m00dawg Posted October 2, 2009 Author Report Share Posted October 2, 2009 Wow that's awesome and really helpful! Thanks Wilba (and NorthernLightX)!So, if I understand that correctly, my resistor choice would be 4Ohm at around 8W (I assume I can get a resister with a higher wattage rating). That would drop the voltage to between 7.4 - 10V (depending on my actual input voltage at the wall) at 1A which is a hellofa lot better than 11-14V.I think I might go that route. If that doesn't work, it's good to know there's a design that seems like it should do the trick. Quote Link to comment Share on other sites More sharing options...
m00dawg Posted October 2, 2009 Author Report Share Posted October 2, 2009 Ok so I've been thinking about this and think I have a pretty good plan to get this thing up and running. I'm going to switch from using my cool plastic case (for now) to using a metal box from a gutted PC PSU. That way, I can mount the huge resistor to the metal chassis and can also connect the heatsink on the regulators to the box as well.If I mount the resistor off board, I can avoid making the board itself super hot and can also just use pins on the power board itself if I ever need to swap out the resistor.For the resistor, I think I may try using a 3.33 Ohm, 10W resistor since the load might be closer to 1.5A given the numbers I've been seeing on the forums (in this post and others). I may continue using the 7805 but I think I'd feel better going a beefier one that can handle up to 2A within the spec.I hope to have something ready to go this weekend but it depends on how many spare parts I have lying around. Will keep everyone posted! Quote Link to comment Share on other sites More sharing options...
fussylizard Posted October 3, 2009 Report Share Posted October 3, 2009 I should try this myself. It would be nice to have a single power supply board for MB-FM. Right now I'm using a Paia power supply board w/ wallwart for +/- 12V AND a separate wallwart to supply the Core with 9VAC. Irritating...Interested to hear how it turns out for you (though you'll not be using the +/- 12V part of it). I'd have to look up transformers though, I'm always confused looking at them in the Mouser catalog. Quote Link to comment Share on other sites More sharing options...
m00dawg Posted October 3, 2009 Author Report Share Posted October 3, 2009 I should try this myself. It would be nice to have a single power supply board for MB-FM. Right now I'm using a Paia power supply board w/ wallwart for +/- 12V AND a separate wallwart to supply the Core with 9VAC. Irritating...Interested to hear how it turns out for you (though you'll not be using the +/- 12V part of it). I'd have to look up transformers though, I'm always confused looking at them in the Mouser catalog.Yeah I'm not doing the bi-polar stuff just yet. Having said that, after gutting my busted PSU yesterday it seems like there is plenty of room for my PSU and I think adding in +12/-12 is very doable. In fact, I might add another +12 or +9 to power a fan on the PSU to help keep things cool.As for the transformers, I actually found Mouser to be far better than any other site. I usually order my parts from Allied Electronics since they are out of Austin, TX and can send me stuff super fast. Mouser is out of Dallas though I believe. There's quite a few center-tapped transformers out there. In fact, seems like there's more with a center tap than without. You would use the center-tap as GND and the outer ends for +12 and -12. Now I've never built a bi-polar supply but I think doing it this way means you may need to further smooth out AC ripples which may explain why the design calls for larger caps than the usual 2200uF caps most people use (I use bigger caps myself, but probably for not good reason :)Once thing you should do, though, is measure your current load. I was estimating 1.5A but broke out my multimeter this morning and noticed my 5V current to be closer to 1A, which does make sense a bit since I'm driving my LEDs with less voltage than is typical and my LCD brightness is all the way down. Point is, that could change what size resistors you would use.Anyways alot of this is speculative since I haven't modified my PSU yet but will be making a trip to Radio Shack today in hopes that they have some power resistors. if not, I may have to wait a few days to order some, but I'll keep everyone posted!The only takeaway I have now is that the using a gutted PSU case looks like it will work really well, at least until I can find a more cosmetic (and maybe safer) case. Quote Link to comment Share on other sites More sharing options...
