Well, it's kinda boring on the list, time to stir things up a little..
I've been threatening to do this for a long time, but I finally had the
time - I modded my MOTM 800s to have an output LED (yes, Barlow, you were
right, it's cooler than a gate LED.) It glows in brightness corresponding to
the level of the envelope output. It gives you immediate feedback on what
your envelope generators are doing in the midst of a complex patch, and
helps to troubleshoot when things are not being gated correctly.
Pix at:
http://www.egroups.com/files/motm/800mod/It's an extremely simple circuit consisting of 1 dual opamp , 1 LED, and 1
resistor. This circuit also could be used most anywhere else you needed a
visual indicator of the signal level. For bipolar signals, you'd maybe want
to use a bicolor LED as in the 320. In addition, you need to mount a small
daughterboard on 2 threaded standoffs, screwed into the embedded studs
behind the front panel.
As usual, I accept no responsibility if you fry anything, burn down your
house, scorch your cat, etc. This is about as easy as DIY gets, but you can
make mistakes, and short power supply rails if you're not careful. Paul will
want me to mention that if you start adding lots of LEDs to your system,
make sure your power supply can handle the extra load.
Referring to the schemo (see the pix link above), the first half of the
opamp buffers the signal, the second provides a current driver to power the
LED. The 470 ohm resistor sets the max current to a little less than 10 mA
for a +5 volt input. You can connect the input to the OUT + jack to get an
output indicator that varies in intensity with the envelope, or to the GATE
jack to get a simple gate indicator. Note that if you are using it as an
output indicator, and you have nothing plugged into the gate or trigger
jack, the LED will glow. This is a good reminder that the 800 does in fact
send its DC sustain level when not connected otherwise.
Notes:
Dual opamp - almost anything will do, as long as it can sink 10mA. I used a
crummy old 1458 I had laying around, and it was plenty fast enough.
LED - I chose green since MOTM-320s use green to display the amplitude of
the signal when in a positive range. Use the Lumex part to match the MOTM
standard (GREEN:Digikey # = 67-1156-ND,Lumex number = SSI-LXH387GD). If you
can't deal with DigiKey, maybe Paul will sell you some.
Standoffs: Use 6-32 threaded aluminum standoffs, 5/16" long works well.
Remove the KEPs nut, put on a small flat washer and lock washer, then the
standoff.
Daughterboard: I went to Radio Slack, bought their protoboard, and sawed it
into strips. I got enough to do 4 800s. I mounted the board copper side up,
components underneath, so that I could bring the LED leads all the way
through the daughterboard when mounted, and still solder on top where I
could reach. Power for the opamp is brought from the back side of the main
board power connector. Be careful you don't short anything.
Enjoy!
Moe "gimme an LED!"