8038 waveform generator

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revtor
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8038 waveform generator

Post by revtor » Tue Nov 26, 2019 12:08 pm

Saw these IC's on sale and remembered S.Stites & T.Henry working out a nice implementation for them.

Linear VCO / Bench waveform generator. A great synth DIY workbench tool or "old school" Pre 1v/octave style audio generator

https://www.bgmicro.com/ICS1069.aspx

and..

https://www.birthofasynth.com/Thomas_He ... l#Features



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Post by Orgia Mode » Tue Nov 26, 2019 4:28 pm

I'll have to check out that second link. I bought a load of these years ago and struggled to get a decent frequency range with what I thought were good rc values.

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Post by revtor » Tue Nov 26, 2019 7:34 pm

They get it 20-20k apparently. Some very creative manipulating of things.. Thomas Henry’s kinda known for that. Fun stuff to research..

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Post by jorg » Wed Nov 27, 2019 9:08 am

I built my very first VCO around the 8038, back in the mid 1970s. It got fairly hot, and tuning was a pain because of the linear scale. But it did sound nice - and had a sine output right out of the chip.

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Post by Orgia Mode » Wed Nov 27, 2019 2:40 pm

jorg wrote:I built my very first VCO around the 8038, back in the mid 1970s. It got fairly hot, and tuning was a pain because of the linear scale. But it did sound nice - and had a sine output right out of the chip.
I didn't run mine long enough to find out if it got hot. Definitely wroth a revisit now that I know so much more about electronics.

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dot matrix madness
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Post by dot matrix madness » Fri Nov 29, 2019 4:07 am

The 8038-based VCO on page 83 of Thomas Henry's (e)book "The VCO Chip Cookbook" shows better V/oct tracking than his other VCOs using that chip.
Anyhow, you can get a very pure sine out of the 8038.
I use mine often as "function generator" as input for other modules under test.
build photo here
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Post by Orgia Mode » Fri Nov 29, 2019 2:03 pm

dot matrix madness wrote:The 8038-based VCO on page 83 of Thomas Henry's (e)book "The VCO Chip Cookbook" shows better V/oct tracking than his other VCOs using that chip.
Anyhow, you can get a very pure sine out of the 8038.
I use mine often as "function generator" as input for other modules under test.
build photo here
Oh, thats nice! I don't think I am familiar with that ebook. I definitely need to find it now.

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Post by KSS » Sat Nov 30, 2019 6:06 am

Orgia Mode wrote:I'll have to check out that second link. I bought a load of these years ago and struggled to get a decent frequency range with what I thought were good rc values.
You were not alone! We were all misled by the datasheet. At least when we look at it in hindsight. Everybody and their brother were publishing the same limited projects when these first came out.

Giving credit where it's due., John Simonton of PAIA was the one who discovered the way to get wide range out of these types of chips. Tom Henry properly credits him as source and has taken it from there. Simonton's work was pusblished in old Polyphony magazine articles. I think the 566 was the first place he used the idea TH has since documented and expanded.

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Re: 8038 waveform generator

Post by jorg » Thu Jan 02, 2020 11:45 am

For fun, I put together a SPICE model of the sine waveshaper from the 8038, using commonly available discrete transistors. I did this in TINA TI. It seems to work very nicely in simulation!
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Re: 8038 waveform generator

Post by Kipling » Thu Jan 02, 2020 3:31 pm

I built a Practical Wireless 8038-based waveform generator back in the 70’s (still have it) but it always had a problem with the frequency peaking before the full travel of the frequency pot and dropping off beyond that, which I never got to the bottom of.

I don’t have the original PW article so I’ll have to reverse engineer it to get the schematic and see if I can resolve it. I did buy a spare 8038 recently so I’ll swap that out first.

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Re: 8038 waveform generator

Post by FredBloggs » Thu Jan 02, 2020 4:53 pm

Is this it?
https://www.americanradiohistory.com/UK ... 0%2004.pdf

The site has some good resources for us oldies!

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Re: 8038 waveform generator

Post by jorg » Fri Jan 03, 2020 9:27 am

This circuit uses the 8038 sine shaper in reverse (in the feedback of an op amp) to convert sine to triangle.
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Re: 8038 waveform generator

Post by Noodle Twister » Sat Jan 04, 2020 3:13 pm

The Zlob modular dual VCO use's two 8038 IC's. It's pretty good. Has sine, triangle and square waveforms.

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Re: 8038 waveform generator

Post by twistedneck » Sun Feb 16, 2020 6:46 am

Hey Noodle Twister i just bought one of these and it sounds real good has some actual character that i don't hear in my other two voices (Joranalogue Generate 3 and SSF Spectrum)

sounds warm and good through the mum 8 Akai 950 based filter

what do you all think makes this chip and its special implementation cool? here is what the Zlob designer said

"Below 300 hz the waveform symmetry is slightly off. triangle waves get a little uneven in the lfo range they are more asymmetrical, the sine is not completely perfect to begin with the bottom trough and in the lfo range it slopes slightly, and the square turns more trapezoidal above 1khz(see scope shots on my site)

Also it doesn’t track 1 volt per octave perfectly. usually the 2nd and 4th octave will be a couple cents off."
Last edited by twistedneck on Mon Feb 17, 2020 10:26 am, edited 2 times in total.

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Re: 8038 waveform generator

Post by Noodle Twister » Sun Feb 16, 2020 7:32 am

twistedneck wrote:
Sun Feb 16, 2020 6:46 am
Hey Noodle Twister i just bought one of these and it sounds real good has some actual character that i don't hear in my other two voices (Joranalogue Gemerate 3 and SSF Spectrum)

sounds warm and good through the mum 8 Akai 950 based filter

what do you all think makes this chip and its special implementation cool? here is what the Zlob designer said

"Below 300 hz the waveform symmetry is slightly off. triangle waves get a little uneven in the lfo range they are more asymmetrical, the sine is not completely perfect to begin with the bottom trough and in the lfo range it slopes slightly, and the square turns more trapezoidal above 1khz(see scope shots on my site)

Also it doesn’t track 1 volt per octave perfectly. usually the 2nd and 4th octave will be a couple cents off."
Hi,
I was drawn to it by reading about Thomas Henry and later the description by Zlob that you posted above. It's imperfections appealed to me.
"There are a couple quirks to these 8038 VCOs" "I'm definitely building this" I thought :tu:

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Re:

Post by EATyourGUITAR » Sun Feb 16, 2020 10:30 am

dot matrix madness wrote:
Fri Nov 29, 2019 4:07 am
Anyhow, you can get a very pure sine out of the 8038
if you adjust the trimmer right maybe
Last edited by EATyourGUITAR on Sun Feb 16, 2020 10:32 am, edited 1 time in total.
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Re: Re:

Post by EATyourGUITAR » Sun Feb 16, 2020 10:31 am

double post
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Re: 8038 waveform generator

Post by CrysWiz » Fri Feb 21, 2020 11:36 pm

Been a long time since i used them but the internal heater burns a lot of current. I wouldn’t use for much these days but they do have their own character (what other ppl might even call “flaws”)
turning the world on its ear since 1981

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