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2-Channel VU Meter with Calibration |
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This two-channel VU meter was made using a handful of spare parts I had lying around. It has a front panel calibration, allowing me to calibrate it for mixes using K-20 or K-14 with ease.
| It was housed in an aluminium frame enclosure half a rack width and 2RU high. I used a 2RU aluminium panel cut in half to make the front and rear panels. The rear panel has two channels of input and output XLR sockets (the inputs are bridged directly to the outputs) allowing it to be placed inline with the output bus. An internal mains power supply was used since I had a spare transformer and PSU-5 module. | Bal-Unbal buffer circuit (pdf) VU Meter driver circuit (pdf) |
 There are two other circuit modules inside. One is a buffer that converts the balanced input to an unbalanced signal to provide the audio input to the VU meter driver module. The VU meter driver module consists of a variable gain amplifier (to allow input signal calibration) driving a current amplifier which drives the meter. The capacitor on the base of the drive transistor allows adjustment of the display ballistics a little.
I had two large Kyoritsu VU meters (with internal rectifiers) which I decided to use. They did not have internal lamps so I added 4 yellow LEDs to provide some scale illumination. They are not high-brightness LEDs since the objective was to provide soft illumination for use in dimly lit situations. Once the unit was assembled and tested I built a simple timber sleeve to complete the housing. 
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