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simple question about microphones

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whatthe

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i need to plug a tie clip microphone into a tv's AV inputs (audio obviously). When i plug it in there is no sound at all. I'm guessing i need a preamp, is this correct ?
 

Optikon

New Member
whatthe said:
i need to plug a tie clip microphone into a tv's AV inputs (audio obviously). When i plug it in there is no sound at all. I'm guessing i need a preamp, is this correct ?
Yep!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
whatthe said:
i need to plug a tie clip microphone into a tv's AV inputs (audio obviously). When i plug it in there is no sound at all. I'm guessing i need a preamp, is this correct ?
Yes, the output from a microphone is at an extremely low level, the AV inputs are at line level - you need a high gain microphone preamp.

Also, be aware you will probably need a video input to the TV as well (although you may already have one?), TV's commonly mute the sound without a video signal.
 

whatthe

New Member
ok. i bought a preamp today from jaycar i have wired it all up but it's not working. when i use a 12vdc power supply it hums like crazy and if you tap the mic really hard you can hear the thump. i am using shielded cable. i thought the power supply might be causing interference so i then used a 9v battery and then there was no hum but if i hit the mic extremely hard i could here a faint thump. whats wrong ? below are amp specs and diagram of what i have done.

kemo m040 preamp
Specifications:
Operating voltage: 9...24 VDC
Frequency response: 10 Hz ... 100 kHz
Input: 2 - 50 mV
Output: 200 mV 1 V
Dimensions: 30 x 25 x 15 mm

mic specs:
Frequency response 20Hz - 16kHz- Sensitivity -65+/-3dB- Low Output Impedence- Directional Omni directional.- Size 30(L) excluding grommet x 13 (dia) mm
 

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Nigel Goodwin

Super Moderator
Most Helpful Member
whatthe said:
ok. i bought a preamp today from jaycar i have wired it all up but it's not working. when i use a 12vdc power supply it hums like crazy and if you tap the mic really hard you can hear the thump. i am using shielded cable. i thought the power supply might be causing interference so i then used a 9v battery and then there was no hum but if i hit the mic extremely hard i could here a faint thump. whats wrong ? below are amp specs and diagram of what i have done.

kemo m040 preamp
Specifications:
Operating voltage: 9...24 VDC
Frequency response: 10 Hz ... 100 kHz
Input: 2 - 50 mV
Output: 200 mV 1 V
Dimensions: 30 x 25 x 15 mm
50mV in and 1V out is only a gain of 20 times, and 2 to 200mV is only a gain of 100 times - this looks far too low for a microphone preamp. I'm also confused why it gives different gain figures like that?.

What is the preamp specified as?, also what is the input impedance?.

As for the hum, it sounds like your 12V PSU probably isn't much good, was it just a cheap wallwart supply?.
 

whatthe

New Member
this is all it says

"for microphones and diverse uses. This mini-module is simply connected between a power amplifier and a weak signal source (e.g. microphone). "

the power supply is off a very old mobile phone

maybe i should try this turntable preamp,but it looks like it has even less gain ?
http://www1.jaycar.com.au/productVi...d2=&pageNumber=&priceMin=&priceMax=&SUBCATID=

Input sensitivity: 2.5mV- Input impedance: 47kohm @ 1kHz- Output: 180mV- Current draw 10mA- Output impedance: 47kohm
 

audioguru

Well-Known Member
Most Helpful Member
I'll bet that your microphone type is electret, that needs power. Connect its "hot" wire to a 10K resistor. That junction will connect to the input of your amp. Connect the other end of the resistor to the + of a 9V battery and the - of the battery to the micrphone's shield.
Keep your TV's volume control turned down to avoid acoustical feedback.
 
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