April 2, 2012
about 2 years ago
I had to chime in here… This preamp is exactly what I needed!
I’ve been messing around with APR9600, ISD1720, ISD1730 and ISD17240 IC modules that allow you to record voice on a chip, with most of the functionality handled by the IC. I used an electret microphone with all these voice recording modules, but found that unless I was talking right into the electret mic, the voice signal was mostly lost.
I tried using LM386-based amplifiers to boost my already-recorded recordings (as well as a Velleman 7W amplifier kit from Amazon), and while these amplifiers worked, I was mostly amplifying the ambient room noise from during the recording.
Using this microphone pre-amp solved my low voice signal problem prefectly! I ordered one of these PCBs (no, they don’t give you any parts but the PCB), added a few resistors, capacitors and jumpers/headers, an LED, a BC547 transistor and a switch, and soldered it up.
I put the electret microphone I had been using for the voice-recording modules on the pre-amp, and hooked the pre-amp output to the input of the voice-recording module. It worked immediately, and amplified the voice recording to a very acceptable level, saving it to the voice-recording module.
One caveat I found (which could certainly be related to the ISD17240 IC module I used for my final recording device), was that the pre-amp worked best for me at somewhere around 4-5 Vdc (instead of 9V as per spec.) As I raised the voltage on the pre-amp toward 9V the pre-amplification effect decreased instead of increasing. I’m sure someone can tell us why this is so, but it works out great for me as this is the voltage of my ISD17240 IC module as well.
Note: As one other user mentioned that the RCA jack PCB hookup was defective (at some point 3 years ago), I did not bother using a jack, and instead used the Out+ and Out- for the output from the pre-amp. This may be fixed by now, but I did not use it…
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