PR12P hum problem

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WayneC
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PR12P hum problem

Post by WayneC » Sun Apr 21, 2013 10:03 pm

Hi: I have a PR12P speaker I use for a monitor, or for stand alone (single) speaker PA use, and ever since I have had it (bought it used), it has been humming whenever I feed a signal in to any of the channels from any line level device (only a microphone in channel 1 is quiet. The rest of the channels are 1/4 inch inputs. Even a feed from a mixer board into the quiet XLR channel 1 input makes the same hum. I have tried many different and known to be good mixers, and the hum always shows up.

I put a spectrum analyzer on the hum and found it to be mainly at 315 hertz with a lower secondary spike at 200 hz and 125 hz.

If I put an inline hum eliminator in the input line, then all is quiet, and it works great.

I am on the verge of bolting my hum eliminator box to the top of the speaker, ot finding a way to put it inside the box.

Any suggestions how I could solve this without the extra box of the hum eliminator to lug around. Could the AC power supply wires be backwards, or something? I am good with a soldering gun.

Thanks in advance. - Wayne

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Peter Richter
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Re: PR12P hum problem

Post by Peter Richter » Sun Apr 21, 2013 11:02 pm

hum from earth loops etc is usually at 50 or 100 Hz (or is it 60 and 120 over there?)
What does your hum eliminator comprise of?
Exactly what leads are you using from your mixer to the speaker?
Peter Richter
Brisbane Audio Services - Sound and Lighting for Any Event
Brisbane, Australia
http://www.brisbaneaudioservices.com.au

Josjor
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Re: PR12P hum problem

Post by Josjor » Mon Apr 22, 2013 6:26 am

I guess my first question would be if it has done it since new, why didn't you take it back to the dealer for repair/replacement?

If it has multiple inputs then it's the older model? (The current one only has one input.) Did you register it at the factory? If so, then you have a five year warranty. If it's out of warranty and you want to tackle it yourself, I'd check for a loose connection on the back of the input plate.
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Don't believe me. I'm just guessing.
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WayneC
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Re: PR12P hum problem

Post by WayneC » Mon Apr 22, 2013 8:18 pm

Hi guys:

Thanks for the replies. I am in Canada, so our power is 120volt 60 hz.

Yeah, it must be an older model as it has 3 inputs. One is xlr and the other two are 1/4 inch.

I have tried all kinds of cables from balanced to simple guitar cords with only tip and sleeve. No change. It just is silent as a mouse until you plug in anything other than a microphone then she hums away. Cannot turn the gain knob above 2 or the hum is so bad the speaker is useless. All my cords are good as I have a cord tester, plus I buy high quality cords with neutrik ends.

Yet plug in a hum eliminator (isolation coil box such as made by ART or EBtech) and she is quite as a mouse with the very same equipment. I use these same boxes to cut the hum that sometimes shows up when I use my VSX26 crossover with older amps.

I plan to try using the speaker on battery power with an inverter and see if the hum is still there.

I won't sell this speaker the way it is. So, I will just use it with a hum eliminator from now on, unless someone can tell me how to solve it.

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Peter Richter
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Re: PR12P hum problem

Post by Peter Richter » Mon Apr 22, 2013 10:05 pm

do you have more of the same type of speaker and it does the same?
Do you have other types of powered speaker and it does / not do the same?
Peter Richter
Brisbane Audio Services - Sound and Lighting for Any Event
Brisbane, Australia
http://www.brisbaneaudioservices.com.au

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Peter Richter
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Re: PR12P hum problem

Post by Peter Richter » Mon Apr 22, 2013 10:05 pm

are you sure about the 315 hz? - thats not hum that would be more like a tone
Peter Richter
Brisbane Audio Services - Sound and Lighting for Any Event
Brisbane, Australia
http://www.brisbaneaudioservices.com.au

WayneC
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Re: PR12P hum problem

Post by WayneC » Tue Apr 23, 2013 7:07 am

I checked the frequencies with 2 different I-Phone RTA apps. I will go back and retest with my Phonic PAA6 unit to make sure, but based on my use of the Iphone and Phonic units together in other venues, the accuracy of the Iphone is quite good.

I only have one of these PR12P units, so comparison is not possible. One of my test devices is a digital piano that I borrowed from a local community choir for a church service, and yes, the speaker hummed away again. Different cords were used, also.

I am not new to sound equipment, and have an inventory of gear. It just puzzles me why every once in a while I come across a piece that just cannot be used without a hum eliminator. I have a system for dealing with questionable cord when encountered during a gig, so it cannot be a bad cord.

I do a lot of odd gigs including outdoor Canada Day celebrations, Corporate events, and even large funerals.

My main system is:

5 of SP1g tops (one is spare or drummer monitor)
4 of SP218

1 of CS1400
2 of CS2000
2 of CS3000
VSX26
a dozen EQs
several compressors

Monitor rig is:

4 of SP115MX
2 of PV1200
1 of CS800x4
4 EQ channels 31 ea
VSX48

Misc and Backup gear

4 of Impulse 200
XR1212 powered mixer
IPR3000 with DSP

Josjor
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Re: PR12P hum problem

Post by Josjor » Tue Apr 23, 2013 8:08 am

As I suggested, take off the back and take a look around for a bad solder joint or........?

I will say that there was an issue with a few of these early models: If you drove them hard enough to make DDT activate once, it would lock up and either not work or produce a squeal until you shut down the power. Then all was well......until you hit DDT again. Perhaps something with that circuitry?

It looks like you have enough gear that you could probably survive without it for a bit. As such, I'd send it to a tech for repair if I were you. If you have to ship it, you can remove the amp/mixer section and ship it alone to save costs.
www.yandasmusic.com
Don't believe me. I'm just guessing.
Neutiquam Erro

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Peter Richter
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Re: PR12P hum problem

Post by Peter Richter » Tue Apr 23, 2013 2:34 pm

I agree with Mr Josjor, but just one last thing to try before you send it...
Using the XLR input here... See if the plug you put into the input connects the cable sheild (Pin 1) to the actual earth of the speaker via the shell of the XLR plug. If so, remove the link inside the plug that is causing that and try it again. (some manufactured leads come with the shell earthed and some don't)
Sometimes you might actually have to disconnect pin 1 altogether at the amp end. If you do that then mark the lead as such so you done end up using it for a mic or something else.

(I'm just dis-regarding the frequency aspect for now)
Peter Richter
Brisbane Audio Services - Sound and Lighting for Any Event
Brisbane, Australia
http://www.brisbaneaudioservices.com.au

WayneC
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Re: PR12P hum problem

Post by WayneC » Tue Apr 23, 2013 10:25 pm

Thanks, I will take a closer look at it this weekend, maybe.

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