A CRT Audio Visualiser For When LEDs Just Won’t Do

It has been a recurring feature of consumer audio gear since the first magic eye tube blinked into life, to have some kind of visualization of the sound being played. Most recently this has meant an LED array or an OLED screen, but [Thomas] has gone one better than this with a CRT television converted to perform as a rudimentary oscilloscope.

The last generation of commonly available monochrome televisions were small 5″ CRT models made in China. They never received digital tuners, so as digital TV has become the norm they are now useless to most people. Thus they can often be found for pennies on the second-hand market.

[Thomas]’s hack involves gutting such a TV and retaining its circuitry, but disconnecting the line driver from the deflection yoke. This would normally leave a vertical line on the screen as it would then be moved only by the frame driver at 50 Hz for PAL or 60 Hz for NTSC. By connecting an audio loudspeaker amplifier to the line deflection yoke he gets that low quality oscilloscope. It would be of limited use as an instrument, but few others will have such a cool audio visualizer. He’s viewing the screen in a portrait orientation, we’d be tempted to rotate the yoke for a landscape view.

It’s worth pointing out as always that CRT TVs contain high voltages, so we’d suggest reading up on how to treat them with respect.

16 thoughts on “A CRT Audio Visualiser For When LEDs Just Won’t Do

  1. Reminds me of a similar hack my father and I did back in the early 70s when as a teen a couple of mates and I ran a disco. Basically took a TV and replaced the vertical field output with the audio transformer output and then fed the audio stage from the disco mixer via another transformer. With a horizontal line frequency of 16khz we got nice scope like traces. Painting the crt with different colour horizontal bands made a cool display.
    And yes looking back it wasn’t that safe either…

  2. Use both horizontal and vertical deflection coils for left and right – the different AC characteristics of each coil mean you always get lovely lissajous figures especially with sustained bass notes. Its quite easy to burn a hole in the centre of the phosphor in the quiter moments.

  3. I did this exact thing as a teenager in 1972. I used a Color CRT TV, and a stereo amp. The stereo amp drove the deflection coils. If I feed a sawtooth wave into the horizontal coil, and some signal into the vertical coil, I had an oscilloscope. It was a bit clunky, but did work. I used it for a few years to play around with electronics. If you feed a stereo sound into the amplifier, large circular patterns would be painted on the CRT screen. It was a totally cool music visualizer way back in 1972.

  4. Using a CRT is interesting but sort of limited.

    I have tested Wacup running Milkdrop visualizations with my 8 year old W530 ThinkPad and I get 4k visuals at 30 fps on my 77″ OLED TV. It’s beautiful! Now I’m deciding whether to build a PC specifically for the purpose or just hunt down another old W530 laptop. If I build a new PC with a modern graphics card I may be able to push the visuals to 60 fps, and a few of the presets that don’t work well with the W530 may work better with more graphics horsepower.

  5. My first thought seeing the picture was rotate the yoke. I did this in ’70 and won a ribbon in a tech/art showing in high school. B/W 19″, the old vertical with it’s “hold” (frequency) control becomes the horizontal timebase. Feed the audio in the wide bandwidth former horizontal coils. I did this again a few years ago with one of those last gen tube portables. The built-in radio became a source of wireless music to display, no mods to the case.

    The big bug in both cases was supplying an inductance for the horizontal flyback to to continue to run well without it’s former load. Years ago I stuffed a junked deflection coil in the case wired in place of the original load. Much later the little set got a small coil out of the junk box.

    Always fun, at least till they are no more.

  6. Can’t help but remember the series of short demonstrative physics videos by the Moscow Engineering Physics Institute in which they were using the TV-sized CRT-based device as an oscilloscope with increased visibility for the auditorium, for example:

  7. Wow takes me back to ~1973, when I took the back off an old monochrome TV and hooked up a signal to the vertical deflection coils. I didn’t have an amplifier though at the time. Use the horizontal hold to adjust the timebase!

    Got my first 20kV bolt off the back – and survived to tell the tale!

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