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



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PostPosted: Mon Nov 05, 2012 1:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
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...


as you replace pots, first replace the coarse tune with a 100k trimmer. it's very easy, and you can desolder after you're done with it.

you know I removed coarse tune pots from all my oscillators for this very reason. I plan on not having even a trimmer there, but just a fixed resistor. Indeed my X-4046 VCO does NOT have a coarse tune.
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fonik



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PostPosted: Mon Nov 05, 2012 3:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
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.

obviously there is something completely going wrong! it is not a faulty part here and there, but a general issue. and it might be specific to your VCO builds or do you experience any downgrading on the other modules?

are all VCOs powered from the same PSU?

did you any measurements following the control voltage path to find out if it is due to the expo, or related to the 4046 itself?

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LektroiD



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PostPosted: Mon Nov 05, 2012 4:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

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


I use the MFOS wall wart supply independent from the rest of the synth, solely driving the 4 oscillators. It's not the PSU, as I get the same results running off my bench.

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elmegil



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PostPosted: Mon Nov 05, 2012 6:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

But is it possible the PSU is doing something to hose the modules? At which point you'll get the same results anywhere....
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LektroiD



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PostPosted: Mon Nov 05, 2012 7:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
But is it possible the PSU is doing something to hose the modules? At which point you'll get the same results anywhere....


If I get the same results off any PSU, it's clearly not a PSU issue...

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elmegil



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PostPosted: Mon Nov 05, 2012 9:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think I must be being unclear.

This is what I mean to propose as a hypothesis:

Let's say I have a handful of modules hooked up to a power supply that is behaving badly. Eventually, each of the modules in turn gets screwed up by that power supply. When I hook a screwed up module to other power supplies, it's still screwed up. But it's still the fault of the original power supply.

Unless you mean that you have one or more of the 4046 modules that has never been hooked to the wall wart supply, and they've gone bad too?
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LektroiD



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PostPosted: Mon Nov 05, 2012 9:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
I think I must be being unclear.

This is what I mean to propose as a hypothesis:

Let's say I have a handful of modules hooked up to a power supply that is behaving badly. Eventually, each of the modules in turn gets screwed up by that power supply. When I hook a screwed up module to other power supplies, it's still screwed up. But it's still the fault of the original power supply.

Unless you mean that you have one or more of the 4046 modules that has never been hooked to the wall wart supply, and they've gone bad too?


Interesting hypothesis, I see your point now. Maybe worth swapping out the power smoothing electrolytics on the 4046 PCB, see if that cures it (I'm hoping it's something as simple as that)...

To be honest, I was never too fond of the WW PSU's, I just wanted an independent supply for stability. There's an irony in there somewhere...

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Argitoth



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PostPosted: Mon Nov 05, 2012 10:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

My theory still stands. Bad pots can go bad slowly, and replacing a bad pot with another bad pot (meaning your entire batch is bad) will only fix the problem temporarily and not 100%. But then I don't have enough experience to say whether an entire batch of pots can be bad or if a specific company is bad. I was having problems with cheap alpha pots (that I did not get from mouser). I am skeptical of alpha pots now.

LektroiD, where did you buy these "cheap" alpha pots? Maybe you purchased the same ones I did?
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LektroiD



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PostPosted: Mon Nov 05, 2012 10:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Argitoth wrote:
My theory still stands. Bad pots can go bad slowly, and replacing a bad pot with another bad pot (meaning your entire batch is bad) will only fix the problem temporarily and not 100%. But then I don't have enough experience to say whether an entire batch of pots can be bad or if a specific company is bad. I was having problems with cheap alpha pots (that I did not get from mouser). I am skeptical of alpha pots now.

LektroiD, where did you buy these "cheap" alpha pots? Maybe you purchased the same ones I did?


I was thinking of testing the value of the pot at an audible frequency, then substituting for a fixed resistor to see if that stabilizes it. I got them from Rapid... My whole synth is full of them, but I guess for most applications it is not critical. that said, I've not noticed any nuances in any other modules.

If that does cure it, I may think about replacing the pot with a rotary octave switch. That would be infinitely more useful and hopefully less troublesome. I'll use the remaining working oscillator to find the fixed resistor values for each octave (unless someone has already done this)...

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Argitoth



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PostPosted: Mon Nov 05, 2012 11:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok. i got mine from futurlec. http://futurlec.com/PotRot.shtml

anyway, i'm not the best person to take advice from. this will be my last post to this thread.
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LektroiD



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PostPosted: Thu Dec 06, 2012 2:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, I have managed to stabilise one by replacing the power electrolytics (at least it looks ok on the scope for now)... I'm wondering, Can I put a higher value electro-cap in place of the 10µF (say 100µF)? Would that be more robust against dirty power, or would a higher voltage tolerance prove more robust? I currently use 10µF, 63V.

Anyway, the other issue still seems evident (particularly noticable on the triangle - I've only tested that and the saw so far). I still seem to have those rogue tails, as pictured below - are they normal?


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fonik



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PostPosted: Thu Dec 06, 2012 2:30 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
Ok, I have managed to stabilise one by replacing the power electrolytics (at least it looks ok on the scope for now)... I'm wondering, Can I put a higher value electro-cap in place of the 10µF (say 100µF)? Would that be more robust against dirty power, or would a higher voltage tolerance prove more robust? I currently use 10µF, 63V.

