Roland GP 100 mod

keithf

Advice needed.

Guys, I got a 110v gp100, I want to run it at 240.

Ideally I'd like to do it with a new internal transformer but roland don't stock them.

Is there a way of getting say, a generic maplins kind of thing to work.

@icbm

http://i20.photobucket.com/albums/b221/keithow/WP_20151112_003_zpszx9q1nbm.jpg~original

http://i20.photobucket.com/albums/b221/keithow/WP_20151112_002_zps8pzhgxr2.jpg~original

http://i20.photobucket.com/albums/b221/keithow/WP_20151112_001_zpsewds9qav.jpg~original

http://i20.photobucket.com/albums/b221/keithow/gp exploded_zpsqxtibqmt.jpg~original

ecc83

If I may? The short answer is, probably!

It is entirely possible that there is a simple internal transformer inside that produces say. 12 0 12 volts which is rectified and regulated for op amp rails and 5V for digitals.....OR! It could have multiple windings for all sorts of supplies.

One sticky point. The unit is Class ll insulated (aka double insulated) and needs no chassis earth. Any replacement MUST conform to this regime. In any case, after mains related work the box MUST be PAT tested.

Open it up and smudge it for the populous!

Dave.

keithf

will do

ICBM

It is quite possible there is a dual-primary transformer in it, in which case it can be rewired for 230V with no new parts needed. It's so long since I've been inside one (and once only at that, I think) that I couldn't tell you without seeing it though.

octatonic

Often Roland gear will have a 110v and 230v tap on the transformer. It could be as simple as moving one wire and replacing a fuse. Most Roland synths are like this. Give me a look at the transformer and I can prob tell you.

keithf

photo a bit later

octatonic

I'll probably not see it until tomorrow.

keithf

pics added

ecc83

keithf said:

pics added

Where?

Dave.

ecc83

ecc83 said:

keithf said:

pics added

Where?

Dave.

Oh! Back up there! Right. AFAICT that is a simple single winding primary with a simple centre tapped secondary. So you need to  measure the secondary volts then get some idea of the power rating, should be a rating plate on it or consumption mentioned in the handbook.

Next find a TOROID that suits. I doubt you would fit a conventional E-I traff in there but in any case you need a low hum field. Toroids should come with a mounting kit that includes a rubber washer which give you your double insulation.

Dave. 

ecc83

Just a cotton pickin! To the lower right of that exploded diagram is a table re traffs with colour codes and various mains voltages.

I still cannot see any extra wires to give a 230V primary but that table suggests that they DID make various voltage traffs? Lying gits.

Dave.

octatonic

Looks like you need a different transformer. In some of the Roland synths you just need to move a black wire off a 110v tab and move it to 230v tab. You don't seem to have that option here.

ICBM

Yes - it is a dual-voltage transformer, but unfortunately it's 100V/117V and not 117V/230V.

There are two secondary windings - the red-black-red which will be a balanced centre-tapped, and the yellow-yellow which is just a single winding. You need to measure the voltage outputs of these to work out what replacement transformer you need.

There is another possible way of doing it though… I am slightly wary of recommending it, but it will work. The unit's power consumption is listed as only 13W. This is pretty low, if accurate - you would need to measure the current draw to be certain. If it is, you could add a large resistor in series with the transformer to drop it to 117V - there's plenty of room in the casing and a 25W chassis-mount resistor should be enough if the 13W is correct (the resistor will dissipate the same power as the unit, roughly). It shouldn't cause the unit to overheat, I don't think - it's quite big.

Again, you would definitely need to make some careful measurements before trying this, but in theory if the unit draws 13W at 117V, that's a current of 111mA. To drop the remaining 113V from 230 would require a series resistance of 1017 ohms - 1K ohm is easily close enough. So a 1K 25W resistor is adequate. If there's room, a 50W resistor won't hurt and will give more safety margin - at that, even if the transformer shorts the resistor will probably withstand the power (just over 50W) for long enough to for you to realise something was wrong.

Needless to say the work would need to be done to a high standard by someone who is familiar with working on mains equipment.

keithf

thanks, guys. ,I like that idea @icbm ,Sadly Im far too inept to try that myself.Probably easier to run one of them step down transformers instead,

It just don't sit right with my ocd