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An idea for a new kind of DIY VCO
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mosc
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PostPosted: Sat Feb 11, 2006 5:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
How do you do "click me to explode me mode".
I was thinking the only way of posting anything with any detail in it would be to zip it.


I'm going to install some software to make this automatic. It should make life easier for the DIY crew.

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PostPosted: Mon Feb 13, 2006 12:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

This might be representing the original idea better.

[Editor's note: The picture down-sizing feature now works. Click on the attached picture and see the larger size. --mosc]



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uncle-2.jpg



uncle-2.pch2
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Another go at a waveform idea by Uncle Krunkus

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Uncle Krunkus
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PostPosted: Thu Feb 16, 2006 5:00 am    Post subject: Reply with quote  Mark this post and the followings unread

When it comes to testing this out. On the circuit as I originally drew it, what should I hang off the output? A volume pot (I s'pose) of what value? Before or after a de-coupling cap (of what value?) Why?
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Uncle Krunkus
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PostPosted: Thu Feb 16, 2006 5:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Jan,
I just tried to load the G2 patches you did into the demo, and it said "unsupported file version" for both of them. What's the story wid dat?

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Uncle Krunkus
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PostPosted: Thu Feb 16, 2006 5:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Mosc,
Does this mean we can attach pics of whatever resolution we like now and they will be automatically downsized for the preview?

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elektro80
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PostPosted: Thu Feb 16, 2006 5:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Sure, now you can at last share those 4500 DPI 6x9 medium format scans of yours. Laughing
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Uncle Krunkus
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PostPosted: Thu Feb 16, 2006 6:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Confused
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PostPosted: Thu Feb 16, 2006 6:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, yes.. you can now upload reasonable large pix and the board software will sort out the rest... Very Happy
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PostPosted: Thu Feb 16, 2006 6:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Smile
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PostPosted: Thu Feb 16, 2006 7:56 am    Post subject: Reply with quote  Mark this post and the followings unread

We've had some problems with files larger than 8 MB. Probably something to do with HTTP timeouts or something. The attachment mechanism is probably not appropriate for files that big anyway so we haven't spent too much time trying to increase this limitation. You can post some pretty huge images now and they should autosize to about 600 px max on a side.
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PostPosted: Thu Feb 16, 2006 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
Hey Jan,
I just tried to load the G2 patches you did into the demo, and it said "unsupported file version" for both of them. What's the story wid dat?


You need to have the last (1.40) version of the demo software, download from http://www.clavia.se/products/nordmodular/demo.htm

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PostPosted: Thu Feb 16, 2006 1:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
When it comes to testing this out. On the circuit as I originally drew it, what should I hang off the output? A volume pot (I s'pose) of what value? Before or after a de-coupling cap (of what value?) Why?

Does anyone have any ideas about this? (Scott? Jan? Stein? Anybody!?!?)
I'll probably start breadboarding this tonight.

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PostPosted: Thu Feb 16, 2006 2:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
Uncle Krunkus wrote:
When it comes to testing this out. On the circuit as I originally drew it, what should I hang off the output? A volume pot (I s'pose) of what value? Before or after a de-coupling cap (of what value?) Why?

Does anyone have any ideas about this? (Scott? Jan? Stein? Anybody!?!?)
I'll probably start breadboarding this tonight.


I'd AC couple it and use a pot of approx 10 K, which sort of sits nicely between (assumed) 100 K input impedance of the circuit coming after it and the about 1 K impedance of the driving circuit. The capacitor should be something in the order of 220 nF ir so then to allow for a lowest frquency of about 10 Hz or so, didn't really calculate it though, but it won't be off by orders of 10. When it turns out it should be much larger an elco is ok, plus side on your "DAC".

