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 Forum index » DIY Hardware and Software » Thomas Henry designs
Whats up with this 8038 Chip?
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Wild Zebra



Joined: Apr 28, 2005
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PostPosted: Wed Oct 11, 2006 11:46 am    Post subject: Whats up with this 8038 Chip? Reply with quote  Mark this post and the followings unread

I'm kinda new to all these fancy specialized chips, and was thinking of ordering some for a few of these projects, like the XR2206, LM566, and I ran across this 8038. Are there any layouts for this chip? Has it been optimised Thomas Henry style? Is it worth getting? What about S&H chips like LF398/389? I have a Delton Horn book that has schems for some specialized chips, like S&H and ASDR blah blah

thanks

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Coriolis



Joined: Apr 11, 2005
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PostPosted: Wed Oct 11, 2006 11:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, I read somewhere that the 8038 is supposed to be hopeless for 1V/oct control, but then they said that about the XR2206 Rolling Eyes (or did they? maybe I'm just exaggerating). But I've never seen it used for anything synth...

C
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fluxmonkey



Joined: Jun 24, 2005
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PostPosted: Wed Oct 11, 2006 4:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

elby designs sells a circuit board for a thomas henry designed linear VCO based on the 8038. tom's usual elegance & simplicity of design, it uses one quad op-amp and a handful of other components, and is very servicable.

a few limitations of the design to be aware of:
    * response is linear, like korg and paia but unlike almost everything else which is exponential
    * it does not go low (bottoms out around 20hz), so it's not suitable as an LFO. goes up to 20k tho, using a vc sweep of 0 to +15v
    * positive cv only

i have 4 behind a dual frac panel, 2CVs with attenuators into each, makes some tasty noise with enough cross-patching.

bbob
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State Machine
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PostPosted: Fri Oct 13, 2006 8:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
8038. Are there any layouts for this chip? Has it been optimised Thomas Henry style? Is it worth getting?


Its a good chip for a voltage controlled LFO (almost) that has all the common waveforms found in a subtractive synthesizer without having to wire in all the usual waveshaping circuits with discreet OP-AMPS. That is it's main benefit, a compact one chip solution. I have not seen it in precision VCO applications though.

I know the Blacet "Klank Werk" uses it for an internal voltage controlled carrier generator and it works fine in that application.

Another BETTER chip for function generation and LOW frequencies for LFO generation is the MAX038:

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257

http://www.futurlec.com/Maxim/MAX038CPP.shtml

I have one or two in my parts bin and you may be able to find them.

Bill
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piedwagtail



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PostPosted: Fri Oct 13, 2006 12:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm getting well below 20Hz....
its my TH 3 wave lfo unit.
It doesn't go much below 0.2Hz though and ranges up to 200Hz or so.

Robert
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State Machine
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PostPosted: Fri Oct 13, 2006 12:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
response is linear, like korg and paia


Linear like PAIA Question My PAIA VCO design has an exponential response. Which PAIA are you referring to Question

Thanks,
Bill
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State Machine
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PostPosted: Fri Oct 13, 2006 12:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
It doesn't go much below 0.2Hz though and ranges up to 200Hz or so.


A 5 second period is good for most applications though Very Happy It did not occur to me that the 8038 went that low. I know you can make it go well above 200 HZ Very Happy

Bill
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fluxmonkey



Joined: Jun 24, 2005
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PostPosted: Sun Oct 15, 2006 8:52 am    Post subject: Reply with quote  Mark this post and the followings unread

piedwagtail wrote:
I'm getting well below 20Hz....
its my TH 3 wave lfo unit.
It doesn't go much below 0.2Hz though and ranges up to 200Hz or so.

Robert


are you gettng that out of the t. henry circuit? what value do you have for the timing cap? i'm using his suggested 500pf. didn't mean to suggest the chip was incapable of lfo, i was referring specifically to tom's circuit.

State Machine wrote:
Quote:
response is linear, like korg and paia


Linear like PAIA Question My PAIA VCO design has an exponential response. Which PAIA are you referring to Question

Thanks,
Bill


fatman, and 2700/4700 series... i know, i'm dating myself...

bbob
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State Machine
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PostPosted: Sun Oct 15, 2006 7:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
fatman, and 2700/4700 series... i know, i'm dating myself...


Ahh, OK Very Happy Thats fine, with age, there is wisdom Wink

Bill
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piedwagtail



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PostPosted: Mon Oct 16, 2006 9:53 am    Post subject: Reply with quote  Mark this post and the followings unread

0.22uF Mr. Green

no problem,just another great adaptable TH circuit!

