I'm building a VCO. At what point do I make it compatable?

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I'm building a VCO. At what point do I make it compatable?

Post by Argitoth » Mon Jun 30, 2008 8:23 pm

Hey, might get a book on DIY stuff, but can anyone explain at what point of the process do you make decisions on what you want the module to be compatable with, be it eurorack, frac rack, or synthesizer.com? Is this part of the process the easiest thing to do?

I'll also take this opportunity to ask about resistors. I'm seeing a lot of talk about 1% temp resistance and 5% temp resistance. Do VCOs usually have one temperature resistor or multiple? If it depends, what would cause you to need more than one?

I'll take this opportunity to also ask: Is it the same level of difficutly to create a VCO that outputs 4 saws VS creating a VCO that outputs 1 sin 1 tri 1 saw and 1 squ?

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Post by Muff Wiggler » Mon Jun 30, 2008 8:54 pm

i'm not a circuit designer, so my opinion on this is bullshit at best, but here ya go anyway -

- first of all I wouldn't start by designing a VCO. That's a pretty complex project. Design something simpler first, and work your way up. It's a lot of work to do, just to scrap and re-do again because you've learned a million lessons. learn the lessons on small, easy-to-swallow projects.

- the compatibility question has different answers. Some of the platforms have different power ratings (12v, 15v etc). I would guess that you would want to determine pretty early on what sort of power you want to be running through the circuit you design. Or you could just design for 15v and use a power regulator later on if you wanted to support a 12v system.

The other compatability issues are just the size of the panel and jacks. This is super easy to change after your circuit is done, it does not impact the circuit. Only issue may be PCB size. A .COM sized PCB won't fit in a eurorack, but a eurorack-sized PCB will fit in a .COM.

The real decision you need to make before starting the circuit is what the core will be, and what waveshapers you need to create. Sawtooth core? Triangle core?

1% vs 5% resistors is really a quality issue. they are the same thing, the 1%'s just have closer tolerances. If you have an 8k resistor, a 5% one won't be exactly 8k - it will be 8k +/- 5%. A 1% resistor will also not be exactly 8k, it will be 8k +/- 1%. Generally people use 1% resistors wherever precision is important, and 5% resistors wherever it isn't.

For temperature resistors, without being an expert I would guess you want as few of them as you can so long as the frequency of the VCO remains stable in changing temperatures. If it's not stable, you add more.

For your final question, the answer isn't simple.

First, yes, it is much easier to create a VCO that emits 4 saws, compared to a VCO that emits multiple waveforms. The way you make a VCO is to create a core that oscillates at a controlallable frequency. This core will oscillate in whatever shape you design it to oscillate in - triangle, saw, sine etc. You then create waveshapers to turn that waveform into whatever other ones you want. For example you will have to create a circuit that acts as a sine-to-square waveshaper, if you have a sine core, and want it to have a square output.

So, you could skip the waveshapers completely and create a sawtooth core VCO that emits, as you would expect, sawtooths.

Now the tricky part is that you want it to output 4 saws. This is not a trick of engineering within the VCO circuitry. It is already oscillating in a saw waveform. If you want four of them, you send it to a 1->4 multiple, and then you have four of them.

However, I know what you are getting at, and I don't think you'll want them. You'll have 4 identical saws. Mixed together, they will sound pretty much the same as just one. There's little point in doing this.

You want to make a supersaw oscillator. What you need is a bunch of saw waveforms that are all SLIGHTLY out of tune with each other. This creates the 'fatness' you are associating with having 4 saw waveforms.

Threre's a few ways to do this, the most common is to simply use 4 oscillators, and slightly detune them all from each other.

Another way is to use a module like the Cyndustries Saw Animator, which accepts an input of a single sawtooth waveform, and calculates a whole pile (the amount is adjustable) of slightly detuned saws to go with it. This is a whole lot easier than tuning 4 oscillators together, and maxed out it gives you WAY MORE fat buzz than any four oscillators ever could.

I suppose if you really wanted to skin this cat this way, here's what you could do - make a sawtooth oscillator core. Then, instead of making a bunch of different waveshapers and putting them on the same PCB, make a bunch of detune circuits, and lay them out on the PCB instead.

Bearing in mind the result would be pretty much just like a conventional oscillator fed into a Saw Animator, however probably with less overall range of added-sawtooth-goodness

hope this helps

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Post by Kwote » Mon Jun 30, 2008 9:43 pm

thanks for the definition on 1% and 5% muff. i never even gave it a thought.

my advice is forget designing and just figure out what format "you'd" like to use personally and get going on it.

buy some assembled ones and just get used to using them for a bit. then get some kits for your format(it'll help to pick a format where kits are readily available). build those and learn what you can from them. then go from there. you'll really start seeing a clearer direction by then i bet.

sorry if this is sorta repetitive answer to another thread of yours but it's worth repeating. that's one of the best ways to learn, especially with all this crazy synth stuff.. repitition.
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Post by Argitoth » Mon Jun 30, 2008 10:41 pm

This helps a lot. Thanks! Kwote, good advice.

here's my idea:

4 saw osc


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