The Thomas Henry VCO-1 Page Is Up

StephenGiles · Joined: Apr 17, 2006 Posts: 507 Location: England

Might TH design a guitar pitch to voltage converter with which to play this wonderful VCO? Laughing

Thomas Henry · Posted: Sun Jun 03, 2007 4:48 pm Post subject:

StephenGiles · Joined: Apr 17, 2006 Posts: 507 Location: England

I think I knew that answer in advance! This might give me an excuse to rebuild the EH Guitar Synth front end, because this worked very well on single notes. See here
http://hammer.ampage.org/?cmd=lt&xid=&fid=&ex=&pg=7

This includes a fundamental extractor providing a good sinewave at it's output which is squared, frequency doubled and fed to some magic around a couple of 4047s and VCOs forming a loop. The "how it works" was explained to me about 27 years ago but I've long since forgotten!

Thomas Henry · Posted: Sat Jun 16, 2007 2:16 am Post subject:

philpeery · Joined: Nov 08, 2006 Posts: 137 Location: new jersey, usa

slo

I built this and it all worked first time, and it sounds great. Thanks to Thomas and Scott. Only wrinkle is the coarse pot audio range is only from about 9 o/clock (lows) to 12 (highs), how can I spread the range out over the full travel of the pot?
I used a linear pot.

George

Scott Stites · Posted: Fri Nov 09, 2007 8:49 am Post subject:

Hmmm....I'd check into that a little further. The coarse pot should give operate smoothly across the range, IIRC. Of coarse (pun intended) my memory slips. In any event, increasing the mix resistor for the coarse control will limit the range more. But, I don't recall it being any diff from the coarse control of any other VCO I've worked with.

Glad to see you got that bad boy going though! Very Happy

Cheers,
Scott

CJ Miller · Joined: Jan 07, 2007 Posts: 368 Location: 127.0.0.1

Wow.. this looks great. And sounds great! How did I just discover this now? This morning I've been looking all over for my PNP pairs - they are not in any of the usual places, which means that they could be anywhere else! I wonder how a dual with 13600 instead of 3080 will work. Can hardly wait to play with a triangle VCO!

I am grateful for the inspiring ideas for us n00bs

Peake · Posted: Sat May 10, 2008 11:10 am Post subject:

Nice PWM!

This is a triangle core oscillator? Has anyone routed two together, sine wave out to frequency input, one to the other, and increased the FM index? The exponential FM on the Buchla 258b goes to chaotic results (pitched noise) and I'm wondering if this will as well, if such amazing expo FM is the domain of all triangle cores.

ryktnk · Posted: Thu May 15, 2008 10:26 am Post subject:

Peake · Posted: Thu May 15, 2008 8:13 pm Post subject:

"Stability" is definitely not desired. I'm just after the acoustic terror that the Buchla 258B can produce with the exponential FM. If you or anyone has a soundbite of the VCO-1 outputting a sine wave of medium or higher frequency, modulated by another sine wave that is higher in frequency, I'd love to hear it, especially a demo of the FM index increasing from zero to full. Thanks for replying and offering.

(Not tooting my own horn, but this all-Buchla 200 piece IIRC uses no white or pink noise- the noise-like sound is oscillator FM through filters. Many of the sounds are sine wave exponential FM, with a lesser index. I'm looking to add this back to my setup.)

Scott Stites · Posted: Mon May 19, 2008 5:47 pm Post subject:

Thanks for the heads up, ryktnk. I re-ordered some of the links on my page, and it looks like the sw changes the URL to do it - I imagine some other stuff has fallen out in other links I've sprinkled here and there. Rolling Eyes

Mike, as far as I'm concerned you don't blow your own horn enough! I'm looking forward to this download (spoken like a true dial-upper here Very Happy

)

Cheerio,
Scott

Peake · Posted: Mon May 19, 2008 7:50 pm Post subject:

Peake · Posted: Fri May 23, 2008 3:09 pm Post subject:

Here's a 1:1 parts placement/parts list diagram. Instead of "C2", etc., the actual value is present. I find it a bit quicker than other methods, but understand the ease in updating a parts list at a later date.

Please point out any mistakes, if so inclined.

