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 Forum index » DIY Hardware and Software » Thomas Henry designs
The Mankato as a VCO only
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Funky40



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PostPosted: Sun Jun 15, 2008 7:52 am    Post subject: The Mankato as a VCO only
Subject description: how about a much smaller PCB ?
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Hi,

I love my Mankato, and i love it expecially as a Sine-only VCO.
I thought i could build some more only as simple Sine VCOs, but it would be a waste.....................hmmm, you know what i mean Wink


How about to have just a very simple Board, only thought as a Cool Sine VCO with very best tracking ( and with range swicth )?
no, no Quadrature needed for me.
Maybe in a dual or even quad configuration instead.
Please think about Tim


Funky (with wishes)40 Smile
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Tim Servo



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PostPosted: Fri Jun 20, 2008 11:08 am    Post subject: The Mankato as a VCO only Reply with quote  Mark this post and the followings unread

Hey Funk,

Well, if all you need is a sine VCO, I guess you could use just about any LP VCF with the resonance cranked all the way up. Of course, the Mankato has other talents that set it apart from other VCFs. Wink A minimal circuit could be done with a 2164 and a couple of TL074s (or maybe a 074 and an 072). This would give you a Sine VCO with 0 and 90 degree outs. My reasoning for going "full boat" and providing all eight outputs was that it wasn't THAT much more circuitry than a minimal configuration. We were originally going to do a four output version and an eight output version, but the difference in the PCB size and cost didn't really justify having to carry two products versus one.

Still, the Mankato does have a much wider range than any VCF I've seen (wider than any VCO I've seen too). If there was enough interest, I could do a Mini-kato, and MAYBE even fit two on a single PCB. What does everyone think? A dual unit would probably have to go on a 5" x 4" PCB, and a single unit might fit on a smaller board.

One thing to be aware of when using a VCF as an oscillator: the amplitude of the output will vary over the frequency range. You'll see this as a gradual reduction in level at the high end in most VCFs. It's not drastic, but it is there. VCOs are generally much more stable in this respect. This means that two oscillating VCFs might not be the best solution for FM-style effects, as the modulation index will be influenced by the signal level. It would be okay over most of the audio range (using the Mankato as an example), but you will see level changes at the very high and very low ends.

And the verdict is?

Tim (moving at the end of the month... oh boy) Servo
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Funky40



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PostPosted: Fri Jun 20, 2008 1:44 pm    Post subject: Re: The Mankato as a VCO only Reply with quote  Mark this post and the followings unread

Tim Servo wrote:


One thing to be aware of when using a VCF as an oscillator: the amplitude of the output will vary over the frequency range. You'll see this as a gradual reduction in level at the high end in most VCFs. It's not drastic, but it is there. VCOs are generally much more stable in this respect. This means that two oscillating VCFs might not be the best solution for FM-style effects, as the modulation index will be influenced by the signal level.

interesting point ! Yes, FM would be an Issue.
For non FM use that is perfect !
not much replies here, so not much interest in this i think.


Thank you Tim
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Peake



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PostPosted: Fri Jun 20, 2008 5:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

One DIY gent did both a quad LFO and a quad VCO using the 2164; you could do a single VCO and also use the remaining cells of the 2164 to control FM amounts, for example.

A drop in level at high frequencies can be a good thing (mainly in polysynths, using keytracking to reduce amplitude).
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Blue Hell
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PostPosted: Fri Jun 20, 2008 6:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
A drop in level at high frequencies can be a good thing


Agreed, it's a natural thing for highs to back off volume wise.

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Peake



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PostPosted: Sat Jun 21, 2008 7:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

http://www.sowa.synth.net/modular/vco4mod.html
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Funky40



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PostPosted: Sun Jun 22, 2008 4:53 am    Post subject: Reply with quote  Mark this post and the followings unread

thank you Peake !
That one would be possible for me to draw a board



I'm not shure if it must be a SSM2164 circuit as i gonna anyway to draw a XR8038 VCO.
something very simple with Sinewave only plus maybe square or saw for Clock application.


What i like on the SSM2164 is the Level the Sinewave has ( hmmm, on the Mankato it has )
Serenadi told me that one thing with the SSM2164 is that it don't distorts when used as a VCA ---> it works with loads of Level.
so i'm not shure if this is a real advantage over other ways to get a sine-only VCO.
My feel is that it is, but maybe i'm wrong.
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Peake



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PostPosted: Sun Jun 22, 2008 7:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Isn't a filter's self-oscillation usually the best way to get a clean sine wave? If so, you have four available at once, right there.
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Peake



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PostPosted: Sun Jun 22, 2008 10:40 am    Post subject: Reply with quote  Mark this post and the followings unread

You could just buy a Magic Smoke PCB and only stuff the minimum of components...and then have the option of seriously increasing your feature set if you ever wish to!
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aerogramma



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PostPosted: Mon Aug 11, 2008 4:37 am    Post subject: Re: The Mankato as a VCO only Reply with quote  Mark this post and the followings unread

Tim Servo wrote:



And the verdict is?



well i must say having just built 2 mankato that the 'resonance' VCO is indeed extremely musical... i'm having lots of fun turning the audio input to null (as tim said) and modulating the resonance sine with the FM inputs...

i wouldn't mind having an array of those sines Smile ...
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