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Old 9th January 2007, 12:43 PM   #1
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Default Need simple low pass for wireless Mic

Hi, I have an AKG wireless UHF transmitter and the particular Countryman Headset mic requires lots of gain. This introduces static and hiss into my Mackie sound board. Other than replacing the wireless unit or mic, does anyone have a suggestion for a simple circuit for vocal frequencies to eliminate this.

I have tried a passive RC with R= 1.5k and C =.022uf

It works, well the vocals seem flat. It cut some of the hiss but the price is overall brightness.

If this isn't the right group, please direct me.
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Old 9th January 2007, 10:58 PM   #2
moamps is offline moamps  Croatia
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The noise you are getting is probably FM background noise, which has a wide spectrum. That's why no filter would be of much use here. If you give us more detail on how the mike is connected to the console and such, we might be able to help more in identifying the culprit.

You're right. The post was in the wrong forum but I fixed it for you.

Welcome to the forums!

Regards,
Milan
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Old 10th January 2007, 07:27 AM   #3
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Well, nothing out of the ordinary.

Akg PT40 bodypack, with AKG WMS40 reciever.
COuntryman Isomax headset mic.

The WMS40 is feeding a Mackie 1402vlz Mixer thru xlr.

The gain is way high on both transmitter and receiver, inorder to get decent input to the mixer. The gain pot for that chanel in this configuration is about mid way. I can decrease the gain from the AKG side and increase the gain on the Mackie side, but with about the same results. THe mackie feeds direct to QSC and behringer amps which don't exhibit hiss normally with other equipment. Tried diff chanels, it's the AKG.

I guess i thought a simple filter would kill some of the hiss.

Maybe an active filter would work???
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Old 11th January 2007, 11:46 PM   #4
moamps is offline moamps  Croatia
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Hi Mark,

It looks to me that you may have a problem with the wiring. Do you get full sound and level from the receiver when you talk directly into the microphone? Does the "signal LED" on the reciever flash when you talk? Have you tried another mic?

Regards,
Milan
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Old 12th January 2007, 03:08 AM   #5
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I have actually 2 different bodypack and transmitters. They both work fine independantly of the Countryman Isomax headset. I emailed countryman and they confirmed that the Isomax does require more gain for this mic. Different cables, diff channels. I mean the noise is not terrible, but I just don't like any noise. The "noise" seems to follow speech patters. I mean it gets quieter when you are not talking, but then if you talk or sing the noise level increses or follows the voice input. I've almost decided to live with it, I mean when the music is playing you can't hear the "noise" over the instruments.

Now you've got me thinking about the wiring of the mic itself. I don't know enough about mic construction, but what if the polarity was swithched inside the mic itself. The mic has a mini-XLR connector. I guess I could rig up something and test switching the + and - on the mic before going to the bodypack, but then again it might not matter.
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Old 12th January 2007, 11:09 PM   #6
moamps is offline moamps  Croatia
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The AKG PT40 transmitter gives only 3.8V on the mike input that feeds the electret capsule. The Countryman Isomax headset needs 15V (as per datasheet) if you're using the electret capsule. It is possible that the supplying voltage is too low for the mike to function properly. The breathing noise is normal when the level of the signal coming from the mike is too low (it is caused by the compander).

Regards,
Milan
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Old 12th January 2007, 11:36 PM   #7
imix500 is offline imix500  United States
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Going off what moamps said, if you have both the transmitter and receiver gain cranked, what you are hearing is the compander which isn't all that great on AKG's. A filter won't really help.
Have you checked to see if the isomax requires a bias resistor with your transmitter?
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Old 12th January 2007, 11:40 PM   #8
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Thanks Moamps for id'ing the problem.
At this point I'm not sure if there is a fix, or if it's worth the effort. Seems like a big leap in trying to get more voltage to mic.

This particular body pack has 2 AA batteries. I will have to check, but maybe a 9v battery could be substituted with a voltage divider network so that the bodypack would operate on 3v and I could supply the mic with 9.

Would it simply be a matter of supplying 9V to the + and - leads?
I know it's not 15v, but it may help?

I guess a lesson in Mic construction might be inorder.
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Old 12th January 2007, 11:56 PM   #9
imix500 is offline imix500  United States
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Depends on the mic element. It also depends on the transmitter and it's preamp.
That element really wants a minimum of 5 volts to sound it's best, so you may be losing some output and s/n.
Looks like on the TA3F:
Pin 1 =S and B
Pin 2 =R
Jumper between Pin 2 and 3
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Old 19th January 2007, 09:41 AM   #10
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Thanks for the info so far

It might help if I knew the full names for the pin out connectors
S=
B=
R=
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