FM-800By Atom Smasher Filter Mod for Korg EX-800 and Poly-800
|Also see the HAWK-800 mod, and keep an eye out for the aTomaHawk-800.
Samples, Reviews, Pictures, Tech Notes
This modification to the Poly-800 series of synthesizers adds the ability to
control Filter Cutoff with DCO1.
This is commonly known as FM control of a filter.
Although it's technically not Frequency Modulation,
the results are capable of sounding very much like an FM synthesizer.
A knob allows the effect to be turned from completely off,
to far beyond the normal capabilities of a Poly-800.
This modification very nicely compliments the
Moog Slayer modification for a total of 3 knobs full of fun.
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.
Although this modification seems easier than the
Moog Slayer, I suspect it will result in more casualties.
Soldering directly to 1/8W resistors mounted tightly to a
board is something that beginers should avoid (but it seems so easy!).
I highly recommend replacing those resistors with vertically oriented 1/4W
resistors before trying to connect wires to them.
Unfortunately, replacing the resistors risks damage to the circuit board
if you don't have a lot of experience replacing components on a circuit board.
If you have doubts about your ability to perform this modification, ask your local
synth/guitar/amp technician if they can do it for you.
The cost of having this modification performed by skilled hands is probably less than the cost
of replacing a synthesizer.
If anyone wants to send me samples of their modded synth, maybe I'll post it here.
This modification is Copyright Atom Smasher and published under a Picture, Sample, Lunch-Ware License:
If you perform this modification send me an email with pictures, samples and your location.
If I visit where you live or you visit where I live (currently Wellington NZ) you owe me lunch.
- Parts list
- 5K (or 4.7K) linear taper pot (1/8W or more will work fine)
- Knob to make the pot look pretty and feel good
- 1K resistor (1/8W or more will work fine. 1/4W will be easy to find)
- Optional parts (recommmended)
- 62K 1/4W resistor
- 22K 1/4W resistor
- Solder the 1K resistor to the arm of the 5K pot. Solder a length or wire to the resistor.
Cover the resistor and it's leads with heat-shrink tubing.
- Locate the ground pad next to connector CN9 and solder a ground wire to it. Connect this to the low side of the pot.
- Locate R74 (62K) near IC4.
One end of R74 is connected to IC4 pin 7; connect that point to the high side of the pot.
Optionally, remove R74 and replace it with a vertically oriented 1/4W 62K resistor. If you connect the wire to the leg of the vertically oriented resistor it will be a better connection and less likely to cause problems.
- Locate R22 near IC1. One end of R22 is conected to R23; connect that point to the wire that's connected to the 1K resistor (connected to the 5K pot).
Optionally, remove R22 and replace it with a vertically oriented 1/4W 22K resistor.
Note that on older models R22 is 33K. On newer models R22 is 22K.
This doesn't seem to be critical, but I would recommend using a 22K resistor if you replace R22.
- Mount the pot on the front panel and amaze your friends!
Black traces show the original wiring. Red traces show the FM-800 modification.
And don't forget to send me samples and pictures!
And take me to lunch!