Yamaha CA2010 LEDs

A simple project this time: improving the appearance and longevity of the panel meters on the Yamaha CA2010 series amplifiers.

A customer wanted his CA2010 lamps replaced and so I set about looking in my stock to see if I had anything appropriate. A number of different incandescent lamps turned up which fit the bill but I still didn't feel satisfied with the appearance and the fact that they'd only burn out again in time. I recalled having obtained a batch of bright whtie LEDs from a friend and so decided to try these out.

A simple circuit modification is required as the original panel meter lamps use 12 volt AC power. Applying AC directly to the LED (through an appropriate current-limiting resistor) would work but leaves one with LEDs flickering at 60Hz which will annoy some users (like me). The addition of a series diode to the LED circuit prevents reverse current from occuring (which can fry LEDs) and also allows the addition of a smoothing capacitor to provide flicker-free operation.

In the original Yamaha circuit all lamps are connected in parallel across the 12V winding on the transformer with the addition of a red power LED in series with a diode. What I've done is remove the original lamps and replace each one with a series LED and resistor combo. As seen in the schematic below, the 680ohm resistors provide the desired amount of current for the LEDs (about 20mA depending on line voltage). The 1N4007 diode is added in series with the original power wire and an electrolytic capacitor added in parallel with the rails along the circuit board to prevent flickering.

The result is as you see below: a row of five LEDs with their resistors in place of the original incandescent lamps. The panel meters have a much sharper and more vivid look. The power LED will also be brighter because of the higher average voltage (rectified and filtered AC becomes DC with a steady voltage same as the peak voltage of the AC minus losses such as diodes and ripple).

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