3.5mm mic's into mixer output to pc?

[kozikowski]

As a "from scratch" construction project, I think the box and interconnect cables are the main place to get your self into difficulties, not the circuit board. I was going to knock the board out in one evening.

I'm having flashbacks to an audio adapter I did where the maker of the cable reversed the expected colours of the wires. It took some quality time with a continuity tester and strong coffee to figure out why nothing worked.


I'm considering building the box if for no other good reason than we don't have to troubleshoot it through four (or more) time zones later.

Koz

[aighead]

Do you think you could build it from that?

I could probably build it from a picture with everything labelled really well, but it would really depend on how much money it would cost for me to make some mistakes. I'd have to use soldering irons at work...

[steve]

Buying a soldering iron would add about $15 to the cost of the project and you would then have your own soldering iron for any future projects, but if Koz is able and willing to knock one up for you... (I realise that he's not said that he can make this incredibly kind offer, just that he's considering it, so I'll keep my nose out and let you guys sort it out )

[aighead]

Yeah, I'd love to have a soldering iron and I certainly understand it's value, maybe one day when I'm 15 bucks richer...

[kozikowski]

Let's assume I do build it. I wouldn't be putting six 9V batteries in there each wrapped in its own bubble wrap. It's too easy to get into trouble with wall power supplies, too, although I had thought about it.

The supply on the Really Big Box is an assembly that accepts four AA cells in series giving me slightly over six volts applied to the circuit. The design center for the microphones is the 5v coming from the computer, so six volts is overkill. That leaves a tiny series resistor (10R??) and a film (3.3uF) plus an electrolytic capacitor (330uF) in bypass to feed all the microphones. I may not even need all that. The internal resistance of a AA battery is alarmingly low. Forget the resistor and electrolytic. Just the film for fun.

That idea also give you one single place to put a power switch and a battery "tester" pushbutton.

Let's see. 6vdc applied and 0.77v drop across the 2200 resistor with the microphone plugged in. That's 350uA current draw times six is 2.1mA. The AA batteries should last for, what, two years?

Koz

[steve]

I'm not sure if I'm correctly following that description Koz, but you need to have a reasonably substantial resistance in the power circuit or the microphone signal disappears through the battery, which as you said has "alarmingly low" internal resistance. The battery voltage is powering a Jfet transistor within the capsule. Electret mic capsules are usually pretty forgiving over supply voltage - they are commonly rated at 10v max and will usually continue to work right down to about 1v (though with reduced SNR).

If I recall correctly, the impedance of a capsule is about 1k, so with a 1k resistor in series with and a 6v supply, each capsule will have 3v across, which should work fine. It's been a good few years since I've played with these things so I could be way off.

[kozikowski]

I don't agree, but how are you posting schematics?
Koz

[steve]

I don't agree,

You could be right - I've not messed with these for a lot of years and I've been to bed since then.

[aighead]

2 year battery life is crazy, and you guys completely lost me on your circuitry talk. Good stuff, it's always interesting to be able to read a "foreign" language.

[kozikowski]

<<<interesting to be able to read a "foreign" language.>>>

You should see the secret handshake when we meet each other.

Koz