unbalanced line and rf??

[imloggedin]

i have a used beyer mpc-65 pzm and it sounds great, but so does the radio that comes in through the line connecting the capsule to the preamp. are all pzm's like this? the shure sm91? it looks like they all have external preamps. i can hear the radio crystal clear. anyone have any fixes for this? i dont know what to do.

[imloggedin]

no comments? was it really that hard of a question?

[JonCraig]

i've used an sm91 once... had no problems with it. i don't recall it having the capsule pre seperate from the body of the boundary mic. i've also worked w/ audio technica boundary mics a couple of times. no capsule pre there, either. i use the term "capsule pre" to emphasize the difference between the on-board pre that every condensor has vs. what we normally think of as a mic pre. do you have a picture of the beyer mic to which you're referring?

--jon

[imloggedin]

http://www.beyerdynamic.com/cms/Acou...ctdatabase_pi1[showUid][backPID]=59&tx_sbproductdatabase_pi1[showUid][showUID]

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0cbe9649ad

the capsule is the only thing in the end. it comes circular tubish looking preamp for the mic (yah the preamp that comes built into mics). the wire runs from the end (that u can see in the picture) to the preamp and then its xlr from there. i opened the end (i dunno what to call it) up and the capsule is the only thing in there. the wire from the end to the preamp is whats causing all the rfi, its unbalanced because it just runs to a capsule. i dunno what to do.

[JonCraig]

hmmm... that's an interesting one...

can you get the (capsule) pre close to the mic element, possibly coiling the excess wire really close together? i'm thinking that maybe this will reduce the rf (less of an antenna stretched across the floor). other than that, i'd say it's a technical issue and in need or repair/replacement. sorry.

--jon

[imloggedin]

i tried coiling it. it just made it worse. i tried wrapping it in tin foil and that didnt work either.

[JonCraig]

you might try opening the pre and seeing if there are any obvious faults--i'm thinking capacitors specifically. otherwise... i dunno.

--jon

[jamesp]

The first thing to do is to check the grounding of all your gear - if the Beyer mic has a CE symbol on it then it shouldn't be susceptible to radio interference but this relies on everything else in your system being properly connected with the correct grounding scheme.

Cheers.

James.

[C/G]

Use a beta 91 all the time in the kick drum and never had a problem with rf. Ah sweet, post #666

[imloggedin]

ive tried 6 different condensers through the same setup and this is the only mic that does it. i agree that grounding might be a problem but none of my other mics do it. should i just shorten the cable? i mean what options do i really have?

[JonCraig]

i would guess that a transistor, or perhaps a filter cap, in the pre is acting up. you could pay for someone to take a look at it, but i'm thinking that this might not be cost-effective. sometimes things just break.

--jon

[imloggedin]

why would the pre do that? i can leave the pre and the capsule on the floor (not moving) and move the wire around and the radio gets louder and whatnot depending on where i move the wire.

[JonCraig]

any piece of wire acts as an antenna. and the circuitry in the preamp has a wide enough bandwidth to "see" radio waves and amplify them. there's usually filter circuitry that eliminates this effect. my guess is that this filter circuitry is acting up--probably a filter capacitor has gone bad.

--jon

[imloggedin]

think i should just return it and get my money back? its such a shame cause the mic sounds great. but the circuit board is so tiny im not soldering on it

[JonCraig]

oh! i didn't realize it was new! yes yes, take it back & exchange it. surely beyer didn't release a defective product... you just got a bum one.

--jon