fun with the SID-Mod-Matrix :-p

[Julian]

hello :)

finally I've got MY SID CS running (so now entering final debugging stage)! it's soooo great to tweak the sound with encoders finally! ^^

but my Mod-Matrix behaves strange.

when no modultion is selected, the sid is very quiet... no humming or so.

but the more lights on the Matrix I activate, the more noise is heard on the audio out.

the funny thing is, its not only a humming thats gettig louder, it's more like a simple additive OSC *G*

every row got a slightly different humming and the more leds in a row are lit the louder the sound gets...

you can even set something that sounds like some kind of chord out of this noise...

but don't get me wrong, i don't like this noise at all and would love to get rid of it... ;)

any ideas?

so long,

julian

PS: I love holliday! finally enough time for the MIDIbox projects (but for nothing else ;)

[moebius]

Hi,

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?

[Julian]

with the encoders i've got no clue...

even the detented one isn't working propperly... tried again several speed values and encoder modes :-p

i replaced all but the menu one with voti encoders meanwhile :-p but they feel and behave much better, so it was worth the work!

for EMI:

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 ;)

but first i've got to improve my psu... it's getting too hot :-p

and for the end of the message a good news:

just got my second core and sid working ^^ *yeaih*

so just some cosmetic changes left over and the EMI problem...

so ong,

julian

[moebius]

for EMI:

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*

Great ;D

Bye, Moebius

[Julian]

this is the PSU I use...

greetings,

julian

[moebius]

Oh,

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.

See: http://69.56.171.55/~midibox/forum/index.php?topic=4074.msg26593#msg26593 for TK's (or originally KDs) suggestion for on-board bypass caps..

Bye, Moebius

[Julian]

I just started with SDIY buisness about summer last year! before I had no idea of electroics ;)

I've go the PSU schematics from http://www.elektronik-kompendium.de  ;)

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)

so long,

julian

[moebius]

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 ;)

Bye, Moebius

[Julian]

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?

best,

julian

[TK.]

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)

Best Regards, Thorsten.