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 Forum index » DIY Hardware and Software
4069 Rene's VCO
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rene_schmitz



Joined: Oct 27, 2013
Posts: 16
Location: germany

PostPosted: Fri Nov 08, 2013 4:34 am    Post subject: Reply with quote  Mark this post and the followings unread

isak wrote:

1. why R27 is a Pot? is it for the amount of the sync?
2. Can I use the sync parts as is in the original scheme?
3. Connected To pin 3 of the 4069, right?


This is some kind of soft sync scheme, and R27 is to set the strength of the sync. You can combine these parts with the original schematic, if that's what you mean.

isak wrote:

4. I will want 2 or even 3 of this vco, if I want to sync between them I will need a sync out, is it possible to do, if yes how?
5. What would be the Vpp output?


You could use the sync with a saw or pulse from another VCO.

Cheers,
René

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isak



Joined: Dec 13, 2009
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PostPosted: Fri Nov 08, 2013 6:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Renè.

I think I got all the answers I wanted Smile

Cheers,
Isak E.

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flab



Joined: Feb 13, 2012
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PostPosted: Mon Nov 11, 2013 8:26 am    Post subject: Reply with quote  Mark this post and the followings unread

here is a pcb im making for this project-yet is NOT ready - is exact the same design with Renes but im adding a a saw amp that then goes to a mixer pulse / saw for more interesting outputs;then the mixed signal passes from an op amp buffer-just like Rene point out before- i also kept the individual saw and pulse outs- and added a synch -
Ill spent some time more and i ll provide with the parts plan so to give me a feedback if thats possibly
,cheers people


4046vcorene.jpg
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isak



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PostPosted: Mon Nov 11, 2013 9:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi flab,

Nice one!
Can you post the layout with parts please?

Cheers Smile

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flab



Joined: Feb 13, 2012
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PostPosted: Mon Nov 11, 2013 10:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi there Isak,

give me a couple of days cause i have to change few things
also I'll update this layout to a dual vco and use the illustrator to give it a nice touch Very Happy
I ll also post a schem with mods.

cheers
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isak



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PostPosted: Mon Nov 11, 2013 11:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Got you Smile

cheers

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flab



Joined: Feb 13, 2012
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PostPosted: Tue Nov 12, 2013 5:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

well here it is isak,
imsure there are mistakes,
feedback is welcome,
also can someone give me directions how we calculate the res at the buffer ?


4069vcoRENE.jpg
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isak



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PostPosted: Thu Nov 14, 2013 8:20 am    Post subject: Reply with quote  Mark this post and the followings unread

thank you flab

maybe this will help you/us with the resistor calculate for the buffer.
op amp buffer:
http://www.eecs.tufts.edu/~dsculley/tutorial/opamps/opamps5.html

non inverted amp:
http://www.eecs.tufts.edu/~dsculley/tutorial/opamps/opamps2.html
move from page to page, happy reading Smile

cheers,
Isak E.

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flab



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PostPosted: Thu Nov 14, 2013 8:56 am    Post subject: Reply with quote  Mark this post and the followings unread

cheers Isak ,
I ll have a look soon -
also if you thinking of etching it , well dont - there are three mistakes for sure + do youthink i should put sth like a protection frrom power to 071 , if yes then please give me a tip mate
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isak



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PostPosted: Thu Nov 14, 2013 9:32 am    Post subject: Reply with quote  Mark this post and the followings unread

actually in Rene's site there is a suggestion to the Saw gain buffer for it to be in the same level as the square (roll down).
http://www.schmitzbits.de/vco4069.html

this is what Rene said to you back then:
Quote:
I'd recommend adding the sawtooth buffer amplifer as depicted on above page, then the crossfading should be more natural, since both amplitudes are (almost) the same. Otherwise you'd also have a change in volume as you fade.


so it should look like the attached pic.


4069 + saw amp + buffer.png
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flab



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PostPosted: Thu Nov 14, 2013 9:40 am    Post subject: Reply with quote  Mark this post and the followings unread

i am using Rene's buffering amp at the above schem - ok i ll start correcting the layout
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isak



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PostPosted: Thu Nov 14, 2013 12:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I see that but I don't think you'll need the op amp after the saw buffering.
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rene_schmitz



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PostPosted: Sun Nov 17, 2013 8:22 am    Post subject: Reply with quote  Mark this post and the followings unread

@flab: You could simply use a unity gain opamp follower for the buffer. I.e. output connected back to - input. And I would make the pads of resistors etc on that layout somewhat larger, makes it easier to solder in the end. Space is available.

@isak: The buffer is needed because the signal at the mix pot wiper has a relatively high impedance, so you'll loose signal amplitude when it is loaded.

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isak



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PostPosted: Sun Nov 17, 2013 8:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Rene.

as i understand we need to buffer the signal before the mix pot, not after,should we buffer the signal before and after the mix pot?

cheers,
Isak E.

