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 Forum index » DIY Hardware and Software » Thomas Henry designs
The Thomas Henry VCO-1 Page Is Up
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Scott Stites
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PostPosted: Sat May 26, 2007 4:07 pm    Post subject: The Thomas Henry VCO-1 Page Is Up
Subject description: Page contains original article by Thomas himself, circuits, PCB, resources
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The Thomas Henry....oh, the title already says that Very Happy

Here's the link:

http://mypeoplepc.com/members/scottnoanh/birthofasynth/id33.html

There are actually two pages, the page linked above and a "Resources" page describing parts procurement, places to find Thomas Henry stuff (including this forum), one stop-downloading. And one forlorn sound file, which is the same one I posted here already.

BTW, if anybody's got any good ideas for stuff to add to the VCO-1 resources page, let me know.

As threatened before, this is only the beginning. In fact, my message to Thomas telling him the page was ready crossed paths with the next cool thing coming over from him.

As George Costanza says, "We're cranking it up another notch". Very Happy

Enjoy the circuit - it's great!

Best Regards,
Scott

Edit: Fixed link.

Last edited by Scott Stites on Mon May 19, 2008 5:43 pm; edited 1 time in total
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Scott Stites
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PostPosted: Sat May 26, 2007 6:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thomas sent me a couple of samples of the VCO-1 that he had - I've loaded them on the VCO-1 resource page:

http://mypeoplepc.com/members/scottnoanh/buildingthevco1/

Check'em out! He uses his MTS100 MIDI to CV converter to control it. One of them has it playing along with a Casio CZ1000! Serious pitch accuracy going on there.

I've got an MTS100 - it's in the queue. Got it during the closing blow-out sale at MAP. I've also got a MAP MIDI Gator awaiting construction.

I need to computerize and MIDI-ize (Germaniac has sent help, but that's in the queue as well .....does anybody see a pattern here? ). Very Happy


Cheers,
Scott

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ian-s



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PostPosted: Sat May 26, 2007 7:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice VCO

Interesting using the sine as the PWM input, as apposed to the triangle. It slows the rate of change at the narrow pulse ends in a good way.
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PostPosted: Sat May 26, 2007 10:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

nice page there! Very Happy

what the burgeoning D.I.Y. community needs is a full set of these concise, clearly-written, easy-to-understand "how to" and "know how" articles.... Oh yeah, Thomas wrote a book... or 5.
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Dan Lavin



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PostPosted: Tue May 29, 2007 5:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Awesome design and awesome page! Thanks Thomas and Scott! My only concern is that if someone in this forum decides to do a professional pcb that they do a 2 sided board. The one sided pcb design from Thomas is about as small as I'd go but does leave a lot of empty real estate between components. It won't be an issue for me as I am a true TH disciple and rack mount my modules, but I know I'm in the minority with most everyone else doing PAIA frac rac, Doepfer, etc.
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PostPosted: Tue May 29, 2007 6:42 am    Post subject: Reply with quote  Mark this post and the followings unread

antman49443 wrote:
Awesome design and awesome page! Thanks Thomas and Scott! My only concern is that if someone in this forum decides to do a professional pcb that they do a 2 sided board. The one sided pcb design from Thomas is about as small as I'd go but does leave a lot of empty real estate between components. It won't be an issue for me as I am a true TH disciple and rack mount my modules, but I know I'm in the minority with most everyone else doing PAIA frac rac, Doepfer, etc.


the current PCB layout will work fine behind a frac/euro panel--mounted perpendicular, short side vertical. there are a couple of easy tweaks that i'd recommend: bring out the power to a single .156 connector, revise the tranny pair to matched pair instead of individual pair...

that said, magicsmoke is considering doing a revised PCB for this project... drop 'em a line if you're interested: magsmoke@gmail.com

b
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chonald



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PostPosted: Tue May 29, 2007 12:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Would this be difficult to build on a stripboard?

Cole
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Thomas Henry



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PostPosted: Wed May 30, 2007 10:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

chonald wrote:
Would this be difficult to build on a stripboard?


Probably not. But do watch out for stray capacitance around the current output from the exponential pair.

Thomas Henry
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v-un-v
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PostPosted: Thu May 31, 2007 1:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Thomas Henry wrote:
chonald wrote:
Would this be difficult to build on a stripboard?


Probably not. But do watch out for stray capacitance around the current output from the exponential pair.


Now this is interesting. I've heard of this before- especially in sample and hold circuits. Thomas, can you explain a little more in detail?

