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Most of those transformers are a bit costly in my region(India). is there any alternative solution that can be employed.

Application in audio amp.

I was thinking maybe use a step-down and step-up transformer, of same ratio, in tandem. Can it work?

Thanks.

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    \$\begingroup\$ Are you talking about isolating the signal line or the power line? Because the answers below had to guess what you mean (and they've guessed differently). \$\endgroup\$ – Fizz Oct 25 '15 at 10:22
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If you use mains transformers for the audio signal it will 'work' but the audio performance will most likely be miserable. Perhaps suitable for voice. The reason is that transformers designed to pass many kHz need relatively thin and expensive laminations or the eddy currents in the laminations will attenuate the higher frequencies.

You might be better off trying to salvage something from a very old transistor radio (not the output transformer but an interstage coupling transformer). Suitable line in/out transformers are sold for auto use.. not too expensive.

Or get rid of the ground loop via a mains isolation transformer (large and not cheap).

Or design a differential to single ended amplifier to deal with the common mode voltage.

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  • \$\begingroup\$ Alternatively a modem [not DSL though] or [electronic/cordless-style] phone might be easier to find and scavenge the transformer from, but those tend to have transformers that begin to roll off around 4KHz. \$\endgroup\$ – Fizz Oct 25 '15 at 10:40
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    \$\begingroup\$ Also toroidal transformers could work, even if intended for mains. Those actually have bandwith to about 200kHz. I was amused that this guy was suprised his encapsulated mains transformer was good on the audio line. He's actually using an encapsulated toroidal, but he doesn't seem to know that, heh. \$\endgroup\$ – Fizz Oct 25 '15 at 10:51
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I assume you are thinking of a mains isolation transformer for your audio equipment.

Using the 230 to 12 to 230 double transformer will work but if you have to drive a 500W amplifier you will need say a 700W and a 600W transformer to do the job remotely well, probably better than consumer grade.

The popular source for 500W to 1200W isolation transformers for hobby use is to hack some microwave oven transformers. If you have two same (or close model) microwave oven transformers with some hard work you can modify them so that you have two 230V primary windings on one core. This gives you a reasonable isolation transformer (it will likely run a bit hot at full load because they are close to saturation on the cores as they skimp on the turns in the windings) from two scrap microwave ovens.

There are lots of tutorials on how to do this on the net, search for MOT and isolation

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