VCO Simmed!

Well, after much tinkering I got my VCO sim working:


Right now it's just a sawtooth, but I plan on adding some waveshapers soon.

Shortly after my first post I found that the Electronotes ENS-75 VCO Option 1 article has been posted on the web here. It was a really informative article and helped me really understand what was going on inside the circuit.

One advantage to the sim is that I found out that I can substitute some of the parts I already own (CA3083, OPA132) and still get similar results. I still need to take stock of what resistors and caps I already have, but that will have to wait for a day when I have some time on my hands. Everything else (caps, missing resistors, tempco, comparator, JFET, tripots, and normal pots) will have to wait until we have some cash to spare. That's fine because I need to work on the waveshapers, and get a board layout together first anyway.

Oscilloscope Get!!

The UPS man stopped by to drop this off:


It's a Kikusui COS600M 100Mhz analog scope. Picked it up off ebay for ~$100 complete with a probe and the manual. Not too shabby. I didn't have a lot of time to fiddle with it last night. Me and wife had to do an emergency clean of our place because my sister's family is coming to stay with us tonight. I did, however get to test all the channels using both the calibration signal on the scope, and my function generator. I think I may have to do some calibration on it which makes having the manual quite handy.

The only downside is the fact that it's analog and not digital. I got spoiled by the Tektronix phosphor screen scopes they had at my old job. This scope is more than adequate for doing synth work. The only thing I need now is a few more probes, but that will have to wait for another day.

It begins

I figured I should have a place to document the synth stuff I'm doing. Right now there isn't a whole lot happening. This is due to the fact that I'm in the process of building a house so a lot of cash is tied up in that.

I did end up getting a scope. A 5 channel 100Mhz analog which, while not as nice as a digital scope, is plenty good for what I want to do. It should be a step up over the 60Mhz Hitachi I used to have.

Unfortunately, I don't really have the space for a proper workshop until we move into said house. Once everything settles down I have a few projects in mind:

1) Give my MidiBox SID a proper home.

I've had the boards built and working for a few years now, but I've never gotten around to putting them in the case I bought. Now that my father-in-law has gotten me a proper drill, and I've gotten my step bit back from my parents house, I should be able to make the front panel look halfway decent.

I also want to end the love/hate relationship I've had with LCD screens. Every time I attempt to wire one up it never seems to work. I even fried a really nice graphical LCD back in my college days. Hopefully I can get the screen I bought for my MidiBox SID going and then I'll be able to actually edit patches w/o having to rely on MIDI.

2) Ian Fritz's Sawtooth VCO

I've been spending some time recently going over this circuit and simulating it in LTSpice. I may end up using a CA3083 instead of the LM394 he has listed. Mostly because I already have 2 CA3083's on hand. So far my spice simulations are looking good. I'm going to attempt to work on a perfboard layout next. After that it's time to order parts and build!

3) AVR based VCDO

I took the inspiration for this from Eric Brombaugh's Digital VCO, which is basically a voltage controlled digital oscillator. I plan on basing this around an ATTiny28, again because that's what I have available to me. I'm also considering an AVR based on the fact that I've seen it used successfully in other synth projects such as AVRSyn.

4) Bench Computer

I have my wife's old college computer just sitting around in the basement collecting dust so I thought I might put it to work as a bench computer. One of the bonuses is the fact that it has hardware parallel and serial ports. This will let me use the AVR and PIC programming cables I already have lying around instead of buying new USB based programmers.

I'm considering putting Linux (probably Ubuntu) on it for a few reasons. First, I would like to try out gEDA. From what I've read it seems like a pretty neat piece of software, but it's Linux only at the moment. I could try and get it running using cygwin, but I'm much to lazy to figure that out. Second I've read about gcc toolchains for both AVR and PIC (including dsPic) that are available for Linux and I would like to see how those work.

So, though I'm not doing much at the moment, I do have a lot of ideas in the hopper. Stay tuned and I'll keep updating