I recently bought a cheap VU meter on Amazon, which looks very cool but needs some circuitry to get running. Unlike vintage meters, which can be driven by the audio signal directly, newer (and especially cheap) meters require DC current. A simple circuit, based on this example by Rod Elliott, uses four diodes to convert the AC audio signal into DC, plus a resistor and capacitor to dampen the movement of the needle.
See Rod’s post for lots more technical detail and a more complex driver circuit. Of course, this is pretty lo-fi and not studio-quality equipment… it also didn’t cost $1000.
The BOM for this circuit. These are pretty common parts and can be substituted for what you have lying around. In particular, the value of the capacitor should be experimented with. 100uF worked pretty well for me, but the choice is forgiving.
| PART | $ EA | QTY | URL |
|---|---|---|---|
| VU meter (500uA, 700ohm) | $10.57 | 1 | http://amzn.to/1J8BZOT |
| 3.3k resistor | $0.10 | 1 | http://bit.ly/1N7zVJk |
| 1N4001 diodes | $0.18 | 4 | http://bit.ly/1HLxaFy |
| 100uF electrolytic capacitor | $0.22 | 1 | http://bit.ly/1JXhsNH |
The VU meter and circuit connected to my full vinyl lathe pre-electronics. A 10W amplifier, volume control, the VU meter, inverse-RIAA filter and output to the lathe and headphones.
And the circuit, prototyped on a breadboard. The crisscrossing diodes make this a little tricky.
I am trying to connect VUs to a standard headphone output of a stereo for fun… can I use this same circuitry? Is that what you were using as an input? What might I have to do differently?
I was using audio out from my computer, so that should work. Most cheap meters are DC, which require the circuit shown. Old ones (salvaged from tape decks, etc) may be AC and will work with your audio output directly.
try using 1N34A’s with a 2.2K before the FWB, then put a 22uf or 47uf(slower) cap across the meter input
@Jeff: can you explain why these additions? My electronics knowledge is pretty limited :)