Topic: 722 noise?

[ts]

Just curious, what mic cables are you using?

-K

I'm using Silver Serpents from mic bodies to 722, 12 inches in length, and AKG mk46 actives from caps to mic bodies, 3 meters in length. I see what your getting at.

[wbrisette]

But I was under the impression that the problem with 744 and radio mics was not that the 744 was effected, but instead that it can produce radio interference that disturbs the radio receiver, quite the other way round. Is this what you have heard as well?

Yes, the RF leakage on the 7xx series seems to be more on the output side of the house, mainly from the battery area and various parts of the case (or at least that is what Lectrosonics found). However, RF leakage is a two-way street. I use to work for a company that built the testing gear for  radiated emissions and radiated immunity, and it's very rare that you have just one, usually if you have poor emissions, you have poor immunity. And as you might suspect, where you fail in one test is usually where you fail in the other. In the case of the 744, according to the tests Lectro ran, the 7xx series isn't out of FCC limits, but they aren't going to set any records in this area either. Jon Tooles is recommending to all mixers that they move their radios and wireless units as far away from the 7xx as possible.

This is why mixers have a love/hate relationship with the device at the moment.

Waynee

[hammerhorror]

I am an ENG sound mixer / Cameraman for my day job. The cable choice seems to make a HUGE difference in determining if your audio will be affected by RF interference or not.

I know that Nextel phones and Blackberry's both affected my sound bag until I switched out my cheap mogami cables with my bumblebee silver clad cables. Now I never have a problem with cell phones whatsoever.

The problem is trying to find out which cables succesfully block RF. I know that my bumblebee cables do.

Hope this helps.

-John

[thegreatgumbino]

Normally the shield is not attached to the xlr connectors on mic cables.

   Since when? 

Here's some info from the following link regarding not connecting the shield:  http://www.taperssection.com/reference/pdf/DIY_CableDiagram_Rane.pdf

"A common solution to these noisy hum and buzz problems involves disconnecting one end of the shield, even
though one can not buy off-the-shelf cables with the shield disconnected at one end. The best end to disconnect
is a matter of personal preference and should be religiously obeyed; choose inputs or outputs and always lift the
side you choose (our drawings happen to disconnect the input end of the cable -- the output of the driving unit). If
one end of the shield is disconnected, the noisy hum current stops flowing and away goes the hum -- but only at
low frequencies. A one-end-only shield connection increases the possibility of high frequency (radio) interference
since the shield may act as an antenna. Many reduce this potential RF interference by providing an RF path
through a small capacitor (0.1 or 0.01 microfarad ceramic disc) connected from the lifted end of the shield to the
chassis. The fact that many modern day installers still follow this one-end-only rule with consistent success
indicates this and other acceptable solutions to RF issues exist, though the increasing use of digital and wireless
technology greatly increases the possibility of future RF problems.
If you've truly isolated your hum problem to a specific unit, chances are, even though the documentation
indicates proper chassis grounded shields, the suspect unit is not internally grounded properly. Here is where
special test cable assemblies, shown in Figure 3, really come in handy. These assemblies allow you to connect
the shield to chassis ground at the point of entry, or to pin 1, or to lift one end of the shield. The task becomes
more difficult when the unit you've isolated has multiple inputs and outputs. On a suspect unit with multiple
cables, try various configurations on each connection to find out if special cable assemblies are needed at more
than one point."

FWIW, the BBee's I owned did have the shield connected to the xlr on both ends.  I think the only time you see it not connected is in an unbalanced cable, but YMMV.

[wbrisette]

I am an ENG sound mixer / Cameraman for my day job. The cable choice seems to make a HUGE difference in determining if your audio will be affected by RF interference or not.

Here is what Larry at Lectro found:

On the 744T we checked (emphasis, on the one we checked), we found no
RF on any of the in or out connectors, power inputs, you name it. Any
wire or cable connection was effectively RF dead. This was actually a
disappointment, since if a connector was the culprit it would be easy
to build in a filter for that connection. What we found was RF leakage
around the battery compartment and some radiation from other parts of
the case. The battery compartment area may be the main offender and
other radiation from the case just a secondary effect.

-=-=-=-=-

Seems that the cables aren't the issue with the 7xx series.