m00dawg Posted October 4, 2009 Author Report Share Posted October 4, 2009 While I wasn't able to move the power stuff to the metal case as I wanted, I was able to add in some power resistors with some very promising results! I ended up using 4 1-Ohm resistors in series (since that is all Radio Shack had) to end up with 4 Ohm. This appears to be just about perfect since, at full load, the resistors drop about 4V, resulting in 8V going into the 7805.The heatsink on the 7809 and 7805 still gets hot, but it's nowhere near 80C like it was. So far, after playing some SID tunes (mostly by 'kb' for the curious - the 2nd Reality SID remixes own face!!) for about 30 minutes, the heatsink temperature reads around 57C. The temperature on heatsink I put on the resistors is about 65C. That's still hot, but I think I can get that down lower by moving to the metal chassis and perhaps getting larger heatsinks. I could probably also throw in another .5-1Ohm power resistor to knock of another .5-1V. That's getting close to spec, though, since I would be supplying 7V to the 7805.At this point, I am almost ready to claim victory except that I may have a few more small issues with my control surface (looks like two adjacent outputs to the CS might be touching since some adjacent LEDs, all on the bottom half of the control surface, appear to be illuminated when they shouldn't be). After that, I need to figure out why my LCD is flaking out. It comes and goes which either means bad cabling or a short (I assume).On an side, yet again, I feel the need to thank both TK and Wilba. TK for adding in the SID player to the MB-SID v2 firmware and Wilba for offering these kick-ass 6582a SIDs. These SID tunes I'm playing sound SOOO awesome! Quote Link to comment Share on other sites More sharing options...
lylehaze Posted October 5, 2009 Report Share Posted October 5, 2009 Excellent for you!Just a few words of unsolicited advice:Some 7805's require up to 7.5 volts to work, so in the interest of margin, you should probably not add any more resistors.Any 78xx regulator that has the center pin at REAL ground also has it's tab there, so using the case for a heatsink is fair play. :-) 79xx regulators and stacking one regulator above another prohibit this.You might try a shorter ribbon to the display, if possible.Have Fun,LyleHaze Quote Link to comment Share on other sites More sharing options...
m00dawg Posted October 5, 2009 Author Report Share Posted October 5, 2009 Well, the only thing I'm curious about is that if I use the metal case, now I should attach the Earth / GND prong to the metal chassis as well? But I was advised against doing that in a plastic case due to ground differentials. So I'm not sure how to handle that now? Otherwise, I think the metal case will rock hard. I don't think it will be a permanent solution but should suffice until I can go all out and get printed boards that fit a specific enclosure, etc. I also thought about finding some low-dropout regulators, which can require as little as .7V about the output voltage. At this point, I'm not so sure it's worth the effort thoughAs for the LCD, I'll try shortening the cable as it is quite a bit longer than it needs to be. I think there's a short somewhere though. The contrast issue seems to be a tale-tell sign of that because it comes and goes. In fact, after I wrote my previous response, I "fixed" the problem accidentally by picking the MB-6582 up (I was playing around with using my laptop cooler underneath it to see if it made any difference in cooling) and noticed that the contrast was MUCH better after I set it down.That said, I also noticed that the LCD seems to work 100% of the time when using the MB-6852 in SIDplayer mode, but almost none of the time when in standard MB-6852 mode.It's got me confused :) I think it's either my LCD cabling, bad connections on my CS to mainboard cabling (there's a few more broken wires - GAH!) or something to do with the CAN bus (since I assume that's not used in SIDplayer mode). Or all of the above :) I've ruled out the LCD itself as the culprit for now I think. Quote Link to comment Share on other sites More sharing options...
seppoman Posted October 5, 2009 Report Share Posted October 5, 2009 Well, the only thing I'm curious about is that if I use the metal case, now I should attach the Earth / GND prong to the metal chassis as well? But I was advised against doing that in a plastic case due to ground differentials.I said it's bad to make a connection between the synth's GND and the Earth prong. For a separate PSU case made of metal, definitely connect that case to the Earth, but still make sure there's no connection to the output GND. The terms "Earth" and "Ground" seem to suggest both are the same potential, but usually that's not true.S Quote Link to comment Share on other sites More sharing options...
m00dawg Posted October 5, 2009 Author Report Share Posted October 5, 2009 Hmm...that might be the limit of my understanding there :/ Because that implies I should not the heatsinks of the regulators to the metal case if I use Earth ground right? Because the heatsinks are grounded using the tabs on the 78xx's. Would it help to use a diode (pointing back) on the GND pin from the synth? Quote Link to comment Share on other sites More sharing options...
Smithy Posted May 20, 2010 Report Share Posted May 20, 2010 (edited) Bump! What fuses would you recommend for the c64 brick, inside the plug itself? (Im assuming the plug fuse can be counted as primary side also?) I was thinking of a 1A Fast acting fuse, just in case anything was to happen the mb-6582, yes i've started it. ;) "Fast-acting fuses have no intentional built in slow-blow and are used in circuits without transient inrush currents. Fast-acting fuse opens on overload and short-circuits very quickly. This type of fuse is not designed to withstand temporary overload currents associated with some electrical loads." Would one of those be okay for use on 230V mains? Have no idea what cases you could have temporary overload currents or not. :/ Edited May 20, 2010 by Smithy Quote Link to comment Share on other sites More sharing options...
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