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sethb
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I volunteer at a public library that has an Anchor AN-130 PA. When I plug the audio line from the DVD/CD player into the mic input, I get what sounds like 60-cycle hum. The more I turn up the volume, the louder the hum gets. But with no connection, no hum (so the unit itself is fine).

I'm using a grounded three-prong power cord, so I can't reverse the plug to see if that solves the problem. And because it's a three-prong plug, I probably shouldn't have this problem in the first place. My only other thought is that perhaps the outlet itself is improperly wired and not grounded correctly?

Any ideas would be appreciated. SETH
"Watch the Professor!!" -- Al Flosso (1895-1976)
"The better you are, the closer they watch" -- Darwin Ortiz, STRONG MAGIC
ClintonMagus
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Are you plugging the DVD/CD player into the "Mic" input or the "Line" input?
Things are more like they are today than they've ever been before...
sethb
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It's going into the Mic input. I tried the "line" input, but the signal from the player wasn't strong enough, so I had to use the "mic" input.

I also got the same hum (but not as loud) when I did use the "line" input.

Now you've got me thinking -- I wonder if the problem is actually with the DVD player, and not the PA?? I hadn't considered that possibility. SETH
"Watch the Professor!!" -- Al Flosso (1895-1976)
"The better you are, the closer they watch" -- Darwin Ortiz, STRONG MAGIC
ClintonMagus
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Sounds like a bad ground in either the player or the cable.
Things are more like they are today than they've ever been before...
sethb
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OK, thanks VERY much for the lead!

I will try a different outlet, and also try a different DVD player. The unit the Library uses works OK but is about 7 years old (combo VHS/DVD unit). I had never considered the player as a possible source of the problem.

As I always say, I'm a magician, not an electrician! Smile SETH
"Watch the Professor!!" -- Al Flosso (1895-1976)
"The better you are, the closer they watch" -- Darwin Ortiz, STRONG MAGIC
Kline
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Seth,
There are a couple things to try -
1. Do not plug the Anchor system and the DVD player into the same outlet.
2. What is ther mic inout ? ( 1/4" or xlr ? )
- since it is a mic input, you might want to try a DI box with a ground lift
3. What type of cable are you using ? if it s a 3 wire ( red, white and yellow plugs ? ) try to by pass that option and use "single" lines for the audio

This should help - hopefully - iut is hard to determine the cause without seeing the set up
Please don't hesitate to email me with any questions
S
Steven Kline
<BR><BR>www.stevenkline.com
<BR><BR>www.stevenklineproductions.com
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Fitz
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You may also want to try a ground lift, it will take the 3 prong Edison plug and convert it into a 2 prong with no ground. They will usually cost you about a buck at Wal-Mart or Home Depot. It's always good to have these when your doing sound.

Fitz
I have a daily web show all about magic at http://FitzMagic.info
g0thike
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Um, Direct Box. Problem solved.
Kline
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That's what I said ! Smile
ha ha
Steven Kline
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Dan McLean Jr aka, Magic Roadie
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Quote:
On 2009-11-10 16:21, wizard_of_oddities wrote:
You may also want to try a ground lift, it will take the 3 prong Edison plug and convert it into a 2 prong with no ground. They will usually cost you about a buck at Wal-Mart or Home Depot. It's always good to have these when your doing sound.

Fitz

Do NOT try an AC (power) ground lift. It's unsafe, and, in many places, illegal. The AC ground is there for safety. The grond lift on a direct box lifts the audio ground, and not the AC ground. A signal ground lift, like what's found on a direct box, is 100% safe. Try what Steve Kline has posted, and please tell us how you've made out.
Dan McLean Jr
sethb
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Thanks to all for your ideas. To answer your question, the mic input is a standard 1/4" jack.

Now I have a question -- what is a direct box? SETH
"Watch the Professor!!" -- Al Flosso (1895-1976)
"The better you are, the closer they watch" -- Darwin Ortiz, STRONG MAGIC
James_Lee
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silverking
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Have you tried different connection cables from the DVD player to the PA?

I'm with Dan, lifting grounds is deadly, don't do it.
There have been many bodies in the morgue over the years as a result of an uniformed sound man sticking a ground lift on a piece of gear, rather than troubleshooting the problem.

Rather than keeping illegal ground lifts in your "fix-it" kit, better to keep spare cables (duplicates of the ones you actually use) and a couple of D.I.'s. A simple plug-in AC analyzer (with the three lights on it, showing that the wall plug is wired properly) is also a good item to have.
Finally, a multi-plug cable tester is priceless in your kit.

