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Very simple sawtooth VCO (V/Hz)
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-minus-



Joined: Oct 26, 2008
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PostPosted: Wed May 01, 2013 6:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh good! yes it seems obvious now if you look at your test results above. Pin 3 should read 0V, the same as pin 6. Glad it's working for you Very Happy .
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jackdamery



Joined: Apr 26, 2010
Posts: 73
Location: UK

PostPosted: Thu May 02, 2013 6:22 am    Post subject: Reply with quote  Mark this post and the followings unread

nicolas3141 wrote:

If you want to convert it to vague V/Octave response (ie not accurate and not worth wasting tempcos on) then the simple V/Oct converters that are often used on the front of VCF circuits could be adapted to this. I haven't tried, but it probably wouldn't be too hard. One or two op-amps and one or two transistors would be all it would require.


Could you give an example schematic of an expo convertor that might work?
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analog_backlash



Joined: Sep 04, 2012
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PostPosted: Thu May 02, 2013 8:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, just been reading this.

Synthmonger has posted a simple expo converter here:

http://electro-music.com/forum/topic-28799.html

Only the bit in the bottom box is required (i.e. the 2 transistor circuit). A very similar circuit is on Rene Schmitz's web site here (see VCO 4069):

http://www.uni-bonn.de/~uzs159/

For a better one with op-amps (as suggested in a VCF circuit) see Ray Wilson's circuit here:

http://www.musicfromouterspace.com/analogsynth_new/STATEVARVCFFEB2006/STATEVARVCFFEB2006.html

It's just the top part of the page 1 circuit you're interested in (i.e. the U1-A & B and Q1/Q2 part of the circuit).

The only problem I can see is that these are all +12V/0V/-12V circuits and some minor adjustment may be required for 9V batteries.

Gary
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jackdamery



Joined: Apr 26, 2010
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PostPosted: Thu May 02, 2013 3:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

analog_backlash wrote:
Hi, just been reading this.

Synthmonger has posted a simple expo converter here:

http://electro-music.com/forum/topic-28799.html

Only the bit in the bottom box is required (i.e. the 2 transistor circuit). A very similar circuit is on Rene Schmitz's web site here (see VCO 4069):

http://www.uni-bonn.de/~uzs159/

For a better one with op-amps (as suggested in a VCF circuit) see Ray Wilson's circuit here:

http://www.musicfromouterspace.com/analogsynth_new/STATEVARVCFFEB2006/STATEVARVCFFEB2006.html

It's just the top part of the page 1 circuit you're interested in (i.e. the U1-A & B and Q1/Q2 part of the circuit).

The only problem I can see is that these are all +12V/0V/-12V circuits and some minor adjustment may be required for 9V batteries.

Gary


Thanks for your help Gary. Today I added a simple expo convertor with a PNP/NPN pair(as per Synthmonger's schematic) and got it tracking 1V/Octave over about 3 octaves reasonably well. Then obviously I connected it to the Arduino MIDI2CV and made it play the bassline to Blue Monday by New Order. Here's the irritating thing though, there is a 300ms delay between hitting the note on the keyboard and the frequency changing, I'm pretty sure it's the expo convertor.

https://soundcloud.com/dot/lm358-vco-blue-monday-bass
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jackdamery



Joined: Apr 26, 2010
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PostPosted: Thu May 02, 2013 3:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

If anyone wants to the know, the transistors I used were BC337 and BC338.
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analog_backlash



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PostPosted: Thu May 02, 2013 4:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi (again).

Glad that you got it working and for such a lo-fi circuit, that sounds pretty good! I'm a bit puzzled by the 300ms delay, as I wouldn't expect that circuit to introduce much delay at all (but I'll probably be proved wrong...). I wonder if you'd still have the same problem with the better op-amp plus transistors circuit?

Good luck Very Happy

Gary
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jackdamery



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PostPosted: Thu May 02, 2013 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi I don't know what the delay was, but it suddenly stopped doing that. Is there any resistors or pots I could change to scale this better over more octaves? It sounds very good in the bass octaves but I'd like the slightly higher ones for sweet pads. Maybe the C1 could be changed for a smaller(if possible?) value to get a higher fundamental frequency?
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isak



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PostPosted: Wed Jun 05, 2013 10:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

hi.

i found a cool scheme from Yusynth to convert v/hz to v/oct
wandering if it will work with this vco.
any one wanna try?
its the first scheme on the pdf.


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elmegil



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PostPosted: Thu Jun 06, 2013 11:35 am    Post subject: Reply with quote  Mark this post and the followings unread

It's a pretty standard Expo converter.

