Yamaha E-70/EX-2

Gosh, this is truly an absolute beast of a... synthesizer, really. And that's the second time I've typed this phrase on this website...

So lets take a deep look at what makes this organ so enticing!

THIS PAGE IS A WORK IN PROGRESS.

About the E-70 and EX-2

Yamaha has made a LOT of organs and synthesizers, the two often blending together in features and hardware.

This is why I've always kept an eye on their analog organs, feeling an hunch that they may well hide some glorious synth hardware that usually is prohibitively expensive to acquire (looking at you CS synths).

To the left you can see the gorgeous fiberglass body version of the E-70 called the EX-2. It's exactly the same sans a few presets being different.

Marc kindly donated his E-70 to me, so I went from an hunch to a deep-dive and oh boy is there a lot of goodness in there.

Thanks Marc!

You may know Marc from his 'Son of GX' project, in which he expanded his E-70 with a bunch of new controls and a CSY-2 synth. Absolutely check out his website for more on that.

 

TODO

The glorious specs

Now what can this thing actually do that makes me rather hyped about it?

The specs:

  • 12 organ voices with 9 octaves of sine waves,
  • 14 orchestra voices with analog VCF and VCA,
  • Oscillators are digital but do things very differently for waveform generation, evading typical issues with digitally generated audio.
  • Digitally controlled analog drums,
  • TODO

 

The IG00155 used in the organs is the same as the IG00156 in the CS synths, but has a slightly "calmer" resonance and more low-end, which makes them very interesting filters.

The E-70/EX-2 use PASS which means digital oscillators but Yamaha did some tricks to avoid aliasing and other typical digital issues from those days:
There's no set samplerate, instead a custom multi-stage resistor-ladder DAC is used which already has the waveform "baked in" if you will. This means the digital phase counter directly drives the DAC with the "sample rate" being 2048 times note frequency i.e. A440 would be just under 1MHz.
The actual digital processing takes place at 891KHz as well, since there's up to 14 channels that need to be processed so extra speed was required.

Another trick the DAC has is that its minimum and maximum voltage are externally controlled by an analog CV. So lowering the volume of the waveform does not lower its bit depth (11-bits i.e. 2048 steps), which avoids another common issue in digital audio back in the day.

The insides of my E-70 and the Tower of Power (E-70 in rack format)

Here's a bunch of pictures I took and screenshots of the video from taking the E-70 apart to build the Tower of Power.