davidv Posted October 2, 2006 Report Share Posted October 2, 2006 Hello. First thanks to TK, smashtv and everyone who contributed all their time and knowledge in this desing. Im an electronic "tourist", but a 10+ years c/c++ programmer, still with all the docs I didnt have much trouble getting this to work. Ive read a bunch of old posts, but when i backtracked to early 2005 i felt lazy after :)(maybe a sticky/FAQ for most common PSU issues might be apropriate?)So ok. I love my box, sounds great, and in my opinion the current S/N ratio i get is JUST fine:-Highest peak freq is 60 Hz @ -77dB when no note has been already played, and after that,no need to calculate, the 6581 (CBM-R3) bug is just all too evident and way higher than the previous noise floor.The catch? Im using TWO SEPARATE walwarts, a 12VAC/1.2A for the sid and a 9vdc/500ma for the core.like many people i have boxes of walwarts to choose from.So its a pain to hook up, But again, i would rather not spend more time and canibalise and hack a C64 PSU, even if everyone says the output will be much better. (in my case im not convinced).Id rather get on with my FM or other MIDIBOX128 hack i have planned.Ok so if i unsderstand correctly, theres no chance i could use the 12VAC/1.2A for both the core(+smashtv lcd) and SID, without having to do as much work as the C64optimised hack? If yes, if a big ass heat sink required for the regulator? What kind of ground loop avoidance trick i could easily use?Otherwise ill just place the two wallwarts ripped open in my 1U rack, and feed them off the same 3-prong power socket Anybody did that? You think the Heat inside the rack mount will be too much for the poor components?Cheers Quote Link to comment Share on other sites More sharing options...
Altitude Posted October 2, 2006 Report Share Posted October 2, 2006 Ok so if i unsderstand correctly, theres no chance i could use the 12VAC/1.2A for both the core(+smashtv lcd) and SID, without having to do as much work as the C64optimised hack? If yes,if a big ass heat sink required for the regulator?What kind of ground loop avoidance trick i could easily use?using the 12VAC for both the sid and core should be fine. Just put a big ol heatsink on the 7805 since it will get pretty hot.Using the c64 is not really a hack, it really solves alot of the PSU issues since it has both 5 VDC and 9VAC which is plenty for all your power needs Quote Link to comment Share on other sites More sharing options...
davidv Posted October 3, 2006 Author Report Share Posted October 3, 2006 using the 12VAC for both the sid and core should be fine. Just put a big ol heatsink on the 7805 since it will get pretty hot.Ok, but what about the wiring?Just Y-splitting each pole of the PSU towards the J1's of the core and SID?I havent completely understood the possible ground loop issues here, but it rings a warning bell in my head. Quote Link to comment Share on other sites More sharing options...
Mr modnaR Posted October 3, 2006 Report Share Posted October 3, 2006 a ground loop problem occurs when you have a literal loop in the ground wire. basically it acts as an aerial, and subsequently adds noise to your audio circuits. i'm sure there are other disadvantages too.you can run two lengths of two wires along to the sid modules and the cores, although y-splitting for each core/sid is a little excessive.hope this helps. Quote Link to comment Share on other sites More sharing options...
davidv Posted October 4, 2006 Author Report Share Posted October 4, 2006 a ground loop problem occurs when you have a literal loop in the ground wire. basically it acts as an aerial, and subsequently adds noise to your audio circuits. i'm sure there are other disadvantages too.you can run two lengths of two wires along to the sid modules and the cores, although y-splitting for each core/sid is a little excessive.hope this helps.Sharing the same PSU did create a ground loop. So i reverted. only one final bug and i can close my 1U Rack... Quote Link to comment Share on other sites More sharing options...
Mr modnaR Posted October 5, 2006 Report Share Posted October 5, 2006 how? ??? Quote Link to comment Share on other sites More sharing options...
davidv Posted October 5, 2006 Author Report Share Posted October 5, 2006 how? ???Im clueless on anything not code related :) Quote Link to comment Share on other sites More sharing options...
davidv Posted October 5, 2006 Author Report Share Posted October 5, 2006 Hi.The only thing left to solve in my setup is that when the LCD is hooked in my core, there is a certain amount of hum that creeps in the analog output of the SID.1)The higher the brightness of the LCD (with the panpot), the worse it gets. 2)The core randomly resets when i wiggle the panpot as well.3)I have two LCDs (one from smashTV and antother generic 2x16 savlaged from the 1U rack im using. Both cause hum with various degrees, but its worse with the generic.Do i have some weirdo short in my bord?My core's PSU (independent of the SID) is 9v 500ma .. is 500ma not enough for a Core+LCD?At this point im thinking of adding a front panel switch to turn off the backlight of the LCD.I will also prepare my second SmashTV core and swap it with my old one as a test. Quote Link to comment Share on other sites More sharing options...
Mr modnaR Posted October 5, 2006 Report Share Posted October 5, 2006 what do you mean by: "Sharing the same PSU did create a ground loop. So i reverted."? Quote Link to comment Share on other sites More sharing options...
Mr modnaR Posted October 5, 2006 Report Share Posted October 5, 2006 i would say 500mA is not enough. LCD backlights vary, but they usually draw around 250-450mA. you have to then add on what the core draws, not forgetting any LEDs on the control surface, if you have any. Quote Link to comment Share on other sites More sharing options...
Altitude Posted October 5, 2006 Report Share Posted October 5, 2006 yea, i dont get that, the boards should be grounded toghether Quote Link to comment Share on other sites More sharing options...
TK. Posted October 5, 2006 Report Share Posted October 5, 2006 It could also be that your PSU works out-of-spec, means: the output voltage already sinks even when the circuit draws less than 500 mA. A better PSU helps to reduce the hum significantlyBest Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
TK. Posted October 5, 2006 Report Share Posted October 5, 2006 (I've merged the two articles in order to avoid, that people miss the new findings)Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
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