coming in somewhere else.

Finally if the amplifier is inspectable you may get lucky and actually  
see a swollen or leaked power supply capacitor.

piglet


Re: Dull Hum Amp Sound Question
says...
Quoted text here. Click to load it

If you have access to an isolation transformer capable of running the  
amp that might help show up if an earth loop is implicated...

Mike.

Re: Dull Hum Amp Sound Question
On 4/13/2019 8:45 AM, Piglet wrote:
Quoted text here. Click to load it

Quoted text here. Click to load it

Quoted text here. Click to load it



Quoted text here. Click to load it


Ok, so based on the collective wisdom of those responders
the source of the Dull Hum is either the Caps in the Amp itself
or some how the unit lost its ground connection.

To provide some more data, I did check the out going connections
and they are/were tight.

With the previous troubleshooting and the new information above,
what would ALL say the odds are it is that the Amp needs replaced??

50/50     60/40     70/30     80/20

Sadly, I may not have a big choice to start.  Replacing the Amp
will prove or disprove it was the right choice or not.

Is there a test tool or procedure with a Volt/Ohm Meter that I could
perform on the out going speaker lead to give some indication that
the speaker and or wiring is or is not the problem.

Any additional thoughts.

Thanks in advance for any input.

Les

Re: Dull Hum Amp Sound Question

Quoted text here. Click to load it

Tho Amp may be  the problem, but it is repairable.  Replacing the power supply caps is not a big deal.    

It sounds as if you do not have  much experience in   trouble shooting  and repair.   Maybe you  could post where you are and some kind sole might help you.

                                    Dan


Quoted text here. Click to load it


Re: Dull Hum Amp Sound Question
On 4/13/2019 8:26 PM, snipped-for-privacy@krl.org wrote:
Quoted text here. Click to load it

Well Dan, I have been running my Security Alarm Dealer Low Voltage  
company for 29 going on 30 years.  I would say my troubleshooting and  
repair abilities are very good.
However, as I stated in my original post that "I am not necessarily a  
"sound guy" but, it is electronics low voltage".  The key point is I  
rarely get involved with Sound Amps & Speakers.  One challenge I have is  
that I am partially deaf in both ears and it makes it difficult to  
"hear" sounds effectively enough to follow a problem.

I am sure I could de-solder and replace the Caps.  My challenge is
which Caps??  How long can I shut down the paging system in the building
just to tear the amp down not to mention the time to acquire replacement
amps and then install them??

My hope here was to get a hint of what I was guessing was the issue.
I have that hint and at this point I need to investigate further
as to the Model and Specs so I can search out a replacement to do the
job.  Then the downtime will be minimal and can be done on a evening  
when paging is less critical for this 24/7 establishment.

Should it not be the Amp then I will have a bigger task trying to find
the issue elsewhere.

And while typing the above it just hit me that I could pull out some old  
ceiling 70 volt speakers from my storage locker and do a quick test by  
clipping on the amp output. I will need another body with good ears to  
make the test work correctly.

Oh, and to answer your other question I am in
South Central Pennsylvania, USA.

Thanks for reading.

Les

to find someone with good ears


Re: Dull Hum Amp Sound Question
ABLE1 wrote:
Quoted text here. Click to load it


** Afraid that does not count - you are not experienced in audio system trouble shooting, particularly line voltage systems which are a special case.  


Quoted text here. Click to load it

**  Irrelevant, nearly all modern electronics is low voltage.  


Quoted text here. Click to load it

** You MUST get someone to help you, with good hearing and line voltage system experience. STOP kidding yourself  !!!



Quoted text here. Click to load it


** Yeah - right.......  

YOU are NOT being realistic !!
  
Like most folk who know only a little about audio, you imagine it is all really quite simple. Nothing could be further from the truth.


Quoted text here. Click to load it

** Such guessing is the mark of a novice.

Guessing gets in the way of proper trouble shooting procedures -  which you do not know and cannot carry out anyhow with your hearing disability.

Quoted text here. Click to load it

 ** You don't say ....  


Quoted text here. Click to load it

 ** Groannnnn......  


Quoted text here. Click to load it

 ** FYI you are posting on the WRONG newsgroup.

 "sci.electronics.repair " is more suitable.  


  
....   Phil  

Re: Dull Hum Amp Sound Question
On Sat, 13 Apr 2019 20:10:35 -0700, pallison49 wrote:
  
Quoted text here. Click to load it

Yes, where he can expect you to abuse him further there.

Alison is an "electrophobic" - don't listen to him as you can easily do  
this yourself.

The caps in question are hard to miss. They'll be the large ones in close  
proximity to the mains transformer about where the mains lead comes in.  
Just turn the juice off and unplug; couldn't be any simpler.



