I want to record the output of a stethoscope. I plan on connecting an electret mic to the earpiece and amplifying the output to feed to a recorder. I have found a one transistor amp with 30 to 40 db gain, but I don't have a transistor with hfe as high as the design(bc549c). I'm looking for a two transistor design using 2n2222 or 2n4401. Most designs I see have an opamp after the transistors. I just want a simple circuit to raise the mic level to line. Thanks for your help Mike
Electret mic to line level amp
Jan 19, 2005
3 Replies
Look around in
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May be something useful there.
- YD.
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I read in sci.electronics.design that Steve Parus wrote (in ) about 'Electret mic to line level amp', on Thu, 20 Jan 2005:
Project 13 Figure 1 looks OK. For transistors of lower beta than BC549C, reduce R6 to 47 kohms. If necessary, adjust that value to get symmetrical clipping of the output with a 1 kHz sine wave input signal.
Figure 2 appears to imply running the LM324 from 30 V, which is a bit too close to the absolute maximum of 32 V for my liking in a homework project.
Regards, John Woodgate, OOO - Own Opinions Only.
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http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
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