Had not seen this before. This picture of a Yamaha E70…with built in SY2 and SGX CONTROLLER, showed up on Facebook

Later the following info was added: Custom made by Marc Brassé. One preset breaks out into the panel with its 3 sets (2 keyboard, 1 set pedals) 11 Yamaha envelope characteristics, IOW 3 full blown synths. Then he stuck a little Yamaha SY synth in there. Converting an E30, E50, E70 and E75 are fully documented, with maybe 5 people in the world having done it.

We found this on the website of Marc Brassé about the Son of GX:My love for late 70ties analog Yamaha technology doesn’t stop with the CS80. What does one do when its GX1 forerunner is totally out of reach e.g. too rare and thus unobtainable for a realistic price? You can just dream on or you can come up with an alternative. A of GX1 technology was later incorporated into the CS synths. It was however also used in the EX and E-series organs. Top of the line of the home organs where the E70 and E75. And guess what: With some difficulty these preset organs can be turned into a fully programmable equivalent to the GX1! And thus my journey began. These articles describe that adventure but it also contains a step to step customization guide. Since I put some clips about it on YouTube a lot of people have already asked for a copy of this via email. Now it is available as a download on this page. If you want to know how the Son Of GX sounds have a listen to Balance in the (Post)Modernisms section of the Electronic Music page. A description of which parts of this track where actually played on the Son OF GX can be found in the accompanying text.”

(c) of the last set of pictures: Marc Brassé

There are even videos with demo’s of these modified Yamaha’s, such as: