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 Forum index » DIY Hardware and Software
Very simple sawtooth VCO (V/Hz)
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Yipdeceiver



Joined: Apr 07, 2014
Posts: 4
Location: Athens GA

PostPosted: Mon Apr 07, 2014 3:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

A friend and I built this and it's pretty rad. One thing though, patching it through the ext signal in on the ms10 and the extra oscillator doesn't respond to the lfo. Is there anyway to make that happen? Might be more of an ms10 question I guess, but I figured you guys might have some ideas.
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bod



Joined: Apr 28, 2009
Posts: 148
Location: Glasgow

PostPosted: Tue Apr 08, 2014 4:28 am    Post subject: Reply with quote  Mark this post and the followings unread

you would need to take a signal from the ms10 lfo output and connect it to the cv input of the oscilator for that to work, but it would work.
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Yipdeceiver



Joined: Apr 07, 2014
Posts: 4
Location: Athens GA

PostPosted: Thu Apr 24, 2014 1:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've been looking around and found this cv scaling circuit. I used an lm324 because that's what I had lying around so I have the extra op amp already. Think it would be worth it to throw this in front of the cv input in an attempt to get this vco to track correctly? Or would that work?


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Yipdeceiver



Joined: Apr 07, 2014
Posts: 4
Location: Athens GA

PostPosted: Thu Apr 24, 2014 2:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

I went ahead and bread boarded this up and after fiddling with resistors for a while I think I've got something. It tracks reasonably well with my ms 10 now. The lowest note and the highest note are perfectly in tune with a little bit of variation in the middle octave. Obviously it's not perfect but it is definitely better. I'm not sure why it is deviating in the middle octave though. Any thoughts?
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Citezyne



Joined: Jan 09, 2015
Posts: 24
Location: Australia

PostPosted: Sat Jan 10, 2015 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

nicolas3141 wrote:
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


Hi again,

I'm curious to know, is there a formula to work out the resistor and cap sizes? I'm keen to put together a power supply like this on a bread board to play around more with some of your other designs. Mostly I'd use a 9v battery or a 12 volt PC PSU supply.

Also working on your simple bleeper using 2 TL074's however I don't have the 750r resistor or the 33k ones so have to wait till payday for them.

Love your work, super simple for a beginner like myself, biggest I have built is an 8 step APC.
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nicolas3141



Joined: May 25, 2007
Posts: 184
Location: Christchurch, New Zealand

PostPosted: Tue Jan 13, 2015 3:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you are wanting to go with option 2 - two resistors and a cap to create a 0V reference - then a rule of thumb would be resistors an order of magnitude smaller than the resistors in your circuit and the cap at least an order of magnitude (or two) bigger than any caps in the circuit. But option 1 is much better if you can buffer you 0V reference with an op-amp.

Nicolas
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Citezyne



Joined: Jan 09, 2015
Posts: 24
Location: Australia

PostPosted: Wed Jan 14, 2015 4:55 am    Post subject: Reply with quote  Mark this post and the followings unread

nicolas3141 wrote:
If you are wanting to go with option 2 - two resistors and a cap to create a 0V reference - then a rule of thumb would be resistors an order of magnitude smaller than the resistors in your circuit and the cap at least an order of magnitude (or two) bigger than any caps in the circuit. But option 1 is much better if you can buffer you 0V reference with an op-amp.

Nicolas


I would use the op amp version as recommended, I have a few TL0XX lying around that would suit the job.

Thank you again for your help, your simple Designs gave me hope when i felt that all hope was lost!

Keep up the Awesome work!
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enomys



Joined: Dec 19, 2010
Posts: 11
Location: italy

PostPosted: Wed Feb 10, 2016 3:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

I did it to use it as a second oscillator with my Korg Ms10 and it works good in the range between C1 and C2, but between C2 and C3 is so detuned.. how can I do? thanks so much
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enomys



Joined: Dec 19, 2010
Posts: 11
Location: italy

PostPosted: Thu Feb 11, 2016 10:55 am    Post subject: Reply with quote  Mark this post and the followings unread

with a TL072 the tracking is good...
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nicolas3141



Joined: May 25, 2007
Posts: 184
Location: Christchurch, New Zealand

PostPosted: Mon May 23, 2016 1:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, this circuit works well with +/-4.5V from a 9V battery and virtual ground type setup, just make sure to either buffer the virtual ground with a third opamp or put a decent sized cap on it to keep it stable during the sawtooth switch.

