Converting something from 220v to 110v...

[WhinyLittleRunt]

...without using a step transformer, is it possible to do / advisable / not worth the risk?

I know the knowledge on these units is few and far between but my Simmons SDSV brain runs at 220v and I've been using a step up transformer with it all along. It was more a curiosity of what is involved in changing a unit internally for different voltage... sometimes I'm sick of that extra transformer being there...

[jxalex]

...without using a step transformer, is it possible to do / advisable / not worth the risk?

I know the knowledge on these units is few and far between but my Simmons SDSV brain runs at 220v and I've been using a step up transformer with it all along. It was more a curiosity of what is involved in changing a unit internally for different voltage... sometimes I'm sick of that extra transformer being there...

If it is advisable to do, IT DEPENDS on how much do You know about Electronics. What things have you built?
You need to know how to measure AC voltage, to know what are the primary and secondary Windings and how the simplest power supplys are built, and certainly to be comfortable with soldering certainly. But most of all -- to know which points not to touch -- so, that you know where the lethal voltage actually is located.

AT FIRST look the transformer. Does it has several voltage taps inside? Like 0V 110V 230V indicated on the transformer? (Post the Pictures how it looks inside around the transformer).


Depending on the transformer it needs primary Winding tap Point to be changed OR the internal transformer to be swapped out totally (and the new transformer must deliver the same secondary voltages to rectifiers).
It involves certainly not only soldering, but also measuring the DC and AC voltage, planning.
If You have built yourself some power supplys for Your experiments then You can do it. But if it will be your
first Electronics Project, ever, then do not do it. Certainly not on a vintage Equipment.
And when done, do test the Power supply part separately from schematic and measure the voltage rails, with dummy loads attached, so you wont injure the machine itself if the voltages are wrong.

Another solution can be also to replace the whole Power supply with a impulse Power supply block which has the suitable Power output rails needed. Process is similar, however its output will be noisier though and it induces ground currents.

[Envergure]

For something that old, what is involved (most likely) is changing the number of turns of wire on a mains-frequency transformer. You could double the number of secondary turns if there is room for all that wire, or you could halve the number of primary turns. In either case, the current through the primary winding will double, possibly overheating the transformer--thicker wire is required to carry the current. If you opt to reduce the number of primary windings, the magnetizing inductance will be reduced, causing even more heat. You should ideally hi-pot test the transformer after the modification. Even just to do this on a DIY basis, you should have some knowledge of safety standards, e.g. CSA, UL, TÜV, because the transformer's insulation (the "isolation barrier") is safety-critical. So, though it's possible in principle, modifying a mains-connected transformer is complicated and somewhat risky.

Like Jxalex said, you can replace old power supplies with off-the-shelf modern ones, provided you know what the requirements of the Simmons thing are: Voltages, currents, ripple, minimum load, etc. If you can do that yourself, great; If not, a good audio repair place should be able to.

For another option, you should be able to find an electronic 110-to-220V converter that will be smaller and more efficient than a mains-frequency step-up transformer, if that's what you're currently using, but there is a possibility of it introducing noise into your sound.

[jxalex]

there are also R-core 30W transformers available (ca 20USD with shipping from china) with several different secondary voltages and have both 110V and 230V mains.
Have someone tried those? My guess is that it is not so far away from the original transformer which has 9V+9V and 15V+15V secondary Windings and should fit for that Simmons, perhaps? To me it was the way how to make the Roland JX10 and other Roland synths from 110V -> 220V mains operation