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Standard behaviour of Darkstar Chaos or somethng wrong?
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Author Standard behaviour of Darkstar Chaos or somethng wrong?
I just received a 2nd hand Darkstar Chaos module. Got some wicked sounds out of it but noticed this not so nice clicking/clipping/glitching sound which rather spoils the fun. Is this normal or is there something wrong?
You're hearing just the VCO without any additional patching, noise to zero.

edit: it's been modified to MOTM format so maybe it has something to do with voltage difference???
AFAIK there shouldn't really be any voltage differences between Blacet and MOTM...

That's odd though, my DSC doesn't do that, so something is definitely up. hmmm.....
my DSC doesn't do that either. it does some weird stuff, but weird stuff that it's SUPPOSED to do.
I don't have a Darkstar any more so no access to the schematic. However it sounds like it could be the noise clock leaking through. Just a hunch.
Thx for the answers guys. The seller says he never noticed it and it might be normal behaviour. He also advised to mail Blacet about it which seems fair enough.
Will report about the results here also.
Liquidcolor wrote:
I don't have a Darkstar any more so no access to the schematic. However it sounds like it could be the noise clock leaking through. Just a hunch.

I'm pretty sure he's right, I tried to replicate your problem, and by just nudging the noise filter a little bit, it sounded very similiar to the file you posted.
Tim Stinchcombe
I can replicate that on mine almost exactly, so I would go so far as to say it is 'normal behaviour', albeit dependent on component tolerances etc. (and I'll add straight away I'm not that familiar with this module, and I also built mine up from a bare PCB).

If I turn 'noise clock' and 'noise filter' all the way to zero (fully CCW) I only get the raw VCO sound out, no glitching. As I then turn 'noise filter' clockwise, at first it starts to warble, then as it gets more clockwise it starts turning to a very glitchy sound, very similar to your sample, only running much faster. I then decided to slow the noise clock down with a negative input CV (pot still fully CCW), and when I do, the glitching slows down to the point where it sounds near-identical to your sample. I've tried to show this in the attached: where I start turning the noise filter is obvious; I start decreasing the noise clock (with the negative voltage) somewhere around 20 seconds. The pot doesn't need to be far around for the glitching to stop entirely (about -0.7V in).

thanks a lot, now I know for sure it should at least be possible to get a clean VCO sound. I hope it can be repaired easily.
nodog wrote:
thanks a lot, now I know for sure it should at least be possible to get a clean VCO sound. I hope it can be repaired easily.

Hi, DSC's have been around a long time. Is it an older one? If so, re-capping will likely fix it. Simple. (Electrolytic capacitors involved in timing or power supply filtering go out of spec over time. Either/both seem likely to be the source of your problem here. Tim's higher speed glitch would point toward this too IMO.) Kind regards, Randal
Tim Stinchcombe
Having had a slightly more leisurely look at the circuit than I had time for this morning, several possibilities exist. The 'noise clock' is the VCO in a 4046 PLL chip, and slowing it down to decrease the frequency of the glitches could be done in three ways: increase the timing cap (C4, spec'd at 2nF - I have a 2n2 fitted); increase resistor R26 (say doubling it, to 22k); or decrease the control voltage (effectively what my negative input did) - there is a positive offset added to this, which could be reduced by increasing R8 (again, perhaps doubling it to around 150k-180k say). This will of course decrease the max frequency overall, which might have an impact on some of the higher frequency noise effects (?).

I have little idea of the internal architecture of the SN76477 chip, but the glitches seem to mostly occur on the falling edge of the noise clock, but sometimes when running really slow it doesn't seem to produce an audible effect at all. Thus whether the effect is coming from within the chip itself, or some sort of coupling on the board, I wouldn't like to say.

Scott Stites
Because the previous owner didn't notice this behaviour and it now occurs, be sure to carefully check any socketed parts to make sure they are seated. Because a lot of the functions (including the noise filter) of the SN76477 are current controlled, a slight mis-seating can cause this sort of thing.

I'm not sure if the MOTMized DSC connects to the PCB with flying leads instead of board mounted pots, but if it does, inspect the wires going from the pots to the PCB, and the associated pads on the DSC PCB. Shipping a module could lead to something not quite making a solid connection.

Barring the above:

I'm assuming that if you leave the DSC with the settings you've described, but then increase the noise frequency, the noise goes away?

If the noise doesn't go away, but fully modulates the VCO while the noise filter is turned all the way down, the obvious path to investigate would be the noise filter control circuitry.

I'm assuming that isn't the case, mainly because you have a second DSC you're quite familiar with, and would have noticed that. The reason I ask is that I can see examing a scope trace of your sample, the oscillator frequency dips down on one edge of the glitch cycle and up on the next edge of the cycle, which is the same effect the noise signal will produce if the filter is cranked open.

Anyway, in the case the noise goes away when you crank up the noise frequency with the noise filter control turned all the way down, it would be as Tim says - coupling, possibly on the power supply lines.

Without going into a public discussion of the circuit, you may want to check the voltage regulation primarily of U8 more so than U10 (though don't discount U10) and associated capacitors, particularly C9.

If you suspect U8, and both of your DSC's have socketed parts, I would suggest carefully swapping U8 from one to the other to see if the behaviour follows. That would tell you a lot about the most vital part of your DSC. If that happens to be the cause, I know a source for a replacement, though it may not be the same size, it would still work.

Good luck and cheerios,
Big thanks for the useful replies. I'm sending the module in for repair with a link to this thread.
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