[sdiy] MS-20 psu conversion from 100V to 240V

Stewart Pye stewpye at optusnet.com.au
Mon May 21 10:17:45 CEST 2012

Hi Andy,

With a 15 volt secondary there is the chance of the unregulated voltage 
being too low, so the regulator will drop out of regulation. This is why 
I said you could change the regulators for low dropout type if 
necessary. Where I live the voltage never goes below 240V so it would 
probably be OK.

Others have said that the regulators in the MS20 don't get too hot so 
you may be better off using a transformer with 18V secondaries, that way 
the drop out voltage won't be a problem. It would be a good idea to 
change the filter caps to 35V as Oscar mentioned. If you change the 
filter caps and fit the 18V transformer the worst thing that can happen 
is the regulators will get too hot and go into thermal shut down. You 
won't kill the synth. Maybe go with that one.

You will have to change the fuse to a slow blow type and lower value 
depending on the transformer you use.

I live in Brisbane. The company I work for purchases some components 
from Altronics wholesale.


On 5/20/2012 1:05 PM, Andrew Simper wrote:
> On 18 May 2012 04:48, Stewart Pye<stewpye at optusnet.com.au>  wrote:
>> Hi Andy,
>> I've converted a few 110V synths for 240V but I can't remember if the MS20 was one of them.
>>  From the circuit it looks like you could just replace the transformer if you can find a suitable one, and fit it in there. If your closest choice is 18V or 15V secondaries I'd go with the 15V one, as the unregulated DC is marked as 18V on the schematic. The power dissipation across the regulator may be too high if you use 18V secondaries.
>> Something like this would be suitable:
>> http://www.altronics.com.au/index.asp?area=item&id=M5015
>> If dropout voltage is a problem you could then replace the regulators with low dropout types such as the LM2940-15.
>> Regards,
>> Stewart.
> Hi  Stewart,
> Thanks loads for going to the trouble to let me know a transformer to
> use! Do you happen to live in Perth as well? You posted a link to
> Altronics which is my local supplier.
> Are there any problems with having a 15V secondary instead of an 18V
> one? Will that still give 15V at the regulator's output?
> Cheers,
> Andy
> --
> cytomic - sound music software
>> On 5/18/2012 12:44 AM, Andrew Simper wrote:
>>> I want to buy an MS-20 rev2, but the only ones I can find all have
>>> Japanese 100V power supplies. I have a friends 240V MS20 rev2 here and
>>> there is a transformer and fuse mounted on the chassie and then a
>>> tripple core wire from the transformer that is soldered directly onto
>>> the main PCB. Does anyone know if it is simply a matter of changing
>>> that transformer?
>>> I'm assuming that the rev2 has the same power supply as the rev1:
>>> http://www.korganalogue.net/korgms/images/service/ms20/circ1.gif
>>> Cheers,
>>> Andy
>>> --
>>> cytomic - sound music software
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