100uF would be okay also, gives you another filter band.
you said you already replaced the electrolytics. did you use another value, too? did you buy these elecs new, or are thay old stock?
BTW the voltage limit does not matter.

Quote:
Anyway, the other issue still seems evident (particularly noticable on the triangle - I've only tested that and the saw so far). I still seem to have those rogue tails, as pictured below - are they normal?

no, not normal.

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LektroiD



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PostPosted: Thu Dec 06, 2012 2:47 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
LektroiD wrote:
Ok, I have managed to stabilise one by replacing the power electrolytics (at least it looks ok on the scope for now)... I'm wondering, Can I put a higher value electro-cap in place of the 10µF (say 100µF)? Would that be more robust against dirty power, or would a higher voltage tolerance prove more robust? I currently use 10µF, 63V.

100uF would be okay also, gives you another filter band.
you said you already replaced the electrolytics. did you use another value, too? did you buy these elecs new, or are thay old stock?
BTW the voltage limit does not matter.


Ok, I'll stick in 100µF, see if that helps, or works any better... They are new (within a year old)

Quote:
Quote:
Anyway, the other issue still seems evident (particularly noticable on the triangle - I've only tested that and the saw so far). I still seem to have those rogue tails, as pictured below - are they normal?

no, not normal.


Hmm, question is, what would cause it, and how to sort it? Maybe the bigger power caps might solve it. I'll report back once they are in...

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LektroiD



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PostPosted: Thu Dec 06, 2012 7:15 am    Post subject: Reply with quote  Mark this post and the followings unread

I tried 100µF electro caps, but didn't really make any difference... As for stability, it is no longer jumping all over the place, but there are slight fluctuations over time. I can see the movement on my scope, but I need to get it up on a frequency counter to see how serious it really is..

Still no idea what causes the spikes...

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LektroiD



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PostPosted: Thu Dec 06, 2012 6:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, I've had this running on my bench all day, and on the bench PSU it has gone back to the random pitch problem. So, there is a problem somewhere in the power circuitry, but it doesn't appear to be the PSU causing it.

So, replacing the 10µF electro-caps solved the problem temporarily, but what could cause it to go back to the random pitch issue?

These are my main oscillators, without them, I have no synth. I need to either get to the bottom of this fault, or find some new oscillators soon.

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diablojoy



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PostPosted: Fri Dec 07, 2012 12:27 am    Post subject: Reply with quote  Mark this post and the followings unread

check very carefully your supply ground for any stray voltage also any slight resistance on this path it sounds as though your ground may be floating.
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fonik



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PostPosted: Fri Dec 07, 2012 2:12 am    Post subject: Reply with quote  Mark this post and the followings unread

good advice!
and if you experience differences in performance whenever you move it around, it could be a slack joint somewhere.

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PostPosted: Fri Dec 07, 2012 4:56 am    Post subject: Reply with quote  Mark this post and the followings unread

I've checked the ground for continuity on one and it seems sound, but It's exactly the same on all 4 of my builds - what's the chances of all 4 exhibiting the same grounding problem?
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PostPosted: Fri Dec 07, 2012 6:22 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
I've checked the ground for continuity on one and it seems sound, but It's exactly the same on all 4 of my builds - what's the chances of all 4 exhibiting the same grounding problem?

maybe the WW/MFOS PSU has. or your distribution scheme. i don't know what you have there exactly...

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PostPosted: Fri Dec 07, 2012 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
LektroiD wrote:
I've checked the ground for continuity on one and it seems sound, but It's exactly the same on all 4 of my builds - what's the chances of all 4 exhibiting the same grounding problem?

maybe the WW/MFOS PSU has. or your distribution scheme. i don't know what you have there exactly...


Both the MFOS PSU and my Bench PSU? As I said in my last few posts, the current tests were done on my Bench PSU.

So, 4 different Oscillators, tested on 2 different power supplies, all exhibiting the same fault. Something is causing those power caps to fail within 12 hours of use. Nothing else on my synth has failed over time like this. Why the oscillators?

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fonik



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PostPosted: Fri Dec 07, 2012 11:28 am    Post subject: Reply with quote  Mark this post and the followings unread

scratch
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Blue Hell
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PostPosted: Fri Dec 07, 2012 12:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is there a schematic for this somewhere publicly viewable?

When changing the 10 µF capacitors cures the problem but it comes back after a while .. what is the voltage rating for the capacitors and what voltage are they working on?

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fonik



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PostPosted: Fri Dec 07, 2012 12:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

hi jan, thanks for chiming in.

the schematic an be found at scott's site (he used to host thomas' projects):
http://www.birthofasynth.com/Thomas_Henry/Pages/X-4046.html

the voltage rating of electrolytics should be double the supply voltage for a longer life ofthe caps.
what i got is that LektroiD used 63V rated...maybe i was wrong?

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PostPosted: Fri Dec 07, 2012 12:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
what i got is that LektroiD used 63V rated...maybe i was wrong?


Ah ok, I did read back a bit but missed it apparently.

They are not put in backwards either? Some electrolytics have confusing polarity indicators.


And thanks for the link Smile

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Blue Hell
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PostPosted: Fri Dec 07, 2012 1:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Regarding the overshoot on some of the wave forms .. that seems to be by design ... http://www.birthofasynth.com/Thomas_Henry/Pages/X-4046.html#Forming_The_Triangle_Wave .
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