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-   -   Weird noises coming through! (https://www.dvinfo.net/forum/all-things-audio/49892-weird-noises-coming-through.html)

Patrick Swinnea August 24th, 2005 10:24 PM

Interesting...

I see exactly what you guys are talking about. Page 7 says unbalanced. Page 9 says balanced, and the block diagram... well I have no idea how to read that.

Just to make sure I'm on the same page here I've highlighted the offending sections of the manual (Page 7, Page 9 and a scan of the Block Diagram - which I think is easier to read than the PDF)

http://www.cheezwhiz.org/Behringer%20UB802

If it is indeed using unbalanced MONO outs, am I right to think adding the DXA-2 to the equation would have no significant benefit? I mean if it's unbalanced at the MAIN OUT, the unbalanced signal would just sail away until it hit another set of circuits (DXA-2) to run through, only to come out just as unbalanced as before on the other end?

Is it common for cheapo mixers like this to use unbalanced main outs like this? It seems a little weird that a mixer of any kind would do this.

Jay Massengill August 25th, 2005 08:01 AM

If it turns out the Behringer main outs are truly unbalanced, then the main advantage to putting the BeachTek between the mixer and the camera would be allowing you to use easily obtainable better shielded cables with more durable connectors for longer runs or moving the camera around.
This specific case wouldn't really benefit from this, but for other people's activities using a BeachTek with an 1/8-inch jack camera does offer that physical advantage even with unbalanced signals.
You may also gain some protection from ground loop hums since the Beach has transformers and two-position grounding switches, but this is highly dependent on the specific camera and what you're hooking to it (especially AC-powered video monitors).
In addition, you could use the EDB-1 or the Ebtech Hum Eliminator to make the signal balanced using a short cable from the Behringer. Then send the balanced signal to the BeachTek and camera.

Patrick Swinnea August 25th, 2005 08:23 AM

Awesome, thanks. The EDB-1 is about half the price of the Ebtech. They both look like they do the same thing. Is it just a case of you get what you pay for or are they essentially the same thing?

Jay Massengill August 25th, 2005 12:50 PM

They perform vastly different functions but use similar passive circuitry.
They can both create a balanced signal from an unbalanced one and that would be their function in this example.
The EDB-1 also provides attenuation of 20 (full time), or switchable 40 or 60db. It's a single channel device whose main purpose is to take a hot unbalanced signal and turn it into the equivalent of a balanced mic signal. It's called a "Direct Box" because its original use was to record an electric guitar or guitar amp output directly into a mic input on a mixer, but they are inexpensive and very handy for lots of other functions.
The Ebtech Hum Eliminator has two channels and can use balanced or unbalanced connections in any combination. It doesn't change the signal level. Its primary purpose is to eliminate ground loop hums, but I use mine primarily for making a long balanced run to a DSR-45 DVCAM deck that uses unbalanced inputs. Since this deck is plugged into AC power some distance from my mixer, it could also have a ground loop hum but that's taken care of automatically so I don't have to worry about it.

Patrick Swinnea August 25th, 2005 01:26 PM

Thanks again.

David Ennis August 25th, 2005 02:35 PM

Just a slight correction on the EDB-1. The two that I have are switchable between 0, -20dB and -40dB.

Audio Technica tech support responded that they have had zero complaints of pin 1 error in the AT3031 over the past five years, but, oddly did not say that that the mic wasn't wired in that manner. I tried one of my own AT3031s, working into my GL2 through a BeachTeck DXA-8, with my Samsung cell phone turned on and sitting in the middle of a small circle created by the the mic, the Beach, the cam and the unbalanced pigtail connecting the Beach to the cam. Full volume on everything. Not a peep in ten minutes. This is all mic level. I was surprised.

[Edit: come to think of it, when I was googling those cell phone detector pens mentioned in this thread, I think the the blurb on one of them named Samsung as one of the ones it wouldn't detect. If so, my test may not be valid. Looking to find that blurb again....]

Sam Gates August 25th, 2005 04:12 PM

The pin 1 problems I have seen seldom occur because of the mic unless there is a very strong field very close. IMHO it is usually caused by improper shield grounding in the mixer or mic preamp. Your BeahTeck is an exellent product with tranformer inputs and outputs. It kept the RF from getting into the electronics.

Sam

Jay Massengill August 26th, 2005 07:44 AM

I should have mentioned the oddity in the switch labelling and the slim documentation that comes with the EDB-1. They don't specifically mention the built-in 20db pad even with the switch set to "0".
I know I found a reference once on the Whirlwind website that confirmed what I found below on a vendor site but I can't find it now.

"Level Change: -20 dB (input to output, pad switch set to zero dB)
Pad: 3 position, provides 0 dB, -20 dB, -40 dB additional attenuation"

This makes sense if you infer from the instructions that come with it-
"Most instruments will operate properly when set to the "0" position."

That's got to include some attenuation built in.

Other uses for the EDB-1: If you have two of them and the right Y cable you can tie a presenter's laptop headphone output into your sound system over long cables and won't have a ground-loop hum. You know, like when the presenter mentions 5 minutes before the conference that they brought a .wmv file that they need to show to the 300 people in attendence and your mixer is 50 feet away from the podium and he also has to run his own PowerPoint show from the same computer...
You can also use one to create a long direct out from a mixer mic input even if it has the normal interrupting direct outs instead of the Mackie non-interrupting direct outs. I think Fred first did that using the Y feature of the EDB-1 for both the send and receive legs of the line-level direct out signal. This allows you to split off a preamped signal from a mic without the mixer operator otherwise changing the level coming to you. Once the mic trim on the mixer is set, you're good to go. And you're both protected from ground-loop hums.

Jeremy Davidson August 26th, 2005 08:22 AM

Fred, try checking your voicemail or making a call. My GSM phone (a Nokia) seems to check for towers about once an hour (if it has good coverage -- maybe more often if it doesn't). Initiating a call will "force" it to transmit RF.

I think the issue is tied more to the technology used (i.e. TDMA vs. GSM) rather than manufacturer. Any idea which one your phone uses? GSM produces short bursts of square waves at roughly 217Hz ('think I found that spec online once). TDMA creates a string of low-frequency pulses.

I know I once picked up a GSM phone on my GL2 (no, not my own phone), but I was not using a balancing converter of any kind, and I think the phone was only about 3' away.

Sam Gates November 22nd, 2005 09:05 PM

I don't know if reserecting this old thread is the correct way to go about this but I found this interesting. I have not tried it so I can not promise it works.

http://www.neutrik.com/start.asp

http://www.neutrik.com/images/ock/do..._431221821.pdf

Sam


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