Modified Yamaha PS470 + the WASP VCF


This little organ is probably the nicest gift the street ever gave me. I found it in a pile of trash right outside of my house in an extra bad shape. I took it home because I’m a total sucker for Yamaha gear, but when I cleaned it up and tried to fire it up it just didn’t work.. I stored it with the thought of studying it further sometime in the future.

What really caught my attention was the fact that apart from the usual features found on such amateurish keyboards is the inclusion of sound editing facilities. This has made me curious since most of these rely on samples or wave tables for sound. After a quick run through Google I learned that this thing actually has an FM engine for its sound generation (however the drum sounds are sample based). Well, the editing sliders actually edit the FM sound.. Wow.. A real synthesizer here!  This could be turned into something usable!

I have found some interesting bends for this keyboard series on the web, and although I adopted one such major mod, I ended up turning most of my attention to other things most people don’t bother with when modding this keyboard. More on this is a sec.

Finally I got around to it. First I had to fix it.. The power socket was busted. After fixing that I realized a third of the keys weren’t working.. fixed those as well (apart from the low C key that is broken off). Finally I could plug it in and give it a try.

Well, an interesting sounding keyboard. The editing functions open up a whole array of sounds. You can start constructing a sound from scratch, or use one of the presets as a starting point. Very nice!

An interesting discovery was the ‘Stereo Symphonic’ button that switches on a nice warm chorus effect. When I opened it up I found an MN3206 chip inside! This chorus is analog! So first I was set to making this nice analog chorus a little more versatile.

The MN3206 is a BBD chip sporting 128 stages. This allows only for very fast delay effects such as the chorus utilized in this device. Luckily I happen to have a few MN3207 chips in my drawer. These have 1024 stages, allowing for longer delay times thus allowing much more versatility. First I installed one of those inside and put it on a switch to allow switching between the two chips. What creates the chorusing effect is an LFO that modulates the delay speed – this was set to one setting. I modded the LFO section to allow for variable speed and modulation depth. I also added a speed range switch. Now the ‘Stereo Symphonic’ function allows for very rich tones.

Next I added a filter. I based it on the WASP synthesizer VCF. The filter has variable states: Low Pass, Band Pass and High Pass. It also has the typical Cutoff and Resonance controls. There’s also a Distortion switch that drives this thing into sheer ugliness. The LFO mentioned earlier can be routed the the filter so that the cutoff can be modulated.

Finally, I added the data lines mod that can be found on various mod sites. The chip that generates the FM sounds has 8 data inputs for shaping sound and other functions. When you select a patch sound for example, the chip retrieves the patch data through these lines. Most these mods involve putting each one of these lines on a switch so that the FM chip does not receive all the required data. Make these patchable and you have endless possibilities, both in generating new random patches and in creating glithcy sequences. This is what I ended up doing and I will probably have to study the different combinations thoroughly before making a more educated demo about it.

The demo video shows the very basics of these mods. I do not change patches on it and hardly even go into the patch bay mod. I mainly demonstrate what breaking one line can make this thing do. Rather I focused on my original mods as the web has enough video demonstrations of the data line breakers in these type of keyboards.

I have to say I’m pretty excited about this keyboard now. It a totally viable musical instrument and one I know I’ll be using in my future recordings. Thanks neighbor!