Finally, have a trouble shooting plan:

In your case that plan would assume (based on what you've told us) that the Anchor itself (when plugged in) doesn't hum.
Then connect the audio cables from the DVD player to the Anchor,
If you then get hum, the hum is likely a result of either the DVD player, or the connecting cable.
Replace the connecting cable, if the hum is gone it was the cable, if it's still there then it's not the cable, and likely focused on the DVD player.

Connect a different device (DVD player) to the Anchor with the original cables, if the hum is gone it was the DVD player, if the hum is still there it indicates a potential problem with the actual building AC, or more likely, a problem with how you've interfaced your equipment with the building AC.

Make sure the DVD player and the Anchor are on the same AC circuit (this often requires an extension cord).
(For testing purposes, you can just place them side by side)

The key to troubleshooting audio is to have a linear plan, and stick to it. That usually (not always, but usually) will get you to a point where you find the culprit with 100% confidence. That linear process usually attempts to start at one end of the signal chain (work from one end to the other), and works it's way in a logical manner through the entire chain.
Fitz
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I didn't realize ground lifts were so bad. What should I do when I'm in a venue I have no control over and it has "dirty power" the ground lift works but I guess is not an appropriate solution? My situation is not a permanent install but a one-nighter.

As far as the Anchor AN-130, from what I remember they have RCA inputs on the back. You may want to try different RCA cables from the DVD player to the RCA inputs on the speaker. (As suggested above)

Thanks,
Fitz
I have a daily web show all about magic at http://FitzMagic.info
silverking
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Fitz, the term "dirty power" isn't really an accurate one for the kinds of hook ups we're talking about in this forum.

Although it's not impossible to get onto the same circuit as a washing machine, or a big fan with bad brushes (which could create some noise in your PA) it's very unlikely it would cause a 60 cycle hum.
In a case like the above, I'm afraid the only solution is to seek out a different, and "clean" circuit (this is where a few extension cords come in handy).

60 cycles is far more likely to be a grounding issue as opposed to a "dirty power" issue.
"Dirty power" is more often something to be worried about when hooking up a dedicated distribution system via a 3-phase tie-in and Cam-Loks, which is essentially creating a complete temporary power service.
Because it's not a permanent install, and because there are so many variables and temporary cables involved, it's easy to create major issues that can be a huge pain to solve...........but pros don't lift AC grounds.

But most importantly, an AC ground lift on a one nighter is just as likely to kill you as an AC ground lift on a permanent install......all it needs is a millisecond where it decides that your body is the ground.

If you lift the AC ground with a "cheater" plug, then your ground-lifted gear begins seeking a new ground......and if it picks you, you're treading very close to the emergency ward, or the morgue.
Fitz
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Thanks for the info! In addition to your suggestion I think I may have found another solution to my problem...

Sincerely,
Fitz
I have a daily web show all about magic at http://FitzMagic.info
rattman
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I agree you would not want to lift the AC ground but using a DI box with a ground lift is completely different and is commenly used by the "pros" to resolve hum in the lines. The problem now days is a lot of new equipment like laptops do not use a groud plug so there is a difference between the ground level of the laptop and the mixer and therfore a hum can develop using a direct box with ground lift resolves the problem.
sethb
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OK, I finally had a chance to connect the Anchor PA to a different DVD player at a different AC power outlet. I also used a different patch cord to connect the DVD audio to the PA. I figured this would certainly solve the problem -- but surprisingly, it didn't.

When I turned on the PA alone, with no external connections, I got a faint hum with the volume up about 1/3. Plugging the DVD audio line into the MIC input made a higher-pitched and louder hum. Plugging the same DVD line into the LINE input gave me a slightly louder hum, at the original lower pitch.

So now I am completely confused. However, if I can solve the hum problem with a $30 direct box, that will be cheaper than dragging the whole thing to a tech. So that's my next step, unless anyone has a better idea. SETH
"Watch the Professor!!" -- Al Flosso (1895-1976)
"The better you are, the closer they watch" -- Darwin Ortiz, STRONG MAGIC
Dan McLean Jr aka, Magic Roadie
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Quote:
On 2009-11-20 17:01, sethb wrote:
... if I can solve the hum problem with a $30 direct box, that will be cheaper than dragging the whole thing to a tech. So that's my next step, unless anyone has a better idea.

A direct box is not a guarantee. Be sure you can get a refund if it doesn't solve your problem.
Dan McLean Jr
Kline
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Seth,
Are you using a grounded AC cord with this unit ?
I do have one of these set up in my studio for quick sound checks for my media star and I have experienced a slight hum from time to time.
Is the DVD player next to the unit ? try to move it so that the audio cable does not touch anyting other than each unit at the ends of the cables ( at the female junction )
The other thing to try with this is to make sure the treble level is to high.
that's about all I have for you .
Hope this helps
Steven Kline
<BR><BR>www.stevenkline.com
<BR><BR>www.stevenklineproductions.com
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