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 Forum index » DIY Hardware and Software » Thomas Henry designs
Alternate Sync for XRVCO
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bugbrand



Joined: Nov 27, 2005
Posts: 845
Location: Bristol, UK
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PostPosted: Sat Aug 09, 2008 7:08 am    Post subject: Alternate Sync for XRVCO
Subject description: Little snippet also useful for other VCO designs (I think)
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Heya,,,

I think I've finally realized how to do a nice little sync addition for VCOs - I have a feeling I'm not re-inventing the wheel here, but I'm happy to have finally cracked a bit how to use JFets for reseting VCO caps.

Inspiration came last night from the AS21C sample and hold schem combined with a bit of testing of other sync bits today.. I just got this working good on the XRVCO and would presume it should work on other apps too (I want to try the CA3080 VCO too). While the XRVCO does already have a sync function, I wasn't totally sure I was happy with the FSK method (maybe I was doing wrong though).

And there'd been other THenry Sync ideas in, for example, the VCO cookbook, but those ones with a 4016 seemed too big (usually no need for the other switch gates).

Anyways, if anyone has comments I'd be happy to hear (-- I always have these feelings that maybe something is being done baddy-ways!) - I have little experience with JFets..


littlesync.jpg
 Description:
Little sync circuit - I think the values are good?

Connect a sqr-wave into the SyncIn (or something with fast transitions)
Connect the JFet legs across the VCO cap.
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littlesync.jpg



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bugbrand



Joined: Nov 27, 2005
Posts: 845
Location: Bristol, UK
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PostPosted: Sat Aug 09, 2008 7:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm, on further investigation with other circuits ----

Well, I tried it with the widely used LFO circuit (eg the CGS LFO but that didn't work straight off.. Oh, maybe that's not so surprising.

But, I did then find that you could do away with the Jfet and 1M resistor and attach the diode straight to the -ve opamp input end of the timing Cap. Sure, it pushes the waveform down low when syncing, but it sounds good.

Maybe there's a better way with these variants of LFOs -- this sort of LFO circuit is very much the basis for the TH Ca3080 VCO (I think, anyways) as Rych used for his Kaos VCLFO investigations..

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