4046 Oscillators progressively getting worse over time

elmegil · Posted: Mon Nov 05, 2012 6:51 pm Post subject:

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

LektroiD · Posted: Mon Nov 05, 2012 7:15 pm Post subject:

elmegil · Posted: Mon Nov 05, 2012 9:32 pm Post subject:

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?

LektroiD · Posted: Mon Nov 05, 2012 9:54 pm Post subject:

Argitoth · Posted: Mon Nov 05, 2012 10:13 pm Post subject:

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?

LektroiD · Posted: Mon Nov 05, 2012 10:28 pm Post subject:

Argitoth · Posted: Mon Nov 05, 2012 11:23 pm Post subject:

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.

LektroiD · Posted: Thu Dec 06, 2012 2:12 am Post subject:

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 · Posted: Thu Dec 06, 2012 2:30 am Post subject:

LektroiD · Posted: Thu Dec 06, 2012 2:47 am Post subject:

LektroiD · Posted: Thu Dec 06, 2012 7:15 am Post subject:

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...

LektroiD · Posted: Thu Dec 06, 2012 6:30 pm Post subject:

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.

diablojoy · Posted: Fri Dec 07, 2012 12:27 am Post subject:

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.

fonik · Posted: Fri Dec 07, 2012 2:12 am Post subject:

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

LektroiD · Posted: Fri Dec 07, 2012 4:56 am Post subject:

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?

fonik · Posted: Fri Dec 07, 2012 6:22 am Post subject:

LektroiD · Posted: Fri Dec 07, 2012 10:17 am Post subject:

fonik · Posted: Fri Dec 07, 2012 11:28 am Post subject:

Blue Hell · Posted: Fri Dec 07, 2012 12:31 pm Post subject:

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?

fonik · Posted: Fri Dec 07, 2012 12:39 pm Post subject:

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?

Blue Hell · Posted: Fri Dec 07, 2012 12:56 pm Post subject:

Blue Hell · Posted: Fri Dec 07, 2012 1:06 pm Post subject:

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 .