Musical Hard Drives

If you love MacGiver you will love how I turned old hard drives into speakers for a Hi-fi system.

One of my favorite spot at work is the electronic dumpster, it's a great source for materials or spare parts.

During my last visit to the dumpster of wonders I found :

• an old Hi-fi system but no speaker to go with it.
• There was also a pile of old hard drives (busted or really old)
• electric wires.

My first intention was to use those old hard drives to add real percussion capability to my Musical Floppy Drive system. But during my fiddling to find out what voltage was required to get the reading head arm to move all the way from one side to another I manage to get sound out of the HDD.

And then things got interesting.

(I apologize in advance for my bad English)

1. Basic tools :
   • Flat, Philips and Torx head screwdrivers
   • Soldering iron
   • Multimeter
2. For the simple demonstrator :
   • Hard drives (HDD), at least one for mono sound and two for stereo sound.SSD are not good for this project.
   • An audio cable with connectors that match your sound source (like mini jack earphones).
   • A sound source (mp3 player / phone / computer / Walkman / ...).
3. Optional (if you are ready to go the extra steps and make it better) :
   • One or two plastic cups
   • Thin Electrical cables (~24 AWG like HDD's IDE cables) and 20 AWG (to connect to Hifi's speakers ports).
   • An audio amplifier or assimilate (hi-fi, car radio) if you want it to be loud and see the actuator arm move.
   • Wood planks or wood box to make a sound box.
   • Nails, hot glue.
   • Small screw terminals.
   • As many different kind of HDDs as you can find.

Now that I have your attention, let's continue.

Ok maybe this one is not that obvious : magnet and coil.

• In a speaker you have a permanent magnet and a coil (impedance can be 4 / 6 / 8 / 16 / 32 Ohms).
• In a HDD you have an actuator with permanent magnet and a coil (its impedance is around 7-11 Ohms).

So those two are really close electrically speaking.

For more informations check the Wiki page https://en.wikipedia.org/wiki/Hard_disk_drive

Let's go to the next step to do silly things.

Identify coil's pins :

• Open the hard drive by removing the top cover (optional, but it make everything easier).
• Remove the electronic board under the HDD.
• Find the actuator arm connector (that's the one with the most pins) and using the multi-meter (10 Ohm caliber or Beep) try to identify the 2 pins going to the coil (you are looking for 7-11 Ohms).

It's a bit difficult. If you can't find them try following the coils wires starting from the coil and going to the connector (It's the bigger tracks on the flexi-cable).

Time to attach everything together.

Solder the audio cable :

Once you have identified coil's pins solder the audio cable to them (there is no polarity).

I used old earphone with a 3.5mm audio jack connector :

• Cut speakers off
• Strip the wires (on a stereo jack you have left audio, right audio and ground),
• For mono sound connect right and left audio together and solder to one pin of the coil, solder ground to the other pin.
• For stereo sound (you need two HDDs), Solder right audio to one pin of HDD1 coil and ground to HDD1 other pin. Solder left audio to one pin of HDD2 coil and ground to HDD2 other pin.

Time for testing :

Connect the jack 3.5 to an audio source (phone, computer, Walkman) and turn the volume up (all the way up !).

The sound is weak but audible (if you attach two HDDs in place of an headphone speakers you'll get a functional, and yet a bit impractical headphone).

You can improve easily the sound by :

• Using IGMEC "I Get My Ears Closer"
• Gluing a plastic cup the the arm (it will act as a flaring horn).

Want more ? I can help with that in the next steps.

Ways to improve :

• Find the right HDD that is loud and have the right pitch.
• Keep actuator arm at a precise position.
• More power from audio source.
• Make a Loudspeaker by combining multiple HDDs together.
• Add a sound box or speaker enclosure.

Try to change some parameters :

• Size : 2.5" or 3.5" or even 5,25" (be careful those ones tend to have a stepper motor in place of the actuator -> that's not good)
• Manufacturers
• Manufacturing time period : old 200Mb from the 90's to some 100Gb or 1Tb modern drives.
• Technology : mono or multi platter, 5400 / 7200 / 10000 rpm.
• Actuator arm that move freely or a more resistant one

It's up to you to assemble the HDD team that will fit your needs.

