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VC sine/cosine generator revisited
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frijitz



Joined: May 04, 2007
Posts: 1710
Location: NM USA
Audio files: 54

PostPosted: Wed Jan 07, 2009 8:35 am    Post subject: Reply with quote  Mark this post and the followings unread

OK, the caps are good. Next guess is that the difference comes from differences in OTA gm. You could try making the feedback trimmable, as in the full 6/8 phase unit and as in Henry's design. The balance between neg and pos feedback is quite delicate. When working properly the system takes several hundred cycles to start up.

So you could try making the 10k a trimmer and take the bottom of the 820k off the slider. You might also need to change the values of the 820k and 4.7M resistors. For example, replace the 4.7M with 1M and the 820k with 100k.

OTA offsets also make a difference in how the system works. Your OTA may just have more offset than the ones I was working with. In fact, I probably used units selected for low offset vs gain variation.

I don't know of anyone trying Henry's design. Rene has a tri core TZ VCO at his site:
http://www.uni-bonn.de/~uzs159/index.html

I'm working on a SAW core unit right now.

Very Happy

Ian
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UofMEShop



Joined: Jan 06, 2009
Posts: 5
Location: MI USA

PostPosted: Wed Jan 07, 2009 8:47 am    Post subject: Reply with quote  Mark this post and the followings unread

UofMEShop wrote:
Can you comment on this LM13700 quadrature sine/cosine VCO that swaps its phases for negative control voltages ("positive and negative frequencies") ? It has a wide range (0 to 10 kHz for 0 to 10 control V) and -40dB distortion.
www.edn.com/filtered/pdfs/contents/images/341451.pdf

Wiring up one half of this circuit since I am only interested in positive control voltages, I get a triangle wave, not a sine wave.
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UofMEShop



Joined: Jan 06, 2009
Posts: 5
Location: MI USA

PostPosted: Wed Jan 07, 2009 10:45 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
So you could try making the 10k a trimmer and take the bottom of the 820k off the slider. You might also need to change the values of the 820k and 4.7M resistors. For example, replace the 4.7M with 1M and the 820k with 100k.


Doing this : Zener to top of 10K trim instead of to 820K/10K junction, 100K (instead of 820K) to 10K trim's wiper, replace 4.7M with 1M gets rid of the clipping. The amplitude varies from 8 to 26 V pk-pk using the 10K trim. One output's negative amplitude is a little smaller than the other's. Thanks.
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frijitz



Joined: May 04, 2007
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PostPosted: Wed Jan 07, 2009 1:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

UofMEShop wrote:
The amplitude varies from 8 to 26 V pk-pk using the 10K trim. One output's negative amplitude is a little smaller than the other's.

thumright
Slightly displaced or unsymmetric or unequal outputs are due to OTA offsets.
You may be able to get lower distortion by increasing the 1M positive feedback resistor.

Very Happy

Ian
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vladosh



Joined: Aug 02, 2010
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PostPosted: Fri Aug 19, 2011 11:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi
i really wanna build the first small version of this vco ..however got a few questions so i hope someone can share their wisdom Smile
from what i read ..to modify it for audio range one needs to change the caps to 120 pF ,change the 4.7 M resistors to 1M .. i got a question concerning the expo converter as i don't have temcos and on the other hand i don't mind if there is a bit of drift or if they are a bit out of tune . I was thinking if it's possible to use the Thomas Henry VCO1 expo converter http://www.birthofasynth.com/Thomas_Henry/pdf/VCO-1/vco1_schem1.pdf..seems it's something i can handle on a stripboard ,i was even thinking if it's possible to use the expo converter from here http://www.modular.fonik.de/files/EFMforum/orgEFMfiles/efm-4600-doc_01.pdf from the 4614 VCO as i already got that one working .. it's possible that i understood all wrong btw Smile as i'm a noob .
any help is great ..as i would really make at least two of these sine/cosine vco's .. thanks
Vlad
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frijitz



Joined: May 04, 2007
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PostPosted: Fri Aug 19, 2011 12:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

vladosh wrote:
I was thinking if it's possible to use the Thomas Henry VCO1 expo converter http://www.birthofasynth.com/Thomas_Henry/pdf/VCO-1/vco1_schem1.pdf..seems it's something i can handle on a stripboard ...

That would probably work OK.

Quote:
...,i was even thinking if it's possible to use the expo converter from here http://www.modular.fonik.de/files/EFMforum/orgEFMfiles/efm-4600-doc_01.pdf from the 4614 VCO as i already got that one working ..

No, that won't work. You need a design that can drive current into the negative supply level.

You could use the converter shown for the second schematic, leaving out the "C" and "D" transistors.

Also, to be sure you are aware, Yves has a nice adaptation of this circuit that might be helpful to you.

Very Happy

Ian
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vladosh



Joined: Aug 02, 2010
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PostPosted: Fri Aug 19, 2011 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks a lot Smile
I'll try that with Thomas Henry VCO-1 expo converter this coming week .. i hope it'll work out ..
greetings
Vlad
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drapdap



Joined: Oct 11, 2004
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PostPosted: Thu Aug 25, 2011 2:13 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:

Also, to be sure you are aware, Yves has a nice adaptation of this circuit that might be helpful to you.


http://yusynth.net/Modular/EN/QUAD-LFO/index.html

I also have a question as i use this a lot (very cool circuit) and i'd like to have 4 sine outs. Sometimes when i use it for mixing/panning they seem just too, hm, spikey. Smile
No other way around than to build 4 tri to sine converters?
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widdly



Joined: Jun 25, 2007
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Location: singapore
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PostPosted: Wed Oct 12, 2011 9:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

The Serge Quadrature VCO has a hold input that takes a gate a freezes the VCO output at it's current level. When the gate goes low it resumes from the point it was frozen.

