Vintage Audio Spectrum Display

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After doing some project with vintage tube I got the idea of doing a audio spectrum display with "magic eyes tube". and drive those with a AVR MCU with Fast Fourier Transform

   I had search the net to find some FFT code.  I found  Mr Chan small FFT library,  I download it and at first try it was working, his code is very simple to use.  Thanks Mr Chan.  The way it work,  I pass the audio (line out of your amp) trough a audio compressor, this way if a song is recorded at a low level or at a high level the spectrum will always display the good information.  I had use a ATMega644, because the FFT need a lot of RAM. And I overclock the AVR to 32Mhz with a external full swing oscillator.  You need speed to make all the computation and give the result almost in real time on your tube. The result of the FFT is send to 8 D/A (4 two chanel digital pot) and the analog value is pass trough 2 opamp, one to setup the offset voltage for the tube and the other is there to invert the signal and amplify it.  To get more speed I had the idea to start my 256 A/D convertion when the FFT is computing,  The A/D use almost only hardware to do the job, and in this time the MCU is computing FFT.  At the end of the FFT those value are output and the next data to compute is already there.  If you check on a scoop with a I/O toggeling you will see that the MCU is almost always working the the FFT loop. Like in my nixie clock I had use the same circuit to generate the 250v needed by the magic eyes.



  • 8 tube to display audio frequancy
  • Audio compressor
  • Unique look



Analog Schematic

Digital Schematic

Source Code

8 Comments to “Vintage Audio Spectrum Display”

  • mohammad garazhiyan(گاراژیان) November 17, 2010 at 8:22 am

    hi dear sylvain
    this project is wonderful too.
    thanks for share your cirqute.
    thanks againe

  • Howard M May 30, 2011 at 9:40 am

    Nice work! Any chance of a video? It'd be interesting to see how fast the tubes respond.

  • Magic eye spectrum analyzer | Daily IT News on it news.. January 14, 2013 at 2:20 pm

    [...] After doing a few experiments with tubes, [sylvain] thought it would be cool to do something with magic eye tubes. He sourced eight vertical ‘bar graph’ magic eye tubes and built an audio spectrum analyzer. [...]

  • DIY-Magic eye spectrum analyzer | Krakendate January 14, 2013 at 3:31 pm

    [...] After doing a few experiments with tubes, [sylvain] thought it would be cool to do something with magic eye tubes. He sourced eight vertical ‘bar graph’ magic eye tubes and built an audio spectrum analyzer.” [...]

  • Alvieboy January 14, 2013 at 3:37 pm

    How stable is your 250V power supply ? The vsense resistors look very high, hence line is very susceptible to noise.

  • admin January 14, 2013 at 4:17 pm

    The 250V is very clean, no ripple at all and no noise at all

  • Magic Eye Tube Spectrum Analyzer « KF7LZE's Blog January 14, 2013 at 4:23 pm

    [...] hobbyist Sylvain came up with a fascinating project using 8 Magic Eye tubes from old equipment to make an audio spectrum analyzer. I’ve worked with magic eye tubes quite [...]

  • MAKE | Magic Eye Audio Spectrum Display January 21, 2013 at 4:02 pm

    [...] AKA MicroSyl, wanted to build an audio spectrum display using old “magic eye” vacuum tubes: After doing some project with vintage tube I got [...]

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Please note

All my source codes were taken from my personal projects.

Everything is for your information only. The C/C++ codes have been written
with ICCAVR. You can find the header and source CRT files by downloading their compiler.

All is for your information and everything is AS IS without any warranty of any kind. No other files are available and I don't make any modification for any body.



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