Rebuilding my old Yamaha CS15D Synthesizer as a Modular Synthesizer.

[DrNomis_44]

Hey everyone,

Got a new DIY project added to my list of projects for 2019, it's a complete re-build of my old Yamaha CS15D analog synthesizer, but I'm adding-in a few twists to expand the range of sounds I can create with it.

First I'll explain why I've decided to re-build it as a Modular Synthesizer, basically, the keyboard circuitry stopped working properly and only a few of the keys would actually sound, I had a good look at the circuit boards underneath the keyboard and some of the copper tracks were corroded beyond fixability, seeing as replacement parts for the CS15D are hard to find and expensive when you can find them, I was going to write-it-off as too un-economical to repair when a great friend of mine suggested something to me which got me thinking.

So, I went online and did a quick google search for some circuit diagrams for the CS15D and found a website where I could download a pdf of the complete Yamaha CS15D Synthesizer service manual, the manual has all the information I need, so I got inspired to do a complete rebuild of it.

Here's what I'm planning to do:

* Rebuild the keyboard so that it is housed in a separate wooden case and connected to the rest of the Modular Synth like the old Moog Modulars of the 60's.

* Add a 16-step Sequencer which can drive the various parts of the Modular Synth as well as the keyboard.

* Add an external audio input so I can do things like feed the signal from a guitar through the Modular Synth so it can be processed by for example, the Voltage Controlled Filter, this should create some interesting and musically useful results.

* Expand the number of raw waveforms that the Voltage Controlled Oscillators can produce, they are currently limited to producing Sawtooth and Square/Pulse waveforms.

* After studying the Voltage Controlled Filter circuits, I noticed that the IC that forms the heart of the VCF has outputs for Low-pass, Hi-pass, and Band-pass functions, so I thought it would be great to be able to have all three functions accessible.

[DrNomis_44]

Hey Everyone,

Thought I'd do a quick update on this thread, anyway, I've been playing around with the design of the wooden cabinets which will be housing all the different modules and I've come up with a design I'm happy with, I'll be using some 18mm pine wood to build the cabinets, hopefully when I get a chance to, I'll be buying all the materials I'll need from my local Bunnings shop next fortnight, I had planned on buying them this fortnight but I had to postpone it cause of some bills I had to pay.

[DrNomis_44]

Update:


Just thought I'd do a quick update, anyway, I managed to finish making the first module that's going in my modular synth, it's a VCA (Voltage Controlled Amplifier) module with a twist, it uses a 12AX7 tube as part of the circuitry, here is a couple of pics of the finished Tube VCA module, note that I haven't tested it to see if it works.....yet:

32535

32536

[DrNomis_44]

So, "What's a Voltage Controlled Amplifier?" I hear you say, it's a specially designed type of amplifier in which the gain, or amplification it produces is controlled by a DC voltage applied to it's C.V. (Control Voltage) input, the higher the voltage, the higher the amplification, a Voltage Controlled Amplifier, or VCA, is typically used to control the dynamics, or loudness, of a signal in a Modular Analog Synthesizer, and to give the signal Attack, Decay, Sustain, and Release characteristics.