Topic: Cell phone interference: how can I shield against it / what's wrong with my rig?

[poorlyconditioned]

I don't have a whole lot of other ideas on this..  I'm wondering if any of the at853's can operate without gsm interference.  If not, then there's no point in more headbanging. You might drop Chris at Soundpros a note.  Those guys sell a ton of at853's and I'll bet they have some experience with this.

The new AT853 series (U853 I think they are called), supposedly reject RF noise.  So that is probably what they are talking about.

So, I think you're going to have to live with it.  Or maybe do some circuit wizardry on the mic body and/or cable.  I've always seen an inductor/capacitor pair (a filter) on the miniXLR sockets in AT8531 powering modules.  I think these are *trying* to remove RF, but might not be doing a great job of it.

  Richard

[SparkE!]

I don't have a whole lot of other ideas on this..  I'm wondering if any of the at853's can operate without gsm interference.  If not, then there's no point in more headbanging. You might drop Chris at Soundpros a note.  Those guys sell a ton of at853's and I'll bet they have some experience with this.

The new AT853 series (U853 I think they are called), supposedly reject RF noise.  So that is probably what they are talking about.

So, I think you're going to have to live with it.  Or maybe do some circuit wizardry on the mic body and/or cable.  I've always seen an inductor/capacitor pair (a filter) on the miniXLR sockets in AT8531 powering modules.  I think these are *trying* to remove RF, but might not be doing a great job of it.

  Richard

Yes, this is a good idea.  You'd use series inductors in the signal path and shunt caps to ground.  It works even better if you choose an inductor that is series resonant at the frequency of interest and caps that are also series resonant at that same frequency.  If your rf interference is broadband, then you just want to pick inductors and caps whose series resonant frequencies are above any frequency of interest.  (Above their series resonant frequency, inductors will appear capacitive and capacitors will appear inductive).

[Sparge Master]

I get interferance from my cell phone when doing transfers tascam tape deck > fire creatpor (mini-me) > cpu also with my tascam da20 > apogee2496. I usually throw my phone in the other room before i deal with shit

[Sparge Master]

This also happens in my truck. I dont need to be in a call or getting a text message phones no days send shit all the fucking time. I hate them and wish for the old days of land lines

[whatboutbob]

Yes, this is a good idea.  You'd use series inductors in the signal path and shunt caps to ground.  It works even better if you choose an inductor that is series resonant at the frequency of interest and caps that are also series resonant at that same frequency.  If your rf interference is broadband, then you just want to pick inductors and caps whose series resonant frequencies are above any frequency of interest.  (Above their series resonant frequency, inductors will appear capacitive and capacitors will appear inductive).

* whatboutbob breaks out the "smart to dumb" thesaurus.

[Church-Audio]

A pot would be a simple approach and you can cook in it after the gig! What more can you ask for. These silly inductors and caps will not fill an empty stomach, but a big pot with a lid. The possibilities are endless

IF you get stuck, I will take a look at your gear and see if I can fix the problem for you.

Chris Church

Yes, this is a good idea.  You'd use series inductors in the signal path and shunt caps to ground.  It works even better if you choose an inductor that is series resonant at the frequency of interest and caps that are also series resonant at that same frequency.  If your rf interference is broadband, then you just want to pick inductors and caps whose series resonant frequencies are above any frequency of interest.  (Above their series resonant frequency, inductors will appear capacitive and capacitors will appear inductive).

* whatboutbob breaks out the "smart to dumb" thesaurus.

[whatboutbob]

A pot would be a simple approach and you can cook in it after the gig! What more can you ask for. These silly inductors and caps will not fill an empty stomach, but a big pot with a lid. The possibilities are endless

...and what it lacks in subtlety, it more than makes up for in fashion sense!

IF you get stuck, I will take a look at your gear and see if I can fix the problem for you.

Thanks again Chris.  I'll keep you in mind as a last recourse.  I'm sure you've got more profitable ways to spend your time.

[Church-Audio]

It is not always about profit I sold you a preamp. I will take the time to take a look and see if I can help you. You helped me when you purchased it from me. End of story so like I said if you get stuck I will try and see what I can do maybe between Me Sparke! and poorly we can come up with a solution for your problem.

Chris Church

A pot would be a simple approach and you can cook in it after the gig! What more can you ask for. These silly inductors and caps will not fill an empty stomach, but a big pot with a lid. The possibilities are endless

...and what it lacks in subtlety, it more than makes up for in fashion sense!

IF you get stuck, I will take a look at your gear and see if I can fix the problem for you.

Thanks again Chris.  I'll keep you in mind as a last recourse.  I'm sure you've got more profitable ways to spend your time.

[poorlyconditioned]

A pot would be a simple approach and you can cook in it after the gig! What more can you ask for. These silly inductors and caps will not fill an empty stomach, but a big pot with a lid. The possibilities are endless

...and what it lacks in subtlety, it more than makes up for in fashion sense!

IF you get stuck, I will take a look at your gear and see if I can fix the problem for you.

Thanks again Chris.  I'll keep you in mind as a last recourse.  I'm sure you've got more profitable ways to spend your time.

+T for the avatar.  Put the mics *and* your head in the pot.  Helps prevent messages from aliens too...

