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 Forum index » DIY Hardware and Software » Thomas Henry designs
VCO-1 on 12V supply
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psioniclabs



Joined: Feb 04, 2009
Posts: 23
Location: Louisville, KY

PostPosted: Wed Sep 16, 2009 11:15 am    Post subject: VCO-1 on 12V supply Reply with quote  Mark this post and the followings unread

Has anyone had experience building TH VCO-1 for a 12 volt power supply rather than 15? I'd like to try this vco and I'm curious what, if any, component values would need changing. Thanks in advance.
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psioniclabs



Joined: Feb 04, 2009
Posts: 23
Location: Louisville, KY

PostPosted: Mon Oct 05, 2009 7:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Well for the most part VCO-1 works on a 12V (MFOS) supply, except for the V/Oct tracking isn't there yet.

I matched the 3906s and had some 1K tempcos I put in series for a nice little heat-shrink wrapped bundle. I played around with some resistor values according to TH's notes. R43 I left at 1.5M. R23 I dropped down to 16K to readjust the max current of the 3080.

It sounds good, but I need to work out the tracking. At 1V tuned to 55Hz, 2V gives me ~ 122Hz, so tracking is definitely going sharp. R2 doesn't adjust enough to bring it back. I've been playing around, substituting R4's 820ohm with 1K and also trying R29 with 75K to try a suss out the problem, but the answer hasn't presented itself yet.

I'm going to keep at it, but if anyone has suggestions on things to try I would appreciate it.
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Sound



Joined: Jun 06, 2006
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PostPosted: Wed Oct 07, 2009 4:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello Psioniclabs,

I would see all the points where +/- 15V is inputed.

In the Scott Stites website they are the schematics and the explanations of the VCO1 http://mypeoplepc.com/members/scottnoanh/birthofasynth/id33.html
There applies the Ohm's law to R43 and R23

I=V/R

So if we want use 12V and Thomas henry says 10μA for reference current it will be:

10μA=-12V/R43 ; R43=-12V/10μA; R43=1,2ΜΩ

About R23 says a maximum current of 0.68mA so:

R23= -12V/0.68mA ; R23= 17647Ω ; R23=~18KΩ

Edit: I removed a incorrect information for no confusion. I suggested adapt the same coarse and fine span but has not sense

Last edited by Sound on Fri Oct 22, 2010 10:30 am; edited 3 times in total
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Sound



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PostPosted: Wed Oct 07, 2009 6:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you have already 10V peak to peak in the outputs, I think that only we need change R41=~263KΩ for same performance than the original.

And off-topic now, but I wondered about, I think it is useful, how to do that the Fine knob respond to a octave span?
Following same steps than before, for 2ΚΩ tempco and 100KΩ V/Octave input, R46(Fine)=~2.4MΩ at +/-12V supply and =~3MΩ at +/-15V supply.

Hope that it helps,

Regards.
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psioniclabs



Joined: Feb 04, 2009
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Location: Louisville, KY

PostPosted: Thu Oct 08, 2009 11:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info Sound!

Yeah I've been experimenting with R43 and R23 based off what resistors I had available. I think you're definitely right about R43. I don't have a 1.2M part around, but I was planning on kludging together a 1M and 200K in series to get there. I got the impression from the design notes that R23 could be a little more variable because it's the max current, but I can try that as well.

Another thing I'm going to try is lowering R22, R15, R13 and R30 values in the discrete Schmitt Trigger to readjust and match the currents expected for 15V. I worked it out as some 8K, 16K and other part values I don't have on hand at the moment. I tried to cheat by lowering R29, but that didn't work out. So if kludging R43 doesn't work out, I'll order some of those next.

I don't think adjustments for the coarse and fine pots are necessary, since it's still in the linear voltage input and they need to manually tuned anyway.

I'll update this thread with what works for me when I get it figured out. I know it's useful to lurkers searching for quick answers such as myself Wink
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Sound



Joined: Jun 06, 2006
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PostPosted: Thu Oct 08, 2009 12:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

psioniclabs wrote:

Another thing I'm going to try is lowering R22, R15, R13 and R30 values in the discrete Schmitt Trigger to readjust and match the currents expected for 15V. I worked it out as some 8K, 16K and other part values I don't have on hand at the moment. I tried to cheat by lowering R29, but that didn't work out. So if kludging R43 doesn't work out, I'll order some of those next.

Hi psioniclabs,
According the explanation of Thomas Henry these resistors decide the amplitude of the wave output that must be 10V peak to peak. If you have already it, I think you will not need change these values. He says that for 10V peak to peak R22 must be double than R15 and R15 double than R13.
I'm intrigued with this, with the original resistors values and +/-12V power supply, do you have 10V peak to peak signal in the outputs?

Quote:
I don't think adjustments for the coarse and fine pots are necessary, since it's still in the linear voltage input and they need to manually tuned anyway.

I think that it affects at the span of the response, I mean if for example with the original values and +/-15V power supply, with the coarse pot, you go, say from 10hz to 20 Khz, if you feed it with +/-12V power supply you will decrease this span, say for example 100hz to 10Khz (hypothetical measures)

Regards.
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psioniclabs



Joined: Feb 04, 2009
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Location: Louisville, KY

PostPosted: Thu Oct 08, 2009 1:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Now that I think about it, I haven't hooked up my multimeter to know if it's *exactly* 10Vpp. But checking it on my scope it definitely looks 10Vpp, based off my calibration. It's definitely worth double checking. I was thinking if the values are a little bit off in the integrator that could cause drift just as well as the exponential converter. But yes, it certainly looks 10Vpp. Definitely the next thing I'll try after the expo conv.

The coarse tuning span is narrower, but not in any musically obstructive way. I can still turn the coarse knob all the way down for an LFO response and all the way up to freak out my neighbor's dog. Laughing
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psioniclabs



Joined: Feb 04, 2009
Posts: 23
Location: Louisville, KY

PostPosted: Tue Oct 20, 2009 7:11 am    Post subject: Reply with quote  Mark this post and the followings unread

I was able to get completely stable 1V/Oct response on a 12V supply over about 4 octaves. It starts to run a little sharp at 5 octaves, but I believe further refinement in these replacement resistor values or adjustments to the high frequency trim could extend the range. As is, this was good enough for me.

These were all 1% precision resistors from Mouser that got close enough to the recalculated values.

R22 - 16K
R13 - 4.12K
R15 - 8.06K
R30 - 80.6K
R43 - 1.2M
R23 - 16K

Thanks to TH for providing great resources to learn about this VCO.
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Sound



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PostPosted: Fri Oct 22, 2010 10:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello, I edited my first post because there was non correct information, so now days, what I would do is only R43=1,2ΜΩ; R23=~18KΩ and check if sine and pulse output are 10V peak to peak , if not, I would adjust R7 on the pulse output and R18, R19 on sine output for 10 volt peak to peak.

This is theoretic, I didn't breadboard it.
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mrand



Joined: Mar 30, 2014
Posts: 56
Location: Yukon and London Ontario

PostPosted: Sat Jan 28, 2017 4:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Does anybody know how I would adjust the skew of the triangle? I've built this one a few times and usually end up with a skewed triangle, leaning towards one side. I don't have a scope, but it is easy to identify the skew when using it to fm another VCO at LFO rates.
My 12v version seems to be more skewed than my 15v version.
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