Electret mic to line level amp

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

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Steve Parus

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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John Woodgate

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