MB6582 External PSU similar to Option E

[m00dawg]

First thanks to dwestbury here on the forums for his work on the JST connectors and power discussions (here and here). It got my back to seeing if I can ressurect my MB6582 in the PT10 case. I've been working on a rackmount version for ... erhm...quite a long time we'll say, but if I can get my normal MB6582 going, that'll let me jam out much sooner and will help me decide if a 3U rackmount version is worth it. I've never been able to get the control surface working properly on mine due to the connectors. So the JSTs seem like an amazing solution!

In any case, previously I made a real sketchy external PSU to provide +9 and +5V and keep all the heat out of the 6582. I thought about moving to Option E but instead, took Option E and updated my external PSU design. It uses a transformer (could be an external wall wart if you wanted) and then turns that into +5V and +9V that you would feed to the MB6582 directly (along with ground of course) via a cable. It's kinda like the C64 PSU in that regard, only there's no regulation going on inside the MB6582 itself and, thus, less heat. Since I had the room, I added protection diodes, an inductor/choke per the spec sheet and some extra smoothing caps. The one downside with an external PSU is wire length to the MB6582 itself. That could cause a bit of voltage drop but I never had any issues with my previous PSU with voltage stability so I think this should work ok.

In my case I can use the same PSU for a rackmount version as well (where wire length also won't be as big of an issue).

Here's the latest design. It uses 4 planes (GND, Unregulated DC, Regulated 9V and Regulated 5V). I'm not sure if that's the best solution (I have a version with just thick traces too) but seems sensible. The boards from Osh Park would cost about $21 (or $7 each) and the BOM from Mouser is about $30.52 if I didn't miss anything.

Curious if anyone had any thoughts or suggestions?

[dwestbury]

Looks like a nice and compact design given all the flexibility it offers. Kudos
 

cheers!

 

[m00dawg]

Thanks! I made a few minor tweaks to the layout but it's basically the same. I forgot to include a 12VAC transformer, so that bumped the BOM price up by $15 (though one could use a DC supply and it would work). I think I'm gonna go ahead and order the board and parts for this and can share my results once I have it built and tested (may not be truly tested until I do the JST conversion on my 6582 though).

The one thing I didn't think about that was mentioned on the Discord chat was having 12V for 6581 SIDs. Couple ways to solve that but I'm going to stick with just the two voltages for now since I only have 6582's SIDs at the moment.

[m00dawg]

Quick update, I finally had time to assemble and test it. Works like a champ so far! I still need to fix my MB6582 control panel wiring fiasco but everything otherwise powered on. Of note, when I checked the voltage from my 5V out on the board, it was 5.00 EXACTLY. Not like 5.05 or 4.99, 5.0. Coincidence surely, but that was pretty wild! The linear 7809 was more like 9.04 for instance.

I'll know more as I spruce up my MB6582 but so far, I think this would be a viable solution! I have yet to test any audio noise though. I'll likely compare my sammichSID (with a linear wallwart) to the MB6582 (using my PSU) to see if the switcher makes any noticeable difference (even then it's a bit apples to oranges given the MB6582 has a lot more going on). Will also have to check again when I add a proper 5V fan (will probably go with a Noctua as that is what I installed in my Deepmind rack to cut down on the OEM fan noise and it seems to work well).