Wiring Antrim ® Toroidal Mains Transformers

. There seems to be an absence of this information on the internet, although I have noticed that Antrim have put up some details themselves when I got round to writing this page, which happens to be here.

For those who are a bit worried about wiring a toroidal transformer for the first time (I know I was), this little article should help you become more confident in how you are wiring the transformer into your system. For the example, I will be showing you how I wired up the toroidal transformer in my main amplifier, of which further details are available here.

This article is specific to Antrim toriodal transformers only, but is likely to be useful for many other types of toriodal mains transformer, only the colouring of the wires is likely to be very different.


Firstly, lets have a look at what the standard range usually have. There are four wires for the primary windings, and another four for the secondary windings. This allows both parallel and series windings. I will explain this a bit more later, but first we shall look at the primary windings.

The primary windings on these transformers are where the mains voltage connects. This is very critical and things must be correct, or consequences will be fatal. The diagrams below are a repeat of the page linked above for convince of printing and reminding you how to wire these transformers specifically.


The transformers you will be likely to obtain will be the twin 115V primary winding versions. You will be one of the two following situations:

  • You are a European or elsewhere in the world where your mains voltage will be 220V to 250V AC.
  • You are an American, and you have 110V to 120V AC mains voltages

If you don't know what voltage your country is using, you shouldn't be doing electronics ;-)

Wiring the Primary Windings

Firstly, lets look at non-American voltages. These are the case in most of the world, including the UK, where I am based. If this is your case, you will need to wire your transformer in exactly the way described by the diagram in the top left above. That means you will be connecting White and Black windings together. I found I cut these quite short, soldered them together and very carefully insulated them.

I found that once the wires were shortened and the main insulation cut back for soldering that there was a protective (enamel) layer over the copper core. This layer would not be burnt off by my 18W soldering iron and I was required to get rid of it by other means. What I did was to get a needle file and file very carefully the edges of the copper core. This needs to be done very mildly indeed and overdoing it means that you will thin the wire too much which can cause it to break in time or provide too much resistance. Remember mains voltages will be travelling in these wires.

Another (and perhaps better) alternative of removing the coating is to use a stanley knife (or similar), as suggested by others on the ESP forum. Small disposable knives are the easiest to use. Usual rules apply when doing this, scrape the coating off in a direction away from your fingers (or anyone elses) to avoid injury if you slip. Also don't do this on your best table ;-) and never leave the knife around once you have finished. Unless necessary, I wouldn't recommend shortening the wires at all for the sake of saving hassle.

Once you have connected the White and Black wires and very carefully insulated them, you now have two wires left, which as you can see connect to your mains input. Rather then joining the wires to others, if you can, solder them straight to a mains input socket, or a switch. Again, if they are shortened, you will need to remove the protective layer. The Brown wire will connect to the neutral input, whereas the Pink wire will go to the Live (active) input.

If you are an American, or other country with approx 115V mains, you will need to wire the primary windings differently. You will need the parallel arrangement, as shown the the top right diagram above. This means that you will be running the White and Pink wires straight to the live input of your mains socket or switch. Standard live colour for US mains is White. Both of these wires will need to be joined together, and the mains input too. I would not recommend soldering three wires together unless it is necessary (i.e. the leads aren't long enough to reach your mains input). The other two wires on the transformer also connect together and run to the other side of the mains input. This means that Brown and Black will join and run to the Black coloured wire on the mains input. Careful soldering and insulation is of course recommended.

Wiring the Secondary windings:

Most of the circuits I have on my page require a centre tapped transformer. This can be easily obtained from these transformers which have 2x secondary windings. We shall have a look at this first.

The diagram above shows how this can be done - you need to look at the bottom left. What you will get form wiring like this from a 2x 12V transformer for example is the configuration 12-0-12. The maximum current that can be pulled in this configuration is half that rated by the transformer (i.e. the rated current for each winding) as you are effectively getting two times the voltage.

From this configuration, it can be easy to set up a single rail PSU as shown below:


Or you can get a split rail PSU, like this one from the TDA2030 amplifier:


To get this wiring arrangement, you need to connect the Yellow and Blue wires together. This will give you the centre tap, or 0V as it gives. This will effectively be the ground in most circuit applications. The other two wires left will be the two AC voltages, in the case of a 12V transformer, it will be two 12V connections. This is obviously given by the Red and Grey wires, and in most PSU applications, they will go to the AC inputs of the bridge rectifier or into two diodes. Again, careful insulation and wiring is required as in some cases, these secondary windings will be of high voltage, i.e. a 2x 40V transformer could kill you, especially after it is converted to DC, which will give you over 110V DC!

The other scenario that you may require is parallel wiring of the secondary windings. What you will get from this is a standard two wire output with no centre tap. For a 2x 12V transformer, you will get 12V AC output, but a current that is twice the rating of each winding individually. To get this configuration correct, follow the diagram at the bottom right above. Blue and Red connect together and give you one side of the AC voltage. Yellow and Grey join to give you the other side of the AC voltage.

Hopefully that should be all you needed, further power supply guidelines are on the ESP website (www.sound.au.com).