Lumina speaker replacement specs?

[daverob]

A second question:
can you use a LED to work as a resistor, On some machine from Japan that are Made into Desktops and Cyclic Machines they do ?

Now that's an interesting question. I assume that it works otherwise they wouldn't have done it, but can't think of how it would work without producing a whole load of distortion.

Not having seen it, I'm guessing that it could be wired in one of two ways, either across the speaker terminals or inline with one of the wires (in the same way as we add volume controls). Across the speaker terminal will probably blow the LED quite quickly, as the amplifier produces a lot more power than an LED can handle, so I suspect it's the other way.

This would effectively rectify the audio removing one half of the AC signal, thus halving the amplitude (but also producing a lot of harmonics and distortion). There would also be a 2v voltage drop across the LED, which would cut about another third off the loud signals, and effectively wipe out the quiet bits. So yes this would cut out about the similar amount of audio as a 50 ohm resistor, but I suspect the distortion would be terrible.

The only way I can think of that it would work the other way (LED across the speaker terminals) is if it makes the amplifier chip thinks that there's a short circuit across the speaker terminals and go into an overload protection mode which attenuates the audio.

I'd be interested in seeing pictures of how this is wired up, and an objective appraisal of the audio quality of this approach.

[arbycoffee]

next time I get one in I will photo and record the sound.

thanks

[logicprobe]

Daverob is dead on in that explanation.
(His teacher HAS to be proud!)

As a volume control, a diode WOULD reduce sound... but at the cost of major distortion.

[daverob]

Daverob is dead on in that explanation.
(His teacher HAS to be proud!)

Thanks Logicprobe. As I'm pretty much self-taught in electronics, I believe you are correct.

The only other thing I thought of, is that with the LED inline with the speaker, you're looking at an LED with a current limiting resistor of only 8 ohms (the speaker) driven by a voltage source that peaks at about 8 volts (which is likely to drive the LED with a lot more power than it's designed to take). So I can't really see how it would work without blowing up the LED. There must be something else going on that I can't figure out (yet!).

[slothappy144]

The job of a diode is to limit current one way like a check valve*, so it would chop the AC signal in half. Distortion would be unavoidable. IMHO.

* There are exceptions to this of course, a Zenner diode will pass current above the design threshold limit.