Capturing Audio without Injury

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VU Buffer PCB and Kits for Rob Squire's DIY VU article in Audio Technology No. 51   Audio Technology DIY VU Article in PDF (140k) click here

The VU Buffer PCB allows for a easy neat way to build Rob Squire's VU Buffer circuit  from the article in the current Audio Technology Magazine. It turns cheap dc type VU meters into working VU meters. It is also extremely useful for buffering a real VU meter as it isolates the Total Harmonic Distortion caused by the internal rectifiers in the VU meter. This will usually drop the output THD of most circuits running VU meter direct another decimal point which is a good improvement. VU Buffer can run on any DC voltage from 9v to 30v.

  • VU buffer kit parts
  • 47k = Yellow Violet Black red
  • 3k3 = Orange Orange Black Brown
  • 100R = Brown Black Black Black

 
  • Install resistors and diodes with there white or black stripes to the left
  • (For SEW Meters BAT85 glass diodes work best in the lower two positions as shown)
  • When using Meter with internal rectifiers like our Nissei AL29 do the mod shown to the right photo to disable the VU buffer recitifier.

 
  • Install IC socket semi circle cut out to the top as shown
  • t

 
  • Install Terminals now if not soldering wires directly to Power and In pads

 
  • Fit Capacitors (Note they all face in the same direction)

 
  • Fit Trim pot and TL071 IC into socket as shown with pin 1 in the top left corner

 
  • The PCB uses the bottom edge to mount on to the VU meter + and - terminals.
    Use any hole on the left for + and any hole on the right for -.
  • (If your meter has solder tags you can solder on directly or if there are 2 bolts use 2 cut off component legs to solder to the PCB and then wrap around the VU meter bolts.)
  • Fold PCB back behind VU meter
  • (Note 100uF cap mounted across SEW / FLASHSTAR meter to slow its response down to normal VU response)

 
  • If using the 12v regulated supply the Lamp or Blue led kit can be wired straight to the power for the VU buffer.
  • (Also the VU Buffer is protected against reverse voltage by the third diode at the top of the PCB)
  • When connecting to a unbalanced signal +in goes to the signal and -in to the audio shield.
  • (A TRS socket will automatically do this when a TS unbalanced plug is plugged in to the TRS socket.)
  • BLUE LED
  • If you want to run the LED on more than 12volts you will need to add a series resistor.
  • Use this formula R = (V - 12) / 0.02.
  • So if you have a supply of say 24v regulated the blue LED would need a resistor =
  • R = (24 - 12) / 0.02 =  600ohm. So use 620ohm or 680ohm standard value resistor.
  • Will need to be a half watt type.

 

  • ORANGE / GREEN LAMP
  • If you want to run the Orange / Green Lamp on more than 12volts you will need to add a series resistor.
  • Use this formula R = (V - 12) / 0.08.
  • So if you have a supply of say 24v regulated the blue LED would need a resistor =
  • R = (24 - 12) / 0.02 =  200ohm. So use 220ohm standard value resistor.
  • Will need to be 1watt type or better use 100ohm 1watt in each wire to the lamp to spread the wasted heat better.

 
  • SEW Meter with Orange Lamp

 
  • Blue LED kit and below how to fit it to the SEW Meter

 
  • Blue LED kit assembled (A is the long leg of the LED)
  • The Blue led kit runs on 12v without a resistor in series.
  • Positive for the LED is on same side as the meter positive.
  • The LED is the 2 outside terminals on the back of the meter.
  • If you want to run the LED on more volts you will need to add a series resistor.
  • Use this formula R = (V - 12) / 0.02.

 
  • SEW Meter without Bezel

 
  • SEW Meter without Clear cover

 
  • SEW Meter orange lamp

 
  • SEW Meter cut orange lamp off leaving wire legs behind

 
  • Fold the two cut lamp wires downwards

 
  • Slide blue lamp PCB on to the 2 wires and solder on

 
  • Blue LED Kit fitted to SEW meter

 
  • Blue LED kit running on 12v

 
  • SEW Meter Glow with Blue LED kit fitted
  • Note. Turn the leds PCB back on a bit of a angle so the tips of the LEDS
  • actually touch the white plastic of the meter back panel so the light is more diffused.
  • I also like to just clip the very tip of the LED dome with very sharp
  • side cutters to diffuse the light even more.

FLASHSTAR Meter dimensions below (Cut out for Black Bezel 84mm x 44mm)

SEW ST-475 Meter dimensions below (Cut out for Black Bezel 88mm x 51mm)

SEW ST-160 Meter dimensions below (Cut out for Black Bezel 117mm x 68mm)

Nessai Meter