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Overheating Coils

March 7, 2014 | 6:46 am

Hello Forum,

I’m not sure this post belongs here but I’m looking for help anywhere I can.

I’m working on a project that requires controlling the frequency and amplitude of multiple string vibrators and the easiest way for me to do this is using audio signals controlled with a Max patch.
I bought this device String Vibrator – WA-9857 : PASCO, it consists of a copper coil, a rare earth magnet and an aluminium reed, I already made my home imitation (http://imageshack.com/a/img542/3199/zzao.jpg). Since this device is made to work with a 5V AC power adapter at 60hz I have the following problem:

- If I use an amplified audio signal the coil overheats.
- If I use a sine wave generator I’m unable to control the signal’s frequency and amplitude from my computer, not to mention that I would need multiple generators to control each vibrator.

I’ve also got Economy Wave Driver – WA-9854 : PASCO, which is basically a loudspeaker with no cone and a reed to insert the string. This one does not overheat but it sounds loud and my project requires no sound or a soft sound. This would be my best solution but I need a way to get rid of the sound.

I am a musician and really don’t know much about electricity or amplification, I would love to hire someone to help me build a device that meets my requirements or I wonder if any of you has any ideas or advice for me.

Thank you very much in advance


March 9, 2014 | 12:11 am

I don’t understand entirely,
but this sounds very interesting.

I would suggest that the 9854 is not going to be your animal,
if it’s mechanical noise is too much.
Although you could isolate it in like a re-amping(noise insulated) box to a degree.
Also you could use a pickup(s) on the string, that would completely
kill the noise.

Be careful if you are overheating coils mate.

I’ll think about this and keep an eye on the thread.
I am a DSP tech within Flowstone, and I use guitar pickups,motors
and magnets to generate audio signals/streams.

I’m interested to hear the goal of your project and to help.
Are you intending to make a piece of music-
or an instrument or experiment?


March 9, 2014 | 12:30 am

What if you used the WA-9857
with a line level signal, instead of amping it?


March 9, 2014 | 5:47 am

Also, I would assume that driving such a device would be best done with a pulse wave signal?


March 9, 2014 | 3:15 pm

however, dont connect it to ifft~, when ifft~ overheats it can destroy all bang buttons in the patch.


March 10, 2014 | 8:53 am

@NIX808: Thank you so much for your interest.

At the moment, is more of a visual project, I’m trying to play with distinct effects that I’ve found experimenting with strings and vibrators.

Regarding your feedback:
The economy wavedriver is basically a 5, 1/4" subwoofer. I don’t believe we’re getting sound from the string but rather from the economy wave driver’s motion, the string is made of a flexible material and it has no resonating box, even if I remove the membrane the device will most likely sound.

- Please elaborate on how can I kill the noise with a pickup.

- The visual motion of the string is the fundamental part of the project, an isolating box would need an opening to let the reed handle the string, wouldn’t this turn it into a resonating box instead?

I’m going to try using the line level signal and get back to you with any further questions.

@Wetterberg: I’m using sine waves at the moment because I like the visual effect of the constant motion.


March 10, 2014 | 3:07 pm

Yeah, the sound-proofed box would need an opening(small hole)(-or be clear/see-through),
sorry that’s not much of an idea.

With the pickup idea, you can stop the mechanical noise in a recording.
If you wire the pickup to your soundcard, you can make a clean recording.
You would need to put a steel string on the device,
or use a piezo pickup with plastic/nylon.

I’ll keep musing on this. It’s curious.
There must be some quiet actuator u could use


March 10, 2014 | 4:01 pm

>I’m using sine waves at the moment because I like the visual effect of the constant motion.

…of the driver? I thought this was about resonating a string?
I don’t think I’m getting enough info to grok your problem at the moment.


March 11, 2014 | 6:33 am

@Wetterberg: It works like this: Theres a copper coil, a magnet inside of it, an aluminum reed attached to the magnet, an elastic chord tied to the reed in one end, and then tied to an immobile object on its other end. The coil is driven by a signal at X frequency, it switches its polarity at that rate, so that the magnet inside of it jumps up and down at the speed of the given frequency (eg: 15hz = 15 jumps per second), as the string is tied to the reed (which is moving up and down), if it is "tuned" to the right distance/tension proportion, it will start oscillating in standing wave patterns, like this: http://www.youtube.com/watch?v=no7ZPPqtZEg

In my research I’ve found several effects and interesting things to exploit working with this, but I won’t go into much detail into it because thats a confidential part of the project, for now I just want to solve a technical issue: My coils are overheating when driven by an amplified audio signal.


March 13, 2014 | 8:29 am

@NIX808: I did try with line signal, with the output of an mbox mini, it does not handle enough power, the coil will respond but nowhere near to the amplitude I require.


March 14, 2014 | 4:52 am

OK, hmm.
I know 2 people on the web who can probably help,
if they are interested.
The range of the unit is +/- 1 amp at 10 volts.
You can measure the watts/voltage/amperage of the
amplified audio signal(with a multi-meter) to make sure it is correct?

I will send mails to these 2 bright sparks, can’t hurt.

The whole AC thing seems problematic though as far as the power supply-
if the power is also controlled by an AC signal/audio line level.
oh I dunno-it’s interesting though.


March 17, 2014 | 3:42 pm

G’day again,
I still have to write to my electrician friends,
I’m thinking I have 4 now.
Just a word of warning-
I would not run your stereo amplifier into this thing,
without consulting an electrical engineer.
It sounds quite iffy now that I think about it.
I’m thinking that volts /amps matching is necessary,
however also there might be an impedance mismatch-
of which I only have a hazy conception.
I think you could easily damage your amp.

So what I propose is to use an amplifier as you already have.
It may need to be a custom job. You can use an audio line signal
to control it. This can be amplified with a DC power supply.
A small amount of infidelity will be fine.
I think you will need to use transistors/mosfets,
however this needs to be built professionally.

Hope helps and be careful, all success mate


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