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 Forum index » DIY Hardware and Software » fonik's place
4046 Oscillators progressively getting worse over time
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LektroiD



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PostPosted: Wed Oct 17, 2012 2:20 pm    Post subject: 4046 Oscillators progressively getting worse over time Reply with quote  Mark this post and the followings unread

Two of my oscillators are stable (at least as stable as an analog oscillator is going to get), but the other two are sounding rather ill, I have no idea why. They started off in good tune, but one went unstable after about 6 months, and now the second one... Is it only a matter of time before the others go? Maybe someone can help me out. I attached an audio file of a direct square output, although all waveforms are doing the same wonky output....


Osc.mp3
 Description:

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 Filename:  Osc.mp3
 Filesize:  339.18 KB
 Downloaded:  211 Time(s)


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fonik



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PostPosted: Wed Oct 17, 2012 11:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

this sounds...errr... funny?

no, not funny.
just a wild guess: maybe something got loose? it is embarrassing that this would happen on two modules, though!?

are the x-4046 from the same batch? and/or the matched pair?

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LektroiD



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PostPosted: Wed Oct 17, 2012 11:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

The PCBs were from the same batch...
The 4046 ICs were from the same batch...
The transistors were from the same batch, hand matched...

Everything was working fine but they have gotten to an unusable state now. I tried wiggling all the components by hand one by one, as well as all the pots & sockets, yet failed to stabilise the pitch.

I can't think of anything else that would cause this (the audio is a mild example, it gets a lot worse).

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fonik



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PostPosted: Thu Oct 18, 2012 3:24 am    Post subject: Reply with quote  Mark this post and the followings unread

for me it still sounds like a loose contact.
but why is it that you experience these problems on two modules, but not on two others?
i would try to think about what was different when building these. solder, potentiometers, other parts...
what is different right now when using them? other cabinet/powering method?

since nobody else experienced such an issue so far we can only try to analyse it.

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LektroiD



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PostPosted: Thu Oct 18, 2012 4:46 am    Post subject: Reply with quote  Mark this post and the followings unread

I built the 4 oscillators as a batch. I was just wondering what components regulate the pitch (other than the matched pair), if the 4046 might be the culprit, I could swap that out... I'll retouch all the joints and post my results...
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elmegil



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PostPosted: Thu Oct 18, 2012 5:12 am    Post subject: Reply with quote  Mark this post and the followings unread

If your chips are socketed, can you switch one from a working module to a non working module?
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fonik



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PostPosted: Thu Oct 18, 2012 11:41 am    Post subject: Reply with quote  Mark this post and the followings unread

and maybe try different pots.


anyways, two modules at the same time???

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LektroiD



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PostPosted: Fri Oct 19, 2012 5:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
and maybe try different pots.


anyways, two modules at the same time???


LektroiD wrote:
one went unstable after about 6 months, and now the second one...


...I'm just waiting for the third

Anyway, I couldn't manage to true the waveform of any of my oscillators. I'll post the photos to see if what I have is normal, or maybe this is an underlying problem that also needs to be sorted. I guess because the square is not a real square, that's why they sound thin compared to my other synths / oscillators?


SAW.jpg
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Sawtooth... This is the best I could get it...
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SAW.jpg



TRI-1.jpg
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Triangle: After hours of perseverance, this is the best outcome
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TRI-1.jpg



TRI-2.jpg
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TRI-2.jpg



TRI-3.jpg
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TRI-3.jpg



SQR.jpg
 Description:
Square, apparently...
 Filesize:  166.64 KB
 Viewed:  6031 Time(s)

SQR.jpg



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Last edited by LektroiD on Sat Oct 20, 2012 4:59 am; edited 1 time in total
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elmegil



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PostPosted: Fri Oct 19, 2012 8:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

It looks to me like you've got some kind of extra capacitance on the line, dragging you back to ground. All the waveforms are exhibiting it.
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Mongo1



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PostPosted: Fri Oct 19, 2012 9:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you used film capacitors in the oscillator core, you may have overheated them while soldering. They're very easy to damage, and I've had them do exactly what you're talking about - start out fine, and then get 'sick' over time. Just a thought...
Good luck

Gary
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LektroiD



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PostPosted: Fri Oct 19, 2012 9:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
It looks to me like you've got some kind of extra capacitance on the line, dragging you back to ground. All the waveforms are exhibiting it.


These waveforms are exactly the same whether I use the bench supply or the PSU in the synth (I recently switched over to a dedicated PSU, solely to drive the oscillators; still the same output). I thought it was normal, since all oscillators are exhibiting the same...

So what would be the cure?

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Last edited by LektroiD on Fri Oct 19, 2012 11:38 pm; edited 1 time in total
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LektroiD



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PostPosted: Fri Oct 19, 2012 11:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Mongo1 wrote:
If you used film capacitors in the oscillator core, you may have overheated them while soldering. They're very easy to damage, and I've had them do exactly what you're talking about - start out fine, and then get 'sick' over time. Just a thought...
Good luck

Gary


I used 'Wima' red box capacitors, would they become faulty/leaky?

