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Custom Power Supply for mb6582


Starfire
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It's been awhile since i posted any updates. I finally managed to get all the parts for the PSU. I will be using a LM22675 for the 9V supply and a LM22676 for the 5V section. These baby's are high efficient (85-95% depending on components) and the switch freq is 500kHz.

Getting my hands on those regulators took me a long time. I initially was going for an older model LM2676. However after 2 months waiting Futurelec couldn't deliver those. So i started looking for another source. To only discover i could source them straight from National Semi as a sample. Apparently this is quiet popular :wink:, so they charge you 12 dollars for shipping. Which is of course only fair and made me feel less guilty. :angel:

After that i used National Semi's online WeBench design tool, to select all the parts. After a hard and long look, i could match selected components with stuff at Reichelt. Only the Power Inductors were not in National Semi's partlist. The WeBench tool has the option to add custom components and it turned out the Power Inductors Reichelt has are up to spec. Only thing i couldn't find was some 0,01 uF ceremic smd in 12xx size. But i found those at Conrad.

The schematics are here:

LM22676 Schematic

LM22675 Schematic

I am currently in the process of designing the boards in Eagle. I am sticking to the design layouts in the datasheets. Only tricky bit it that both IC have an exposed pad. Which basically is a small metal surface on the bottom of the IC for heat transfer. You need to solder this to the board. And it has to have vias to the other side of the board for additional heat transfer. If you want to hand solder them, apparently you need to add one big via in the middle. So that you can stick your solder iron through it. Another option of course is to use thermal adhesive. I haven't decided yet.

Here is a preview off one of the unfinished boards:

lm22676.png

Edited by Shuriken
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  • 1 month later...

so if i read this correct. I could use the standard RPT-60B to power my mb6582a instead of the original c64 psu. I only need to get a nice case for it and do some cabeling to it to connect to my mb658. I wonder if the RPT-60B fits inside the original case of the c64 psu.

regards

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The old portable (luggable)c64 used a switched mode psu for all voltages. Personally, I would use a switchmode for the +5v (digital) supply as HF has no effect here, plus you get the benefits of higher efficiency (lower heat and electricty bills) smaller size and more ouput per euro. There is no need to filter when used for this purpose. They normally include over voltage and short circuit protection as standard. I would not take a DIY approach to switchmode design, as the internal voltages are significantly higher than mains levels. Even after switch-off they can deliver lethal currents. In a commercial design, all components are caged for this reason. By all means build a linear psu for the audio portions of the circuit. When building, it is a good idea to first solder up the mains side of the transformer, and then tape off or otherwise insulate the bare tags before continuing. I have used the LM723 voltage regulator in combination with a power transistor for linear regulation in the past. You can set the voltage precisely if you want, and also set your own current limits. It has better line and load regulation than fixed voltage regulators too, which is important with analog synths.

Edited by middleman
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While most of the above info is both appreciated and helpful, I have to mention that the C64 PSU looks far more like a linear PSU to me. Check this out. Part of the reason it was so damn heavy was the transformer stuck inside. A switchmode PSU would not have a need for such a big transformer, nor would the bricks be prone to overheating like they tend to be.

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While most of the above info is both appreciated and helpful, I have to mention that the C64 PSU looks far more like a linear PSU to me. Check this out. Part of the reason it was so damn heavy was the transformer stuck inside. A switchmode PSU would not have a need for such a big transformer, nor would the bricks be prone to overheating like they tend to be.

He's talking about the sx-64 it was a portable commodore with integrated display and disk drive, the granfather of the laptop.

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I haven't finished building my MB6582-based synth but I have decided to go with a linear. I like most of the ideas behind a switch-mode but regardless of whether I can actually heart the switching I just like the idea of analog equipment to have analog PSUs. *shrug* Plus it's easier to build and building PSUs is something I enjoy. That said, the modern switchmode PSUs are actually quite efficient and switch well above the audible range (most of them - at least the ones in this thread) so it's generally a good way to go. I agree with sidmonster though, it would be unwise to try to build one but the Mean-Wells are pretty good for their size and performance.

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Dammit... reading this thread has got me worried about smoking my SIDs and they haven't even arrived yet.

Until there's an mb6582 PSU for dummies, I'll have to take my chances I guess. I'm the last person who needs to be playing around with mains electricity.

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The MB6582 can use the C64 PSU so you have a hands-off option there. I think the C64 PSU is a piece of shit but others on this forum will disagree :) There are, however, some designs and maybe even some places to purchase a C64 compatible PSU so you could try that. The switch-mode PSU would be safer than building your own PSU for the 6852 itself since it already supplies the voltages your SIDs need - you'd just need to put it in a case and cable it up to the 6582 and boom, done. I think the MB6582 also lets you power it with a single wall-wart supply with some work (though I don't think that is recommended due to heat).

