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 Forum index » DIY Hardware and Software » Thomas Henry designs
XR-2206 VCO problems
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ungleichklang



Joined: Dec 03, 2011
Posts: 104
Location: East-Belgium

PostPosted: Wed Jul 30, 2014 10:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Now I double checked all soldering and ground .. even the +-15V all seems propper so no cold solder found ...
Changed the XR2206 .. same behavior .. only noise ... Mad

so I will give up on this board and solder some other VCOs I have around Sad
Maybe one day I will go back on this or even solder the second board that I have

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ungleichklang



Joined: Dec 03, 2011
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Location: East-Belgium

PostPosted: Mon Aug 04, 2014 11:55 am    Post subject: Reply with quote  Mark this post and the followings unread

o.k. still can't get my hands off this thing ..

it seems that some resistors are bad manufactured ....
some 10k only tell me 6,0k, some others also with wrong value .. so I will go on debugging tonight

OMG DIY is a drug Very Happy

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elmegil



Joined: Mar 20, 2012
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PostPosted: Mon Aug 04, 2014 12:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Are you measuring the resistors while they are soldered into the circuit? This can affect what resistance reading you get checking them. For example if my circuit somehow had two 10k resistors going from a common point to ground, measuring one would show me 5K instead because they would be parallel to each other.

You generally can only be sure you're measuring just the resistor in question if you lift one of the legs out of the circuit.

If you meant you measured those in the batch you selected from, without being in a circuit, disregard all that Smile
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ungleichklang



Joined: Dec 03, 2011
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PostPosted: Mon Aug 04, 2014 12:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the hint elmegil ... yes, I have exaclty that effect . so I will desolder one leg an check them again ...

else it must be the XR2206 that is not well working

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ungleichklang



Joined: Dec 03, 2011
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Location: East-Belgium

PostPosted: Tue Aug 05, 2014 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

IT WOOORKS

had a little visit at serendai today ... he managed to fix the XR2206 .. I soldered one tansistor in wrong direction aaand the XR2206 was broken ..

thanks a lot Bernd for your help

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elmegil



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PostPosted: Tue Aug 05, 2014 6:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Awesome Smile

Good to hear....
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Skysurfer



Joined: Sep 16, 2014
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Location: Florida

PostPosted: Sun Jul 26, 2015 6:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Amazing what you can find if you dig a little...
Was my first synth piece and it wouldn't go correctly. A bit disheartening for your first piece, the heart of the synth to come up bust. Mine wouldn't oscillate below ~500Hz just make noise. Ended up setting it aside rethinking my approach and moved on to some other projects. Was going to email my old friend Scott but he seems to have fallen off the radar then ran across this now that I have some time between projects.

Turns out I was also fighting the bunk F0919 XR2206. Between 5 of them the low end would cut off between 300 and 500HZ from there down just noise. Varying the + power supply would correct the problem I had to go all the way down to 10V on some of them. What clued me in was it would run down with a nice tone when I cut the power.

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macumbista



Joined: Sep 12, 2007
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PostPosted: Sat Jun 25, 2016 5:25 am    Post subject: Reply with quote  Mark this post and the followings unread

If this is the "problems" thread, then I've got one of my own. I've seen someone else posting about this someplace here but I can't seem to find it.

Since I [finally!] started using an oscilloscope to tune the waveforms of the XR-VCOs I build, I notice that there is often a small error at the peak of the ascending half of the sine wave. A small notch in the waveform exactly at the point where the skew starts to fold it over. Sometimes it's a big bigger, more noticeable and definitely more audible!

I imagine this could have to do with slightly mismatched (although still 1%) resistors in the skew section, but I'm still at a lack as to which ones. Does anyone have experience with this or suggestions?

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macumbista



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PostPosted: Sat Jun 25, 2016 5:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Actually, even the screenshots on the Birth of a Synth project page have this glitch. Does that mean it falls in the realm of "acceptable" noise?

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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LFLab



Joined: Dec 17, 2009
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PostPosted: Sat Jun 25, 2016 7:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Because of the way these sines are made, there will always be a little niggle at the tops and bottoms of the sine. So rather than using a scope, can you tune it by ear so it has the least amount of harmonic content? Or does it still not sound like a pure sine?
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ungleichklang



Joined: Dec 03, 2011
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PostPosted: Sat Jun 25, 2016 7:14 am    Post subject: Reply with quote  Mark this post and the followings unread

I tune my VCOs by ear ... who wants a perfect sine just to route the Audio through wavesahpers for more harmonics Wink
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macumbista



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PostPosted: Sat Jun 25, 2016 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes I've been tuning them also by ear, however the trimmers only affect the offset, roundness and symmetry. The little glitch remains regardless, making me think it could be trimmed elsewhere if I could just figure out where.
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elmegil



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PostPosted: Sat Jun 25, 2016 7:49 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd swear that not only does the screen shot show the little glitch, but Thomas' text on that page talks about it briefly too, as in --yes, this is normal, and when you minimize it inaudible.
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macumbista



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PostPosted: Sat Jun 25, 2016 7:59 am    Post subject: Reply with quote  Mark this post and the followings unread

That's all there is about tuning the waveshape (below). I also seem to recall this, maybe it was on an earlier version of the site (on the other server?). I'll keep futzing around with the trimmers and see if I can get all 7 of the XRs I just finished to similar levels of non-distortion...

Quote:
Next, calibrate the Sine Shape. Set the sine/triangle output switch to 'sine'. Calibrate the sine shape by alternating between the Sine Symmetry Trim (R22 25K single turn trimpot) and the Sine Round trim (R3 500R single turn trimpot). You can do this by observing the waveform on an oscilloscope, or you can use your ears. You will be surprised at how accurately your ears can tune a sinewave - just adjust the pots until you detect as much of an absence of harmonics as possible.

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