One of my interior neons (OPTX Radio Bar) has a music interface with the transformer built into it. The music interface makes a really anoying high pitched hum that I would like to get rid of. So appropriately, I would plan to cut the interface module out, and just put a transformer in (Can I do this?). I don't know what kind of transformer I would need, can I get it at RadioShack, or do I need to go bug the guys down at the Car Electronics Shop?
No, the power suppply provided is a high frequency switching power supply - obviously with very poor shielding. That not withstanding, your car cannot power a "transformer" as there is no such thing as a DC to AC transformer.
Your best course of action would be to buy a better quality version of your interface... OR, you could try to shield it better, at the risk of voiding any warranty.
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."