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Getting +/- 12V from C64 PSU?


ytsestef

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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 by ytsestef
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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 by m00dawg
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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!

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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?

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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

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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.

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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

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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.

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