fadedpaper Posted October 7, 2010 Report Share Posted October 7, 2010 Hello, I built my MBSID a couple years ago and never got it working perfectly. Now it's driving me crazy and I would like to get to the bottom of this. I'm having 2 main issues and I don't know enough about electronics to even guess where to start looking for solutions. 1) There is a constant loud buzzing around 120hz. 2) When I change patches or turn the unit off, there is this EXTREMELY loud, falling high pitch sound. Imagine a C64's version of a cartoon bomb being dropped. I've attached sound clips of both issues I'm having. Be careful with the file called "turn on, play, turn off" because the turn off sound I'm talking about is very loud! Keep your volume down when listening to that one. Note I am not touching the gain at all on any of these sound clips, but the volume of the SID's output seems to fluctuate a little right when I first turn it on. As if it has to charge up or something. I think I built the SID V3, and I used a kit from smashTV that says SID R3A and core R4D. It's only got a single SID 6581 chip in there. Anyone got any ideas how a total newb like myself can get this thing working properly? Thanks. constant noise.mp3 turn on, play, turn off.mp3 Quote Link to comment Share on other sites More sharing options...
Shuriken Posted October 7, 2010 Report Share Posted October 7, 2010 What type of PSU are you using? Quote Link to comment Share on other sites More sharing options...
fadedpaper Posted October 7, 2010 Author Report Share Posted October 7, 2010 It's the original C64 power brick. Quote Link to comment Share on other sites More sharing options...
Wilba Posted October 8, 2010 Report Share Posted October 8, 2010 It could be PSU related, but also, 6581 SIDs are notoriously noisy. How exactly are you powering the SID module (i.e. circuit)? I'm assuming you are using an 78L12 voltage regulator on the module (for 6581 SIDs). What is the voltage going into the 78L12? and what voltage going out? (should be 12V). Test these on startup, when you are experiencing low volume... maybe you can observe the voltage being lower than expected. Have you connected the audio in to ground on the SID module? This is a common cause of noise, if you're not using it, ground it! If you haven't done that already, do that, and record new audio clips. Quote Link to comment Share on other sites More sharing options...
JRock Posted October 8, 2010 Report Share Posted October 8, 2010 Which pads did you put the Filter Caps in? Quote Link to comment Share on other sites More sharing options...
fadedpaper Posted October 11, 2010 Author Report Share Posted October 11, 2010 Hey guys, thanks for responding. The circuit I used to power the whole thing was from the schematic on the sid page called "mbhp_sid_c64_psu.pdf. It's the simple drawing with only one sid module. I'm using an L7812CV on the sid. I'm getting 15V input and 11.94V output. Is that close enough, or should it read 12V exactly? And yes, the Audio input is grounded. And perhaps it's a silly question, but which ones are the filter caps? I just followed the instructions for smashTV's kit, so I'm pretty sure I put the right caps in the right places. Another thing worth mentioning, I re-used the big 470uf cap from the original c64 unit for the psu. Could the fact that it's old be a source of noise? Any other thoughts, places I should look? Thanks again for your help! Quote Link to comment Share on other sites More sharing options...
Wilba Posted October 12, 2010 Report Share Posted October 12, 2010 I would suggest replacing the big 470uF cap... it might not be working and sufficiently smoothing the voltage after the bridge rectifier. Oops. I assumed there WAS a bridge rectifier... looks like it's only a diode. http://www.ucapps.de/mbhp/mbhp_sid_c64_psu.pdf It is relying on AC->DC rectifying on the SID module, and the big 2200uF cap there. I think this circuit is better: http://www.ucapps.de/mbhp/mbhp_8xsid_c64_psu_optimized.pdf I can't say this is going to fix your noise problem, but it might be easier to diagnose what is wrong. It's doing the opposite of the other circuit... it powers the 5V/ground of both modules with the already regulated 5V DC/ground... then the separate 9V AC from the C64 PSU is rectified/regulated into 9V DC, and this 9V DC is added to the 5V DC (note 7809 middle pin is connected to 5V, not ground like most PSU circuits, therefore it's output is going to be 9V higher relative to the middle pin). Something to consider anyway. Try replacing the 470uF first. Quote Link to comment Share on other sites More sharing options...
fadedpaper Posted October 12, 2010 Author Report Share Posted October 12, 2010 Cool thanks for the suggestions! I'm kinda nervous about switching the psu setup now that it's all built, because I'm not sure I understand it enough to know which components to swap. If I get to that point, I'll definitely have a few more questions for ya. Quote Link to comment Share on other sites More sharing options...
fadedpaper Posted June 9, 2011 Author Report Share Posted June 9, 2011 Wow, only took me several months, but I FINALLY got the optimized psu figured out, and it solved all of my woes! Happiest day ever! Thanks again for your help guys! Quote Link to comment Share on other sites More sharing options...
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