intro Build a Battery-Powered Amp for an old Carbon Mic
A friend of mine acquired a 1970's aviation-style headset for use as a live gaming prop. This Instructable documents the development and construction of a stand-alone amplifier and general-purpose adapter for it. I was much aided in my task by other Instructables, as well as helpful hints in various audio forums.
The first problem to solve is that carbon-button microphones , like condenser mics, need an external source of power. A battery and a resistor in series with the mic gets you a current loop (the resistor limits the current) and then you can pick off the audio at any two points with a voltage drop between them. A single AA battery and a 1K resistor is enough to get a s…
Once it is working on the breadboard, record everything for transfer to the more permanent circuit board. Don't forget to note the polarity of components like electrolytic capacitors and LEDs! Protoboard is "perf" board with a copper pattern on one side. The copper is laid out similarly to how a good breadboard is laid out. It is much easier to connect up IC's on…
This starts with a metal "project box" bought at the local electronics hobby store. The knobs came from the same place -- or you can salvage for that good vintage look. We all know how to design a case. Collect the knobs and switches, balance them on top or stick them on with masking tape, and move them around until you like the arrangement. However, a tight case l…
Cover the areas where the drilling is to take place with masking tape, use rules and straight-edges to make centers, and use a center punch if you have one to tap the holes for better centering of the drill. For larger holes, start with a pilot bit (a small drill bit) and then enlarge. If the drill gets caught in the thin material, reverse it to break the chip loose. …
step 5Finishing Up
There are always new mistakes to be made. The LED bezel has a rubber insert designed to be slid over the LED's leads. I forgot and soldered the LED. Fortunately, the insert could be sliced lengthwise with an X-acto knife and squeezed around the leads and it worked just fine. The speaker had no mounting holes, and the bots from the decorative grill stuck out. I cu…
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