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PostPosted: Thu May 31, 2007 6:29 am    Post subject: Reply with quote  Mark this post and the followings unread

I'll let Thomas explain, but I do know things can get pretty picky around the expo pair. I recall when I put together my Schmitz Late MS-20 filters, I couldn't tune one of the filter's response to save my life. I triple checked the components and connections and couldn't find a thing wrong. Then I realized I hadn't cleaned the flux off the bottom of the board, and there was quite a bit around that pair - I cleaned off the flux, and sure enough, the thing tuned up just fine.

Having said that, I think the VCO would work pretty well on stripboard.

Cheers,
Scott

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chonald



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PostPosted: Thu May 31, 2007 9:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Woo!
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Randaleem



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PostPosted: Thu May 31, 2007 2:21 pm    Post subject: TH VCO-1 circuit question
Subject description: Where's the precision voltage reference?
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Hi Thomas,

Sure do appreciate your work! I have a quick question about the VCO-1 circuit and it leads to a VCO in general question.

Yes, stray capacitance can be sneaky. It appears there is something less sneaky that I'm wondering about. I don't see the usual voltage reference source in this circuit?

Is it a concession to simplicity; or just an example of something we in SDIY have been led to believe must be part of a decent VCO? Or am I missing something obvious?

Thank you for the design and detailed circuit description. (Thanks also to your wonderful advocate Scott! It must be nice to have such a champion on your team.)

Randal


Thomas Henry wrote:
chonald wrote:
Would this be difficult to build on a stripboard?


Probably not. But do watch out for stray capacitance around the current output from the exponential pair.

Thomas Henry
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PostPosted: Thu May 31, 2007 6:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

v-un-v wrote:

Now this is interesting. I've heard of this before- especially in sample and hold circuits. Thomas, can you explain a little more in detail?


It goes like this. A linear control moves from note to note by adding a fixed constant. This is an arithmetic relationship, and the progression is very pedestrian in nature.

But an exponential control moves from note to note by multiplying by a fixed constant. This is a geometric relationship, and the progression moves alarmingly fast. (Like the population of this weary planet going from 2 billion to 6 billion in less than my lifetime).

So this means that an exponential VCO will have very small control currents possible. A cruddy rosin blob will act as a dialectric with whatever it's touching. In very short order, you've got a capacitor robbing bits of that tiny control current.

Just remember it like this: linear adds, exponential multiplies, and hence the latter covers very small currents as well as large. Rosin blobs and untidy boards are the kleptomaniacs of the amperage world.

Hope this helps,

Thomas Henry

Last edited by Thomas Henry on Thu May 31, 2007 8:36 pm; edited 1 time in total
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PostPosted: Thu May 31, 2007 6:19 pm    Post subject: Re: TH VCO-1 circuit question
Subject description: Where's the precision voltage reference?
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Randaleem wrote:

Is it a concession to simplicity; or just an example of something we in SDIY have been led to believe must be part of a decent VCO? Or am I missing something obvious?


As Sherlock Holmes said, there's nothing so deceptive as the obvious fact.

No, you're not missing anything. In fact, this is nothing more than an instance of a maxim which has long guided me: "Never open a can of beans with a stick of dynamite."

I think I'll turn this over to Scott now; he's an expert on band-gap diodes, servo op-amps, superfast comparators and the like in VCO design. Let's hear what he has to say, and then I'll chime in again.

In the meanwhile, I think you can trust this VCO. It's not perfect, but you'll certainly make serious music with it.

Thomas Henry
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PostPosted: Thu May 31, 2007 6:27 pm    Post subject: Re: TH VCO-1 circuit question
Subject description: Where's the precision voltage reference?
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Randaleem wrote:

Thank you for the design and detailed circuit description. (Thanks also to your wonderful advocate Scott! It must be nice to have such a champion on your team.)


And thank you! As I creep into my dotage, I find I do this more and more just to hear the pleasant responses from builders who are having fun with this stuff. And, yes, it is great having a colleague like Scott. I truly admire his can-do attitude, attention to detail, and ethics (even though I wish he would stop speaking of the greatest fairy tale ever perpetrated, by Charles Darwin).

Why not ask him for whom he was named? There's only two of those guys left now!

Thomas Henry
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PostPosted: Thu May 31, 2007 8:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
No, you're not missing anything. In fact, this is nothing more than an instance of a maxim which has long guided me: "Never open a can of beans with a stick of dynamite."