Another question - has anyone added hard sync between two of these? There are a few different ways to add sync to a sawtooth, but I haven't tried adding to this circuit, not sure what would work best.

Thanks,
Nicolas
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danfan



Joined: May 26, 2008
Posts: 6
Location: chicago, il

PostPosted: Mon May 23, 2016 10:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Bear in mind that I have little understanding of what I'm doing. What I did:

I was able to coax some OK hard sync using ken stone's gate-to-trig circuit with its output fed to the gate input of an NTE467 n-channel JFET. I tied the gate input of the JFET to the negative rail via an 18k resistor (a la the mfos vco value) to keep the JFET open/timing cap working properly. Then I connected the JFET's drain and source to either side of the oscillator's timing cap. I keep going back and forth between 10n/1n caps for ken's circuit to shorten the pulse time/get the best response.

I was able to coax sync at audio rate from tri and dirty sine, but in low audio/sub audio rate I was only able to use a hard edge.

Side note: I'm using this to consistently trigger the osc of a kick drum from zero. I get a click on reset (clicks every time is better than clicks some of the time!). Shortening the pulse time was where I was looking to diminish the click but still get the reset...unless it would be easier to just throw a high cutoff RC low pass on the output.

Better ways of sync'ing this little guy?
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Blue Hell
Site Admin


Joined: Apr 03, 2004
Posts: 21743
Location: The Netherlands, Enschede
Audio files: 175
G2 patch files: 319

PostPosted: Fri Jun 03, 2016 3:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

In http://electro-music.com/forum/post-419924.html#419924 sharkattackeddie posted a question re. the oscillator in this thread. I can not merge that message into this thread, but it would have been .. oh well .. maybe someone can help sharkattackeddie :-)
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nicolas3141



Joined: May 25, 2007
Posts: 184
Location: Christchurch, New Zealand

PostPosted: Sun Jun 05, 2016 10:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

The issue mentioned with bad sound from a power supply choice is hard to diagnose without more info, but here are some suggestions:

- it could be insufficient buffering caps on the 0V virtual ground. If it is getting pulled one way or the other by a couple of volts that may not matter so much on a higher voltage supply, but on a lower voltage supply it may cause you to run out of headroom.

- it could be that the bad sounding power supply is particularly noisy, some just are not well suited to audio use. Adding regulators, caps, etc can help, but some switchmode power supplies designed for charging batteries, etc are almost beyond redemption.

- you could have a ground loop problem with the power supply and the oscillator and the amp interacting. Experiment with a battery powered headphone amp and avoiding all mains powered equipment such as mixers/effects/amps/computers/oscilloscopes/etc. See if it still does it when the oscillator is the only mains powered module in the whole system.

Nicolas
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sharkattackeddie



Joined: May 24, 2016
Posts: 6
Location: UK

PostPosted: Mon Jun 06, 2016 2:44 am    Post subject: Reply with quote  Mark this post and the followings unread

nicolas3141 wrote:

- it could be insufficient buffering caps on the 0V virtual ground. If it is getting pulled one way or the other by a couple of volts that may not matter so much on a higher voltage supply, but on a lower voltage supply it may cause you to run out of headroom.

Nicolas


I didn't use a capacitor in my power supply splitting, just two 100k resistors. Could you recommend the value of cap to go in and where it should go? I reckon I could probably still squeeze it onto the vero board I used to build the circuit on.
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nicolas3141



Joined: May 25, 2007
Posts: 184
Location: Christchurch, New Zealand

PostPosted: Tue Jun 07, 2016 12:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, I would try switching to somewhat smaller resistors, say 10-22K, and in parallel with both resistors put an electrolytic cap, say 33-100uF. If you can still hear some noise, you could also add in parallel small ceramic caps of 100n, to filter the high frequency noise that the electrolytics are not so good at.

If you have space problems on the pcb you can stack the components into one set of holes, for example by putting the electrolytics on one side of the board and the resistors on the other side.

Nicolas
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