BootlegMic doesn't work...

[kweks]

Hi.
It's summer and music-festival season, so thought I'd make a bootlegMic.

I grabbed the parts from my local electronics shop (Paris, France). They didn't have any 4 prong jacks, so I just used the cable from an old hands-free kit.

The build went fine, but when I try to make recordings with it (iPhone) - I get 'generated noise' - it goes:
Click-click-CLICK ... Click-click-CLICK ... Click-click-CLICK ... Click-click-CLICK ...
with little snatches of audio. It's perfectly timed and repetitive.

I've tested everything for continuity, it's all in order - no shorts, no shorts between components or cables.

There are only two things I can think of:

1: the microphone I have (see attachment) - has a slightly different layout - I cut on the right side, between the leg and the 'bottom' pad - as per the instructions.

2: perhaps I melted the microphone while soldering - but not sure how that would generate repetitive static.

The mic (untouched)


The mic (in situ)


The audio file:


Any ideas? Thanks a bundle!

[guest]

the audio coming in and out is usually due to the iphone trying to detect whats attached. it pulls a little current through the circuit, and if its out of range, it assumes nothing is attached, and shuts off the mic in circuitry.

this current is fixed for a particular microphone. so it might be good to check that the microphone works with the circuit before putting the mods in. short out the 2.2k resistor, and disconnect the capacitor, and see what it does.

[kweks]

Thanks kindly.
OK - so, disconnecting the cap and shorting the resistor - the mic works perfectly w/ the iphone.
Re-connecting: clickity-click.

The only difference between the specs and what I have is that the cap is rated to 100V (they didn't have 10V on hand) - but that should be ok - ditto on the 1% tolerance resistors.

Most perplexing, any ideas where to go from here?

[guest]

try just putting the 2.2k resistor back in
and see if it works with that part

[kweks]

Hey - works without the capacitor.
Swapping the old one out for a new one, same thing - clickity-click.

Again, the only difference is that these caps are rated to 100V - seems odd that that could be it - but I guess it must be ?

[guest]

so here is what i think is happening:
when the iphone tries to detect what is attached, it puts a bit of current into the microphone. but, since the capacitor is there, all the current goes into the capacitor, and it gets a false reading. i was having some trouble exactly as you described when i was prototyping the bootlegmic. i was also using a long cable. perhaps the cable has something to do with it. perhaps try with a shorter cable. and if that doesnt work, try with a smaller capacitor, perhaps 10uF.

and give it a listen without the capacitor. the main function of that portion of the circuit is to reduce the volume a bit more. so maybe the volume is ok without it.

[kweks]

Hey - thanks kindly for your prompt replies.

Here's what I did:
Cut the cable right down - same deal (clickity-click)
Changed the cap for a 22uF, 50V - same deal (clickity-click)
Changed the cap for a 10uF 50V - same deal (clickity-click)

It seems that the inclusion of the cap is what is inducing the click click...

[guest]

are all the connections going to the right places
ground should be going to the second to last ring
and the microphone signal on the very last ring
and the capacitor/resistor combo goes from signal to ground

does unplugging it and then replugging it in quickly make any difference

i wonder if its possible to tell the iphone to not switch
are there any settings where it can be placed into external mic mode?

[kweks]

Hey -
Double checked everything from the ground up (From measuring the resistors to make sure they were the correct values) - desoldering everything and starting all over again.

Ground is 2nd last ring - and is bridged via the 2.2k resistor to the source pin.
Signal is last pin - and is bridged via the 470ohm + (now) 10uF 50V cap to ground.

There are no leaks. When I bridge the cap (leaving the 470ohm in place) - it works w/ the iphone.

Unplugging / plugging rapidly doesn't seem to make much of a difference.
Bridging the cap and then unbridging after recording has started results in the clickity click.

... :-/

[guest]

you can try recording with the 470ohm resistor in place and bridge the cap. the capacitor is just there to keep the voltage in the right range, but the microphone you have is different, so maybe it is not necessary.

another thing to try, is to put another resistor in parellel with the 470ohm/22uf combo. try 2.2k. the larger the better, but too large might not have the bypass effect we are looking for.