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rene_schmitz



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PostPosted: Sun Nov 17, 2013 8:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Isak,

Yes, the sawtooth is brought up to the same amplitude first with the "sawtooth buffer amp". And after the mix pot, you should buffer it again.
So it is buffered twice, but the sawtooth amps main purpose now is to match up the amplitudes. (Just as flab has drawn it in the schematic)

Cheers,
René

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isak



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PostPosted: Sun Nov 17, 2013 8:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Rene.

i understand, thank you for the input!
sorry flad, it seems i was wrong Embarassed


cheers,
Isak E.

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flab



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PostPosted: Wed Nov 20, 2013 7:43 am    Post subject: Reply with quote  Mark this post and the followings unread

i did correct some mistakes also i chanced the buffer as you suggested Rene - i dont have the space for etching though - so i cannot verify it yet

have a look -
cheers


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emmaker



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PostPosted: Wed Nov 20, 2013 2:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Has anyone taken the 3 inverters used to do the wave shaping and used them for a second oscillator?

Wondering if there are issues like them syncing together or not working correctly.

Thanks
Jay S.
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rene_schmitz



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PostPosted: Tue Nov 26, 2013 5:56 am    Post subject: Reply with quote  Mark this post and the followings unread

emmaker wrote:
Has anyone taken the 3 inverters used to do the wave shaping and used them for a second oscillator?

Wondering if there are issues like them syncing together or not working correctly.

Thanks
Jay S.


I've never tried it, and I wouldn't recommend it either. There is already an ever so slight interaction between the PWM and the oscillator frequency, resulting in a tiny detuning while turning the PW pot/or external PWM. (It seems that the internal bonding wires, and their resistance cause this.) I guess that two oscillators in the same package will interact similarly. Which should lock the two frequencies together.

The 4069 is really cheap. Just get two. If you don't want the pulse, just tie the unused gate inputs to gnd.

Cheers,
René

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J3RK



Joined: Jun 05, 2006
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PostPosted: Tue Nov 26, 2013 12:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

rene_schmitz wrote:
I've never tried it, and I wouldn't recommend it either. There is already an ever so slight interaction between the PWM and the oscillator frequency, resulting in a tiny detuning while turning the PW pot/or external PWM. (It seems that the internal bonding wires, and their resistance cause this.) I guess that two oscillators in the same package will interact similarly. Which should lock the two frequencies together.

The 4069 is really cheap. Just get two. If you don't want the pulse, just tie the unused gate inputs to gnd.

Cheers,
René


Hi Rene,

I ran into this with one of my own VCO designs recently, and there were a couple of causes for it. (not 4069 based) One was that I didn't have enough bulk capacitance on the board, so I increased the power filtering caps. The other was that I was using low R resistors on the power rails, which were causing some current fluctuations under certain circumstances, the main one being while adjusting PWM. It would pull the pitch up and down very slightly. I replaced those resistors with ferrites and the problem went away completely.

I'm wondering if the same could be true on this design, or if maybe adding some extra capacitance might help mitigate it a bit.

Just a thought anyway.
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flab



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PostPosted: Wed Nov 27, 2013 7:36 am    Post subject: Reply with quote  Mark this post and the followings unread

i did build the vco four days ago at a strip board so i haven't yet tested the pcb uploaded above the other day -

I am getting a funny thing from the vco though - every time I power up the module you can hear it to tuning up more than an oct needs more than 10sec to get almost stably. and then when im trying it to send CV some times it responds and sometimes not-

Could that be that i use a bad quality bc548?
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rene_schmitz



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PostPosted: Wed Dec 04, 2013 7:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi flab,

I've never noticed this behaviour. Are you sure your circuit is ok?
Does it correspond with the heat up of the 4069?

Cheers,
René

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Audiobubble



Joined: Dec 09, 2013
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Location: Liège (Belgium)

PostPosted: Mon Dec 09, 2013 7:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Folks,

It's my first post here and after a lot of reading here and there I built rene's VCO on perfboard. It's my first step in sdiy.

It seems to work fine, but the level of the saw output is really really low.
So i built the buffered output found on the rene's documents. The level is higher now but still really lower than the pulse output.

Is it a normal beaviour ?

The vco is powered +12v/-12V and i use 2n3904 for npn (for the buffered output too) and 2n3906 for pnp.

Thanks for the help,
cheers,
Guillaume
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flab



Joined: Feb 13, 2012
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PostPosted: Mon Dec 09, 2013 9:58 am    Post subject: Reply with quote  Mark this post and the followings unread

hi Rene ,
it is obvious that is my fault and not your circuits - i ll start from beginning soon , and it does correspond to the 4069 heat , hmmm , never mind i ll start again , cheers
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airfrankenstein



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PostPosted: Wed Feb 12, 2014 10:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Flab, have you gotten a chance to verify your pcb layout?
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