THVCO1Parts_c.pdf

Description:

1:1 Parts placement guide to the TH VCO-1 PCB. Untested, may contain mistakes.

Download

Filename:

THVCO1Parts_c.pdf

Filesize:

1.93 MB

Downloaded:

512 Time(s)

Peake · Posted: Fri May 30, 2008 7:23 pm Post subject:

Hi, I plan to build one or more VCO-1s and have a question. I've just received a THAT 320 matched trannie IC for use with this VCO, just to see what happens (and to add a switch if needed to use a pair of 3906).

The much-appreciated VCO-1 reference page says "An exponential converter is a rather sensitive device and a mass of tangled wires coming and going from it can often create stray capacitance problems." Obviously, I'm going to have to daughter-board the IC, and since it has a second set of matched trannies in there, I can use it for another VCO as well. However...due to the above statement, am I getting into trouble if I run wires to another PCB, or if the daughterboard is positioned in between two VCOs, with wires running to each? Should I use shielded cable to ground? Should I just try it and simply see for myself? Very Happy

Thanks for the great project!

Scott Stites · Posted: Sun Jun 01, 2008 12:32 pm Post subject:

I'm going to be honest and say - I dunno! Laughing

If it's any consolation, I would probably try it as you describe as well.

I think you would probably be OK - I'm not sure if shielded cable would help or not, but it wouldn't hurt to try I suppose. I sure would be interested in hearing your results - especially your experience with the THAT device.

Take care,
Scott

Peake · Posted: Sun Jun 01, 2008 1:14 pm Post subject:

Thank you Scott! The THAT device is rated seven times better than the SSM but I don't know if that sort of difference is important, at those depths of decimal points! Incredibly quiet for audio, though.

I've been rearranging the PCB to work with the inexpensive trimpots from a local supplier- not very difficult so far (photoshop). I've been wondering about the waveshaping as well- will post any results.

BTW, the PCB artwork PDF is printing at "93% zoom" for some reason. Something alerted me to this, and yes, pressing a DIP socket into the paper shows that it's a tad small. Obviously others have not been experiencing this or they'd have posted. Ah, the steps required to get from A to Z Smile

Scott Stites · Posted: Sun Jun 01, 2008 1:41 pm Post subject:

BTW, Mike - I remember you asking how the thing does with FM. I still have the VCO partially on breadboard, but I'd really have to do a re-build to get it back. I've been cobbing parts from it now and then (just snagged a 100K pot off of it last weekend for TH's latest project).

Anyway, I was going through the VCA 1 page and found a short sample I did of the VCO-1 being linearly modulated. Here's the text and link to the sample (it's not a very long sample):

Peake · Posted: Sun Jun 01, 2008 6:48 pm Post subject:

a.b.o.z. · Posted: Sat Aug 23, 2008 9:23 am Post subject:

Mike how did THAT 320 responded in VCO-1?
I'm soon to finish one and looking for something to substitute 2N3904s.
Ones that I got from local store had different pin-out. E-C-B instead of standard E-B-C. Weird stuff.
What other monolithic PNP pair should I look for? (beside SSM2220, THAT320 and 2SA798 are there any else?)

Thnx

Ivan

edIT: and with matching I came to find one with hFE 208 and other 215. This is closest I could find in this batch..is this close enough or need to be exact values?

Peake · Posted: Sat Aug 23, 2008 7:17 pm Post subject:

I believe that Thomas said that you can just drop in two 3906s and get good results. It's far less expensive than a THAT or SSM, etc., unless you have to have such extreme matching. I'm no expert; perhaps one might chime in?

widdly · Posted: Thu Aug 28, 2008 1:06 am Post subject:

I just used 3906 in the two I built. Sounds good to me. If I was building another I might use one of those 2saxxxx (or should it be 2scxxx) dual transistors. They are cheap and easy to get in my neck of the woods.

I'd love to see a good saw ouput mod for these. It's the only thing missing.

Tim Servo

widdly · Posted: Sun Aug 31, 2008 6:44 pm Post subject:

Thanks for the tip. I have the 3080 book which is very enlightening. Perhaps it's time for the VCO book too.