SID Optimised PSU modification for seq

[dcer10]

Hi Everyone,

Does anyone know how what would be involved in changing the Optimised 4xSID PSU board to be suitable to power a midibox sequencer? Ive still notfitted a power board into my sequencer that will give power to both the core and Aout. I thought since I have some  C64 PSU bricks laying around I could use one to power my sequencer? Is this possible?

Thanks,

John

[doc]

For Sequenzer:

Not useful, because the C64PSU doesn't deliver enough current to drive two backlights for 2x40 LCD. It will get pretty hot also.

FOR AOUT:

Not usable, because you'll need another winding for the symetrical power supply (+/-).

Perhaps you can try to use the 9V-windung and built a sym. PSU around it. But I think, this is a waste of time and parts...

greets

Doc

[Wilba]

I will have to disagree  ;D

Isn't 1 amp of 5 volts enough for two LCD backlights and a Core?

My "black" C64 PSU brick is rated at 1.5 amps for 5V and 1 amp for 9V AC.

There are two "windings" on my PSU's transformer, though I haven't tested it, I'm assuming they're identical, both delivering 9V AC, one 9V AC output goes direct to the plug, the other goes into a 7805 regulator with a HUGE aluminium heatsink.

In my MB-SID v2, I rectify the 9V AC into 9V DC and join the ground with the 5V DC ground, and have had no problems with it at all.

So I don't see any problem with using a half-wave rectifier on the 9V AC and getting +/- 9V DC for your AOUT, and the 5V DC to power the Seq, and joining the grounds together at a central point (you want to keep your AOUT's ground well away from the digital ground of the Core and other modules). You can effectively treat the 9V AC and 5V DC outputs as separate, as if they were coming from two separate AC adapters.

Something like this ought to be adequate (taken from the PAiA ribbon controller circuit):

That's the general idea - feed your AC into two diodes so that your matching pair of positive and negative voltage regulators each get the positive and negative "phases" of the AC power. Each regulator only gets half the power, so the current output is half (probably less) for each regulator, i.e. for 1 amp 9V AC, you can get +9V at ~500mA and -9V at ~500mA. My advice is to increase the capacitors C6 and C7 to be big, like 1000uF - 2200uF perhaps... this will ensure there's enough voltage stored in the capacitors during the gaps in the phases to supply the regulators. Remember to use POWER DIODES not those tiny signal diodes, you want the big black ones that can handle the current.

The beauty of this idea is that you can use any old AC adapter that outputs AC (not DC) and get a symetrical DC supply out of it, without needing to buy a transformer and wire it to mains power.

I can't tell you if this is better or worse than a symmetrical PSU built like the one presented here, but it should do the job and will be easier to construct.

[dcer10]

Will the Aout run on 9v dc? The psu diagram shows +-12v. I hope it can be used, this way looks good!

[doc]

Hi Wilba,

of course you're right. It might work this way.

Isn't 1 amp of 5 volts enough for two LCD backlights and a Core?

My "black" C64 PSU brick is rated at 1.5 amps for 5V and 1 amp for 9V AC.

I think these are maximum values. I recognized that my C64 PSU is getting pretty hot driving a SIDc with only one display. Never tried two displays with backlight. I think it would get even hotter then.

Also I'm pretty unsure if you can truly seperate the AOUT and the CORE through the transformer of the C64 PSU.

Perhaps you'll get a lot of digital noise in the AOUT part by using just one transformer. But someone have to try this!

greets

Doc

[Wilba]

Will the Aout run on 9v dc? The psu diagram shows +-12v. I hope it can be used, this way looks good!

I don't really know... I suppose in theory you can make the AOUT work with +-9v but the voltage output range is also reduced, so no good if you're driving gear that needs -10v to +10v.

I don't think digital noise is a problem because I don't get any with my SIDs, where digital noise is more noticeable than with AOUT... i.e. for the SID box the 9v (analog) and 5v (digital) grounds are joined at one place, close to the power socket. So similarly, splitting AOUT power from Core power at one point as near to the transformer as possible should be fine.

[Lall]

Hi all,

I've got to learn lately about the following modules: http://dsb.tracopower.com/PPF/PublisherID/tracopower/KundenID/tracopower/VKundenID/tracopower/S/2/Anbieter/24409/anchor/TOP/Branche/6958/L2Mnu/0/Level/3/Mode/STANDARD/NavigationLevel/0/NFP/00101/OrigAnbieter/24409/PM/5/ShowNav/1/ShowSubNav/1/ShowTitle/1/DSB_Anbieter_03_Shw.asp

These are pretty cool beasts that take AC as an input and provide 1 or more regulated outputs.

Drawback is that there's no 9V output available and that they are rather expensive but on the other hand building the same kind of PSU from scratch also costs quite a lot.

I'm seriously considering to use one of these in my SEQ as in this case the potential noise it may generate if of less importance and that these modules are quite small and do not heat.

Best regards,

Lall