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 Forum index » DIY Hardware and Software
Sine core VCO?
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formant84



Joined: Nov 13, 2011
Posts: 7
Location: Wirral, England

PostPosted: Mon Aug 13, 2012 2:42 am    Post subject: Sine core VCO? Reply with quote  Mark this post and the followings unread

Hi all,

I've built a couple of VCOs recently , namely THs XR-VCO and VCO-1. Whilst i'm very happy with how these have turned out, i can't seem to adjust the sine wave well enough so that it sounds pure at really low frequencies, and one thing i wanna do with my kit is produce some really fat sub bass, so this is a small problem.

So what I was looking in the LM13700 datasheet and there is a schematic there for a sine core VCO, so I thought it'd be cool to build that and then derive all the other waves from the sine, but looking around online I can't seem to find any evidence of anyone doing things this way around. Is there a good reason for this which I haven't spotted? Because it seems to me that a perfect sine is the hardest wave to produce and the easiest one to hear the difference in when it's not quite right, so surely a sine core VCO is a good idea?

I'm guessing i'm totally wrong here because if it was such a good idea then there would probably be lots of them about, but i'm just curious as to why this isan't a more popular approach?

Any answers appreciated,

Cheers,

John
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frijitz



Joined: May 04, 2007
Posts: 1712
Location: NM USA
Audio files: 54

PostPosted: Mon Aug 13, 2012 11:42 am    Post subject: Re: Sine core VCO? Reply with quote  Mark this post and the followings unread

formant84 wrote:
... Because it seems to me that a perfect sine is the hardest wave to produce and the easiest one to hear the difference in when it's not quite right, so surely a sine core VCO is a good idea?

Detailed discussion and circuitry here:
http://www.electro-music.com/forum/topic-19841.html
Yves sells a nice VCQO board.

As far as your other comments, human hearing falls off at low frequencies, so any harmonics will sound especially loud.

Trouble with a Sin core is there is no easy way to get the other "standard" waveforms. You can do a "Sin-Saw", and it is probably about as useful as a Saw, but not the same thing. Pulse is easy to do, but the PW response is nonlinear.

Ian
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formant84



Joined: Nov 13, 2011
Posts: 7
Location: Wirral, England

PostPosted: Mon Aug 13, 2012 4:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah right, i just assumed that since the sine seems to be the most fiddly waveform to produce from a triangle or saw then it'd be easier to start with the sine and go the other way, silly me!

That's a really cool circuit, i think i'll have to build one of those this week to have a play! Looks like it could provide me with a good sine for my sub bass as well as the wave mixing features, and you can never hav too many oscillators!

Thanks again for the advice,

John.
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Peake



Joined: Jun 29, 2007
Posts: 1109
Location: Loss Angeles
Audio files: 3

PostPosted: Tue Aug 14, 2012 11:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

You could try a Mankato or other wide-range VC filter in self-oscillation..
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