Sorry I was kinda rambling but hopefully there is some worthy tidbits in there :)

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As this alternative hasn´t been mentioned in this thread yet... I built mine according to retro-donalds spec and it works - it has four fuses and a crowbar overvoltage protection... and was not difficult to build...

http://www.retro-don...wernetzteil.php

pics here:

Me haz a much better feeling now regarding the well-being of the SIDs :-)

Greets!

Peter

Edited by Hawkeye
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Thanks a lot - I tested it with my original C64 and played a game of "catalypse" (awesome, btw!), before I dared to plug it into the MB6582 :-).

The only thing, I would add to retro-donalds design, is a load resistor right ahead of the 78S05 to relieve it a little - the input voltage is a bit high (9V * 1.41) for a 5V regulator - if a few volts are burned off before, it should run a little bit cooler.

Otoh, you can go as insane as you like with oversized passive coolers :-). The unit is nearly twice as heavy as the original C64 PSU :-).

As a conclusion, it is linear, easy to build, not too expensive and the crowbar protection also works really nice (tested with a lab PSU).

Bye,

Peter

Edited by Hawkeye
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Well, to be fair, you would still have to build it if it were a MidiBox project - keeping in mind the safety considerations when doing so. Having it as a MidiBox project just means it might be easier to get ones hands on pre-printed boards, kits, and schematics. That's not to say having a place where one could by new C64-compatible PSUs would be a bad thing - it just can't be a MidiBox project according to the license (as I understand it anyway).

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@Dreamer: Cool - but someone else must do this - I didn´t post explicit instructions in the build tutorial, because I didn´t want to take the risk of bad karma, when someone rebuilds this, forgets that it is plugged in and has a hell of an electrifying trip :-).

And also, there are many good (probably better) designs out there, some surely being more efficient (e.g. not pumping 9v * 1.4 into a 5V vreg) or having even better ic-controlled over-voltage protection circuits.

Edited by Hawkeye
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i understand youre concern. Thats why it should be a safe build. I'm digging into internet to see if there is maybe somewhere on this globe a nice replacement option. Will post the findings in this topic, if i can find any. I noticed the power suplly nothern descriped is hard to get especially in holland.

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@Dreamer: Cool - but someone else must do this - I didn´t post explicit instructions in the build tutorial, because I didn´t want to take the risk of bad karma, when someone rebuilds this, forgets that it is plugged in and has a hell of an electrifying trip :-).

And also, there are many good (probably better) designs out there, some surely being more efficient (e.g. not pumping 9v * 1.4 into a 5V vreg) or having even better ic-controlled over-voltage protection circuits.

I am going to use the same size Transformer for my psu, but just a 15V version. Since i am going to use a switching psu, i cannot heat my room with it in winter. Simulations suggest it's going to be 40 Degrees Celsius max.

Using a switching PSU does not imply not using a transformer. The IC i use are DC-DC switchers and not 6a00d83458654369e200e54f36a40c8834800wi.jpg?crop=1%3A1&width=64. Although the later sound a lot cooler :wink:

Edited by Shuriken
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Okay i found a nice site:

http://www.sunpower-uk.com

This site has loads of different power supply's too bad no price and no option to add to basket. But you can request a quote.

I checked some specs, i listed a few of them that has I think the correct specs:

SPP-D043 - 30-45W Dual Output Open Frame Power Supply

http://www.sunpower-uk.com/product/30-45W-Dual-Output-Open-Frame-Power-Supply/SPP-D043/default.htm

PD-45A - 40W Dual Output Open Frame Switching Power Supply

http://www.sunpower-uk.com/product/40W-Dual-Output-Open-Frame-Switching-Power-Supply/PD-45A/default.htm

SNP-YL63 - 57W 5V & 12V Dual Output Open Framed Power Supply

http://www.sunpower-uk.com/product/57W-5V-and-12V-Dual-Output-Open-Framed-Power-Supply/SNP-YL63/default.htm

RPD-60A - 49W Dual Output Open Frame Medical PSU

http://www.sunpower-uk.com/product/49W-Dual-Output-Open-Frame-Medical-PSU/RPD-60A/default.htm

SPS-G050-ID1 - 51W Isolated 5V & 12V Output Enclosed Power Supply

http://www.sunpower-uk.com/product/51W-Isolated-5V-and-12V-Output-Enclosed-Power-Supply/SPS-G050-ID1/default.htm

I don't have a clue if any of these will work on a mb6582 with 8x sid 6582 in it. Maybe someone could give feedback on this. And especially what specs are important for a power supply for a music instrument.

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