I think I'll turn this over to Scott now; he's an expert on band-gap diodes, servo op-amps, superfast comparators and the like in VCO design. Let's hear what he has to say, and then I'll chime in again.


I'll follow that up with the bench technician's "If it ain't broke, don't fix it."

Certainly one could put in all of the ensurances that a VCO stay locked on frequency in perpetuity. Band gap diodes, voltage references, syncing to GPS - it's all good. Many people pride themselves on building the perfectly stable VCO. I've got nothing against that, and I admire their skill - it takes a lot of thought and ingenuity to do figure out some of the things these guys have done. Everybody has their own requirements.

By the same token it takes a lot of thought and ingenuity to create an effective "simple design". A lot of designs may look simple, but they're not simplistic - one of the reason's why I like Thomas' designs so much is you can look at it and the first thing you know is that you can build it with ease. And you know it will work. Experience has proven me that he never leads one down the primrose path - if there are warts, he's the first to point them out. Sometimes he even see's warts where I can only see skin as smooth as a Victoria's Secret model's backside.

His forte is the effective, elegantly designed circuit. For example, he certainly could build a VC quadrature generator - in his sleep, no doubt - but he chose instead to abandon the project because it didn't meet his personal design criteria - IE, it was looking more and more like a stick of dynamite, and all he was after was a can opener. He realized it would be just as effective to add the functionality on to some existing design. The same thing applies with the extra VCO measures - is it absolutely required to accomplish the task of making music? No. Then stick with the can opener.

Back on the subject of VCOs - IMO, a VCO does not have to be a super involved design in order to make serious music. In fact, before the late twentieth century, how many instruments did not require the occasional tuning? I played French Horn, and had to tune it every day to be in tune with the orchestra before practice, and certainly before performances. The first thing I'd do with my guitars when I picked them up would be to tune them up. What law says that your analog synth should never need tuning before a practice, recording or performing session? They're not derived from the steely, unforgiving logic of software - they're made up of natural elements just as real as the brass in a French Horn or the wood and catgut of a violin.

And I'm not saying that you have to put up with a VCO that drifts all over and is a general pain in the ass, or that somehow you're settling for less - this VCO is not that kind of VCO. It's accurate, it's stable and it's a transparently good design. There's a lot of Henry and Hutchins in this VCO. Having no voltage ref puts it in the same class as a lot of VCOs - how about the ASM, or the CGS, or the Wilsons', or my old mainstay, Rene Schmitz's VCO3, to name a few? I've heard sounds out of all of them that I guess I'd have to classify as music. Very Happy

Quote:
Why not ask him for whom he was named? There's only two of those guys left now!


It was just a little over 45 years ago my namesake guided the Aurora 7 around the earth (a few weeks before I was born, so my folks thought "What the hell.....").

Cheerio,
Scott

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PostPosted: Fri Jun 01, 2007 2:48 pm    Post subject: possible vco-1 enhancement???
Subject description: where's the saw?
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Hi Scott and Thomas,

How hard would it be to derive a saw wave from the triange? I've breadboraded this vco (it sounds GREAT!), but I really miss the saw waveform.

Also, I'm thinking about mod'ing the pcb so that it can use an ssm2220, MTA power connectors, and bourns/vishay style trimmers ('cause I have a ton of them!). And maybe if the saw wave mod is possible, that could be a piggyback pcb.....


Just thinking out loud!

Phil
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PostPosted: Fri Jun 01, 2007 3:23 pm    Post subject: Re: possible vco-1 enhancement???
Subject description: where's the saw?
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philpeery wrote:

How hard would it be to derive a saw wave from the triange? I've breadboraded this vco (it sounds GREAT!), but I really miss the saw waveform.


It can be done with two op-amps and a FET. There will be an announcement made here soon by someone other than me which will have a direct bearing on this question. In the meanwhile, let me build the suspense by saying: see pages 38, 70 and 94.

Don't like the suspense? Just think of this as that little snare drum icon that beats while Windows is slowly "configuring" something...

Thomas Henry
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PostPosted: Fri Jun 01, 2007 3:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

DOH! The suspense is killing me! Must be part of that afore memtioned "Global Domaination" plan! Can't wait, but I am sure it will be worth it!

Very Happy Very Happy Very Happy
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PostPosted: Sat Jun 02, 2007 7:04 am    Post subject:   Reply with quote  Mark this post and the followings unread

[quote="Thomas Henry"
A cruddy rosin blob will act as a dialectric with whatever it's touching. In very short order, you've got a capacitor robbing bits of that tiny control current. [/quote]

This brings up an interesting point: cleaning the populated circuit board.
What do folks here use for flux solvents?
I've always soldered with rosen core lead solder (Kester "44"). I've used a citrus based solvent called Opticlear to clean up (thats WHEN I clean the board). Its meant as a safe replacement for trichloroethylene.

