Something new I built - fun with decade counters

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devinw1
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Something new I built - fun with decade counters

Post by devinw1 » Sun Apr 19, 2020 4:04 pm

So, I've had the idea for a while to use a decade counter and make each step of the counter be a modulate-able segment of a waveform. So, I built it up on the bread board and it works pretty well! At first I was using VCAs for each step, which also works, but then I figured you can buy a quad switch DG211 for under 2 bucks, so why not just use switches.

My plan is to have each segment have a switch to enable or disable modulation, because you can have some good fun with that. If you select every other segment, the modulation sounds a lot like thru zero FM, because you are basically forcing "digital" zero crossings at each segment that has modulation turned off.

The next step is to find something suitable for a clocking VCO that is good from about 200Hz to 200kHz (since you are clocking at 10x frequency due to the counter). I think there's probably something off the shelf (3340?).

Finall, I slapped the 2 pole Butterworth VCF from the datasheet on the output for optional smoothing of the wave. My plan is to pipe the frequency CV to the filter so if you select a smoothing level, it will remain at that level regardless of frequency.

Here is the schematic of the waveshaping so far:
TS0-WS-Beta0.jpg
Here is a video of modulating every other segment:


Here's forming a "triangle" with the pots and then putting some filtering on it:
triangle.png
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Re: Something new I built - fun with decade counters

Post by guest » Sun Apr 19, 2020 5:12 pm

thats pretty cool. if you want to look at some high frequency VCO ideas, there was a thread on that a while back:

viewtopic.php?f=17&t=208725

for speeds up to 200kHz, the 3340 might work, and if you have one kicking around, its worth a try. the 13700 version i did could also make it up that far, but not any higher. a 4046 would also work, but it has poor linearity. the HC221 version can definitely do it, but its a bit more parts. since you only need 200kHz, perhaps one of the simpler 221 versions would be fine.

on the schematic, it looks like R7 might be going to the wrong rail.
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Re: Something new I built - fun with decade counters

Post by KSS » Sun Apr 19, 2020 5:35 pm

That looks like fun.
Ian Fritz Dodeca? module needs and has a high freq VCO. Some of his other OSCs should also be candidates

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Re: Something new I built - fun with decade counters

Post by guest » Sun Apr 19, 2020 5:49 pm

i just had a look at the deka, and it lists 20ppm/K thermal stability of the oscillator. that makes me think its a digital core of some sort - maybe done with a microcontroller or one of the ADI digital synthesis ICs.
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Re: Something new I built - fun with decade counters

Post by devinw1 » Sun Apr 19, 2020 5:54 pm

Ah yes, the 4046. That seems like a good place to start. I have one or 2 of them, as well as 3340s so I'll play with both. Gonna have to get a second protoboard if I want them to coexist. The whole wave shaper with all the pots took up most of mine :D.

Regarding the first schematic, I hadn't run annotate on it yet so due to resolution, the ?s probably look like 7s. Lol. Here is it annotated:
TS0-WS-Beta0_1.jpg
Checking out the Doubledecka now. Aha.. I figured somebody had to have done something like this before. I *think* though nobody has done the modulating segments though. :despair:
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Re: Something new I built - fun with decade counters

Post by guest » Sun Apr 19, 2020 5:56 pm

ah, yes, R254 is the resistor in question, then.

another idea i just had, was that maybe the SPST switches can be replaced with an 8x1 analog mux to the mixing port (or 3x 4x1 mux)?
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Re: Something new I built - fun with decade counters

Post by KSS » Sun Apr 19, 2020 6:18 pm

guest wrote:
Sun Apr 19, 2020 5:49 pm
i just had a look at the deka, and it lists 20ppm/K thermal stability of the oscillator. that makes me think its a digital core of some sort - maybe done with a microcontroller or one of the ADI digital synthesis ICs.
That would be a surprise. Mr Fritz prides himself on his analog prowess and extreme VCO accuracy.

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Re: Something new I built - fun with decade counters

Post by guest » Sun Apr 19, 2020 6:22 pm

yeah, i found some pictures, and it looks like its a thermistor on top of a 3046 or other such 14-DIP package transistor array. in which case, im not sure how that 20ppm/K is measured, as the best i was able to do with the AD633 and MAT14 was 25ppm/K, and that was just for the exponential converter, not the integrator and reset circuit. getting capacitors with that little drift is quite difficult. although the drift at various CVs is not the same. in theory, the midscale drift should be zero.
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Re: Something new I built - fun with decade counters

Post by KSS » Sun Apr 19, 2020 6:23 pm

Ian also did something called the 5pulser using a 3914. Not the same, but was the first thought I had when reading your OP. Then the Deka, then the new Marienberg EG which has 8 modulatable segments AA,DD,SS,RR. Active thrread in the 5U section of MW.

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Re: Something new I built - fun with decade counters

Post by KSS » Sun Apr 19, 2020 6:25 pm

I think Ian said he found a 3081? to be more accurate for expo duty. That's probably what's under the tempco R.

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Re: Something new I built - fun with decade counters

Post by KSS » Sun Apr 19, 2020 6:29 pm

Ian has described his 'oven' testing method either here, on his site, or on electro-music forum. It's not a guess and by golly procedure.
edit: no snark intended. Ian's always been pretty rigorous in his testing and evaluation. /edit

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Re: Something new I built - fun with decade counters

Post by guest » Sun Apr 19, 2020 6:40 pm

and i mean no disprespect to ian, he is obviously very knowledgable and makes great designs. its just that 20ppm/K is the same drift as a fixed frequency crystal oscillator.
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Re: Something new I built - fun with decade counters

Post by KSS » Sun Apr 19, 2020 8:07 pm

Yes, I do not mean to imply anything. Only sharing data points about his typical practice to aid you and devinw1 towards a suitable hi-freq osc solution.

