Moog Slayer_{By Atom Smasher} Filter Mod for korg EX-800 and Poly-800

atom@suspicious.org

Samples, Reviews, Tech Notes

It all started when my comrade, Tom, asked me to do the original filter mod to his EX-800.

I gave him back his synth, and he said "Atom, it does this," while holding his fingers about an inch apart. He continued, "make it do this," now holding his hands about a foot apart. Back to the bench.....

This time, when I took it back to him, he plugged it in, and said "Holy shit! It's like this!!!", grinning, and holding his hands as far apart as he could get them.

At the time I wasn't that big a fan of the Poly-800 series... but after doing this mod, I picked up an EX-800 for myself (pictured here).

This thing can do dangerous sounds, like the speaker-blowing (and ear-blowing!) sounds of old modular synths. It's really sick.... In addition to the usual disclaimers (if you break it, it's your problem, not mine!), I'd like to also point out that I will not be responsible for blown speakers, amps & ear-drums.  -- YOU HAVE BEEN WARNED! --

If anyone wants to send me samples of their modded synth, maybe I'll post it here.

1. First, install the new pots in the front panel.
   Knobs, front
   Knobs, back
   Knobs, back, close
   Use 50K-Ohm audio taper pots.

2. Remove pots "VR2" and "VR5" from the main board. They are located behind the audio-out jacks.
   Main board.
   Pictured with wires leading to the new pots.
   Note how the dots in the diagram relate to the holes on the board.

3. Wire it all up, like this:

   + VDC * | | | \ / 470-510 Ohm \ / \ / | | *RESONANCE* *CUTOFF* | 50K Audio 50K Audio | | +-----/\/\/\/\/\-----+ +-----/\/\/\/\/\-----+ | | | | /|\ | | /|\ | | | | | | | | | | | | | | | --- | | --- | ground /// | | ground /// | | | | | | | | / | | / | | / | | / | | / | | / | o o o o o o VR5 VR2

   The ground (black wire) and +V (red wire & resistor) are wired up here
   There is a diode just next to where the power jack is. Wire up the 470-510 Ohm resistor to the cathode. Make sure there is heat-shrink or tape over the resistor, or else it might short out against the power-jack, or something. This picture shows it without the heat-shrink, for clarity. Wire up the ground connection to the big pad, just next to the power jack and connector "CN9".

4. While I had the unit opened up, I decided to fix the TUNE knob that always got knocked out of tune.
   My solution is a knob that has to be turned with a small screwdriver, to avoid unintended adjustments. You can see it in this picture.
   1. Remove the small board with the tuning knob. Remove the tuning knob from the board.
   2. With a Dremel tool, shorten the shaft to about ³/₁₆ in (about 5mm) and cut a slit in it, so it can be turned with a screwdriver.
   3. Using a small drill, cut four holes in the small board, so the tuning pot can be moved back, about ³/₈ in (about 9-10 mm).
      See picture.
      
   4. Cut the circuit board traces, and re-wire the tuning knob.

5. Like (almost) always, assembly is the reverse of disassembly.

6. Have fun!

Knobs 2
View shows the knobs, but they can be mounted more towards either side, as long as they don't interfere with the display/button board.

Knobs 3
Close up of knobs shows wiring.

Main Board
Note how the holes here line up with the holes in the diagram.

POWER!!
Don't forget the heat-shrink!! Or sparks will fly!!

Tuning knob
Even if you don't do the filter mod, this is a cool mod by itself.
The holes towards the left are the original mounting holes. The pot is moved away from the front panel (towards the right, in this picture) into the new holes, and wired-up like a broken jaw to the connector terminals.