S/PDIF isolation transformer

Graeme_Finlayson · March 20, 2021, 2:55pm

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!

rrwwss52 · March 20, 2021, 3:56pm

Nice handywork. Is this on the same order?

Graeme_Finlayson · March 20, 2021, 4:38pm

Thanks.

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!

rrwwss52 · March 20, 2021, 4:44pm

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

Graeme_Finlayson · March 20, 2021, 4:50pm

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

rrwwss52 · March 20, 2021, 5:25pm

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.

Graeme_Finlayson · March 20, 2021, 6:46pm

Wow, that’s a bit of a monster!

Chrislayeruk · March 20, 2021, 7:28pm

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

EnjoyTheMusic · February 27, 2024, 4:06pm

Great work. I have build a few streamers over the years and know you are on the right lines here.

EnjoyTheMusic · February 27, 2024, 4:50pm

@rrwwss52 I bought the ifi SPDIF iPurifier2 and then ifi Lan Silencer.

I have built my own streamers over the years and trailed them against a retail $2.5k streamer (roon ready) streamer until I home built a ‘stop spending $£’ model as you as mine is better, model that $3.5k model. I know streamers can make a difference (after speakers, Amp, DAC?? Stopped me changing my DAC!!!)

Anyway, I had the chance to pick-up a converted streamer ($4.4k MRRP) that included CD buffered play back and ripper + art worked displayed, HDD storage music server and amazing build quality. Oh and a streamer.

However, I was gutted as the SQ was a step back worse than my ‘stop spending $£’ model’ I looked at its internals and thought 1. May need a better power supply? 2. Where is the re-clocker/clocks? 3. Where is galvanic isolation? 4. Output stage looks!?!?!? 5. The computer board and the sound board are on the same board ….NOooooo Etc.

So, I bought the ifi SPDIF iPurifier2 – expecting not a lot of difference and that I would send it back! However straight out the box the ‘Sound’ had changed. So dived into a playlist for a few hours and the ifi SPDIF iPurifier2 sounded better than my ‘stop spending $£’ model home build streamer’.

A keeper in this use case. I suspect the kit and the case are key.

AudioDreamer · February 29, 2024, 2:27am

I demoed this thing about 5 years ago. Surprisingly, every piece of music I ran through it sounded different. Sometimes a bit better, but mostly not. This was with a modest 2010 dac.