New to constant voltage paging systems.
I have a customer with a Bogen C100, many speakers.
It has developed a loud popping and crackling noise from the speakers after it is on for 30 minutes or so and it is idle. Paging does not trigger it. Nor does it stop it.
The noise does not change with the knobs on the front. It seems to be worse on the 70V circuit, as once it starts doing it, it never stops. On the 25V circuit it will come and go.

I have it on the bench at the shop right now with one horn hooked up, and have only heard a few pops out of it.

It sounds just like a bad volume control potentiometer would sound on any other audio device. BUt again, twiddling the knobs does not affect it at all on this Bogen.

What is the typical cause of the popping noises when the system is idle? Is it a load issue?

Edit. I did relocate the unit to a different room to rule out power. The room it was in also had a lot of high draw devices in it and was not climate controlled, so I figured that couldn't be good for it.

A couple of questions. Is it running at 70volts or 25 volts or both? When you say many speakers how many is that? The first thing I would do is check the total load the amp had on it. A C100 is 100 watts. I would make sure the total draw is less than that.

It was running on 70. I switched it to 25 just for hahas. Still did it, except it went from doing it constantly to the noise coming and going.

I'm not sure how many speakers are on it, didn't count. I just assumed it was going to be a bad amp, but where it doesn't do it on the bench, now I'm not too sure. Of course it loaded differently on the bench with only one horn instead of the many speakers.

I'm just looking for the most common cause of popping and crackling so I can start there.

I would measure the entire wattage draw using an impedance meter. It could be someone added speakers and you are now over 100 watts or an 8 ohm speaker was installed by mistake or one of your speaker cables has a leg going to ground. Personally I would start by measuring the total draw and go from there.

So I've read that I can use a regular DVOM to measure AC amps and voltage and work the watts from there...

Then check what the speakers are set to and see if it makes sense. I don't have the impedance meter.

If it's only a few speakers go around and check the taps on them and add them ll up. See if they're tapped for 25V or 70V. Make sure no one slipped a speaker without a transformer in.

If you've got too many speakers to do this comfortably, get an impedence meter and test the line. If it's under 100 Watts (and it should be under 80) then play music over the speakers. Walk around and see if one or more speakers sounds too loud or too low. Check their taps.

Work it from there. Check your connections and make sure they're mechanically sound. If necessary split the system in half. Run half the speakers (with music or test tone) through them and see if the problem is localized to one section or the other.

Let us know what you find.

Sam

Bad amp. End of story.

-Hal

That's what I'm thinking, but it's quiet as a mouse on the bench. Again, though, there's only one speaker attached.

So far, no one has come forward with the most likely cause of popping noises on this type of system. That seems odd.

So far the consensus seems to be check the entire system to ensure that the amp is not over loaded. Does being over loaded cause popping noises from the speakers?

I agree with Hal.

If you are really into bench teching, check the output section of the board for broken, loose solder joints, damaged looking components ie: output power resistors, transistors, etc...

If it is mostly solid state/chips, just replace it.

So I'm on site now. 26 speakers. No volume controls that I can find. Checked voltage and amperage on the 70 and the 25. Volume turned all the way down on the amp, 1 kHz test tone. 70: 24.8 v 1.18 amps for 29.3 watts. 25v: 10.5 volts .4 amps for 22 watts.
Still waiting for the amp to heat up to see if the problem occurs again.

Do any of you suppose that the humidity was too much for this thing being in that outside closet and maybe it just needed to dry out for a bit? Not making a peep now.....

What do you think putting the speakers on the 25 volt output is going to prove? It's just another tap on the output transformer. And your voltage/current measurements mean nothing, it ain't that easy to measure wattage else why would you need an impedance meter?

If you are absolutely sure that this is not coming from an input or dirty controls are the culprit, if you still think this intermittent problem occurs when the amp heats up it's the amp. And no, overloading the amp won't cause this kind of problem. Repair or replace.

-Hal

Definitely not from an input, as the only thing connected to it is the phone system, and it does it even if you're not paging.

As far as "proving" anything by putting the speakers on the 25 volt side, I was thinking the fault might only exist on the 70 volt side. As I stated, this is my first time trouble shooting these, so you'll have to bear with me as since I didn't design the thing I don't know any better.

Last time I checked watts is a function of Volts times amps. I figured since I don't have the proper meter, this would at least tell me if there was something really wrong with the draw if it was ridiculously high for 26 speakers. Which I'm assuming are tapped at 1 watt, since the one i pulled down was, and the math makes sense.

I guess this is not the way to do it, and I'm sorry if I offended your delicate sensibilities.

Thanks for at least one useful(?) piece of advice in that too much current draw won't cause the issue!

Using a multimeter to check those values won't tell you anything really. The 70V and 25V are RMS values and even if you have a true RMS multimeter it won't provide the correct reading (multimeters are designed to provide the correct RMS reading only at 60hz, although some of the cheap ones do give a close reading). Without an impedance meter, the next best this to use is an O'scope and calculate the RMS value.

The only way the values are going to be correct is when you input the test signal at the correct level and then take your reading. You'll never see an actual 70V or 25V signal on the lines as an example the last system that I worked on had a changing voltage reading around 4V.

Having 26 speakers can mean you are using 26 watts or up to 360 watts. It's the tap setting that you need to figure out if you don't have an impedance meter.

Here are a couple of good sources that will give you a better understanding on how this works.

Guide to constant-voltage systems
A Handy Tool for Measuring “Constant Voltage” Sound System Impedance and Calculated Power

doing a google search for 'testing a 70v system using a multimeter' will provide you with a wealth of information.

CAUTION - As with all google searches there is a lot more junk than useful stuff so be sure to cross-reference what you find with other sources

Hey, if you don't like the advice here I'm sure there are other places that might be more to your liking and won't hurt your feelings.

-Hal

No hurt feelings here, I was just busting your you know whats a little.

At any rate, this thing has been up and running for 3 days now with no reports of failure. So maybe it was environmental.

Thanks for the links! You're right about there being a lot of different crap online about these systems. It's hard for someone new to these systems to differentiate between good and bad advice. Thanks again for some links from someone who can verify the reliability of the information presented.