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 Forum index » DIY Hardware and Software » YuSynth
VCO waveforms
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capicoso



Joined: Nov 19, 2012
Posts: 127
Location: Argentina

PostPosted: Wed Apr 24, 2013 1:05 am    Post subject: VCO waveforms Reply with quote  Mark this post and the followings unread

Hello. After hours and hours of debugging my vco module, i managed to make it work(had a very tiny shortcut... i etched my board) Now i'm calibrating the waveforms and these are the results
i'll keep trying though...
F is at 6khz

What bugs me is that peak the SAW has and that it goes from -4 to 4v(but almost 5v because of the peak)... i tried at lower freq and it's the same, trimming T3 didn't help, it only changed the negative part.
And the TRI goes from -3,80v~ - 3.80v... At 5khz or lower it amplifies to -4v 4v. Although on the site on the end it says that it should be -4 4v... but before that it says -5 5v so i'm not sure...
The sine looks good i think. And the SQR too...

One more thing i'm not sure, when moving pulse width pot to + it shrinks the sqr, that's ok, but it starts to offset the 0, and at max it starts at 0v... and the same but to the negative range when lowering... i'm starting with this so i don't know if this is how it's supposed to be?
thanks


SDS00002.BMP
 Description:
PULSE

Download
 Filename:  SDS00002.BMP
 Filesize:  329.12 KB
 Downloaded:  85 Time(s)


SDS00003.BMP
 Description:
SAW

Download
 Filename:  SDS00003.BMP
 Filesize:  329.12 KB
 Downloaded:  88 Time(s)


SDS00004.BMP
 Description:
SINE

Download
 Filename:  SDS00004.BMP
 Filesize:  329.12 KB
 Downloaded:  80 Time(s)


SDS00005.BMP
 Description:
TRIANGLE

Download
 Filename:  SDS00005.BMP
 Filesize:  329.12 KB
 Downloaded:  72 Time(s)

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yusynth



Joined: Nov 24, 2005
Posts: 1222
Location: France

PostPosted: Mon Apr 29, 2013 2:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello,

You're waveforms are all OK.

Concerning the offset when you change the Pulse Width, it's an artefact of the oscilloscope mode you are using. You are probably using the AC mode, in such a case the energy is balance around 0V, when square there is an equal amount of energy on the positive and negative side, when changing the PW you create an unbalance between positive and negative value this result in a shift of the average voltage creating the observed offset.
If you use the DC mode such behaviour must disappear.

In conclusion all is normal.

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Yves
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capicoso



Joined: Nov 19, 2012
Posts: 127
Location: Argentina

PostPosted: Sun May 05, 2013 5:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. Yes it was on AC.
It sounds amazing, i just asked because i couldn't believe that it was fully working, my first vco build.
Thanks for everything
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yusynth



Joined: Nov 24, 2005
Posts: 1222
Location: France

PostPosted: Sun May 05, 2013 11:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well done then, time to build a filter now Wink
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capicoso



Joined: Nov 19, 2012
Posts: 127
Location: Argentina

PostPosted: Mon May 06, 2013 3:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, i have lfo and steiner vcf pcbs... i don't know which one to start first, vcf is simpler, but i have no instrument to match the caps... i don't know how important is to match them and how unmatched caps would affect the circuit?
thanks again
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prgdeltablues



Joined: Sep 25, 2006
Posts: 176
Location: UK
Audio files: 11

PostPosted: Tue May 07, 2013 5:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Most decent and inexpensive digital multimeters can measure capacitance, but if you don't have/can't afford one, you can match capacitors using a 555 oscillator circuit: see eg
http://home.cogeco.ca/~rpaisley4/LM555.html

If you use 1% resistors, you can match the capacitors to 1% too, by matching the frequency (either by ear or with a tuner/frequency counter). You've probably find caps within 10%, so adding some 0.1 or thereabouts nF caps in parallel will be necessary.

Peter
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capicoso



Joined: Nov 19, 2012
Posts: 127
Location: Argentina

PostPosted: Tue May 07, 2013 8:20 am    Post subject: Reply with quote  Mark this post and the followings unread

prgdeltablues wrote:
Most decent and inexpensive digital multimeters can measure capacitance, but if you don't have/can't afford one, you can match capacitors using a 555 oscillator circuit: see eg
http://home.cogeco.ca/~rpaisley4/LM555.html

If you use 1% resistors, you can match the capacitors to 1% too, by matching the frequency (either by ear or with a tuner/frequency counter). You've probably find caps within 10%, so adding some 0.1 or thereabouts nF caps in parallel will be necessary.

Peter

Thanks. Well now i have the most inexpensive multimeter so... and the cheap ones i found that measure capacitance, minimun is only 2n, so i couldn't match them at 1.5n... and here in Argentina what is cheap everywhere, here is expensive Razz with lot of work i could afford a digital oscilloscope... inflation Rolling Eyes
I'll try with the 555 circuit, thanks!
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prgdeltablues



Joined: Sep 25, 2006
Posts: 176
Location: UK
Audio files: 11

PostPosted: Wed May 08, 2013 3:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Glad to help. You could always match using the multimeter you describe - it's the difference rather than absolute values that matters most here, so you could measure a (say) 10n in parallel with one of your 1.5n (call it A) to measure a notional (11.5n) capacitance of (10+A)nF. Then swap out A for 1.5n cap B reading = a notional (10+B)nF - keep testing different 1.5n caps until you get the two measurements as close as possible to each other - the absolute values don't matter as (10+A) - (10+B) = A-B. For a 1% match, you'd be looking for A-B to be 0.015nF or less.
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