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PostPosted: Thu Feb 16, 2006 2:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

I never know these things until I try them, so I would look at the following:

1. Run it through a voltage follower (op amp buffer) through a 1K resistor and perhaps a 1uF cap (kinda like Ray did with the WSG)

or

2. Run it to a two stage mixer (two inverting op amp buffer stages), and mix in a bit of +V via a trimmer into the second stage to center the signal around 0V, with a 1K resistor on the output of that. A bit more parts-wise, but then you don't any capacitive coupling/frequency content concerns.

or

3. Run the signal through a cap and resistor to the input of a voltage follower (op amp buffer) with a 1K on the output. This would center the output around 0V with less parts than (2) and not have the cap matzoh ball on the output (1). Not sure if the cap on the output is a big deal, but I like to keep my outputs 1K output impedance, and I'm never sure if Xc is a factor there or not when interacting with my other modules (most likely not). Still, I like to have just the resistor on the output.

This is all assuming you have +/-V rails on the circuit.......

Cheerio,
Scott
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PostPosted: Thu Feb 16, 2006 2:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Scott's ideas are better than mine, I was just thinking you could do that later, when you like the results :-)
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PostPosted: Thu Feb 16, 2006 3:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Actually, I like Jan's idea - it got posted while I was typing.
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PostPosted: Thu Feb 16, 2006 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
Uncle Krunkus wrote:
When it comes to testing this out. On the circuit as I originally drew it, what should I hang off the output? A volume pot (I s'pose) of what value? Before or after a de-coupling cap (of what value?) Why?

Does anyone have any ideas about this? (Scott? Jan? Stein? Anybody!?!?)
I'll probably start breadboarding this tonight.


I think both Scott and Jan have great ideas here!

Very Happy

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PostPosted: Fri Feb 17, 2006 3:12 am    Post subject: Reply with quote  Mark this post and the followings unread

That's exactly the reason I asked.
Two independant answers to a question like that cement the important, (common) part and elaborate on an advanced design in two different directions. Or, to put it another way, two heads are better than one.
Hey Jan,
I tried the G2 patches (on the newer version) they are both very cool noise makers, but I must admit that I envisioned a much more tonic output. The overall wavelength should remain the same, so I'm expecting the overriding fundamental to be quite solid, with basically no enharmonic overtones, no matter what the other oscillators do they should really just add or subtract "bits" from the waveshape. Does that make sense?
I played around with this excel sheet today in class which illustrates the resulting waveshape quite well. It plots three wavelengths so you can see the resultant lead in and lead out for the middle wave. I haven't sorted out automating the cycling of the bits as a running binary counter would do yet, but I need to find a bitwise function in excel for that, and it may not exist. VB might do it though. Just press F9 continously to regenerate the bits randomly.


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PostPosted: Fri Feb 17, 2006 4:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Jan,
should the cap come before the pot or after?
Sorry, these questions seem a bit remedial, but I've never actually conceived a circuit from scratch before, and there are some fundamentals which I wonder about. I assume the cap and the pot form an RC network which dictates the lowest passable frequency yeah?

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PostPosted: Fri Feb 17, 2006 7:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Well it's up and running on the breadboard.
I'm pretty impressed with it so far, and I've only heard a couple of it's possible waveshapes. It's got a PWM square wave kind of timbre, (as you'd expect) but there's also some beating going on in there. (I think the 555 is contaminating the supply rails slightly and the propagation delay of the 4017 means it's always slightly out of tune with it) Cool
It'd make a great bender. If you touch any of the diodes feeding the switch matrix it affects the ability of the 4066 to switch at the right speed and you get instant phasing like effects. The actual backboard of the breadboard also acts like some kind of aerial, touching it makes a definate change in the timbre of the wave!! Cool
It seems so far that running the 4017 at about 2K is as far as I can go before the 4066 can't switch fast enough. Sad At that point the switches stop reacting and everything goes quiet. 2K/8=~250Hz fundamental)
I'm thinking that improving the wiring and layout could improve that. Maybe there's a faster version of the 4066?
So I'm really quite happy with it so far.
It's got a fat square weird phased PWMed twitchy kind of sound which is about as stable as any other badly constructed high speed digital switching circuit! Rolling Eyes Which I reckon is pretty cool Cool
I'll try to get some samples soon.
Thanks heaps everyone for all your help.

