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In old CRT televisions, the deflection yoke is the device that controls the electron beam flowing towards the screen. It’s run by an internal circuit board, but also has external pins that control the horizontal and vertical axes. Electro-music user dnny exploited this design feature by connecting audio inputs to these pins.
yoke1
Internal view of the CRT with exposed deflection yoke pins.

Please note that hacking an old television like this can be very dangerous. If you don’t know what you’re doing, experimenting can result in fire, explosion, injury, or death. That being said, this successful mod on an old portable TV results in some impressive visualizations when a synth is run through it. The post on electro-music gives detailed instructions on how to do this safely.

[via Palm Sounds]

Michael Colombo

In addition to being an online editor for MAKE Magazine, Michael Colombo works in fabrication, electronics, sound design, music production and performance (Yes. All that.) In the past he has also been a childrens’ educator and entertainer, and holds a Masters degree from NYU’s Interactive Telecommunications Program.


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Comments

  1. miroslava von schlochbaum says:

    Good for you guys for taking the risk with an article like this! (there’s a meta danger to posting about danger) There’s a risk in all creative activity, but some of the most rewarding efforts come alongside sources of significant energy or toxicity. But with some due caution and planning that need not activate the overzealous prohibition of parents, neighbors, or (worst yet), lawyers.

  2. Dave says:

    Ahh, good ideas keep on keepin’ on! We did this in the early-mid ’60s for venues in Berkeley and surrounds, including the old Fillmore Auditorium.

    A few comments/suggestions on the visualizer:
    Many TVs will not generate the required high voltage to operate the CRT unless the yoke (the horizontal coils in particular) is in circuit. To get around this, I would carefully remove the existing yoke from the CRT neck (there’s a clamping ring), and leaving the witing connected, wrap the yoke in insulation and set it inside the cabinet. Then, slide a second yoke, taken from another old set, onto the CRT and use that one’s coils for the audio.

    Rather than driving the two coils from a stereo source, try driving them from a monaural amp; place a large, non-polarized capacitor in series with one coil, and drive the other directly. This introduces a phase shift that depends upon frequency, creating very cool looping Lissajous figures.

    Have fun, but be safe!

    Dave

  3. chuck says:

    OMG! That will fit very nicely into my current project. I’ve built a unit that uses photoresistors on long, flexible wire antennae to control the pitch of two frequency modulated synths. The photoresistors are positioned against a TV screen or monitor and as video plays the pitch changes. This works really well with high contrast video loops and can be very musical. Off to butcher a TV!

  4. Balloondoggle says:

    It reminds me of the opening title sequence for The Outer Limits.

    “There is nothing wrong with your television set. We control the horizontal. We control the vertical.”