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 Forum index » DIY Hardware and Software » Developers' Corner
Expo converter trouble - need some help
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L´Andratté



Joined: Sep 23, 2012
Posts: 60
Location: Hamburg, Germany
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PostPosted: Sun Dec 08, 2013 5:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello Beep!

Just to make sure: you are aware that a dual supply can easily be generated with 2 batteries?
+9V/-9V should work with most +12/-12 circuits also(probably minor changes...).

Otoh maybe you just wanna do it your way! Smile
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beep



Joined: May 05, 2013
Posts: 84
Location: Germany

PostPosted: Mon Jan 06, 2014 11:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey L´Andratté Smile

I know the two battery dual supply solution, but my
intention was to design an easy to build synth, which
will run from battery as well as from a DC wall wart,
like the SH101.


back to topic:

I soldered the latest schematic by René on stripboard
without breadboarding before. I used an op amp like
in the single op amp saw vco. but with a 2.2nF poly cap
instead of the 100nF from Metal_head's design.

It works, but its pitch is much to high even if CV is 0V
should I use a 100nF cap?

edit: Tried a 100nF cap now, got lower pitch but at higher pitches
the oscillator stops oscillating somehow. I can re-activate it
by touching some random pins on the stripboard

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Last edited by beep on Tue Jan 07, 2014 1:25 am; edited 1 time in total
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beep



Joined: May 05, 2013
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Location: Germany

PostPosted: Tue Jan 07, 2014 1:17 am    Post subject: Reply with quote  Mark this post and the followings unread

...aaand collector AND base of Q4 are connected to the base
of Q5, is this right?

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beep



Joined: May 05, 2013
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PostPosted: Wed Jan 08, 2014 7:21 am    Post subject: Reply with quote  Mark this post and the followings unread

I made a voltage divider with a trimmer at the power supply to connect R4 to a lower voltage than 12V. Now I can adjust the initial pitch of the VCO,
then connected a squarewave LFO to another CV input and adjusted its
modulation intensity to get a musical interval (5ths) then I swept through
the available audio range (~4 ovtaves) and it worked great. at the higher pitches, the modulation range is still fucked up, but it works very well already. I want to take further research on this to improve the tracking.

I also have to figure out, where to place the NTCs. The vco is very temperature sensitive.

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beep



Joined: May 05, 2013
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PostPosted: Wed Jan 08, 2014 7:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

I figured out in the simulator that lowering the value of R5 (which is 6,8k here and was 47k in the vco40106) could increase the range.

please tell me what you think


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rene_schmitz



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PostPosted: Thu Jan 09, 2014 5:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Beep,

nice to see that you're also working on it.

I've breadboarded it, and I noticed too that the range is set too high. I was using only 5V supply.
However if you change the cap, you'll have to adapt/adjust the HFT as well.
Another option is to make the R4 resistor bigger than 1M to shift things down. I think best is to use both approaches. Maybe 22n and 4M7 or so.

Oh, and you're right about the base and collector of Q4 being tied together.

Cheers,
René

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beep



Joined: May 05, 2013
Posts: 84
Location: Germany

PostPosted: Thu Jan 09, 2014 1:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

And how happy I am that you're also working on it Smile
I added a 47nF capacitor without changing any resistors
and I got nice low pitch at lowest cv. but when I increased the
cv, the vco suddenly stopped to oscillate. I had a 2n2 poly cap
in parallel with the additional 47n ceramic cap.

is the HFT the reset time compensation trimmer?
It slightly changes the pitch. But this is not the
replacement of the v/oct trimmer, is it?

can I just add the 10k NTCs and the 1k v/oct trimmer
as in the vco4069?

The simulator told me that I can get lower pitches when I apply negative
CV, but there is no source for negative CV, so lowest CV must be 0V


ROCK'N'ROLL!

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MickeyDelp



Joined: Feb 26, 2010
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PostPosted: Mon Feb 10, 2014 5:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

I breadboarded this circuit today. Given that breadboards introduce lots of parasitic capacitance and power supply noise and switching noise, etc. The 40106 oscillator is horribly noisy and unstable. The waveform was jiggling all over the scope. It also made it impossible to use any of the other Schmitt triggers in the 40106. The op amp version, however, sounds beautiful!
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beep



Joined: May 05, 2013
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PostPosted: Tue Feb 11, 2014 8:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Heyy, did you have success getting it working with 1V/oct properly?
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MickeyDelp



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PostPosted: Tue Feb 11, 2014 2:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

beep wrote:
Heyy, did you have success getting it working with 1V/oct properly?

I did not try. It is not necessary for my application (drone synth).

I hope that you and René continue to work on it though. The world needs a good single supply exponential converter.

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JingleJoe



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PostPosted: Thu Feb 13, 2014 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

MickeyDelp wrote:
I breadboarded this circuit today. Given that breadboards introduce lots of parasitic capacitance and power supply noise and switching noise, etc. The 40106 oscillator is horribly noisy and unstable. The waveform was jiggling all over the scope. It also made it impossible to use any of the other Schmitt triggers in the 40106. The op amp version, however, sounds beautiful!

did you tie the unused 40106 inputs to GND? and use a power supply filter cap? missing either of those can cause the problems you had.


by the way I tried the expo converter posted by Rene but in a different circuit, I couldn't get it to work... Sad i also don't fully understand just what's going on there (with the expo) I thought I did but I think not now because of my lack of ability to make it work Confused

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MickeyDelp



Joined: Feb 26, 2010
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PostPosted: Thu Feb 13, 2014 8:24 am    Post subject: Reply with quote  Mark this post and the followings unread

JingleJoe wrote:
did you tie the unused 40106 inputs to GND? and use a power supply filter cap? missing either of those can cause the problems you had.

Yes, and yes. Tying the unused inputs to ground did stabilize the waveform a bit, but the other inverters in the 40106 are still unusable. Basically, it is using a 16 pin chip where an 8 pin op amp works better.

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JingleJoe



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PostPosted: Thu Feb 13, 2014 8:35 am    Post subject: Reply with quote  Mark this post and the followings unread

MickeyDelp wrote:
JingleJoe wrote:
did you tie the unused 40106 inputs to GND? and use a power supply filter cap? missing either of those can cause the problems you had.

Yes, and yes. Tying the unused inputs to ground did stabilize the waveform a bit, but the other inverters in the 40106 are still unusable. Basically, it is using a 16 pin chip where an 8 pin op amp works better.

I agree entirely, it is a bit of a waste of most of an IC, however if it gets the job done and doesn't break the bank or cause mass destruction, then by my standards that's okay for some kind of ramshacke hacker like me Smile

oh also I wanted to add, I made a single supply expo converter, it's not the best but it gets the job done for what I wanted: exponentiation for the CV applied to a VCF or VCA. Tuning is a bit fiddly but it can be made to work with a VCO... I thought I posted it here? I'm sure I made a thread about it, have a search Smile

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