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Mains Voltages

Posted: Mon Feb 23, 2009 10:07 pm
by ppyvmw
Hi everyone,

I've just bought a couple of yamaha CS synths (5 and 10), and both are the Japanese models that require 100V mains. I'm in the UK and so I have 240V on tap. The transformers on the market are a little sloppy on whether they go from 240V or 230V or 220V to 100V or 110V or 120V. Is the voltage absolutely critical? Being analogue, I thought that they might be sensitive to voltages more than a digital device, which would work perfectly within a tolerance. I understand they also use a multi-tap transformer, how easy is this to adapt? I had a peek at the service manual for the CS-10 (not arrived yet so cant look inside yet..) and it looked quite complicated. Don't want to ruin the beast! Especially if I'm going to sell it again in the future when I've had my fill.

Ta for any advice!

Mike

Re: Mains Voltages

Posted: Tue Feb 24, 2009 12:29 am
by Ian S
Mains voltages generally have a tolerance of around 10%, UK mains is nominally 230V, but generally won't cause problems if it goes up to 240 or drops down to 220 At the other end things are a little more critical, because if your synth runs on 100V, then yes, 110V should be OK, but an output rated at 110V might go up nearer 120V, and that could well fry something. Ultimately it depends on the power supply in the synth itself & how tolerant that is. If you can get a transformer with an output rated at 100V, then go for it. The 220-240V part isn't really important, if it's rated for UK mains then that's what matters at the input end.

Re: Mains Voltages

Posted: Tue Mar 10, 2009 12:23 am
by Kent
Transformers work by ratios. Something close (obviously if you do the maths) to a 2:1 ratio would be used to step down from the average of 230V that is coming out of your wall socket to the 100V that your synth expects to be fed. The circuitry in the power supply in the synth (after the synth's own internal transformer) is regulating the voltage(s) yet can only go so far. The problem arises when the voltages at your wall socket go up by a certain percent. The voltages will also go up on the other side of that transformer. If you wish to use an external step-down transformer, I'd advise finding one that is purpose made for outputting 100V for Japanese gear.

The other option, as you mentioned, is to move the wire on the internal transformer. If the synth is equipped with this option, and lots of things were back in the day, then that's what I'd advise. It save a small amount of energy and the expense of more transformers that are also prone to acoustically humming after a period of time.

Re: Mains Voltages

Posted: Tue Mar 10, 2009 12:46 pm
by nathanscribe
It's also possible to replace the transformer inside the synth, but this brings its own problems.

For what it's worth, I've been using a 240-110 step-down with my Jap CS-15 for two years with no problems at all. I measured the voltage on the output of the stepdown, and it's 120V,so it's 2:1 really,but the output of the regulator in the synth is correct and it doesn't overheat, so for now I've left it. I intent to fit a proper UK transformer some time though just to be sure.