Some HDDs have a parking position for actuator's arm and a locking mechanism, you will need to disable it (refer to pictures to see some of those I came across).

Some HDDs were having their actuator arm hitting the magnet metallic casing and creating unwanted clatter. I glued small pieces of rubber in those spot to solve it.

Actuator arm position influences the sound level :

• The sound is louder when actuator arm is close to center or edge of the platter.
• The sound is quieter when actuator arm is in between those positions.

You can fine tune different HDDs to works together at the same volume by adjusting the arm position and then using tape / glue / plastic bits to keep it there.

In my case I wanted to see actuators arms moving to the music. Music fidelity was not my goal, so they are free to move.

• You'll need to use an audio amplifier / Hi-fi / car radio with audio output impedance that match your HDDs. It's written next to the speakers output (standard values are 4 / 6 / 8 / 16 Ohms).
• You need to have your speaker impedance that is equal or superior to the impedance written at the back of your audio amplifier if you don't want to overload (and eventually fry) it.

In my case I have 6 Ohms output impedance on the Hi-fi, so any HDD 6 Ohms and above is OK (not completely true, I'll go back to that shortly).

We will use the same process as the one for building regular loudspeaker.

We will need to connect ours HDDs in serial and / or parallel to have the an impedance that match to the one from the amplifier (it's not a perfect world, just try to get close to it or above).

1. Let's start by getting impedance from both side
   • My HDDs impedance are between 8 and 12 Ohms depending on model.
   • My Hi-fi audio channels need to have 6 Ohms minimum (normalized value are 4 - 8 - 16 - 32 Ohms)
2. A bit of Ohm law and I have the following possibilities (remember I need to be equal or superior to 6 Ohms) :
   • Two 12 Ohms HDD connected in parallel => 6 Ohms, Good
   • Two 8 Ohms HDD in serial -> 16 Ohms , Good
   • Two 8 Ohms HDD in serial -> 16 Ohms, in parallel with a 12 Ohms HDD => 6.86 Ohms, Good
   • ...

I used IDE-33 data cables (the ones that were with the HDDs) to make the leads for all HDDs (it's small enough to fit actuator pins and big enough to be manipulated easily).

To be able to change HDDs connections configuration toward each others I used screw terminal.

Note :

HDDs in parallel sound louder than HDDs in serial. So you have to listen to each of them and connect the loud ones preferably in serial and the quiet ones in parallel (if they have to work in the same loudspeaker). ==> At the same time don't forget to get the correct impedance. It's not an easy task.

Note 2 :

If like me you don't care about the Hi-fi (it's from the dumpster) just connect everything in parallel and make the Hi-fi suffer.

I ended up with two loudspeaker made of 3 HDDs connected in parallel and an impedance at 3.6 Ohms.

For the sound box :

a wood desk / wood box / metallic box will do the trick.

I built my own using a wood tablet, leftover particle boards and nails.

The size was determined by the thicker wood board (the smaller ones were easier to cut).

I put both channel on the same box because :

• Not enough wood to make two
• Not enough space for something bigger

If I had the time (and though about it back then) it would have been better to build the box in the shape of a flaring horn.

• Loud-HDD-speaker left channel to Hi-fi (or audio amplifier / car radio) left channel.
• Loud-HDD-speaker right channel to Hi-fi (or audio amplifier / car radio) right channel.
• Hi-fi to music source (via Aux input)
• Select a music to play

And Voila, done !

The sound is not so bad, I have real speakers (bought in shop) that are way worst.

Note :

actuator arms on my HDDs move more with bass line / drums or metal music.

Here some ideas (did not had the time or parts to try)

• Make the platters spin :

  • Try reconnecting its motor to the electronic board and power it (not sure if it will work properly and you won't have any speed control).

  • Connect a hobby brushless motor controller to platter motor and a servo tester (or Arduino) to the brushless controller (start a slow speed to check for the correct direction).

• Add some audio amplifier IC before each HDDs (like LM386 IC or 2N6292 transistor amplifier circuit) to get rid out of the Hi-fi or adjusting the volume of each HDDs separately.

• Add audio filters to dedicate some HDDs to low or high frequencies.

My microphone is not really good, it don't sound that bad in reality.