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 Forum index » DIY Hardware and Software » Thomas Henry designs
XR-VCO at +/-12V
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macumbista



Joined: Sep 12, 2007
Posts: 360
Location: berlin
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PostPosted: Fri Aug 23, 2013 11:42 am    Post subject: XR-VCO at +/-12V Reply with quote  Mark this post and the followings unread

Is anyone running the Thomas Henry XR-VCO at +/-12V, and if so can it be done without modifications? If not, what did you mod?
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macumbista



Joined: Sep 12, 2007
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PostPosted: Mon Aug 26, 2013 4:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Received the following from Tom Bugs, would be happy to get feedback from anyone else running at +/-12V:

Quote:
I think I was using +/-12V supplies at the time when I did the XR-VCO pcbs.

Quick thoughts based on the schems:
- maybe R20/R21 (on the TH schematics) values would need to be adjusted - forget what these are for exactly - says more in, I think, the TH VCO Chip cookbook
- offset / voltage scaling around the Skew input summers may need adjustment - from what I remember, the first half of travel of the skew dial did nothing - which'd make sense given the diodes cancelling half the voltage swing! So initial Skew could possibly just go Gnd to V+ (rather than V- to V+). You may want to play with values then of the summing resistors.


FWIW, the Skew control is also dead at half its travel at +/-15V.

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macumbista



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PostPosted: Tue Aug 27, 2013 4:04 am    Post subject: Reply with quote  Mark this post and the followings unread

This thread has also been useful:

http://www.electro-music.com/forum/topic-54360.html

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Thomas_Henry



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PostPosted: Tue Aug 27, 2013 11:54 am    Post subject: Reply with quote  Mark this post and the followings unread

I get the "dead travel" comment quite a bit on all my designs. Just so you know, that design feature is intentional and based on something picked up from Bernie Hutchins of Electronotes fame decades ago. In particular, the values for the Initial and VC input resistors are carefully chosen for maximum versatility. That is, the VC input can accommodate either a +5V envelope, a bipolar 10V signal, or any other weird mixture of control signals. So, yes, if just using Initial by itself, or VC by itself, it might seem like there is dead travel. But when doing sophisticated VC summing, you will never bump in into a rail or pin the response at the extremes.

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