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From: "Bevan Weiss"
References: <3DB1323B.1F9EA4F0@stanford.edu> <email@example.com> <3DB929D1.F8551A8C@stanford.edu>
Subject: Re: powering a bulb or led(s) with audio amplifier?
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Date: Sat, 26 Oct 2002 11:52:44 +1300
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The current being drawn from the amp by the load (speaker and bulb) will be
the sum of the currents drawn from each device. Hence if your amplifier is
rated at 100Wrms(@say 14Vrms) then you can draw ~7.1A rms in total. If the
speaker is a 4Ohm speaker (typical car speaker) then the current drawn from
it would be 14Vrms/4Ohms = 3.5A rms. Hence you could draw 3.6A rms through
the bulb. Allowing for a 50.4W bulb.
You could use a resistor in series with the bulb to limit the current to
this level, and then place this is parallel with the speaker. I'm just not
sure whether the bulb would then get enough power to illuminate correctly,
and the resistor might need to be capable of dissipating a lot of heat.
However these values will all change for different voltages etc...
To ensure the brightest light, use the highest power dissipation in the bulb
that you possibly can (up to the bulbs rating), note however that this will
reduce how much power you can put into the speakers...
"Adam Bowen" wrote in message
> thanks everyone for ideas on how to get leds to work, but i've decided
> for aesthetic reasons to go with a simpler lamp setup, as dmb suggested.
> i forgot that with leds' on/off nature, it won't glow with variable
> brightness. so a simpler question: how do i hook up a bulb so as to
> ensure the brightest peak light without damaging my amp? put the bulb and
> a resistor - relative to the impedance of the speaker - in parallel with
> the speaker?
> i know these are basic ?s, but it's been a while & i couldn't find the
> answer in my electronics textbooks.
> dB wrote:
> > The maximum reverse voltage which a led can tolerate is rather low, 3
> > to 5 volts, so they would need protection.
> > Using incandescent bulbs is easier. The bulb voltage would depend on
> > how severely you want to deafen your audience. Playing a Beethoven
> > symphonic work at a realistic (high) volume develops around 4 to 5
> > watts average in 8 ohms speakers. 5 watts in 8 ohms means that the
> > voltage across it would be a little over 6. Experiment with
> > flashlight bulbs.
> > > I'm interested in hooking up light-emitting devices in parallel with
> > > home stereo speaker. I just want it to glow with the overall
> > >
> > > I've read most stereo amps push 4-30V; don't know if this is true.
> > > like basic DC lamps should work, but I"ve never tried it. LEDs would
> > > cool - ideally, those sequenced flashing RGB leds. If necessary, I
> > > run the light device on a separate channel and rig whatever
> > > necessary.
> > >
> > > Any ideas about these, or zanier options? (this is for an art
> > >
> > > Thanks,
> > > Adam
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