Sync for VCO1

[zipzap]

Is it possible to implement sync on the vco 1?

[toppobrillo]

hey zipzap, welcome back by the way.. i tried to implement sync a while back on a tri-core vco i was working on that started off as this one.. quickly discharging the integrating cap was easy to do with a FET and a comparator, but it wasn't quite the sound i was after and this led to me trying the reversing direction thing in the thru-zero vco, which is a much better sounding sync IMO..

anyways, recently i was able to play with a Wiard VCO [a tri-core as well] and was surprised to hear that the sync seemed to work on it about like the first method i describe here. i thought it wasn't good enough, but i guess it is- it certainly syncs

playing around with it a bit, i decided it would be neat to try to vary the comparator's threshold to get a variable-sync-width and that was cool, you can see some scope-shots of it here:



you could differentiate the comparators action into a predictable narrow pulse for a more standard operation of course.

anyways, i don't know where the notes i made on this are, i will look for them, but go ahead and give it a shot if you can..

keep posted here,\

josh

[Rykhaard]

Please post it if you find it! I JUST finished Ferric Chloriding a double T.Henry precision VCO. (Intend to use as a VCLFO but if I can get at least a couple of octaves - hey! 2 bonus VCOs! )

[toppobrillo]

precision VCO?

[Rykhaard]

[Strazdas]

I know it's old post, but do someone can post schematics to add sync to TH VCO-1?

Many thanks

[Tim Servo]

Hi Straz,

You can find the VCO-1 schemos on Scott Stites "Birth of a Synth" web site:

http://www.birthofasynth.com/Thomas_Henry/Pages/VCO-1.html

<plug> I also sell "Making Music With the 3080 OTA" and several other Thomas Henry books at http://www.lulu.com/spotlight/Magic_Smoke
</plug>



Tim (plugging away) Servo

[Strazdas]

I've got schematics, but I'd like to have sync (hard or soft or both - no mater) input for this VCO

[Strazdas]

Enyone PLEASE!!!

[Matt C.]

bumping this ancient thread because I have the same question. I've built one of Thomas Henry's VCO-1 modules, and I'd like to build another with a sync feature, but I'm not quite savvy enough to know if it's possible. Any tips on how this could be done?

I'm going to experiment with the comparator/FET shorting out the timing capacitor, but I'm not sure exactly how to configure that (anyone have an example schematic?), and I'd also be interested in hearing any other possible methods. Thanks.

[J3RK]

Hey!

About half-way down this page:

https://www.muffwiggler.com/forum/topic-151416-0-25.html

I made a post with a schematic that should show you how. There are a few different ways you can do this. You basically need a comparator to take in the signal you want to sync to (I like the threshold nice and low, so maybe 1.5V or so.) Use that to trigger a FET across the timing cap. (or possibly a CMOS switch, but I haven't tried that...) While the comparator is high and the FET is on, the VCO will be stopped.

So, you can do a few different things here. One is to just use a short duty pulse or maybe a sawtooth to sync from, or two, you can put a small cap at the front of the comparator to make a high pass filter kind of like a gate to trigger converter. The cap will condition most signals into short spikes this way, which will result in a more classic sync sound.

You could do other things like use CMOS gates an caps, etc. to get short pulses, but just a small cap should work. You'll notice on the schematic I posted I have a switch for the cap, because I also like to be able to completely stop the VCO with a high pulse/gate/etc. It's kind of handy especially if you're using it as a clock.

You could use a transistor based comparator, op amp, or comparator IC to handle this. I used an op amp in the schematic there, but an LM311 is cheap, easy to configure, and might be a bit more elegant.

The core of my VCO is very similar to the VCO-1 (in fact I consulted with Thomas Henry about it a bit (as well as Dave Brown)) when I was designing it, and adopting parts of their (as well as the Electronotes guys Bernie Hutchins etc.) work. Please feel free to use anything you like from the schematic. It's all common knowledge for the most part. The sine shaper is a bit Thomas Henry, a bit Marc Bareille, and a couple of my own tweaks.

Just wanted to give full disclosure on where everything came from. I came up with the sawtooth shaper, but I've also seen a similar one somewhere else that was probably invented way before I started playing with mine, so credit to whoever that was (since I can't remember off the top of my head...)

Edit: Hmm... I just now realized that I pretty much said the same thing that Josh did above seven years ago.