Topic: Any experience with snap choke core to eliminate interference

[DigiGal]

Not exactly, it doesn't impead phantom power, it uses the Neutrik integrated LC-filter to avoid RF-interference and LF-noise from their EMC XX series of connectors.  The Neutrik EMC XX incorporates circular capacitors that act as high-pass filters with a cut-off frequency around 10 MHz and also an EMI suppression ferrite bead with 24 ohm at 1 MHz btw. pin 1 and the cable screen providing a low-pass filter for improved RF rejection.

Tech notes: INLINE-EMCM is not designed to remove phantom power.

FWIW: My AKG Bluelines are balanced phantom power only even using the stock optional active cables and they were connected to a balanced recorder providing phntom power.  At any rate I ordered EMC XX connectors to replace the standard NC series Neutrik connectors on my mic cables.

But, yes of course you would need to be running balanced mics to use the SESCOM inline filter.



A pictorial view of the EMC connector, courtesy Neutrik.

http://www.rane.com/pdf/ranenotes/Pin_1_Revisited.pdf

[DigiGal]

I agree the stock active cables from AKG Blueline's while balanced are really pretty wimpy and probably not shielded all that well.  It would definitely be worthwhile to rewire them with better cable.  I only use the active cables when I need a lower profile but luckily never got hit with cell phone interference using them before.  In addition to the Neutrik EMC connectors I also ordered a few cable samples to examine, if going that route they could be tech flexed together too which would be beneficial for low profile. 

[kleiner Rainer]

Jon, does it matter where the ferrite bead is placed?  Wondering if it should be placed as close as possible to the recorder/premap end.. or should it work just as effectively placed anywhere on the cable?

Boy, I'm a little weak on antenna theory to answer that.  SparkE or Rainer would know better; I would guess it limits the effective length of the antenna for transmission purposes (which would be good, and probably why it's at the cable ends for digital cables), but for induced noise I don't know.

Hi Jon and the rest of the gang,

antennas are reciprocal: what works for transmission also works for reception. I put clip-on ferrites as close as possible to the input of the recorder and also close to the mic. The reason: many mics we use contain electronic circuits (think phantom power supply components and the FET in electret capsules), and those circuits can and do rectify RF currents present on the cable. No cable shield is perfect, and therefore the wires within the shield will also carry rf currents. If those currents get rectified, they are added to the weak audio signals we want to record. In the case of GSM cell phones, you get the dreaded BRAP-BRAP-BRAP noise, other signals may give a kind of PLOP due to shifts in the DC level.

Another problem is to find out what type of ferrite you just found in your junk box. If you are lucky, it has the right suppression frequency range for your problem. But most of the time, you are probably out of luck...
I can order my ferrite beads via the company since I am involved in EMC work, and we are talking tens of thousands of ferrites I specify, so I can select the correct ferrite material with the correct properties.

Try to find a source where you can get  informations about the frequency range the clip-on ferrite is designed for. If the junk box part doesnt help, this does not mean that the clip-on approach does not work. You simply used the wrong material!

If you build your own mic cables, get the one with the thickest shield (=lowest resistance) and highest coverage ratio (=no voids in the shield). Foil shield with drain wire gives nearly 100% coverage BUT has rather high resistance. I had hum and RF problems with such a cable until I switched to a cable with a really fat braided shield. For hard-core DIYers I can recommend double-shielded teflon isolated RF coax. Its awfully expensive, but the best money can buy...

It is also recommended to use well-made connectors from manufacturers with a reputation of good quality (Switchcraft and Neutrik come to my mind...). It is very important to remember that all shields should be connected with a low-impedance connection. This includes the metal cases of mics and recorders! As soon as there is a hole in your shield, the RF will find it, even if the rest is double-or triple-shielded.

I hope, this sheds some light on the RF noise issue.

Greetings,

Rainer

[bonghitwillie]

i did not read all the responses. i thought these things are used to eliminate static electricity.

[bt2002]

Hi

Sometimes making several loops of the cable and taping them together into a coil of cable can help with RF interference.
I believe this creates some inductance and can reduce the RF which runs along the outer metal skin, which is the shield.
I also want to give a +1 to Rainer's explanation above.

Good luck

[Chilly Brioschi]

Slide-ons work better than snap-ons, for equivalent size and weight.
Be careful that the extra weight doesn't add more problems than it is intended to fix by stressing connectors

[BlingFree]

The first two rigs that I ever used were
mics > XLR > deck
and I never once had cell phone issues... even while leaving my phone in the bag.

I didnt even KNOW about the issue until I got my own rig that was like
mics > XLR > preamp > whatever cable > deck

My assumption was that the "whatever cable" is the culprit and it needs to be better shielded like the XLR. I've gotten a quote from GAK for a good RCA > 1/8'.. hope it fixes it.