Hi, I have a small mic very similar to the one shown here: http://www.altronics.com.au/cat.asp?cat=7&grp=72&id=C0160 except a little higher quality. I was wondering is someone could give me a schematic for a circuit I can attach this to so I could plug the output into my guitar amp? Preferably the circuit would have a volume control plus maybe a tone control!
Thanks for your help!
No tone controls but:
http://minidisc.org/mic_preamp/Simple%20Stereo%20Electret%20Mic%20Preamp.htm
Not sure how well the output of it would behave with a guitar amp either. If you plan to play at a decent volume, my guess is feedback will a problem with that mike into an amp?
Kerry M
I made something like that about 15 years ago to record class lectures with something better than the usual built-in condensor mic in cassette machines. Worked great.
The gain on the one linked to by Kerry goes from a little over x2 to x23. The higher gain is probably enough to bring the output of the mic cartridge up to what a guitar pickup will normally deliver. If you want, replace the 27k fixed resistor with a 25k pot wired as variable resistor.
For altering the frequency response, you can play with the values of the series caps, in this case the 2.2uf caps before and after the op-amp, to alter low end response. High end shaping can be addressed by altering the value of the capin the feedback loop. In the circuit shown, a 2pf cap will yield a rolloff starting at just over 2mhz. The author of the design provides what is likely a reasonable approach to setting the value, except that it is geared towards something a little more audiophile-oriented than a guitar amp. If the intent is to plug this sucker into a guitar amp that will also be carrying guitar signal, you can relax your requirements for keeping phase shift to a minimum and bandwidth to a maximum.....a whole lot. T'wer me, I'd stick a 330pf cap in there, for a rolloff starting around 14khz. More than enough bandwidth for your average guitar amp speaker.
One of the things I did to my mic preamp was to stick in a bypass cap on the output level control, just as you'd find on some guitars and on the "bright" channel of some amps. By tweaking the value of that cap and the value of the feedback cap, I could get a nice upper midrange peak in the output of the preamp that made voice more intelligible. Of course in my case, the intent was to have all the usual classroom noises (mumbling, paper shuffling, ventilation, etc.) recede into the background. Your particular context may have different sorts of bandwidth or band-sensitive requirements. Still the basic principle works nicely: you can use different cap combinations to emphasize and de-emphasize in such a way as to shape preferred frequency response for your purpose. Just be aware that the more you restrict bandwidth, the less amplitude or cutting power the mic is likely to have. One more reason I suppose to have a broad range of gain possibilities.