It’s probably DOUT updates switching bleeding thru to audio output somehow.. To rule out EMI (Electromagnetic Interference) - While MB is running (and your listening to the noise), try moving core and SID boards as far as you can from DOUTs/LEDs and/or change the angle, how these are fitted towards DOUTs/LEDs.. (Sorry. it’s hard to explain, but if it’s EMI, you should hear noise levels/sound change as boards are moved - This should be easily tested)
What kind of Power Supply are you using?
A more probable cause is switching transients from DOUT chips making supply rails noisy. This could (?!?) be cured by adding Bypass Caps to DOUTs between the rails as close as possible to 74HC595 supply pins.
Bye, Moebius
p.s. Hey - Did you find out what was the problem with the encoders?
the leds and dout pcb’s are on the right side in my case and the core and sid are on the left side… about 20-30 cm between them.
even if i lift the frontpanel the noise is as loud as before…
maybe i’ll make some experiments with some alu foil as shield
It probably doesn’t make things worse.. but now I think it’s the power rails. I’d start by adding few caps between DOUT power traces.. If you have any in hand, you could give that a try.
and for the end of the message a good news:
just got my second core and sid working ^^ *yeaih*
I forgot that your’re in SDIYing business.. ;D Quite nice PS, it will power your SIDs with no problem.. (I guess you have underestimated the output current on purpose?!) If the regulators are getting hot, just heatsink 'em.
what do you mean with undererstmated current? isn’t 1A enough? (cause my regulators are getting REAL hot! I installed a real big heatsink yesteray, now it works)
I just started with SDIY buisness about summer last year! before I had no idea of electroics
You’re making a good progress! (I’m not.. :'()
what do you mean with undererstmated current? isn’t 1A enough? (cause my regulators are getting REAL hot! I installed a real big heatsink yesteray, now it works)
You underestimated how much current that PS CAN supply. Regulators are getting hot, because they have to spend “excess” voltage from input somehow, so they dissapate it as a heat. LM3*7’s are more that a step above typical LM78**/79** regulators. Those are designed to supply more that 1,5Amps, and maybe in your PS with big heatsinks and not too big input voltage it’s more than 2Amps
I just refered to the datasheet I have for the LM3*7’'s and it says they can handle about 1,5-2 A …
the LM3*7 are not as hot as my LM7808 supplying my cores (godda find better solution for this… mayber a 2nd transformer…)
anyway I’ve got a bad humming in the background, much too loud to ignore… :-p
godda improve my wiring I think!
about my progress in SDIY: yes, but i had very much ime in the last year and if you don’t at and sleep, because you have to solder you learn quick! *hrhr*
what are you doing besides midibox projects, moebius?
You will propably notice big improvements when the +5V/ground input of the SID modules are directly connected to the +5V/ground output of your PSU, and to to port J10
Also adding a 100 uF cap to the voltage input of each DOUT module + 100 nF cap to each IC can improve the audio signal in addition (but this measure alone doesn’t help)