Robert
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mediatechnology



Joined: May 10, 2006
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PostPosted: Thu Jan 25, 2007 3:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

I happened to stumble upon this today while going through an old file. It's a 1975 Electronic Design cite with op amp linearization of an 8038. It would obviously need, in some apps, expo scaling but might make a simple LFO. I'm pretty sure I used this technique once in a sweep generator.

www.ka-electronics.com/images/Electro-Music/VCO_8038_ED30175.pdf

IIRC 8038s are still pretty easy to get. I think I see them at Jameco.
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State Machine
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PostPosted: Thu Jan 25, 2007 4:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
It would obviously need, in some apps, expo scaling


Yes Wayne, and probably some temperature compensation as I am not sure how much this IC will drift Very Happy
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mediatechnology



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PostPosted: Thu Jan 25, 2007 5:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes 250 ppm/C (max) in the lowest grade for the 8038.

EDIT: The XR2206 in commercial specifies a typical number of +/-20ppm/C but no maximum figure. The MIL version is +/-50ppm max so I would think the commercial 2206 would have a significantly worse-case figure. It might approach the 8038's 250ppm/C.

A linearized 8038 might still be a good candidate for an LFO.
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Eric G



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PostPosted: Thu Mar 08, 2007 1:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, I'm Eric G and new to this forum (but not new in DIY)

The 8038 and 2206 are OK as modulation generators (LF or audio) or oscillators for crazy sounds, but don't spend time to make them track musically. Neither linear nor exponential (via expo converter). I tried that for months, it really doesn't work.
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Coriolis



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PostPosted: Thu Mar 08, 2007 2:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Eric and welcome!

You need to check this out...

http://mypeoplepc.com/members/scottnoanh/birthofasynth/id20.html

Cool

C
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bugbrand



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PostPosted: Thu Mar 08, 2007 2:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Coriolis speaks the truth!

If you see the Youtube Vid of my new stylus keyboard that's it controlling two of these XR2206 VCOs - tracking is pretty good (considering I've only roughly tuned these oscs and I didn't implement the temp-compensation).

I'm a BIG(BUG) fan of the Thomas Henry XRVCO!

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synth_ollie



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PostPosted: Thu Mar 08, 2007 3:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Coriolis wrote:


http://mypeoplepc.com/members/scottnoanh/birthofasynth/id20.html


Im building one (bugbrands pcb layput) right now ! Smile
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Eric G



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PostPosted: Thu Mar 08, 2007 5:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Coriolis wrote:

You need to check this out...

http://mypeoplepc.com/members/scottnoanh/birthofasynth/id20.html

C


Yep, I've seen this one. I don't know anything about it, so maybe I'm wrong. The design is pretty much like what I did.
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Scott Stites
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PostPosted: Thu Mar 08, 2007 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Eric,


welcome

Are you the Eric G of the EH-30 modular? If so, you must realize, you are partially to blame for my getting back into Synth DIY after a ten year or so hiatus - I think it was your page and Ray's that inspired me to get back into it. Very Happy

Nice to see you here!

Cheers,
Scott
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Scott Stites
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PostPosted: Thu Mar 08, 2007 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Regarding my EHS-30 site


I guess that answers that question Very Happy

Cheers,
Scott
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Eric G



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PostPosted: Fri Mar 09, 2007 12:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Scott Stites wrote:
Eric,

Are you the Eric G of the EH-30 modular? If so, you must realize, you are partially to blame for my getting back into Synth DIY after a ten year or so hiatus - I think it was your page and Ray's that inspired me to get back into it. Very Happy
Scott


Great! Nice to hear that it did some good. The EHS-30 site will be up'n'running in a couple of months.
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iorobyy



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PostPosted: Fri Mar 09, 2007 1:48 am    Post subject: Reply with quote  Mark this post and the followings unread

8038 is a good misunderstood circuit.
It have linear response but the problem is that is a inverted linerar
response Shocked ...not gooood!
The elby circuit is a good point for to start some experiment with a cv driver circuit....uhmmmm....antilog cv driver i think? right?
However the guru thomas henry some time ago made a good vco using 8038.
But response was always linear....is a perfect vclfo! but.... is not the 1V/oct VCO that we like.
Elby use very similar schematic (so linear response again).
However i know that Thomas was studying for 1V/octvize this chip.
Like the xr2206VCO....great!!
So guys.......Thomas go! go! go! Wink
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Thomas Henry



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PostPosted: Sat Apr 07, 2007 12:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Try this on for size. This is something I came up with in a book I wrote three years ago but haven't published yet. I used the AD821 because I had one, but feel free to try another matched pair.

This is for Forum users to play with only. Obviously, don't do anything commercial with it without permission, and please don't Web-publish this anywhere, but provide links back to this message.

Note the unusual power supply connections.

Thomas Henry


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goodrevdoc



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PostPosted: Sat Apr 07, 2007 12:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow! Shocked Mr. Henry strikes again! Very cool, unfortunately I recently got rid of my two 8038's as i didn't see myself using them. I'll have to get some more and try them out.
-justin
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iorobyy



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PostPosted: Sat Apr 07, 2007 2:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Great!!!!! Thomas you're my only Guru!!! Wink
I'm going to search a 8038 in my chips cemetary.
Uhmmmm...2sa798 transistor pair could be ok?
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