ytsestef Posted July 11, 2012 Report Share Posted July 11, 2012 (edited) Hey guys! I just started a fairly twisted version of MBSID, it's a synthbasss/lead-oriented dual-mono version(6581 and 8580 blendable and routable to either of lp,bp or hp filter inputs) with a 3-octave keyboard, a Steiner VCF (controlled by AOUT_LC), built-in Big Muff fuzz pedal, built-in digital delay and more. The basic problem i have stumbled upon for the moment is how on earth am I supposed to power up all these different modules? I already have a C64 PSU which I want to use, I need +5V for the PIC and stuff, +9 and +12 for the two different SIDs, these are already there, but I also need -12v because some modules use inverting op-amps (such as the aout, the mixer, the filter etc)... I have already the "impoved c64 psu" circuit. Can I take the +14vdc (sum of +5dc and rectified 9vac) and drop it down to +12 then convert it into -12? I am no electronics engineer, though I heard this can be done but you need to keep both sides equally loaded. Any help/ideas? Thanks for your time Rock on! EDIT/PS: I also have a PC ATX 350W PSU lying around should I have to modify it, but I don't see any difference, ATX doesn'y have -12V either plus it's more bulky and needs a case so I'd rather stick to the C64 PSU... Edited July 11, 2012 by ytsestef Quote Link to comment Share on other sites More sharing options...
m00dawg Posted July 11, 2012 Report Share Posted July 11, 2012 (edited) I'm not aware of an easy way to get +/- 12V from a C64 PSU. It offers a 9VAC signal but that isn't enough to get up to 12VDC and I'm not sure if the GND can be treated as a center tap. There are differing opinions but my personal opinion on C64 PSUs shouldn't be used for anything. Including powering C64s. Your best bet is to build your own PSU or buy a linear multi-voltage PSU. They aren't cheap but will avoid you having to make your own if you would rather avoid it. You can find both good options for linear and switch-mode in this topic: It's a long topic but covers DIY, off-the-shelf switchmode, and off-the-shelf linear power supplies so it should cover you one way or another. Edited July 11, 2012 by m00dawg Quote Link to comment Share on other sites More sharing options...
ytsestef Posted July 11, 2012 Author Report Share Posted July 11, 2012 Thanks for your reply! Where's the topic? :P Well, it's DIY we're talking about, i don't have any objections building a PSU. Depends actually on the price of the factory-made ;) Quote Link to comment Share on other sites More sharing options...
m00dawg Posted July 11, 2012 Report Share Posted July 11, 2012 Thanks for your reply! Where's the topic? :P Well, it's DIY we're talking about, i don't have any objections building a PSU. Depends actually on the price of the factory-made ;) Sorry it was supposed to be an in-line link but I didn't check my work :) Edited my original post that now should have the URL for you. Oops! Quote Link to comment Share on other sites More sharing options...
ytsestef Posted July 11, 2012 Author Report Share Posted July 11, 2012 That was very helpful, thanks! Seems like Meanwell RPT-60B is ideal for me, could even fit inside the synth (since it is 3 octaves long) so, no need for a case. Has transformer built-in, too, i just need to mount an IEC socket on the back panel and i'm good to go. What do you think? Am I missing something? Quote Link to comment Share on other sites More sharing options...
Altitude Posted July 11, 2012 Report Share Posted July 11, 2012 (edited) You can get +/- DC from a AC source with a half wave rectifier but you wont be able to get +/-12 from 9VAC though.. Edited July 11, 2012 by Altitude Quote Link to comment Share on other sites More sharing options...
m00dawg Posted July 11, 2012 Report Share Posted July 11, 2012 I tried using half-wave before and I never had any luck with it :/ I just steer clear of it these days :) But someone with more skill than me can probably solve that problem :) Quote Link to comment Share on other sites More sharing options...
Shuriken Posted July 11, 2012 Report Share Posted July 11, 2012 Maybe it can be done with a stepup dc-dc converter. But it would be complex. Quote Link to comment Share on other sites More sharing options...
ytsestef Posted July 12, 2012 Author Report Share Posted July 12, 2012 I ordered a RPT-60B. Fingers crossed! :P Quote Link to comment Share on other sites More sharing options...
Altitude Posted July 12, 2012 Report Share Posted July 12, 2012 I ordered a RPT-60B. Fingers crossed! :P Wow, those look nice, make sure you let us know the results since a +/-15V with a +5V is pretty cool Quote Link to comment Share on other sites More sharing options...
ytsestef Posted July 13, 2012 Author Report Share Posted July 13, 2012 Its +/-12V with a +5V, still very cool, though :) Quote Link to comment Share on other sites More sharing options...
Altitude Posted July 13, 2012 Report Share Posted July 13, 2012 Its +/-12V with a +5V, still very cool, though :) I was looking at their full line, dont see very many 15/-15/5 supplies and something like that is perfect for an analog synth project. Hopefully the 100kHz switching frequency will be high enough to be inaudible Quote Link to comment Share on other sites More sharing options...
m00dawg Posted July 13, 2012 Report Share Posted July 13, 2012 Should be unless there are harmonics and things. Even then I don't think it would change things much. Humans top out at around 22kHz or so and even sampling up to 96kHz is below the switching frequency. In the forum thread I linked to, I thought I read some good successes with it. Those wanting more filtering can try using additional filtering caps. Quote Link to comment Share on other sites More sharing options...
ytsestef Posted July 13, 2012 Author Report Share Posted July 13, 2012 I will post my results when I finish building it :) In the meantime, here is a photojournal of my build Quote Link to comment Share on other sites More sharing options...
Janis1279 Posted July 15, 2012 Report Share Posted July 15, 2012 Hi, That was very helpful, thanks! Seems like Meanwell RPT-60B is ideal for me, could even fit inside the synth (since it is 3 octaves long) so, no need for a case. Has transformer built-in, too, i just need to mount an IEC socket on the back panel and i'm good to go. What do you think? Am I missing something? only +9V output for the 8580 chip . But the 7809 linear regulator i.c. can do it from +12V output easily. Regards, Janis Quote Link to comment Share on other sites More sharing options...
ytsestef Posted July 15, 2012 Author Report Share Posted July 15, 2012 I think there is already a 7809 on the MB_SID module (specifically for 8580s, otherwise 7812 has to be used). Quote Link to comment Share on other sites More sharing options...
m00dawg Posted July 15, 2012 Report Share Posted July 15, 2012 I think there is already a 7809 on the MB_SID module (specifically for 8580s, otherwise 7812 has to be used). There is and that should work just fine. You may get some benefits by making your own 9V PSU off of the 12V rail and supplying the boards with 9V directly. You will save a bit on parts, but mostly it would give you more room to handle things like circuit protections (the diodes above the regulators in the schematic Altitude provided for instance), heat management (heatsinks) and extra filtering caps. But that is generally optional. Quote Link to comment Share on other sites More sharing options...
ytsestef Posted July 15, 2012 Author Report Share Posted July 15, 2012 We'll see if there is any room for that after the main build is finished :D Thanks for the tip! Quote Link to comment Share on other sites More sharing options...
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