Sound AND Visuals

[Mark Hammer]

I picked up a Visual Sound VV1 Visual Volume pedal a number of years back, at a gear swap.  Cripes, now that I think of it, it must have been about 8 years ago.  Tried it out but never really "used" it.  The VV1 has a 10-LED display that uses an LM3914 display chip.  I could never get the LED display to work, although the volume attenation worked fine.  It has two inputs and 3 outputs (an extra one for the tuner).  BUt it doesn't appear to be true stereo, even though the treadle moves two slider pots.  One of the pots essentially provides a variably attenuated voltage that the 3914 chip registers and uses to show where, in the overall range of null-to-full volume you are (hence the name "Visual Sound" and "Visual Volume").  I should emphasize that it doesn't show the absolute volume level, merely how close to, or far away from, the maximum volume-pot setting you are.  Even so, the "graph" can be useful.

As the pic below shows, there is no indication on the chassis of what the DC jack polarity is.  Well-made product, but that info is issing.  And since I bought it at a gear swap for $5, there was no instruction manual.

In any event, I was poking around in the basement, saw it and thought I'd try and get the visuals going.  Looked at the 3914 datasheet, and the board.  Did some continuity-testing of the power jack's connnections to the board and realized it was the opposite of the standard polarity: outside ground, inside connector V+.  The unmarked voltage regulator inside seemed to be fried.  I unsoldered it, and replaced it with an LM340-5, making sure to trace out what pins led to where.  Wired up a 2.1mm power plug to a 9v battery snap...backwards...to provide the required polarity, and bingo bango, I now have a lovely visual display of where the volume setting is. 

One of the smart things Bob Weil did when originally designing it was having a green LED at the halfway mark as well as full-tilt.  The LED display is intended to be informative to the user.  If one had to count "how many LEDs from the bottom/top" were lit up, it would be distracting.  This way, you have a visual "centre detente", and can quickly and easily see that it's maybe one below, or one above the midpoint, or one or two LEDs below the top.  Nice.

Now I'm wondering if I can use the internal power to install a buffer or simple preamp.