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.