However, I don't think it will do what you want. This VCO is driven by V/Hz, to use it with other equipment you need something that takes V/Oct in and outputs V/Hz.
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tupinamba



Joined: May 14, 2010
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PostPosted: Tue Jul 02, 2013 2:58 am    Post subject: Wow! Reply with quote  Mark this post and the followings unread

I just built this circuit to add a VCO to my Korg MS-10 and it is working great! I first had a problem as it wouldn't stay tuned (an octave on the keyboard resulted in about 9 to 10 semitones on the VCO), but this was because I was using a single 9V battery with a virtual ground. I switched to a pair of 9V and now it is great!

Just one thing I don't get... inlifeindeath, you said :

inlifeindeath wrote:
it already has a freq pot. two pots are shown; one can be wired as a CV attenuator and the other one can just be hard wired to V+ on the CV end and you have a freq pot.


But I'm not sure what is "CV end" where I should connect the second pot...

Thanks Nicolas and thanks Chris, as it is your video that made me try this circuit!
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inlifeindeath



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PostPosted: Tue Jul 02, 2013 12:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

CV end meaning the side of the pot on the schematic where CV In is indicated. Rather than having CV on that end of the pot, just wire it to +V for a frequency control.
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tupinamba



Joined: May 14, 2010
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PostPosted: Wed Jul 03, 2013 7:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Alright, thank you inlifeindeath!
About the CD40106 schmitt trigger inverter, do I simply need to connect V+ to VDD pin (14), 0V to Vss pin (7) and saw output o one of the inputs? Is this as simple as that to get a squareware form?
Thanks!
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tupinamba



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PostPosted: Sun Jul 07, 2013 2:22 am    Post subject: Building a more stable v/hz VCO ? Reply with quote  Mark this post and the followings unread

Hi again,
I'll still pretty astonished by the results I got with this basic VCO ; I built a +-12V PSU for it and I'm working on a nice little enclosure that will nicely get on top of my MS-10.
I'd like now to go one step further and built a more stable v/hz VCO for my MS-10. But the schematics (and boards, as I'm not very good at translating a schematic into a PCB...) are mostly v/oct.
Is there a not too complicated but still efficient and stable DIY v/hz VCO out there?
Thanks in advance!
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david.tb303



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PostPosted: Sat Sep 21, 2013 12:18 am    Post subject: add fine tune to this VCO Reply with quote  Mark this post and the followings unread

hi! i build this VCO and works fine ( thnks Nicolas for your designs, pretty simple for a newbie as I'm! Surprised ).

But now i would like to add a second potentiometer to allow fine tune the frequency, because the range playing now is so big. This is very nice but if doesn't very dificult i like to know how to connect this VR. Rolling Eyes

Thanks in advance
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jackdamery



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PostPosted: Sun Sep 22, 2013 4:27 pm    Post subject: Re: add fine tune to this VCO Reply with quote  Mark this post and the followings unread

david.tb303 wrote:
hi! i build this VCO and works fine ( thnks Nicolas for your designs, pretty simple for a newbie as I'm! Surprised ).

But now i would like to add a second potentiometer to allow fine tune the frequency, because the range playing now is so big. This is very nice but if doesn't very dificult i like to know how to connect this VR. Rolling Eyes

Thanks in advance


Hi david,

Try adding a 100k potentiometer, with one end connected to +9v and the other to -9v then connect the wiper (middle leg) to one end of a 1M resistor then the other to the inverting input (-) of IC1A.

Basically you have a resistor (your pot) between your supply voltages and your wiper is the potential divider between those two. So you can sweep the wipers output between 9v and -9v by adjusting the pot. The 1M resistor will limit how much of this can get to your oscillator to a very small amount though thus affecting the frequency only a little, giving you fine tuning.

Try between 1M and 3M by adding resistors in series until you find a range of fine tuning that suits you. A standard one might be to try to get 1 semitone of adjustment from one end of your potentiometer to the other. giving you 50 cents each way, this is the range of fine tune on the VCO2 of the Jupiter 8.
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david.tb303



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PostPosted: Sun Sep 22, 2013 10:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

thank you very much jackdamery! Many thanks, not only for the answer, but the explanation which I think helped me to understand Wink
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jackdamery



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PostPosted: Mon Sep 23, 2013 12:02 am    Post subject: Reply with quote  Mark this post and the followings unread

david.tb303 wrote:
thank you very much jackdamery! Many thanks, not only for the answer, but the explanation which I think helped me to understand Wink


No worries, here's the same thing applied in Thomas Henry's VCO1. The first opamp is acting as a DC signal mixer that you feed all your control voltages to. It combines them and then the sum of them determines the gain of the opamp.

