03/15/2026
DX1 transformer revarnishing:
We recently finished working on this DX1, which is the most "premium" of Yamaha's FM synths. It has the brain of a DX5 (exact same synth engine), but is upgraded with features like a wood hammer action keyboard, rosewood body, and these fancy displays that do make it a lot nicer to use.
The worst problem this one had was something I've heard one have before, a horrible acoustic ringing coming from the small transformer in the switched mode power supply. This is the result of cracks and voids forming inside the transformer from its varnish drying out over time, allowing it to vibrate and resonate, and can happen to any old transformer.
Luckily, I have worked out a reliable, inexpensive method for vacuum impregnating transformers. Revarnishing them in a vacuum ensures that all these voids can be filled despite the surface tension of the varnish, as long as they are contiguous with the outside.
All that is required is a mason jar big enough to fit the transformer, a small vacuum hand pump (used for canning food), a clamp, silicone tubing and matching silicone grommets, and a second airtight container like a jar or valve bag.
With the tube to the second container clamped, the pump is used to remove all the air from the jar. When the clamp is released, varnish is siphoned over and you can actually see it being aggressively sucked into the transformer in a way that it wouldn't be without the vacuum. I pump a few more times after the varnish comes in to remove any bubbles that come over too, but I'm not sure it's even necessary.
Sometimes transformers are also heated before being re-varnished, but based on my research I didn't think it would be necessary for transformers this small + that have been kept dry + when a vacuum is being pulled.
The revarnishing was successful and the ringing is gone!
(I always get this song "Walk of Life" by Dire Straits stuck in my head, which is basically a boomer dad song that you hear at Home Depot. But there's a video of them playing it live and the d***y organ sound at the beginning is a DX1)
