Need meter light alternative for Sunfire Cinema Grands

[daiku]

I have 2 Sunfire Cinema Grand Amplifiers that I have been using with my various Martin Logan Surround Sound systems. On both amps, over time, the light for the front meter burnt out. I am new to Electronics, but I am building some Twisted Pear Audio kits to get me started.

Can anyone recommend a simple LED solution and schematic that I can easily introduce into the Sunfire amps as an alternative to the bulbs? Keep in mind, I am a newbee, so please point me to the attachment points etc.

Also, does anyone know if Sunfire is still around and servicing their products? I am guessing I probably will need some cap replacements sometime soon, or at least a checkup. Amps have been great in general, however, and have been a constant in my various high-end systems for a long time.

[Michael Bean]

Why don't you just replace with the same lamps that are already there?

MIke

[daiku]

Been there, done that. They have gone out twice in each amplifier, so I am looking for a longer life solution like an led

[Michael Bean]

LEDs tend to emit a narrow beam of light and bulbs will usually have a nearly omnidirectional illumination pattern, so you'll need to figure out if LEDs will be able to adequately illuminate the meter face. Then you'll need to figure how to physically mount them in place of the lamps which will probably involve some modifications to the amp. Then you need to know if the lamps are powered by AC or DC source and what voltage, if it's AC you'll need to add a rectifier, and in either case you will have to calculate the resistance and wattage for a current limiting resistor.

MIke

[daiku]

So the led acts as a resistor? All I know about diodes is that they allow current to flow in 1 direction? Could i test for a dc voltage supply and tap off of that or would that change the values in the rest of the circuit?

[Michael Bean]

No, a resistor is necessary to limit current through the LED. And although LEDs are a type of diode, they generally have specs and ratings that are very different from diodes used for rectifying AC. In normal operation, they generally need anywhere from 1.4 volts to as much as 5 volts, and current range from around 2 mA to no more than 40 or 50 mA depending on what type it is. They also tend to have a rather low reverse breakdown voltage, about 5 volts, and cannot tolerate any more than about 100 micro-amps reverse current, thus needing a rectifier diode if operated from AC. You should be able to operate LEDs off the DC supply in the amp. Take a look at this to help you calculate what you need:

LED Resistor Calculator

or this:

LED series parallel array wizard


Mike

[jkuetemann]

The rectifier is to prevent the reverse voltage that would occur once in every AC cycle from damaging the LED, they tend to have low reverse voltage ratings.