[Sticky] USB-C Microphone (official topic)

is it normal that the drain and source pins on the transistor make contact? if yes how does he check the polarity of the thin copper wires when soldering them to the actual audio cable? 

Its been a few weeks since I last posted anything here. 

I thought I would provide an update. I could not figure out what was wrong with the other board unfortunately, I gave it an hour or so and I could not for the life of me figure out where the issue was. So I ended up de-soldering all of the components except for the resistors and DIP socket and just remaking it on a new board, which in hindsight was a great idea as it made the whole board much cleaner and it fixed my zero-noise issue.

Unfortunately I have a new issue now, however I think I can probably fix it this time. I think I need to just redo the connection between the capsule and the cord on the arm where the solder braid is. 
By touching where it joins I can make it make some interesting noises, and I think there is probably something loose inside of it where I spliced the cable to the solder braid. I can hear my voice fine (sometimes) and a few times it has been pretty clear audio. For the enameled wire I just used wire from an old car relay I had for some reason, and since I am going to remake this part I ask the question: How thin is too thin? My wire measures around 0.1016mm (.004" with my 1" micrometer) and I am wondering if maybe Its a tad too small. I can easily source a slightly thicker wire if it is thought a good idea. 

Also, I have attached a few pictures of the board, the wire, and the 'finished' microphone just in case you wanted to see it. I have also added an audio clip, where I first turn the gain select switch up higher and higher, then after I speak for a second I start pinching the connection I referred to above. As usual I am happy for any feedback you may have and am curious if you would agree with my thoughts on what to try next.

Thanks!

Posted by: @jonata

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is it normal that the drain and source pins on the transistor make contact? if yes how does he check the polarity of the thin copper wires when soldering them to the actual audio cable? 

The drain and source aren't special on this particular part. It's as easier to think of them as a three terminal device with only the GATE having to go in the right place. The other two leads (which aren't shorted!) provide a route for the current to follow.

@guinea First of all, bravo dear boy. That puts mine to shame I can tell you!

I think there might be a tiny short in there but you can use any screened cable you can get in there. The diameter of the twisted pair isn't particularly problematic, thinner wires might look nicer but they're a nightmare to work with.

I'll let you in on a little secret - you don't *need* to screen the interconnect, but it's a good idea if you do. The three wires twisted together (and they can be normal cable) can run a metre or so without picking up a huge amount of RF (which is going to be mains hum and its harmonics).

I've done this with a variety of designs and it seems to work - at least it's good enough to test stuff and see that a voice is coming out and it's not distorted. You can deal with the mains hum (if present) afterwards!

I want to make this project on a copper clad board do you have the diagram to do this? and can you use a 600k pot for the gain 

@diyperks the link is a dead link

@autismdad There's the open source one I did (probably a couple of pages back now) the Perks Alpha which has a couple of minor improvements. A guy did one years ago that looked interesting but it's WAAAAY back.

Sorry, yes you can use a pot but you obviously are going to be cognisant of volume. Once you're comfortable with the gain you can put a fixed value in there. Probably a few hundred ohms.

Posted by: @autismdad

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@diyperks the link is a dead link

Which link has gone to Wave Function heaven?

@marcdraco https://www.computersense.co.nz/forums/showthread.php?tid=209&pid=365 this link is broken

I've emailed them. Is it Oz's Gebers you were looking for?