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 Forum index » DIY Hardware and Software
Buchla VCO
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Snaper



Joined: Feb 28, 2014
Posts: 149
Location: Hungary

PostPosted: Thu Aug 14, 2014 3:43 am    Post subject: Reply with quote  Mark this post and the followings unread

vladosh wrote:
Snaper you can use SSM2220 in the v/oct expo converter and use matched 2N3904 for the other as it's in the original Mark Verbos pdf somewhere on this thread if it isn't removed just gotta watch for the pinout ,thanks L1 for sharing the layout ,it is a great VCO ,i wonder what is the best choice for initial freq pot ,my 258 sounds great to me but the init freq pot can act bit weird when moving from zero ,and soldering those SMD isn't much of big deal ,they are really tiny , but it is actually easy once you try few times

Thanks for the info.
Can I use matched 3904 in both places with a tempco?
For me V/Oct tracking isnt that important :S
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vladosh



Joined: Aug 02, 2010
Posts: 432
Location: macedonia
Audio files: 6

PostPosted: Thu Aug 14, 2014 2:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

you can use 2N3906 for the other as it's a PNP ,but i'm not an expert really ,well matched transistors are well matched it's up to how good is your DMM and if you've made the Moog matching circuit or other and making it precise ,if you couple them thermally and all that ,i think it's not only about v/oct tracking.. match 2 x 2N3906 and try it ,i sourced those SMD somehow
cheers

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Snaper



Joined: Feb 28, 2014
Posts: 149
Location: Hungary

PostPosted: Mon Oct 20, 2014 1:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Did somebody built this?
I think I've wired wrong the switch...
No sound...just kind of "buzz", hum...and...weird...but it seems that I can receive local AM radios with this :S
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Snaper



Joined: Feb 28, 2014
Posts: 149
Location: Hungary

PostPosted: Mon Dec 15, 2014 10:07 am    Post subject: Reply with quote  Mark this post and the followings unread

My last silly question.
Is it possible to do a mod to avoid the switch?
I mean, Im ok with one waveform, but I think the cause of my not working modules are those damn switches. Hate them:)
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thermionicjunky



Joined: Dec 07, 2006
Posts: 75
Location: san francisco

PostPosted: Tue Dec 16, 2014 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Snaper wrote:
My last silly question.
Is it possible to do a mod to avoid the switch?
I mean, Im ok with one waveform, but I think the cause of my not working modules are those damn switches. Hate them:)


The switch is a mod. Simply install either the resistor values listed for saw or square in the schematic. And of course, infinite resistance means that no resistor is installed.
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J3RK



Joined: Jun 05, 2006
Posts: 113
Location: Seattle

PostPosted: Fri Dec 19, 2014 9:55 am    Post subject: Reply with quote  Mark this post and the followings unread

I agree 100%. Ditch the switch. It's a nice idea, but the execution is very unreliable. Lifting resistor ends, and wiring a 3P switch... IMO it's not worth it. If you want both square and saw versions, I'd say it's easier to build both, one per PCB.
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Snaper



Joined: Feb 28, 2014
Posts: 149
Location: Hungary

PostPosted: Sun Dec 21, 2014 9:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

J3RK wrote:
I agree 100%. Ditch the switch. It's a nice idea, but the execution is very unreliable. Lifting resistor ends, and wiring a 3P switch... IMO it's not worth it. If you want both square and saw versions, I'd say it's easier to build both, one per PCB.

I see. I think I should buy 2 of your pcbs instead.
Have you some spare?
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J3RK



Joined: Jun 05, 2006
Posts: 113
Location: Seattle

PostPosted: Mon Dec 22, 2014 2:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Snaper wrote:
J3RK wrote:
I agree 100%. Ditch the switch. It's a nice idea, but the execution is very unreliable. Lifting resistor ends, and wiring a 3P switch... IMO it's not worth it. If you want both square and saw versions, I'd say it's easier to build both, one per PCB.

I see. I think I should buy 2 of your pcbs instead.
Have you some spare?


Unfortunately I don't stock the 258J anymore. I believe Synthcube and Thonk should have some. (I send these to them every so often.) The reason for that is that I did the UltraFade VCO as a successor. It refines and fixes things, as well as provides more features. It's also a lot easier to build and wire. There's a thread on Muff's in the DIY forum, if you'd like to see more details on it.

FYI: In case my comment wasn't clear, my 258J boards still need to be modded in the same way if you want to add that waveform select switch. It still requires lifting the resistors, and using a 3 pole switch.

The UltraFade uses a different crossfade circuit, and only uses a simple SPDT switch for selecting the faded waveform.
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akrearke



Joined: Sep 08, 2008
Posts: 50
Location: US

PostPosted: Sat Mar 14, 2015 7:40 am    Post subject: Reply with quote  Mark this post and the followings unread

does anyone have any idea on a low frequency setting for this vco? possibly increasing the .0047 uf capacitor in the core?
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m.o



Joined: Jul 05, 2014
Posts: 35
Location: Sweden

PostPosted: Sun Mar 15, 2015 9:16 am    Post subject: Reply with quote  Mark this post and the followings unread

akrearke wrote:
does anyone have any idea on a low frequency setting for this vco? possibly increasing the .0047 uf capacitor in the core?


Yeah, that would seem like the first and best approach.
Possibly you could start messing with the expo converter currents, maybe increase the 1.5M resistor in the lower left beside the 3140...
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J3RK



Joined: Jun 05, 2006
Posts: 113
Location: Seattle

PostPosted: Mon Mar 16, 2015 3:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

You should have no problem doing this with a capacitor. What I would do is connect one lead of a 100nF cap to one lead of the 4.7nF cap. Then use an SPST switch between the other two ends. That way you can switch the low frequency cap in and out.

When they are connected in parallel the slower speed will occur. When you disconnect the 100nF cap, only the 4.7nF will be used.

It's not terribly critical which type of cap you use for the LFO cap. I'd still use something fairly stable though. MLCC, Styrene, Polypropylene or the like. (though even a standard ceramic or Polyester will be fine.)
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Karlisss



Joined: Apr 20, 2015
Posts: 13
Location: Latvia (EU)

PostPosted: Yesterday, at 12:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Can it run from 12v dual?
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