I don't know how to solve this problem.  I would ask SoundProfessionals if they have heard of others experiencing it.  They outta know.  I'm suspicious since AT introduced the new U853 line and specificially mentions reduced RF problems.

The next step would be to put some small capacitors on the miniXLR connectors in the battery box.  The pins are: 1 (ground), 2 (audio), and 3 (battery).  Put a small cap between 1 and 3 and between 1 and 2.  The value should be something like 22pF.  That is a *really* small value, but even something bigger like 100pF (0.1nF) should work to test it out.  Try that and see if it fixes the problem.  I'm suggesting this because just about every regular XLR connector I see has caps from the two signal pins to ground.  Maybe it just stabilizes the phantom power, but it is still worth a try on the miniXLRs.

Let us know...

  Richard

[whatboutbob]

I don't know how to solve this problem.  I would ask SoundProfessionals if they have heard of others experiencing it.  They outta know.  I'm suspicious since AT introduced the new U853 line and specificially mentions reduced RF problems.

Will do.

The next step would be to put some small capacitors on the miniXLR connectors in the battery box.  The pins are: 1 (ground), 2 (audio), and 3 (battery).  Put a small cap between 1 and 3 and between 1 and 2.  The value should be something like 22pF.  That is a *really* small value, but even something bigger like 100pF (0.1nF) should work to test it out.  Try that and see if it fixes the problem.  I'm suggesting this because just about every regular XLR connector I see has caps from the two signal pins to ground.  Maybe it just stabilizes the phantom power, but it is still worth a try on the miniXLRs.

Ok...will do.  I've already glued up my bbox, so I'll have to make up another one to test.

The only caps I could find that small are ceramic.  Is that an issue?

[Church-Audio]

Ceramic are not the best for audio but for this test they will do.


Chris Church

I don't know how to solve this problem.  I would ask SoundProfessionals if they have heard of others experiencing it.  They outta know.  I'm suspicious since AT introduced the new U853 line and specificially mentions reduced RF problems.

Will do.

The next step would be to put some small capacitors on the miniXLR connectors in the battery box.  The pins are: 1 (ground), 2 (audio), and 3 (battery).  Put a small cap between 1 and 3 and between 1 and 2.  The value should be something like 22pF.  That is a *really* small value, but even something bigger like 100pF (0.1nF) should work to test it out.  Try that and see if it fixes the problem.  I'm suggesting this because just about every regular XLR connector I see has caps from the two signal pins to ground.  Maybe it just stabilizes the phantom power, but it is still worth a try on the miniXLRs.

Ok...will do.  I've already glued up my bbox, so I'll have to make up another one to test.

The only caps I could find that small are ceramic.  Is that an issue?

[Humbug]

I don't know how to solve this problem.  I would ask SoundProfessionals if they have heard of others experiencing it.  They outta know.  I'm suspicious since AT introduced the new U853 line and specificially mentions reduced RF problems.

Probably no help at all, but I have never experienced cell phone interference on my recordings; I turn my phone off when taping, even once when I forgot to turn it off and someone called me, there's nothing on the recording.

This is for running both rigs below, one of which is similar, though simpler (no-pre or external A>D) to the rig whatboutbob is running. 3-wire bb was built by Sanjay.

[whatboutbob]

Bah Humbug! (sorry...I've always wanted to type that)

Do you know if your phone is GSM?

I do get interference running a very similar setup: AT943s > 3wbb > iriver.

I built the Y cable tonight so I ran at853 > Y cable > iriver.  Interference resulted.

So while it could be the Y cable, it does seem to point to the mics or mic cables that are the problem, rather than the iriver (ruled out because there's no interference running the GSA's into it) or the pres(s)/bboxes.

Will try building the new bbox on the w/e as per Richard's directions.  I've sent off the email to SP.

[Oysterhead00]

I had a GSA phone through Cell One and got interference on ANY type of microphone or speaker.  On conference calls at work I'd get a high pitched "waaaaaa (pause) waaaaa (pause) waaaaaa".  I got it on one recording and if I put my phone on my night stand before going to bed, It would cause the noise to come through my alarm clock.  It doesn't happen all the time so I assume it's caused by some regular interval connection check or something.  I recently switched over to Verizon (not sure waht type of phone it is) and after 3 months have had zero interference.  The good news is it would always stop if I turned it off and if it was on my far shelf in my cubicle (4' from the phone) it wouldn't interfere.  So it seems to be a GSA thing and has a very small radius of effect.

[SparkE!]

Do you know if your phone is GSM?

He's in Europe, so it will be GSM.  GSM phones tend to cause more problems with audio circuits if the high impedance points in the circuits are not bypassed with small caps like poorlyconditioned was mentioning.  He's right that a small capacitor would probably be a good choice.  You'll want to use low loss chip capacitors whose series resonant frequency is above the cellular band. (NPO or COG dielectrics have low loss at cellular frequencies.)  A typical 15 pF COG chip cap would have a series resonant frequency of around 2 GHz, so that would cover the 1900 MHz cellular band where your GSM phone probably works.

Will try building the new bbox on the w/e as per Richard's directions.  I've sent off the email to SP.

Yeah, I'm suspecting the battery box at this point too.