Audio Amp Puts VFDs To Work In An Unusual Way

It’s safe to say that most projects that feature a VFD emphasize the “D” aspect more than anything. Vacuum fluorescent displays are solid performers, after all, with their cool blue-green glow that’s just the right look for lots of retro and not-so-retro builds. But that doesn’t mean there aren’t applications that leverage the “V” aspect, such as this nifty audio preamp using VFDs as active components.

The inspiration behind [JGJMatt]’s build came from the Korg Nutube line of VFD-based low-voltage dual-triode vacuum tubes. Finding these particular components a little on the expensive side, [JGJMatt] turned to the old standby DM160 VFD indicator tube, which is basically just a triode, to see how it would fare as an amp. The circuit takes advantage of the low current and voltage requirements of the VFDs — the whole thing runs from a USB boost converter — by wedging them between a 2N3904 input stage and a 2N2007 MOSFET output. There’s a mix of SMD and through-hole components on the custom-etched PCB, with a separate riser card to show off the VFDs a little bit through the front panel of the 3D printed case.

All in all, we find this little amp pretty cool, and we love the way it puts a twist on the venerable VFD. We’ve seen similar VFD amps before, but this one’s fit and finish really pays off.

14 thoughts on “Audio Amp Puts VFDs To Work In An Unusual Way

      1. I first thought they were talking about variable frequency drives too, but they’re really talking about vacuum fluorescent display tubes being used as amplifiers. If you look at the schematic, you can see it’s Class A.

    1. Make music all the time with drives, can tell you what thirty hertz on a motor from across the mechanical room. Sweet purr of a Yaskawa. Awful, choppy high frequency switching of an ABB trying to speed search. Going to YouTube right now to search breakbeats on variable pumps

    1. I learned that as a little nipper when I put a 9v battery to the filament of one and they glowed bright like a bulb.. then burned out ! Wasn’t smart enough to figure out the rest of the drive circuit

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