Maybe I'll swap them out anyway.

Which capacitors are most likely to stabilise the pitch on these oscillators?

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elmegil



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PostPosted: Sat Oct 20, 2012 6:19 am    Post subject: Reply with quote  Mark this post and the followings unread

I meant the audio path, not the power supply.

I would start with caps closer to the output and pull back. I'm assuming those are the output waveforms, do you have anything any better if you probe closer in to the oscillator core or within the oscillator core?
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Mongo1



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PostPosted: Sat Oct 20, 2012 6:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
I used 'Wima' red box capacitors, would they become faulty/leaky?

Maybe I'll swap them out anyway.

Which capacitors are most likely to stabilise the pitch on these oscillators?



I haven't used that exact type before, so I'm not sure if they have the same problem. The little silver tootsie-roll film caps are very sensitive. One trick for those is to attach an alligator clip between the caps body and solder point to act as a heat-sink when you solder.

I'm not sure if that applies with the redbox type, but it might be worth swapping them out. Couldn't hurt....

Gary
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elmegil



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PostPosted: Sat Oct 20, 2012 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

So thinking about the "over time" aspect ... What kind of solder did you use? Did you clean the board when you were done? Is it possible that flux has caused bridges to areas that will cause trouble?
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LektroiD



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PostPosted: Sun Oct 21, 2012 2:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Mongo1 wrote:
Quote:
I used 'Wima' red box capacitors, would they become faulty/leaky?

Maybe I'll swap them out anyway.

Which capacitors are most likely to stabilise the pitch on these oscillators?



I haven't used that exact type before, so I'm not sure if they have the same problem. The little silver tootsie-roll film caps are very sensitive. One trick for those is to attach an alligator clip between the caps body and solder point to act as a heat-sink when you solder.

I'm not sure if that applies with the redbox type, but it might be worth swapping them out. Couldn't hurt....

Gary


If I'm right, I think you're referring to polystyrene, like these:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

I didn't use those in my build, I used mainly this type:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Maybe the ones I used are the wrong type for this build...?

I'll have a go at swapping them out, but to be honest, I'm probably heading towards digital oscillators now. Analogue ones are evidently too unstable to rely on.

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LektroiD



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PostPosted: Sun Oct 21, 2012 3:06 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
So thinking about the "over time" aspect ... What kind of solder did you use? Did you clean the board when you were done? Is it possible that flux has caused bridges to areas that will cause trouble?


I use 60/40, I can't get on with lead-free stuff, it just doesn't flow like 60/40. I've been using that for years with no problem, I've retouched all the joints, but doesn't seem to have cured anything.

I always clean my boards with isopropyl alcohol and a toothbrush after they're built, so there's no flux residue.

I'm clueless as to what it could be really... If I can't get to the bottom of this, I think I'm going to see about sourcing some digital oscillators (suggestions?). Seems analogue are too troublesome, but then that is common knowledge anyway.

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fonik



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PostPosted: Sun Oct 21, 2012 5:38 am    Post subject: Reply with quote  Mark this post and the followings unread

the effects you experience are too heavy to be realted to just the capacitor type.

BTW did you replace the 4046 allready? or replace the pots? did you re-heat all solder joints related to the expo and the 4046?

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fonik



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PostPosted: Sun Oct 21, 2012 5:39 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
It looks to me like you've got some kind of extra capacitance on the line, dragging you back to ground. All the waveforms are exhibiting it.

yep. there is a slope added to all waveforms.

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PostPosted: Sun Oct 21, 2012 6:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry if my questions about flux are things you've known how to deal with for ages, just trying to brainstorm for ideas....
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LektroiD



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PostPosted: Sun Oct 21, 2012 10:08 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
Sorry if my questions about flux are things you've known how to deal with for ages, just trying to brainstorm for ideas....


Of course. I'm really looking forward to getting this back on the road, so please don't apologise. It's sometimes easy to miss the obvious, so every suggestion is very much appreciated.

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PostPosted: Sun Oct 21, 2012 1:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

check the value of C3 and how it is soldered in
should be .01uf
less likely but also possibly relevent did you use LF442 for IC2 ? or just a TL072
LF442 has substantially better offset specs

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PostPosted: Sun Oct 21, 2012 5:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Did you try removing the coarse tune pot from the circuit? also try removing the fine tune after that. Use DC offset to get it to an audible pitch.. or try 100k trimmers.

sounds like bad pots.

did you try PUSHING on the knob of the pot? So push down as if you were trying to force the knob further on the shaft. See if that affects the pitch deviation. Give it a push pull push pull to see if you hear the pattern.
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LektroiD



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PostPosted: Mon Nov 05, 2012 9:56 am    Post subject: Reply with quote  Mark this post and the followings unread

That's another one just gone down (same symptoms), I only have one oscillator left now. At this rate it won't be long before my synth is kaputt.

I'll try swapping pots, I just used cheap Alphas. Wiggling them in or out makes no difference, but I'll swap them out and report back...

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Benjamin AM



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PostPosted: Mon Nov 05, 2012 12:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD: Just out of curiosity, what are you using for a power supply?
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