Science Buddies: "Ask an Expert"

Hey, i have built the wire recorder as described by the "Recording on a Wire" article, and during experimentation I encountered a slight problem.

I have the apparatus set up, and I know all the connections are working beacuse i get an equal resistance reading throughout the circuit, and when i have the core plugged into the input of the amp i can touch the steel wire to the core and I can hear the disturbance through the amplifier. I also know that during recording, voltage is entering the transducer because i have a volt meter hooked up to it, and can see it fluctuate with the various intencities of sound that i put through the microphone. The only problem is that during playback, i can only hear a very very faint reproduction of the recording, and the playback voltage is so low that I get the odd reading of -0.01 volts if anything.

So, the question is if anyone has any ideas as to why the recorder is perhaps not recording anything on the wire, keeping in mind that I am using the suggested materials, or how to make the recorder embed an actual high fidelity recording on the wire. The wire I am using is some steel guitar wire, much thinner than the piano wire used in the article (im pretty sure thats a good thing). I did before have some old wire recorder wire, but it was breaking way too often so I decided to go with the more durable and thinnest guitar wire at the local music store.

Some other details include that the gap cut into my core is similar to the one shown, and I have a resistance reading of around 10 ohms in my core.

Perhaps if the core is separated in the back of the ring, where i super glued it together and wrapped it in wire, if those two ends of the iron core were to not be touching, would that ruin the transducer?

anwyays, any ideas would be appreciated. Thanks.

Hi Ayman33.

Three hunches:

1. If you input "Recording on a Wire" into the Search box on the top of the "Ask an Expert" page, you get as one of the top hits a posting by amyc:
The "Recording on a Wire" project (https://www.sciencebuddies.org/science- ... p015.shtml) on the Science Buddies site has been updated to include information about the size of the ferrite beads that can be used for the project.

The materials list now includes this updated information:

"at least 5 ferrite bead cores, more if you want to experiment with the number of turns on the coil. For example, part # 495-3847-ND from Digi-Key. Other ferrite beads with similar dimensions (10.00mm O.D. x 6.00mm I.D. x 4.00mm L) should work too; "

Have you tried this?

2. Look under the "Experiments" section on the project page, particularly #5:
Use the digital multimeter to measure the voltage of the coil on the read/write head during playback.

3. Read the text under "Note Before Beginning". It's difficult to do remote troubleshooting. If the above don't work, is there anyone local who can help?

Given that you can

hear a very very faint reproduction of the recording, and the playback voltage is so low that I get the odd reading of -0.01 volts if anything.

Congratulations you have a "working unit", not ideal, but it IS working. If you are trying to use a DC voltage meter to measure your low voltage AC audio signal, you are going to get some random readings. Measuring AC signals with varying frequencies and amplitudes even on the lowest AC voltage scale using a digital volt meter is problematic. These meters are designed to measure steady state (constant frequency and constant amplitude) signals.

Now, what can you do to get more output from your recorder? You can try increasing the voltage/current/power used to record the signal on the wire. You can try decreasing any spacing between the wire and the gap. You can try using a smaller gap. You can try increasing the magnetic field interactions by adding more turns to the recording and playback head(s). At some point, you will distort the signal recorded on the wire if you attempt to increase the power/magnetic field coupled into the wire beyond its saturation levels. You can try a higher gain playback amplifier.