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Re: Something new I built - fun with decade counters

Post by devinw1 » Sun Apr 19, 2020 9:00 pm

Thanks guys. Any and all discussion is always appreciated!

Looks like there actually are some 10 channel switch ICs but non in thru hole. MUX idea is interesting too but again the 10 channel thing. I could trim it to 8 but 10 is better!

Re: R254 I think it's ok. Just a ref current for a standard white bread PNP expo converter

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Re: Something new I built - fun with decade counters

Post by devinw1 » Sun Apr 19, 2020 9:05 pm

I was also thinking it would be cool to have a rotary selector that would enable modulation on all segments, every other, and 4 or 5 out of 10 (evenly spaced) or some other combinations. I think this might be doable with MUXs but perhaps getting into the realm of needing a micron controller haha

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Re: Something new I built - fun with decade counters

Post by KSS » Sun Apr 19, 2020 10:03 pm

Build the proto with 'patch-programmable' normalled modulation jacks on each segment. Learn what sounds good, is useful etc. And whether patch programmable is cool or a pita. Iterate.

Once you 'micro' it's a whole new thing.

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Re: Something new I built - fun with decade counters

Post by KSS » Sun Apr 19, 2020 10:09 pm

You proabably are past gaining much from this, but the Digisound module 80-21 VCDO -forerunner to the Wiard-Blacet Miniwave- also used a 'high freq' 3340 and a look at its schematic and build notes could be useful?

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Re: Something new I built - fun with decade counters

Post by guest » Sun Apr 19, 2020 10:41 pm

devinw1 wrote:
Sun Apr 19, 2020 9:00 pm
Re: R254 I think it's ok. Just a ref current for a standard white bread PNP expo converter
youre totally right here, my mistake.
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Re: Something new I built - fun with decade counters

Post by EATyourGUITAR » Sun Apr 19, 2020 10:48 pm

Was the schematic ever released for the high frequency VCO core?
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Re: Something new I built - fun with decade counters

Post by devinw1 » Mon Apr 20, 2020 10:32 am

KSS wrote:
Sun Apr 19, 2020 10:09 pm
You proabably are past gaining much from this, but the Digisound module 80-21 VCDO -forerunner to the Wiard-Blacet Miniwave- also used a 'high freq' 3340 and a look at its schematic and build notes could be useful?
Nice! I found the article w schmatic here:

http://www.digisound80.co.uk/digisound/ ... 21_ETI.pdf

If I understand this correctly, they have the 3340 going even higher frequency than I will be needing it (They have 64 segment wavetables)?

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Re: Something new I built - fun with decade counters

Post by ersatzplanet » Mon Apr 20, 2020 1:06 pm

Another fun thing to do with counters is to put a cheap Vactrol at each stage. Doesn't work at high speeds as a waveform generator of course, but as a audio/signal switcher with no clicks they work great.
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Re: Something new I built - fun with decade counters

Post by KSS » Mon Apr 20, 2020 1:12 pm

devinw1 wrote:
Mon Apr 20, 2020 10:32 am
If I understand this correctly, they have the 3340 going even higher frequency than I will be needing it (They have 64 segment wavetables)?
Correct. I had to go back and look because 32 was in my head. But that was the total number of 64 segment wavetables available. How things change.
And stay the same. ;)

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Re: Something new I built - fun with decade counters

Post by cygmu » Mon Apr 20, 2020 5:10 pm

Ian Fritz’s DoubleDeka is described on his web page: http://ijfritz.byethost4.com/DD_web.pdf

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Re: Something new I built - fun with decade counters

Post by devinw1 » Wed Apr 22, 2020 11:50 pm

Well, the CEM3340 works great with this setup. I used a 47p cap and mostly the same circuit as the Digisound unit (which is basically the datasheet recos)

What's killing me know is that I my breadboard was so full I setup the CEM on another little auxiliary board powered from the big board and it worked great. Then I broke it all down so I could do some more tests on the 3340 on the big board and it's not being stable. Even as low as 10khz the waveform is super jumpy. I've seen this type of behavior before when a connection is iffy or a ground line is loose so I'll continue to track it down but no luck so far. This sort of thing can be so frustrating when prototyping !!

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Re: Something new I built - fun with decade counters

Post by Studioalethea » Thu Apr 23, 2020 12:27 am

devinw1 wrote:
Wed Apr 22, 2020 11:50 pm
Well, the CEM3340 works great with this setup. I used a 47p cap and mostly the same circuit as the Digisound unit (which is basically the datasheet recos)

What's killing me know is that I my breadboard was so full I setup the CEM on another little auxiliary board powered from the big board and it worked great. Then I broke it all down so I could do some more tests on the 3340 on the big board and it's not being stable. Even as low as 10khz the waveform is super jumpy. I've seen this type of behavior before when a connection is iffy or a ground line is loose so I'll continue to track it down but no luck so far. This sort of thing can be so frustrating when prototyping !!
You do all the datasheet stuff? Pin 3 @ -5V, polysty timing cap, correct current at Pin14? Are you running at Eurorack voltages with adjusted resistors?

I hear you on the breadboard frustrations. That was my entire week last week just trying to troubleshoot my Moog ladder.

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