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Upon the advice of this question/answer I have added a 1:1 audio isolation transformer to my circuit.

I picked up a transformer at the local radio service shop and dropped it into my bread-board prototype; it's a Shaffener IT237 as shown in the spec sheet below. It works well in my application. I'd like to purchase an SMD equivalent, but I'm not sure what paramaters are most relevant for this circuit.

I don't fully understand how this transformer affects the circuit, but I do know that it fixes the issue outlined in the post linked above.

The circuit shown below is a simplified version of my project. The input is the line-level AC coming from a CD player, ChromeCast, or similar appliance. The output of the Class A amplifiers is sampled by an Arduino.

What parameters of the existing transformer shown in the specs sheet below should I consider when looking for an alternative SMD version of this component? I would guess that I need a low impedance device as this is for use with very low voltages (5-50mV), but beyond that I have no idea what I'm looking for.

schematic

simulate this circuit – Schematic created using CircuitLab

spec sheet for IT237

Aaron Ciuffo
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  • Since this is audio, I'd be more worried initially about Webers. So the column that has the "1100" figure in it (the English used seems weird to me), the one that says \$\text{V}\,\mu\text{s}\$, would be my first item to focus on (aside from the main ones about 1:1 ratio, for example.) – jonk Apr 13 '19 at 21:16
  • @jonk While this is audio, I'm not actually doing anything with the audio other than sampling the average voltage over time. The Arduino that is connected to Channel 1 and 2 is just looking for activity on a channel. I don't need a clean signal. The overall purpose of these two transformers is to isolate each channel from the other. Does that make any difference in what you would recommend? – Aaron Ciuffo Apr 14 '19 at 06:27
  • Would one of the transformers in the series linked below be an adequate substitute? https://www.murata-ps.com/pub/data/magnetics/kmp_da100j.pdf – Aaron Ciuffo Apr 14 '19 at 19:42
  • I don't know your sampling rate. All I see is a class-A amplifier getting its input across the transformer. And I think I gathered the frequencies are audio. You used a particular part that worked well, according to you, but it has a large value for the Webers (just into the milliWebers.) Without sitting down and doing the best I'm able (which isn't the best anyone is able, since I'm just a hobbyist), I can't say that these new devices on the linked PDF have any chance. Yours, the one that worked well, is 40 times the Webers of the largest of those. Audio is slow and needs Webers. – jonk Apr 14 '19 at 20:07

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