Problem: Why is my speaker singing?

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percussion boy
carpal tunnel
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Problem: Why is my speaker singing?

Post by percussion boy » Wed Nov 14, 2012 7:25 pm

Wanted to get the board's take on a speaker problem, since I'm getting no response from tech support.
The patient: Old-style Event 20-20 BAS powered monitor
Precipitating event: After years of not using this speaker, I hooked it up to a +4 connection from Audiofire Pre8 interface>

* Ring-tip-sleeve cable
* I believe speaker and interface are happy balanced or unbalanced.
* Power plugs of interface and speaker are two-pronged, and were plugged into same grounded power strip.

I played a mono mix through the speaker at moderate volume.
Symptoms: Speaker played music normally for a maybe a minute, then a LOUD STEADY LOW FEEQUENCY HUM began and continued.

* This was not background-volume ground hum -- this hum was louder than the music.
* The speaker has hummed on power-up ever since. Doesn't matter if anything's connected to it or not.
* Changing the input gain trimmer on the back of the speaker doesn't change hum's volume.

Diagnosis? I assume this will hurt . . . but hoping there's some obvious stupid fix . . .
"The world don't need no more songs." - Bob Dylan

"Why does the Creator send me such knuckleheads?" - Sun Ra

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Snarl 12/8
ghost haunting audio students
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Post by Snarl 12/8 » Wed Nov 14, 2012 8:11 pm

I'm a total hack at electronics, but this sounds like there's a bad cap somewhere (power supply?!) that's supposed to be filtering out AC from the power. You said you hadn't used these in a while? How old are they? Caps can go bad. Either that or a fucked ground. Open it up and poke around carefully with a chop stick and see if poking anything in particular makes the problem better or worse. Like I said, I'm a hack. Someone will have a more logical troubleshooting procedure. Also, look visually for either bulging, burnt, or leaking caps.
Carl Keil

Almost forgot: Please steal my drum tracks. and more.

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Post by elbows » Wed Nov 14, 2012 9:34 pm

+1 filter cap.

can you even do +1's on these kinds of things?

I just agree with Carl.

Probably a very simple fix if you're handy with a soldering gun and an electronics parts supplier (Digitech, Mouser, etc.).

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carpal tunnel
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Post by joelpatterson » Wed Nov 14, 2012 10:25 pm

Did a brief search... does this help?

My life goes on in endless song above earth's lamentations,
I hear the real, though far-off hymn that hails a new creation.
Through all the tumult and the strife I hear it's music ringing,
It sounds an echo in my soul.
How can I keep [my speaker] from singing?
Mountaintop Studios
~The Peak of Perfection~
Petersburgh NY 12138

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Darlington Pair
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Post by Darlington Pair » Thu Nov 15, 2012 9:58 am

I had a monitor blow and hum once during a mixdown and it's because I lost a 100 ohm resistor and a zener diode on my +15 volt rail causing the power amp to go all unbalanced and throw negative DC across my speaker (sucking it in) if it sucks in or throws out then this might be your problem. Just remember that DC is REALLY bad for speaker coils and it doesn't take much to cook one, I got really lucky. I was even luckier because I actually had the right zener diode in my parts bin.

I would disconnect the speaker and look for DC across the terminals. Then get a schematic and start making sure all of your power supply voltages are right. Always start at the power supply, if it's a bad filter cap causing the hum it is also a power supply problem.

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