Adding 1/4" output to telephone handset - diyAudio
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Old 21st February 2006, 06:23 AM   #1
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Default Adding 1/4" output to telephone handset

Hello,

I just added a 1/4" output jack to a telephone handset to be used as a microphone but am experiencing some problems. What I did was take out the rj-45 connector and connect the positive and negative connections on the microphone element right to the jack. The microphone only works correctly when the element is exposed and I touch the positive contact with my hand. This is quite strange and I don't know what could be causing it. Does anyone have any suggestions? thanks.
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Old 21st February 2006, 09:04 AM   #2
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Join Date: Jul 2005
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You don't give many details? - but what type of microphone is it?, and what are you trying to plug it in to?.

I imagine it's probably an electret mike?, so it will require powering.
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Old 21st February 2006, 07:30 PM   #3
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I am trying to plug it into a guitar amp. I actually tested it with a 9volt battery wired to it and it worked fine. However, what I cannot understand is how it works without the battery when my hand is touching it, but will not work when I put it back in the chassis. I think it is an electret mike. Are these usually powered by internal circuitry that gets juice from the phone connector? thanks.

RJ
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Old 22nd February 2006, 08:52 AM   #4
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Quote:
Originally posted by RJSkypala
I am trying to plug it into a guitar amp. I actually tested it with a 9volt battery wired to it and it worked fine. However, what I cannot understand is how it works without the battery when my hand is touching it, but will not work when I put it back in the chassis. I think it is an electret mike. Are these usually powered by internal circuitry that gets juice from the phone connector? thanks.

RJ
Yes, it gets it's power down the connector lead, have a look


here for examples!.
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Old 6th March 2006, 03:39 AM   #5
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Join Date: Apr 2005
Location: Simcoe Ont
Default telephone

I don't fully understand telephone circuitry but was commissioned to do a telephone talk show to be recorded and later broadcast (radio caroline).
I tried everything with the phone and eventually bought a telephone interface and used it with mixing console. The only other solution that worked pretty good was using an Aopen FM56 fax/modem and routing it to soundcard.
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Old 6th March 2006, 07:43 AM   #6
dnsey is offline dnsey  United Kingdom
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Join Date: Mar 2004
Location: Shropshire, England
I'm curious - why are you doing this?
If the 'phone's still on the network, it's almost certainly against regulations to connect peripherals this way, and there are easier ways of going about it. OTOH, if it's as a prop of some sort, why not just fit the handset with a suitable mic capsule (cheap computer mic, maybe?) which you know works OK.
BTW, if you're trying to get 'telephone' type bandwidth restriction as a special effect, this won't work - phone mics are relatively good these days - the filtering is done in the network. It can easily be reproduced in software or hardware though.
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Old 6th March 2006, 08:08 AM   #7
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Join Date: Dec 2005
Location: Kuala Lumpur
Not all modern phones are electret, my local telco demanded we use a dynamic microphone when we made phones for them.
Remember that the phone microphone is not isolated from the phone network and is sitting at about -28V with volts of 50Hz on top.
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