Electronic Keyboard Piano Synth (eKPS)
Instroduction
Before going to University I acquired a Yamaha DGX-620 from around 2006 on Gumtree. I wanted to get an 88-key keyboard so that I could still practice piano whilst in an entirely different part of the country. Given that I use an upright piano at home, it wasn't exactly feasible to bring.
So what do I want to do with it? Since making an analogue polyphonic synthesiser for my A-level coursework, I've had ideas of how to expand it, improve it and make it more efficient at scale (it only had 4 keys and was not very playable). This meant that I needed to produce some platform at which I could start to experiment.
The Plan
This is going to be a very long term project. It will require significant planning, testing and brain-time. The idea is to still have a functioning keyboard to play until I have done as much design and testing as a I can. Currently the intention is to basically replace the 'brains' of the keyboard with my own. Whereas my last synth was entirely analogue, this one will have to be at least hybrid, if not purely digital. I will try and update this page when there is more to say.
Disassembly
I took it apart. There was 120 screws just to get inside. There was another 104 to remove all the electronics (not that I wanted to). There was another 24 screws in other places (including the stand). Why did they need 248 screws in total? I don't know. My wrists don't know either. And that's assuming I found all of them.
From this, I have documented as much as I could about the existing components within the system, and I am looking in to how to best use them. The keybed seems to consist 13 x 14 diode matrix, allowing for more-than the 176 buttons required, as two are allocated per key. This allows for the velocity to sensed as the time delta between two buttons presses can be measured. The power and audio amplification share a PCB, where there is a barrel jack for 12VDC in (1.5A), and a 6.35mm headphone jack. This also connects to two 4.5” 10W 4Ω speakers and two 1” tweeters. All the buttons are just membrane switches on two separate PCBs.
The majority of the internal space is occupied by the keybed. It is massive due to the design implementing weighted keys via different length metal rods. The next largest space-consumer is the bass reflex enclosures for each speaker, as they take up all the space either side of the buttons.
