[H.P. Friedrichs] sent in his Sanfordyne project a while back, but It took me a while to appreciate the effort he put in. (Partly because the write up is so long – but thorough) Grab some of your favorite caffeine supplement and take your time reading over the details. Most of the parts were scavenged, and he mechanically etched the pc board with a dremel tool.
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Pete (AC7ZL) wrote in to tell us about his latest project: building a flat response microphone and channel amplifier. You may remember his previous project: building a crystal radio from modern junk. Sounds are “colored” by their surroundings; things like furniture, wall coverings, drapes and building materials all affect the way something sounds. To measure the effect that a space has on sound you need a microphone with a flat frequency response. The core element of Pete’s mic is a modified Panasonic WM61A condenser capsule. He rewired it so that it had a broader dynamic range and could handle a higher SPL at the cost of reduced gain. To boost the signal to a usable level he built a preamp with three stages of amplification. He’s got schematics and a more detailed description on the site.
[h. p. friedrichs] (AC7ZL) has some great plans for building a crystal radio. The stator coil and output coil are wrapped around the outside of a CDR sleeve. The tuning capacitor is constructed by sandwich two clear CDs between metal and attaching this inside the top of the sleeve. The rotor shaft is mounted using the bushings from a pair of disassembled potentiometers. A hot needle is used to tap the stator coil through the housing every fifth turn. Even though the parts aren’t very traditional it looks like a really solid radio. He’s got instructions for building a matching ear piece out of tea tins too.