S/PDIF isolation transformer

In my office setup, I have a RPi which connects to my DAC (S.M.S.L. Sanskrit 10th V2) via USB, a TV which connects to my DAC via TOSLINK, and a connection to my PC over S/PDIF. The DAC connects to a WAD HD83 headphone amp and I’ll soon have a pair of desktop speakers.

The problem I had was ground loop from the PC to the headphone amp caused by the ground of the S/PDIF. I rummaged around online for a S/PDIF isolating transformer and couldn’t find one.

Lundahl make a transformer for digital audio, the LL1572 which would have done the job, but they seem to be in short supply.

Where else could I find a digital transformer? Ethernet uses transformer coupling and I just happened to have a surplus to requirements PoE injector lying around. Prised the lid off and lo and behold there’s a transformer inside:

Quick look at the PIN out

and picked pins 5 and 6 and 19 and 20 as the input and output pairs.

Some fiddly soldering later, tested it and it worked!

Now for something to put it in. Pack of plastic project boxes from Amazon, and a couple of RCA sockets.

Works a treat. Passes hi-res audio with no hum!


Nice handywork. Is this on the same order?


Hmmm, It’s designed to reduce jitter, which it sort of does, but then again:

and at £199.00 it costs more than my office DAC. It’s way overpriced for galvanic isolation!

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True that, but your time and labor has value too.

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That’s true, but tinkering is another hobby of mine :wink:

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Isolation transformers are useful. Borrowed one from my brother last month. Wanted to eliminate some hum issues. Wasn’t a ground problem after all.

I just returned it this week. A large Topaz unit (guessing it’s from late 70s or early 80s). Thing weighs a ton. Looked kind of like this one.


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Wow, that’s a bit of a monster!

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I use a Meridian 518 for my SPDIF sources which does so much more than one of these iFi products and on the second hand market it’s probably cheaper too. Max 48K

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