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A very common guitar upgrade is to swap out crappy, cheapo, open-backed (or “stamped”) tuners and replace them with better, enclosed die-cast tuners. I’d like to show you how to do that, and point out a few potential dangers along the way. The example shown uses an acoustic guitar with 3-a-side tuners, but you could follow the same process for an electric, be it 3-a-side or 6-in-line. Click on any of the images to see bigger versions. Here’s the patient. The guitar itself plays well and sounds pretty good, but the tuners have become almost impossible to turn, so it’s time for a change. Although these may look like enclosed tuners, they are simply open-backed tuners, with nothing more than a back cover, which doesn’t even stop dust from getting in. Decent enclosed tuners can be had very cheap these days. This particular guitar didn’t really warrant Schaller or Grover tuners, but the replacement no-name tuners it is about to receive are a huge improvement over what was there before. I sh...

On most FM tuners, the stereo indicator lights upon detection of the 19-kHz pilot tone. However, this doesn`t mean that the program is actually stereophonic, since the pilot tone is often transmitted with mono programs also. A similar situation exists on stereo amplifiers, where the stereo LED is simply controlled from the mono/stereo switch. The LED-based stereo indicator described here lights only when a true stereo signal is fed to the inputs. Differential amplifier Al raises the difference between the L and R input signals. When these are equal, the output of Al remains at the same potential as the output of A2, which forms a virtual ground rail at half the supply voltage. When Al detects a difference between the L and Rinput signals, it supplies a positive or negative voltage with respect to the virtual ground rail, and so causes C3 to be charged via Dl or C4 via D2. Comparator A3/A4 switches on the LED driver via OR circuit D3/D4. The input signal level should not be less than 10...