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Q. Can I run US gear off UK mains supply?

By Hugh Robjohns

There are three different types of power supply. A fixed PSU like this will only accept one mains voltage.There are three different types of power supply. A fixed PSU like this will only accept one mains voltage.

I've recently bought a couple of bits of recording gear from the US via eBay (I'm in the UK) and wondered if I have to run them off a transformer (240V to 110V) or whether they can run off 240V? Is this likely to blow up my gear? Should I just play it safe and buy a couple of transformers, or is there some other kind of adaptor you could recommend?

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Technical Editor Hugh Robjohns replies: It depends on each piece of equipment. There are three possibilities and you can find out which is appropriate by checking the label near the mains power inlet on each product. The products' user manuals should also state the mains requirements and options. If you don't have them, most manufacturers make their manuals available to download from their web sites and, if not, you could always try contacting them or their local distributor directly.

A universal power supply, typically marked '110V-240V', can deal with any voltage in the stated range.A universal power supply, typically marked '110V-240V', can deal with any voltage in the stated range.

The first possibility is that the equipment is configured at the factory to operate only on one mains voltage, specific to the local region to which the product is shipped/sold. The label will say something to the effect of '110V only'.

In this case you will have to run the unit from a step-down transformer to convert our 240V mains to 110V. Alternatively, you could have a different mains transformer installed by a competent electronics engineer, although this is usually a difficult and expensive process.

A switchable PSU lets the user set the unit to accept the local mains voltage, often by means of a recessed red switch, as seen here.A switchable PSU lets the user set the unit to accept the local mains voltage, often by means of a recessed red switch, as seen here.Very little equipment relies on the AC mains frequency these days, so the change from 60Hz (USA mains) to 50Hz (UK mains) is unlikely to make any difference other than possibly increasing vibration and hum in the transformer. However, some tape machines and record turntables do rely on the mains frequency for the speed accuracy, and these can not be operated on the UK mains supply without the use of (expensive) frequency converters.

The second possibility is that the unit has a switchable mains input. The label will say something to the effect of '110V or 240V', and there will be a switch or reversible module to change the mains voltage over.

The final possibility is that the unit uses a 'universal' or 'switched mode' supply. In this case the label will say something like '110V-240V'. This type can handle both UK and US mains voltages.

In the case of both switchable and universal power supplies, you may also need to change the size of the fuse to maintain the safety protection. The label should say what value to use on 240V supplies, but it will be roughly half that used on a 110V supply (eg, 0.5 Amp instead of 1 Amp). Make sure you replace the fuse with the correct type (quick blow, anti-surge and so on).

If there is any doubt or confusion, the use of a step-down transformer is the safest solution. Obviously, connecting a device expecting 110V to a 240V supply is likely to cause serious damage, so take care!

Published March 2005