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Re: [Phys-l] amplifier

To echo Barry, I rarely make amplifiers (although this chip at $1.50 each being surplussed at Electronic Goldmine looks very interesting). Instead I go to Goodwill and Salvation Army with a speaker and a source and just try out what they have. You can easily get 50 to 100W amps for $10 or $15 with lots of handy imputs and multiple speaker outputs. One amplifier can usually run at least two pair of speakers. I particularly like using off the shelf stuff so that students won't think there is anything funny going on.

If you are willing to spend more money and have some good 12 V power supplies hanging out, you can get car amps. The advantage of these is that they will often handle very small impedances without melting. When I run my vibrating wire resonance lab -- running an amplifier output of a varying frequency through a stretched wire near a magnet to find resonances -- I use a car amp. The impedance of the arrangement is tiny, but the amps get hot, but don't seem to mind.

My favorite sound generating device is the xPlorer GLX from Pasco. It's pricey but handy for other things and seemingly bullet proof. My favorite sound generating software is Test Tone Generator, but it isn't free. This program, Scope, works great. It produces tones, including sweeps, can do frequency analysis as well as acting as a low frequency scope.

Marc "Zeke" Kossover

----- Original Message ----
From: "Carolan, Barry" <>
To:; Forum for Physics Educators <>; Forum for Physics Educators <>
Sent: Wednesday, April 2, 2008 6:11:11 AM
Subject: Re: [Phys-l] amplifier

I'd keep an eye out at yard/garage sales in springtime. It's amazing how many
people will sell decent amplifiers (10 or 15 years old but still working great)
for $1- $5, especially when so many people want to replace their old amps with
"surround sound" amps. You will need to buy a mini-plug to RCA cable at
radioshack or a dollar store to connect your ipod. The back of a decent amp
will have plugs that you can quickly switch the speakers out of phase with each


From: on behalf of Arlyn DeBruyckere
Sent: Wed 4/2/2008 8:33 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] amplifier

Amplified speakers for computers are rather inexpensive (I got some for
about $20). Cut the cord on the "last speaker" (the one without the
controls etc) and reconnect the wires backward. If you still want to
normally use these speakers I suppose you could put on some RCA male and
female connectors or other similar connectors and switch them as
required. Otherwise just keep the modified set for your experiments.

Anthony Lapinski wrote:
I'm teaching about sound and want to reverse speaker wires (red/black) to
show constructive/destructive interference of sound waves (music) with two
speakers/microphones and an oscilloscope. In the past I used cassette
tapes, an old boom box (volume turned up), and old speakers. I would
reverse the (red/black) wire connection (via alligator clips) for one
speaker while the music played. A bit cumbersome, but it worked.

I now have some songs on the computer (iTunes) and wish to repeat the
demo. However, the old stereo speakers (connected via the earphone jack on
the computer) are not loud enough. The new computer speakers are very
loud, because of the amplifier built in, but I don't want to strip the
wires on them.

So I need an "inexpensive" amplifier to boost the loudness from the
computer (1/8 "earphone jack) to my old speakers. Does anyone know where I
could purchase such an item? I assume Radio Shack might have some stuff.

Any better ways to do this demo?

Forum for Physics Educators

Arlyn DeBruyckere
Science Teacher
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Hutchinson High School
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