MBSID clicking

[H2O]

Hi everyone!

Got an issue with my new MBSID that I'd like advice on.  I got a bunch of kits from SmashTV and some 6582s from Wilba (thanks guys!).  2 SIDs are hooked up and making sound (very exciting), with 6 more to come.  Trouble is, they're making too much sound!  I'm getting some strange (and annoying) low-pitch clicks during note-on and note-off.

I've attached a picture which shows the click waveforms.  I tried using several oscillators and no oscillators (via NRPN 32) and it's always there.

My best guess is that it has something to do with my PSU.  I couldn't find a C64 power pack, so I put one together myself.  I was surprised that it actually worked at all!  ;D  I'm just using a DC adapter power pack, thought I would get all sorts of nasty hiss and hum from it, but it seems work quite well.  It's running at around 14V, with 7809s on each of the SID boards and a low-noise DC-DC converter dropping it down to 5V for the core electronics.  The thing is, there are no capacitors at all to speak off.  I've haven't got much of an idea when it comes to power supplies, but the waveforms suggest to me that I need a voltage buffer of some sort.  My multimeter isn't telling me much, except perhaps for a very small voltage drop in the power adaptor whilst the note's down.

So my questions to the MidiBox experts are:

1) Could capacitors help with this (am I even on the right track?)

2) If so, what capacitors would be recommended?

Thanks.

[stryd_one]

I looked at the pics first and went "look at all that DC shift..that's not just the env bug" then read the post...

The thing is, there are no capacitors at all to speak off.

Ahh that might explain it :)

I don't know a lot about these things but I do know that caps are used as DC filters in a PSU. I think that might be the electrolytic caps' job but I'll let someone with a clue tell us both :)

Hmm...have you grounded the SID inputs?

[H2O]

Hmm...have you grounded the SID inputs?

Yep, all grounded.

I'll have another check over all the grounding though.

EDIT:

Grounding all seems good.  Audio out 'ground' is up by around .01V, grounding that out doesn't help the problem though.

I do notice a very slight drop in the input voltage whilst the synth is playing; but then it has quite a large natural drift anyway...  :-\

[bugfight]

...just the env bug" ...

mmmmm bug envy

The thing is, there are no capacitors at all to speak off.

you did stuff the caps for the voltage regulators, right?

use that scope on your psu input, the input to each regulator, and the output of each regulator...

[H2O]

you did stuff the caps for the voltage regulators, right?

Yeah, sorry should have mentioned.  The caps for the 7809s are in as per the SID modules.  The caps for the CORE module are also in, even though the 7805 is bypassed.

use that scope on your psu input, the input to each regulator, and the output of each regulator...

The scope I was using (screenshot above) was just a recording through my sound card, I don't have a proper scope.  (Would it be safe to plug the 14V power supply into my sound card?)

Also, I've tried 2200uF, 10uF and 330nF caps (individually) between 14V and 0V, with no change in performance.

[Foona]

Im not an expert...but i still don't think you should plug 14v into your soundcard.

And youv'e stated that you've "tried 2200uF, 10uF and 330nF caps (individually) between 14V and 0V, with no change in performance."

Did you mean youv'e just tried using the caps and then removed them,

or that these capacitors are still installed?

[buhler]

i get a small click as well with my MbSid but i'm using 6581's and i've tested 10 different ones in my box.  most of them don't click but it just so happened that one of the two that matched (filter, clip etc..) had the "click."  i don't know about 6582's as i haven't received mine from wilba yet but i assume that clicking is just  a "chip-trait" that these Sids have.  i don't think you can really do a whole lot about it.

[TK.]

The "click" happens since the DC offset changes at the audio output whenever different waveforms or filter modes are selected. With 6581, this effect is more dramatical than with 6582/8580.

Unfortunately different volume values cause a DC offset change as well, otherwise MBSID could simply fade out/in the volume whenever a new patch is selected...

Best Regards, Thorsten.

[H2O]

Thanks for your help everyone!  It's reassuring to know I haven't just stuffed it up somewhere.  ;D

The default patch generally sounds great, it's only when I start mucking around with the sound it that the clicking becomes audible.  A bit of reverb, EQ, delay and a drum beat tend to drown out the click anyway ;).  Once I get the control surface working properly and install some backsticks, I'll have a go at all the sound parameters, that may improve performance as well, or just make it less noticable.

(I might also have a look at the midi stream, make sure my sequencer's not doing anything weird with volumes, controls and such...)

Will keep you posted if there's any changes or I make any startling discoveries, but for now it all looks good.

Did you mean youv'e just tried using the caps and then removed them, or that these capacitors are still installed?

I installed one, noticed no change in performance, then removed it and tried the next.  I've now just gone back to my original design.