Ruby amp as a mic pre

[juancra]

Hi All!

I've built a ruby amp as it is in GeneralGuitarGadgets site to use it as a simple mic preamp. I didn't need something very special, just wanted to amp a PC Mic, but it doesn't work. I know the circuit is Ok because I tested it plugging in a FM receiver, and also tested the mic in this PC and works OK, Does anyone have an idea if the Ruby is suited to that particular task?

Thanks a lot in advance
Sebastian.

[brett]

Hi
what type of mic are you using?
A condenser mic will probably want "phantom" power.  A dynamic mic will want a heaps of gain (ie leave pins 1 and 8 disconnected).  Do you have both "hot" and "cold" as well as earth?  If so, are you connecting cold and earth, or are you doing something different?
Any answers will help us to help.
cheers

[juancra]

Hi Brett!

I'm only using one of those cheap PC mics. Not a professional one.I built it because I work as a cashier and some people doesn't hear me well at the other side of the glass.

[brett]

Hi
there's a good chance that it's an "electret" type mic, and needs a few volts of powerfor it to work (it's got a JFET inside IIRC).

Here's a link showing how to get 4 to 9V into the mic, and get the signal out. (and a bunch of other stuff about PC microphones)
I'm sure Wikipedia would also have something, under "electret microphone".

Because electrets have high output, I'd guess that the Ruby would work in standard form.

cheers

http://www.epanorama.net/circuits/microphone_powering.html

[juancra]

Thanks for the help,Bret  I will see if it helps and post an answer when I get it!