--  
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
We've slightly trimmed the long signature. Click to see the full one.
Re: Dull Hum Amp Sound Question
On 14/04/2019 11:32, Cursitor Doom wrote:
Quoted text here. Click to load it

Except for all those times when the really big bulk reservoir caps are  
just fine and it is the smaller ones in supply decoupling the preamp  
that have failed :)

piglet


Re: Dull Hum Amp Sound Question
Quoted text here. Click to load it

Such things keep life interesting. Now that this thread's drifted to
dark humor, allow me to embellish my first followup, which talked about  
the direct connection of a twisted pair to an audio jack of a phone  
system. Neither an amp nor a passive balun was installed.
    Phone guys usually excel at pulling twisted pair cable. Except when
they leave one end of a cable coiled up and unterminated in the plenum,
for the next guy (me) to discover. :)

Thank you, 73,

--  
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
We've slightly trimmed the long signature. Click to see the full one.
Re: Dull Hum Amp Sound Question
On Sun, 14 Apr 2019 11:47:42 +0100, Piglet wrote:

Quoted text here. Click to load it

Would that cause the symptoms reported, though?



--  
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
We've slightly trimmed the long signature. Click to see the full one.
Re: Dull Hum Amp Sound Question
On 14/04/2019 16:24, Cursitor Doom wrote:
Quoted text here. Click to load it
Could do. The main rails, filtered by the BFCs, may happily have 0.5V or  
more ripple at idle but the input stages demand a much smoother supply  
and are fed by RC decoupled quiet rails. Those BFCs tend to last much  
longer in my experience than the little cheapies!

piglet


Re: Dull Hum Amp Sound Question
Cursitor Doom, Lying Troll wrote:
Quoted text here. Click to load it


** Huh ?  More rabid insanity from the resident troll.  


Quoted text here. Click to load it

** Having snipped the entire context - the fuckwit, CD lying troll pretends I posted something I did not. Again.  

Wot a pile of putrid shit he is.  



....   Phil  


Re: Dull Hum Amp Sound Question
On 4/14/2019 5:58 AM, snipped-for-privacy@gmail.com wrote:
Quoted text here. Click to load it

  Just because you are an expert having great knowledge in the audio  
field, doesn't mean you need to be an expert with great knowledge to  
replace defective power supply caps in an amplifier.
  I did that my first job out of a gas station fuel pumper at 17.
  Starting with the Dynaco 120.
Now as to whether that fixes the problem is still in question but
  with your HELP, he might be able to figure out if the odds are most in  
favor of bad caps.
  What do you say, do you want to help or just bitch.
                      Mikek

PS, if you decide to deride and berate me, try to use something new that  
will at least entertain myself and fellow posters. Thanks

Re: Dull Hum Amp Sound Question
amdx trolling fuckhead wrote:

Quoted text here. Click to load it

 ** Find where I said otherwise and POST under it.  

    You won't be able to - you stupid, ASD fucked nut case.  

    

.....   Phil



Re: Dull Hum Amp Sound Question
On 4/14/2019 10:27 PM, snipped-for-privacy@gmail.com wrote:
Quoted text here. Click to load it


OK Assuming I'm wrong, I haven't checked,

does that mean you are know going to pitch in and help?




Quoted text here. Click to load it

Tired old Same O same O.
  Really now, I ask for better*, step up your game Phil!

* even though you snipped it.


Quoted text here. Click to load it


Re: Dull Hum Amp Sound Question
On 4/13/2019 11:10 PM, snipped-for-privacy@gmail.com wrote:
Quoted text here. Click to load it

Dearest Phil,

I had typed a very nice and pleasant detailed response to you message.
Sadly, I clicked on the wrong button and it was lost..... to a deep
dark hole and will never return.  So much for being nice.

I was going to try and retype it all again but, I then figured whats the  
point.  You would only find a way to have the last word anyhow.

And 'Yes', I did mistakenly type to the wrong newsgroup.
Whoops!! My bad.

I would like to thank all those that have responded to my quest with  
some insight on the problem.  I will move forward by getting the
Mfg. and Model number of the Amp.  Hopefully I can then find the manual  
and maybe the schematic. Might even be lucky enough to get the specs
on the Caps that would be installed.

BTW the Amp is mounted on a wall in a small closet.  When it was  
originally installed it would have been easy to access.  Now, there is a
Network rack, router, PC, etc. in the way with makes it extra  
challenging.  Evolution is not your friend.

To all those that are reading and not posting my hope is that you will  
benefit from this thread as well. Over the years I have gleaned added
bits of information from various newsgroups just in reading the  
postings.  It has all been a silent bonus.  Enjoy the benifits!!

Again thanks to all for the assist and insight.

Have a good week.

Les



Site Timeline