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Mic will only pick up breathing... not talking

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daviddoria

New Member
i got this:

http://www.electro-tech-online.com/custompdfs/2003/01/k32.pdf

mainly just to practice soldering and learn basic color code/ cap codes

when i turn it my radio locks on perfectly. i hear absolutely no static. when i blow into the mic, i hear it on the radio (this is the whole point). when i talk into the mic, i hear nothing. I tried lowering the 47k resistor before the mic all the way down to 1k, and nothing changed. anyone have any ideas?

also, not shown in the diagram in the pdf, there is a hole in the PCB that says TAP. i am wondering what this is?

thanks
david
 

herbymcduff

New Member
Why don't you check cap c1, and make sure it is not leaky. Also check t1 and see if is working properly.

Also, why don't you run through your circuit and check all the soldering connections with a magnifing glass. It could just be human error.

And if all else fails, your microphone could be bad. It should be a sensitive mic, and it should be able to pick up you voice easily.
 

daviddoria

New Member
1) what does leaky?
i check the soldering, no problems.

am i right in assuming that the circuit is fine because its transmitting breating easily?

would that then mean its a bad mic?
 

bogdanfirst

New Member
well, i had that kind of problem. many kits come with not such quality mics, so that might be the problem, but could be something else, if u have a big signal, then you hear it(considdering that when you blow into the mic you create a bog singnal), but a smaller signal from the mic like the voice is not transmitted. try r1(47k) ttry to replace it with a smaller one, a 33k or 27k, it might work. an check the bc547 transistors, some of them have a much smaller gain then on the catalog.
but still i would try another mic, buy a cheap one, but is you see the same results it means its not the mic.
also check c1 and c2, and maybe put a 47n in place of c1
 

daviddoria

New Member
i replaced R1 with all the way down to a 10k and also i replaced C1 to be sure it wasn't "leaky". still all i get is that blowing into it works, but speaking does not.

any other suggestions?

thanks
bump
 

bogdanfirst

New Member
well, it might be the microphone...try another thing: disconnect the 47k resistor and in place of the microphone put a normal speaker...it should work, although you would have a smaller signal.
o, and another think, are you sure that you dont hear your voice in the radio because you speak too loud? just a suggestion :D
 

daviddoria

New Member
haha yes, i had a friend listen for me so i knew i wasn't just talking too loud.

also, i just bought a brand new mic so i'm sure its not the problem.

any other ideas? doesn't make too much sense to me.

david
 

kinjalgp

Active Member
I think its tunnig problem. Try turninig C12 entirely on both sides and se where you get perfect sound. I had a FM mic which I use to get on 2 different frequencies on my radio. One was clear and other was similar to yours, I could only hear the tapping sound. This I guess was due to absence of harmonic suppressers in the transmitter circuit and thus my radio was also catching harmonic frequencies but not very clear enough.
 

daviddoria

New Member
hey, what do you mean by C12? i dont see a 12th cap... i would really like to get this resolved though. thanks

david
 

kinjalgp

Active Member
C12 is 5-20pF trimmer capacitor in the LC tank circuit connected to collector of T2.
 

daviddoria

New Member
sorry to keep this thread going... but this is still not working. I've tried all of the suggested remedies..... just doesn't make a whole lot of sense to me.

maybe someone will have an interesting insight?

thanks
david
 

wovk

New Member
just a suggestion... I don't know if it's a good idea but you can put an op-amp voltage follower before the C1 cap... to make a kind of pre-amp .... could anyone can tell me if that take sense?


you said : also, not shown in the diagram in the pdf, there is a hole in the PCB that says TAP. i am wondering what this is?

in the PDF it say that you must connect the center tap of the coil L1 to it.. that's done???

good luck!
 

daviddoria

New Member
haha yes i found that, and did it... didn't seem to change anything....

also, how do i make an op amp voltage follower?

i've kinda set this aside, but it would still be cool to get it working

thanks
david
 
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