Kit 23: Poulsen Wire Recorder

Kit #23: Poulsen Wire Recorder (2500 yen, approx. $25).

Valdemar Poulsen is probably one of the greatest inventors you’ve never heard of. But, if you’re over 20 years old, you’ve probably heard one of the offspring of his principle invention.

(Full kit: circuit box, wire with stiffener and eraser.)

First, a little history. If we look at a timeline of related inventions, we have Samuel Morse and the telegraph in 1844; the first fax machine in 1863; Thomas Edison’s electric typewriter in 1872; Alexander Graham Bell’s telephone in 1876; Edison’s wax cylinder phonograph in 1877; Edison’s patent on the vacuum tube in 1883; Heinrich Hertz detecting and producing radio waves in 1888; and Oberlin Smith describing the principle of magnetic sound recording, also in 1888.

Which brings us to 1893, and the Danish inventor Valdemar Poulsen. Valdemar took Oberlin’s idea and turned it into the first practical wire recorder, the precursor to magnetic tape recording, the cassette tape, the 8-track tape and ultimately, the floppy disk and hard drives.

The principle is simple. Take any metal that can be magnetized (initially, iron) and put it next to a coil of wire with an electric current running through it. The coil will produce a magnetic field that will magnetize the metal. Move the coil along the metal (such as along a wire made of iron) and the magnetism along the metal will vary with the strength of the current in the coil. Attach the coil to a microphone, and viola, you’ve recorded your voice on the metal. Attach the coil to a speaker and move it along the wire again and you’ll faintly hear your voice playing back. Add an amplifier between the coil and the speaker and your voice will be louder. Change the metal to a magnetized flexible tape, and you have the cassette recorder/player.

The amazing thing to me is that the wire recorder was in use over 115 years ago, but there’s little mention of it in school textbooks (at least, not when I was in school). Anyway, Gakken’s kit #23 is a very simplified version of the Poulsen wire recorder. It consists of a handful of plastic parts, some screws, two recording wires, and the pre-assembled circuit board with mike and speaker (circuit schematic is not provided, but looks primarily to be just a simple op amp amplifier). Assembly takes about 10 minutes, and you need 2 AA batteries to operate it. You can spend another 10-20 minutes cutting out the paper labels from the mook to fancy up the case and create a speaker cone if you like. The recorder wire is mounted on a stiffener plate. You start out by erasing the wire with a permanent magnet, then, with the kit’s switch set to record, run the recorder head along the wire while speaking into the microphone. You have about 1 second of record time. Change the switch to play and run the head along the wire again. Be amazed at being able to hear your own voice played back at you!

(Speaker with cone (mike is just below the speaker) and amplifier circuit. Record/playback head shown in inset.)

Suggested mods include adding the speaker cone from the book, or a larger cone as you like; attaching a weight to the playback head by a string and let gravity pull the head along the wire; and, the “biggie”. The “biggie” is to take Gakken’s Edison cylinder phonograph kit and replace the plastic cylinder with a core with the wire wrapped around it, replace the needle with the playback head, and then route the output of the Poulsen kit to a 9V amplifier and an external speaker. Of course, the “biggie” includes adding an audio out jack, and it’s a small step to adding a 3V DC power adapter jack (however, the case has no available unused space so you’ll either have to lose the batteries to make room for the jack, or let the jack dangle in the air).

You don’t need to use the recorder wire if you don’t want to. The mook shows the author trying out a kitchen knife, a scissors, the spokes of a bike wheel, a steel guitar string and the side of an escalator. Keep in mind, the kit’s amplifier circuit is pretty weak and you’re not going to hear much of anything during playback (if you shout it just garbles the sound more because of clipping). Wiring up the audio out jack and then listening with earbuds will make a big difference in what you can hear, but you might also want to add a volume control just in case, to protect your hearing.

The mook, as always, is a great look into the history of recording. It starts out with Poulsen, then moves forward through cassette tapes (with different pictures of weird designs for players with and without AM/FM radios added), video tape, and floppy disks to end with a look at the components of a modern hard drive. There’s an explanation of magnetic recording; an interview with Yuzo Kayama, a Japanese actor and musician that used to use a wire recorder for his work; a look at multi-track recorders; and, a reprint of an old manga showing a boy detective using a compass to prove that a thief stole some pipe from a friend. The manga goes on to demonstrate that when you pound on an iron pipe with a hammer, the impact on the pipe causes the iron to partially magnetize, and the orientation of the resulting field can show if two pieces of pipe were once part of the same pipe. But, the mook is kind of short this time, lacking articles on unrelated subjects (unlike the other mooks in the series).