If you remember with an inverting opamp gain is the sum of your feedback resistor divided by your input resistor you can work out what the gain will be for each part. http://lambertsound.com/forums.html?pr=Op-Amp_Basics.

A higher input resistor (1M) will equal a smaller gain, thus making a smaller difference to the sum of your control voltage.


http://www.birthofasynth.com/Thomas_Henry/pdf/VCO-1/vco1_schem1.pdf

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Ruebezahl



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PostPosted: Sun Mar 09, 2014 8:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello. First thank you for the noble work to design these kind of simple, understandable circuits. I am a Beginner, and those circuits are very helpful. I would like to integrate this vco in a chain of some other small devices. in the end its planned to be something like a little sequencer feeding a square wave (4046) and sawtooth vco used interchangeable (that would be this one here), afterwards filtered through a LP-Filter (i used a schematic from mfos).
well, but now all the other parts running from a single 9V Battery. Although i finally understood the concept of this "Dual Power Supply", or whatever is the proper name for that, i am still not sure what exactly is the advantage of that.
Could you build a similar circuit powered by a single 9V, or is it something completely different? Because since all the other parts are working that way, i am tempted to build the whole device on one battery. But i guess there is a good reason for this "special" power supply.

So i hope someone can bring some order in my confusion, maybe even a link, providing me with some basic information on this sort of power supply and what are the advantages of it, could help me already a lot.

Thank you!
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nicolas3141



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PostPosted: Sun Mar 09, 2014 8:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes this design runs fine from a single 9v battery. You just need to create a midpoint voltage to use as the 0V reference. See the latest circuit i just posted the other day that does this using a spare opamp. Or you could do it with a couple of resistors and caps. This is a very common approach in the stompbox world.

Nicolas
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Ruebezahl



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PostPosted: Sun Mar 09, 2014 9:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow thank you for the super fast reply. And good news as well Very Happy . So i will try it out as soon as i am back home.

But since i also want to learn and grow, and since a lot of your circuits use this special power supply, what is the advantage of having this 0V Ground instead of having just +9V and +9V (wich also works as a ground)? Because thats the way i actually learned it a few months before (in the book of nicolas collins). if you don't feel like going deep in that topic maybe you could give me a name for this method, so i could google it and find informations myself.
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Ruebezahl



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PostPosted: Mon Mar 10, 2014 8:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Just to make it sure: The circuit you are talking about is this one right? http://electro-music.com/forum/phpbb-files/bleeper_250.jpg

And the part in it, wich operates as the midpoint-voltage-generator, is the circuit in the middle of the sketch right? the one working with IC1 and IC2 op-amps.
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nicolas3141



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PostPosted: Wed Mar 12, 2014 2:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, there are three main approaches to powering audio circuits from a single 9V battery (or any single ended supply).

1. Use a voltage divider to create a midpoint voltage, buffer it with a spare op-amp, then use this as your 0V reference throughout your circuit. The resistors can be large (50-100K). This is a good way to do it if you have a spare op-amp available.

2. Use a voltage divider to create a midpoint voltage, buffer it with capacitors, then use this as your 0V reference throughout your circuit. The caps need to be largish (10-1000uF) and the resistors smallish (1-10K). This usually works very well, but can create an added drain on the battery. If you want to have a power status LED this can be combined with the voltage divider as I did in the bleeper circuit to enhance the performance.

3. Use separate voltage dividers throughout the circuit wherever you need a 0V reference. This works well for smaller circuits and used to be the preferred approach for discrete transistor circuits. It reduces the risk of unforeseen feedback loops via the 0V connection which can occasionally lead to odd behaviour in some circuits.

Nicolas


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-minus-



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PostPosted: Wed Mar 12, 2014 2:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is handy information nicolas. Could you explain what the IN is about in figure 3? Thanks.
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nicolas3141



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PostPosted: Wed Mar 12, 2014 2:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

In fig 3 i am just trying to show some generic amplifiers as examples, in and out are the signal in and out connections for inverting amps. Not really anything to do with the current discussion. Sorry for the confusion.

Nicolas
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cablebasher



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PostPosted: Tue Mar 18, 2014 2:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey dudes,

Is anyone able to upload any photos of this curicuit on breadboard or perfboard as a reference?

Not that great at following schematics.

Thanks.
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