Material from Revision 2020 seminar: Designing a better Amiga PSU

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Don't Panic. Please wash hands.
  • Hi Jens,

    My 2c worth. Have you considered providing PSU design details online, allowing us to fabricate our own? This will avoid the necessity to achieve certification. I guess it doesn't help you with your support model because you will never know if the builder used good components or built it right, but it would be a potential cost saver to an experience technician.

    One other thing I have considered in the past is using a sense wire, but unless you design the hell out of the supply you run the risk of the supply trying to fill the bucket on a short circuit. You'd need to put some real smarts into fault detection, or have a hard- set current limit.


  • Have you considered providing PSU design details online, allowing us to fabricate our own?

    The simplicity of the circuit should enable anyone who knows a tiny bit about electronics to make his own DC-DC converter. If you can't, then you should probably purchase a finished PSU when it's available (ours will probably be available late next week).

    One other thing I have considered in the past is using a sense wire,

    Did you watch the seminar? A sense wire will only compensate for the loss on the cable, but not in the input filter and the contact resistance of the square DIN connector. Further, compensating cross-regulation due to GND rise on 12V load will only "seemingly" solve the problem (if you use two sense wires, one on GND and the other on 5V): While you have a perfect 5V at the connector, you have an unknown loss in the input filter, because the sense wire will only tell you about the current voltage, but not the current.

    I believe you're best off using a shunt resistor in both the 5V and the 12V rail, so you know the total current that flows. Two op-amps aren't the most expensive thing in the world, and you also don't have the pain to take care of possibly-failing sense wires (you need to make sure that your regulation does not go over board in that case).

    I believe that cable drop compensation using current measurement is easier to handle and has less failure possibilities than three sense wires. With the added benefit of also taking care of contact resistance and input filter loss, it's beyond any doubt the better solution.

  • Thanks Jens

    I wasn't trying to diminish anything you are doing and for one am a supporter of all that you do in keeping our beloved machines running in peak condition. I guess for me, I'd be much happier using a design that was thought through by someone who has more experience in design, where my skills were and still are repair, not so much design.

    Please don't take my comments as negative as they certainly were not intended that way.

    I had not watched the video and was only looking at the presentation. The video makes things very clear and I think I would not have posted if I had seen that first.

    Sign me up for a new PSU when you have them ready, and maybe a couple of ACA12xx's too.


  • Nothing to worry about - I'm just in a "defend the necessity of this approach"-mode anytime when the topic turns to PSUs.

    I did get a few eMails criticising the whole video as "competition bashing", although I'm merely showing the right path. Yes, the competition is looking poor, but that's only because I point out the obvious.

    I'm trying an even more open approach now: I have designed a small circuit that shows the accuracy of the voltage and ripple level with a few LEDs. It plugs to the joystick port and it's fairly cheap to manufacture (in quantity, that is - high-precision resistors aren't really common if you go for 0.5% or better). I'll open the schematics so everyone can see that I'm not "competition bashing", but merely verifying the original specification given by Commodore.

  • Wow, I finally found this and it was very interesting. I never knew so much went into making a quality power supply for the Amiga! Just after I 'fixed' my 'light' A600 power supply that was starting to stink like fish with a 4A on the 5V rail MeanWell RT-50B chassis power supply. I do have this running on an Amiga 1200 with a Blizzard 1260 with SCSI and mechanical hard drive. I had it running for days on end doing full formatting on old SyQuest SyJet 1.5 GB disks with no problems. I just ordered an Indivision AGA MK3 and since it's based on newer technology it will be interesting to see if the high ripple of the MeanBad will cause problems. If not, well, new power supply it is.

  • Hi Jens,

    My new „old A2000“ with 68060 turbo card needs a new psu. So, great to see that you are working on it. How is the status and when can I go shopping in your shop?