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PostPosted: Fri Feb 17, 2006 8:45 am    Post subject: Reply with quote  Mark this post and the followings unread

A had a quick look at the 4066 data sheet, it should be able to go much faster than 1 kHz (maybe even up to 10 MHz).

My guess is that the diodes together with the input capacitance of the switch control lines is the limiting factor. The control lines have hardly any ability to go low now. You could add pull downs (10 .. 100 k I'd guess) on the switch controls, or alternatively replace the diode's wired OR function by real CMOS OR gates - pull downs is probably nicer from a benders perspective :-)

Re. the capacitor, probably between the DAC and the pot, that way you are guaranteed to have no DC over the pot, but after it would work just as well otherwise.

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PostPosted: Fri Feb 17, 2006 4:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Jan,
I tried out an advanced 555 clock with separate mark/space pots which uses a couple of diodes to force the charging through one and the discharge through the other. This should be stripped right back as the PW of the 555 really should have no affect. I just need as short as possible a pulse to clock the 4017. I'll shift the cap to the DAC side of the pot too, and see where it's at.
I'm thinking now of two quite separate versions. One which is all gates and binary counters. It would be more "automatic" except that the counters could be VC. The other one would be an enormous diode/DIL switch matrix which lets you force the wave shape. The first one should have more predictable results + randomness, the second would be better for whackyness / circuit bending / immediate control.

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PostPosted: Fri Feb 17, 2006 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

BTW,
I kind of thought their could be something I could do with the control lines. I hadn't thought of pull downs though, instead I was thinking of hold up caps!! (for the situations where the same switch is closed for two clocks in a row, to minimise the noise of the switching) Does that hold water?
Now I like the idea of experimenting with both. Would one 100K from each control to ground do it? That's only 4 resistors which could add heaps to the stability.

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PostPosted: Fri Feb 17, 2006 5:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry for my shortisih earlier message, but its great you got it going ! I'd love to hear some sound samples, once you're happy with it.

Putting in extra capacitance would help your max. frequency down even more, and as you can now unly run up to 250 Hz you seem to have plenty of filtering. When you need additional filtering it would be better I think to run the output signal through a tunable low pass filter that you match a bit with the primary oscillator.

Re the pulldown resistors its a bit of guess work. Based upun the input capacitance of the switches alone (5 .. 8 pF) 100 k or even 220 k would be low enough to allow for a primary clock rate of 50 to 100 kHz, but the diodes add in capacitance as well and this is hard to guess (depends on actual type used and actual voltage over it). But it might result in the resistor values to have to be somewhat lower. You'll have to experiment a bit to find a good value. You could go down to a few 100's of ohms without worrying for damage, so there is quite some experimental room here.

What voltage do you run the circuit on, everything on 12 V ?

And I was wondering why you need the 555 to make short pulses. The 4017 shift register should act on an edge, or ?

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PostPosted: Fri Feb 17, 2006 5:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, exactly what I was thinking too!! (the lowpass which automatically tunes (CV?) to just below the carrier. (I don't want to wipe out the carrier completely as it is 8 (or16) * the fundamental it actually adds a lot of harmonic overtones))
I added the pull downs. 100K seems to be fine. The 555 can get right up to 14K now with no decernable breakup in the 4066 switches. I'm reading 3K5 on the output, but I think that's because I've inadvertantly setup a double wave in the switching. The trace is now showing very clear steps across the waveshape, (I can almost count them!)
Unfortunately (or not) the pull downs have also banished the bending diodes, backplate aerial effect. I'm using 1N4148s BTW (cheap and plentiful) But at least I know how to get it back. (pulldown pots maybe? with metal knobs/case to tag 3, what a diabolical plan!! Twisted Evil )
I'm testing it at this stage on a 9V battery.
Sorry, you're right about the 555. I just crank up the frequency and the PW will look after itself! Doh! Embarassed

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