Is that possible with this design? Maybe a cmos switch on the cv input to force it to ground? I'll have a play on my breadboard.
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frijitz



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PostPosted: Thu Oct 13, 2011 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

widdly wrote:
The Serge Quadrature VCO has a hold input that takes a gate a freezes the VCO output at it's current level. When the gate goes low it resumes from the point it was frozen.
Is that possible with this design? Maybe a cmos switch on the cv input to force it to ground? I'll have a play on my breadboard.

Should be possible. You'd want to gate in a large enough negative CV to bias the expo converter off (without putting to much reverse bias on the expo transistors, of course). Perhaps a CMOS switch from the summing node through 220k to the negative supply.

Or do it externally by inverting your gate and putting it into an FM input.

Very Happy

Ian
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widdly



Joined: Jun 25, 2007
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PostPosted: Thu Oct 13, 2011 6:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Ian. I like your idea of inverting the gate and feeding it to an FM input.
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reppiks



Joined: Jan 04, 2013
Posts: 4
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PostPosted: Fri Jan 04, 2013 12:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

I'm interested in trying out the first schematic in this thread for my first DIY electronics project (I did basic practical electronics at school and have a degree in theoretical physics, but that didn't cover any electronics/circuitry aside from the theoretical background) - how feasible do you think that is for a beginner's project? I don't need the additional phases so am not wanting to tackle the larger second schematic.

I'm planning for this to be my 2013 new hobby/project but probably won't get much time to dip into it for a while yet.

Cheers
Dave
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LFLab



Joined: Dec 17, 2009
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Location: Rosmalen, Netherlands

PostPosted: Fri Jan 04, 2013 1:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Without having looked at this in depth, I think something simpler and more documented will suit you better. Have you had a look at some of the Yusynth projects, or the MFOS website?
The more people building a certain project the more information is available, and more people will be able to help you.
In this particular project, the last reply before yours was well over a year ago. You might very well make this work, but nothing is more frustrating than a project that takes more time to get working properly.
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reppiks



Joined: Jan 04, 2013
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PostPosted: Fri Jan 04, 2013 2:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for you reply.

Yeah, you're probably right I should start with some other stuff first that has more support documentation etc, I looked around the MFOS site recently.

But still, I am very interested in this circuit and want to get to it as soon as I feel confident tackling it... I wonder what level of trickiness it would entail...

Cheers!
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LFLab



Joined: Dec 17, 2009
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PostPosted: Fri Jan 04, 2013 4:27 am    Post subject: Reply with quote  Mark this post and the followings unread

If it is the functionality you are looking for, did you look at the Yusynth quadrature LFO?
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reppiks



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PostPosted: Fri Jan 04, 2013 6:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, I'll check it out (found the link: http://yusynth.net/Modular/EN/QUAD-LFO/index.html)

Although actually I'm not interested in the first place in the quadrature functionality (though that does look super-fun), my main interest was in finding a sinecore VCO for nice sines. Tracking/stability is not necessary, and other waveshapes are not necessary (I have other VCOs that cover me there)

Cheers!
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frijitz



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PostPosted: Fri Jan 04, 2013 9:30 am    Post subject: Reply with quote  Mark this post and the followings unread

LFLab wrote:
Without having looked at this in depth, I think something simpler and more documented will suit you better.

Oh, come now. It's a simple circuit -- just two chips. And I am usually around to provide help. Sheesh!

Ian
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frijitz



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PostPosted: Fri Jan 04, 2013 9:33 am    Post subject: Reply with quote  Mark this post and the followings unread

reppiks wrote:
Tracking/stability is not necessary, and other waveshapes are not necessary (I have other VCOs that cover me there)

What exactly do you need for frequency control? The first schematic just has a knob, so you might need to add an expo converter. If you need a 1V/Oct input, I recommend the Yusynth version.

Ian
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LFLab



Joined: Dec 17, 2009
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PostPosted: Fri Jan 04, 2013 10:07 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
LFLab wrote:
Without having looked at this in depth, I think something simpler and more documented will suit you better.

Oh, come now. It's a simple circuit -- just two chips. And I am usually around to provide help. Sheesh!

Ian


lol, alright, alright Very Happy
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reppiks



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PostPosted: Fri Jan 04, 2013 3:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'd like to have attenuated Lin and Exp FM inputs, 2 of each. 1v/oct not required.
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knutolai



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PostPosted: Wed Dec 11, 2013 7:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

What supply voltage would you use for the "VC quadrature sinewave oscillator"? I cant seem to find it anywhere in the tread. The reason I ask is I know this is more of a synth forum while I'm more of a guitar stompbox person. So could the circuit be operated at 9 volt unipolar supply or 4,5 volt bipolar supply?
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frijitz



Joined: May 04, 2007
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PostPosted: Wed Dec 11, 2013 9:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

knutolai wrote:
What supply voltage would you use for the "VC quadrature sinewave oscillator"? I cant seem to find it anywhere in the tread. The reason I ask is I know this is more of a synth forum while I'm more of a guitar stompbox person. So could the circuit be operated at 9 volt unipolar supply or 4,5 volt bipolar supply?

Ooops! It's for +/- 12V.

Ian
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