The original concept I had for this thing no longer apeals to me. (see below)
Now, I am working on a new idea. I decided to give the single DAC and multiple Sample/Hold thing a fresh look. Now, I have to admit, that what I am doing is sort of like killing flies with nuclear weapons, but, hey, what the heck.
I aquired a large number of Xilinx XC4003A-PC84 FPGA IC's a while back. They were free, I wasn't going to refuse them. There isn't a whole lot you can do with 3000 gates (yeah, right). But, it is posible to make a DMA controller using them. So, that is what I am going to do. This will be part of a system that also involves a 68008 microprocessor, since I will also be using a RTOS (see my glockenspiel) to handle the midi data. The DMA controller will read data from memory directly and output it to a 12 bit DAC. The DMA controller will also supply a 6 bit selector word to a MUX that will make up the Sample/Hold circuitry. The idea is that the DMA controller will update each Sample and Hold every 64 mSEC, or so. The rate will be adjustable.
So, for now, here is the DMA controller schematic. I will have the rest soon, I hope.
This project will probably be wire wrapped first.
Here for your amusement