3 gain ranges: 2x (concerts), 23x (acoustic music), 72x (nature sounds).9V "plug in" power for microphone input (no additional battery module needed).microphone in and out (1/8" stereo jacks).My 1st prototype was built on protoboard (see pictures below). I also have a (as yet untested) PCB layout design below, which should make building this unit very easy. The preamp runs off a 9V battery, and has an on/off switch.įor size, stealth, and plain "cool factor" i've housed all this into an Altoids tin. The preamp also supports 2 types of electret microphone, standard, and "modded" - which is the wm-61a's FET wired up in "source follower" mode (some call this the "linkwitz mod"). The preamp supports 3 different gain levels, 2x, 23x, and 72x, and has an attenutation (volume) knob at the output of the circuit. It's expected that 9V is applied across the microphone capsules, which help them handle higher SPLs, and the preamp provides this voltage at the input. The microphone is simple, just solder on some capsules to the ends of 1/8" minijack cabling and secure with hotglue and heatshrink. Compare this to professional models at $200 or higher. The whole kit can be built for as low as $30 in parts. When powered, it supports very high SPL and can record quiet ambient sounds as well as loud concerts. It is based on 2 Panasonic WM-61a electret microphone capsules (about $1.80ea at digikey), a preamp circuit running off of a 9V battery all packed into an Altoids tin. This is a high quality, yet inexpensive, stereo microphone suitable for line-in level inputs. MintyMic - a DIY powered stereo microphone + preamp with line-level outputs and adjustable gain control
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