Has everyone else switched to lead free/rosen free solders? Whats recommended? Thanks!

Peter
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Randaleem



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PostPosted: Sat Jun 02, 2007 8:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Photon wrote:

This brings up an interesting point: cleaning the populated circuit board.
What do folks here use for flux solvents?
Peter


99% Isopropyl Alcohol, Denatured alcohol, and/or Acetone. Sometimes a commercial flux remover from MG chemicals or Puretronics.

Followed up with Distilled (de-ionised) water.

The 99% Isopropyl works well for most freshly soldered stuff, and is cheap and leaves minimal residue. A good overall first choice.

Denatured is stronger, and then the commercial cleaners, followed by Acetone which is strongest of all. (Great for removing OLD flux when you buy someone else's problem board Wink )

Be sure to work with continuously clean fluids, or you're just spreading the flux and contaminants around.

This is another of those subjects you can go into great detail about; so part of the answer is finding the sweet spot of effort vs. results in YOUR situation. I've left some detail out of the description above.

These cleaners work for me and it often DOES make a difference you can hear.

Randal
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Photon



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PostPosted: Sat Jun 02, 2007 9:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info. I didn't realize rosen flux was soluble in isopropanol. That should be pretty straight forward. Cool

Randaleem wrote:
Be sure to work with continuously clean fluids, or you're just spreading the flux and contaminants around.

I've cleaned enough optics to know about this one Crying or Very sad Wink
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Tim Servo



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PostPosted: Sat Jun 02, 2007 9:08 pm    Post subject: Re: possible vco-1 enhancement???
Subject description: where's the saw?
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philpeery wrote:
Hi Scott and Thomas,

How hard would it be to derive a saw wave from the triange? I've breadboraded this vco (it sounds GREAT!), but I really miss the saw waveform.

Also, I'm thinking about mod'ing the pcb so that it can use an ssm2220, MTA power connectors, and bourns/vishay style trimmers ('cause I have a ton of them!). And maybe if the saw wave mod is possible, that could be a piggyback pcb.....


Just thinking out loud!

Phil


Hey Phil,
I've been thinking of the same mod. Thomas is right, it can be done fairly easily in a typical tri-core oscillator because you have access to a square wave that has the right phase relationship. A circuit that should do the trick also appears in "An Analog Synthesizer for the 21st Century" which will be out in August (or hopefully earlier) from Magic Smoke.

Tim (got saw?) Servo
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PostPosted: Sat Jun 02, 2007 10:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the cleaning tips - back in the day I used to use trich as well, I've never found anything quite as effective as it - how come all the good stuff has to be so deadly?

Phil - cool! If you come up with a PCB, and if you don't mind, I sure would like put it on the page (I'd of course credit you with the layout). I'm waiting on this sawtooth thing myself.....blasted world domination, anyway! Heck, I'd just settle for......one beeellion dollars!

Cheers,
Scott

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PostPosted: Sat Jun 02, 2007 11:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

That old trich-based spray cleaner was NASTY, and my local guy (an NTE shop) won't sell it anymore. I think I still have a can of it in my "bad stuff" cabinet. I've switched over to the Kester water-clean and no-clean solder, which I really like. The no-clean flows like toothpaste, but once you get used to it, it's not that bad. The water-clean is great, as long as you do a board wash within an hour or so.

I've got a "working" single sided design that I hope to do a press-n-peel test with in the next few days or so (got to finish painting the entry hall first!!!). I can tell you that a single sided design for this one was tough, and I even used the layout from your VCO-1 page (done by Thomas I assume) as a solid starting point. But it is a bit kludgey right now, with more jumpers than I would like to have. I did get the ssm2220 and vishay trimmers in there. I also really like to have my pots connect to the board the way that Fonik has done some of his boards - each lug on the pots have a corresponding connection to the pcb. I do the output jacks MOTM style since I feel that using the RG174 does keep the outputs a bit cleaner. I've built a few of the MFOS projects and I always seem to screw up with the point to point wiring! This way, the only goof you can make is reversing the outer pot lugs, which is not a big deal. I will post my results, and if it's a workable layout, I will certainly make it available. My honest opinion is that a double sided board with a good ground plane is probably best for this one. But we shall see.....

Phil
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