In summary, this is a fun little kit and a fascinating peek into a segment of electronics history that most people don’t get to see. However, don’t expect much from it – the recorder wire only holds one second of garbled sound, and even if you mod the kit to mount a longer wire on a cylinder and put the mag head on a mounting arm over the wire, you’re not going to get that much more recording time. This is a kit that looks great on your shelf, to be pulled down occasionally to show off to your friends at parties. Or, if you feel like looking like you’re recording yourself on escalator railings.

Other links:
The Gakken online magazine for kit 23.
Gakken’s video showing the kit in use with different recording materials.
Yuzo Kayama’s official site

As a side note:
Yuzo Kayama (1937 – ) is just one in a line of famous Japanese performers that Gakken chose to include in articles regarding their perceptions of Gakken’s kits. What concerns us here is that you may not be familiar with him. (I certainly wasn’t.) According to the wiki entry, Yuzo is the son of one of Japan’s most famous 1930’s film actors, Ken Uehara (Uehara himself is worth mentioning, since he played Dr. Harada in the 1961 “Mothra”). Yuzo started out as a musician, debuting in 1961, and establishing himself as a guitarist in a pop band. The group was influenced by the surf music of The Ventures, and their Black Sand Beach has been covered by a variety of American groups. Currently, Yuzo performs as a solo crooner. On the other hand, he’s also made a career as a film and TV actor, first coming to notice as Dr. Noboru Yasumoto in Akira Kurosawa’s 1965 “Red Beard” (“Akahige”), opposite Toshiro Mifune (although he had been in several movies before that starting in 1960). He still appears on TV as a “talent”, and had a cameo appearance as a voice actor in episode 2 of the “Kochira Kameari” TV anime.

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  1. stephanie

     /  June 12, 2013

    Hi, I wanted to order this kit but it seems to be sold out everywhere, so I’m trying to make my own. I wired a tape head to the upper tip and ground parts of a quarter inch audio cable. To record, I ran a microphone into the input of a powered mixer and made the tape head the output. I ran the tape head along a piece of steel while making noise into the microphone. To playback, I made the tape head the input and a pair of headphones the output and ran the tape head along the same area of steel. Before recording, I swiped the area with a magnet (passes were in the same direction as the recording). But I do not hear any of my recording. Is there something special in this kit, that I am missing in my homemade version? Any help/tips you can offer would be greatly appreciated! Thanks very much.

    • Hi Stephanie, thanks for dropping by.
      The electric signal from the tape head is really small. Generally, you need to run it into an amplifier, or a pre-amp and the output from the pre-amp into the amp and from there to a speaker. Because a cassette deck already has all the electronics you need for recording and playback, what you can do is take the heads out of the deck (or from a handheld player/recorder if you want) but keep the wiring intact. Usually, though, the heads are welded into the metal frame of the player, so you’ll need to saw or grind the heads out, which will otherwise destroy the unit.

      • Anonymous

         /  June 25, 2013

        Thanks so much for getting back to me. I tried keeping the tape head in tact. I also tried another method that seemed to work about the same, just thought I’d share it:
        I ran a mic into one channel of my mixer and a high frequency into another channel to add bias. I put the tape head in the out for recording. After recording onto my metal, I switched the tape head to an input on my mixer and a speaker to my output. I am able to record/play onto thin sheets of steel. If you have any ideas on how I can record onto thicker metal, please pass them on. A bigger tape head/magnet? A stronger output signal? Thanks again. This is a great blog!

  2. Thanks.
    You’ve hit on the main problem with recording on thicker metal – you need a stronger record magnet. The thinner the metal is, the easier for the magnet to align the crystal structure of the metal – that is, the easier it is to magnetize the metal. However, as the magnet gets stronger, it affects a larger area at one time, which kind of acts as a demagnetizer for the surrounding metal. What this means is that your sound will be muffled because you’re erasing and overwriting part of it as the record head moves along the metal. So, you could use a stronger record magnet, or a stronger output signal. But the most effective thing is to use thinner metals.


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