Wayne

[terrapinj]

FUCK!

just realized I picked up a couple seconds of cell noise while stealthing moe on Tues night, mod 460 (ck1x/mk46) > 722

i was the only taper too, its only a couple seconds but still - FUCK im gonna be really paranoid now about cell phones

[Genghis Cougar Mellen Khan]

I am an ENG sound mixer / Cameraman for my day job. The cable choice seems to make a HUGE difference in determining if your audio will be affected by RF interference or not.

Here is what Larry at Lectro found:

On the 744T we checked (emphasis, on the one we checked), we found no
RF on any of the in or out connectors, power inputs, you name it. Any
wire or cable connection was effectively RF dead. This was actually a
disappointment, since if a connector was the culprit it would be easy
to build in a filter for that connection. What we found was RF leakage
around the battery compartment and some radiation from other parts of
the case. The battery compartment area may be the main offender and
other radiation from the case just a secondary effect.

-=-=-=-=-

Seems that the cables aren't the issue with the 7xx series.

Wayne

They didn't find any RF leakage on any of the connectors, that doesn't rule out the possibility of a cable being the culprit.  It's entirely possible mic cables could act like monopole antennas.

Generally it's probably a good idea to keep a cell phone as far away from any recording device just to be safe.

I say do a test run, place the cell phone close to the 7XX, start recording, call it and see if you get interference.

try: just 722 no cables attatched
            722 cables but no mics (cables vertical as if you were running them with a stand)
            722 cables and mics

It might not have even been your phone, but it's worth testing.

[terrapinj]

is it possible that the active cables may be the culprit?

so far Tony and I are  the only ones here that seem to have had interference with the 722 and we were both running the mk46 cables

[nickgregory]

is it possible that the active cables may be the culprit?

so far Tony and I are  the only ones here that seem to have had interference with the 722 and we were both running the mk46 cables

maybe.  I run the 4022s and havent had an issue, but it could be a construction difference between DPA and Schoeps

[terrapinj]

is it possible that the active cables may be the culprit?

so far Tony and I are  the only ones here that seem to have had interference with the 722 and we were both running the mk46 cables

maybe.  I run the 4022s and havent had an issue, but it could be a construction difference between DPA and Schoeps

Schoeps 

give us some credit Nick we have better taste than that. mk46 are AKG active cables

[nickgregory]

is it possible that the active cables may be the culprit?

so far Tony and I are  the only ones here that seem to have had interference with the 722 and we were both running the mk46 cables

maybe.  I run the 4022s and havent had an issue, but it could be a construction difference between DPA and Schoeps

Schoeps 

give us some credit Nick we have better taste than that. mk46 are AKG active cables

my apologies

[it-goes-to-eleven]

Anyone have any mfgr info on the mk46 cable?

[Genghis Cougar Mellen Khan]

Interesting read, something to give consideration.

RF Susceptability in microphones:
http://www.audiosystemsgroup.com/RF_in_Microphones.pdf

Cheap, but it might help!

http://cgi.ebay.com/20-pcs-Clamp-On-Ferrite-EMI-RFI-Suppressors_W0QQitemZ320008966145QQihZ011QQcategoryZ15051QQcmdZViewItem

http://media.digikey.com/PDF/Data%20Sheets/TDK%20PDFs/ZCAT%20Series.pdf

Other related articles:
Understanding and eliminating RF problems.
http://www.audiosystemsgroup.com/Ferrites-Ham.pdf
http://www.audiosystemsgroup.com/AESPaperNYPin1-ASGWeb.pdf

[mhibbs]

So how common is RF with the 722?  Is everyone with a 722 on the board having issues?

I haven't heard it on mine, and I've definitely had my blackberry on at many shows in the last year and been standing close and had no issue.  Mine is Cingular GSM (I'm guessing providers can differ due to the different technologies).  It makes a ridiculous amount of racket next to my monitors on my DAW and anywhere near my laptop speakers but doesn't bother my home Snell's or the radio in my Tahoe either.  Regardless, I've been turning it off for the last month or so after reading so many posts about RF interference.  Going to test at home and see if I can't cause it at some point when I have some time...just to see how close it really has to be.

Mitch

[terrapinj]

picked up a little sample of cell noise agian last night at CSNY

mod 460 (ck1x/mk46) > 722

i believe it occurred when i remembered to turn off my phone right at the end of the 1st song, not devestating but its clearly there