Inverted strange shaped sawtooth, normal square wave

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mavzz
 
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Inverted strange shaped sawtooth, normal square wave

Post by mavzz »

Hi folks,

I'm in the process of putting together a Willzyx x0xb0x for the first time, and everything seems to be going smoothy except with the sawtooth wave.

I soldered all the parts and viewed the sawtooth wave using my laptop and Zelscope. The first thing I noticed is that the wave is inverted (as someone explained in a previous post, it looks like this |\|\|\ rather than this /|/|/|). After inverting it in Zelscope this is what it looks like:

Image

However, the square wave looks normal without having to invert it in the first place:

Image

Both of these change frequency when adjusting TM4, TM5, VR2, and the CV.

How is it possible that the sawtooth wave is inverted when compared to square wave?

I've triple checked that all the parts are in their correct spot. Here's a photo of the board with all the components, just in case I've missed something:

http://i.imgur.com/TDDNNEL.jpg

All the voltages I've tested (12V, 5.33V, 3V CV) are normal. So are the DC biases of the sawtooth and square waves.

I've read all the posts I could find in this forum about the subject and it seems that I should keep going with the x0xb0x and by the time I build the VCF things will sort themselves out. I am curious on any ideas about why this might be happening, mostly because I am hoping to get a better understanding on how these waves are generated. Maybe it's just my soundcard acting up? Or perhaps a faulty C11? How do I test this when it's already soldered on the board? Thank you very much!

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antto
 
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Re: Inverted strange shaped sawtooth, normal square wave

Post by antto »

if the sawtooth was wrong - the square wave would be totally "wtf"
i think the problem is your soundcard inverting the audio..

the waveforms should look like this:
Image

and yes, the sawtooth starts from a higher voltage (near 11V), while the square starts at 5.333 and goes up afterwards

mavzz
 
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Re: Inverted strange shaped sawtooth, normal square wave

Post by mavzz »

Thanks for your reply antto!

I guess the only way to be check this would be with an oscilloscope. I'll get hold of one and post the output.

In the meantime, would it be OK to continue with the build and start making the VCF?

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antto
 
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Re: Inverted strange shaped sawtooth, normal square wave

Post by antto »

IMO it smells fine, if a real scope is hard to obtain - don't bother, continue with the vcf :wink:

mavzz
 
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Re: Inverted strange shaped sawtooth, normal square wave

Post by mavzz »

I will try to get an oscilloscope, it might take me a week or so, but I know where to borrow one. Will I be able to test the sawtooth wave the same way I do now if I build the VCF?

Also, I haven't soldered S1 in yet and I've seen it soldered it already for this section, however I can't imagine making any difference.

I've uploaded some .wav of both waves, as well as newer images of the (uninverted) waves; if you can have a listen and tell me what you think I would really appreciate it!

https://www.dropbox.com/sh/ckpce9zu5knqd9l/o_QDY5bzeH

Thanks for your help!

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mmm
 
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Re: Inverted strange shaped sawtooth, normal square wave

Post by mmm »

mavzz wrote:I will try to get an oscilloscope, it might take me a week or so, but I know where to borrow one. Will I be able to test the sawtooth wave the same way I do now if I build the VCF?
Yes, this will be no problem. You'll always be able to measure the VCO output directly at the waveform switch.
mavzz wrote: Also, I haven't soldered S1 in yet and I've seen it soldered it already for this section, however I can't imagine making any difference.
No, it won't make any difference.
mavzz wrote: I've uploaded some .wav of both waves, as well as newer images of the (uninverted) waves; if you can have a listen and tell me what you think I would really appreciate it!
If you invert the pictures of the waves they look absolutely fine. I wouldn't worry the slightest bit about this.

The recordings are not too helpful since they are very noisy; I'm also getting the impression they have been clipped (this may have something to do with the major DC offset the waves have directly after the oscillator). I attribute that certain "hoarseness" to this.
As I said: I wouldn't worry right now; even if there are problems they will be much easier to debug once you have the rest of the xoxbox finished.

mavzz
 
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Joined: Sun Mar 31, 2013 1:59 am

Re: Inverted strange shaped sawtooth, normal square wave

Post by mavzz »

Thanks for your help MMM. I will take your and antto's advice and keep going with the build.

The bad quality of the .wav is likely due to me using a "soundcard oscilloscope" and a crappy microphone jack.

Hopefully I'll get an oscilloscope soon and I'll post the waveforms I get with it.

Thanks again!

mavzz
 
Posts: 22
Joined: Sun Mar 31, 2013 1:59 am

Re: Inverted strange shaped sawtooth, normal square wave

Post by mavzz »

So I finally got hold of an oscilloscope and the waveforms look normal now :)

Thanks everyone for their help!

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