Step down transformers detrimental to SQ?

interesting Georgehifi on the 1:1 that may be useful for DC blocking. DC on the line can cause transformer mechanical hum.

Yes also RF as well.

Cheers George

I heard some crazy Japanese audiophiles do double conversion, up and down, and claim it improves the sound.

Not quite but close, there is a bit of a fad at the moment over there, to use 1:1 isolation transformers, which are 100v in 100v out they are doubling up on these.
I’ve used a 2amp one now for 20 years now for my source equipment only, and will always do so.
https://www.servostabilizer.org.in/wp-content/uploads/2017/10/images1.png

https://www.servostabilizer.org.in/isolation-transformer/

here is a US made one, I’m sure there are others.
http://www.solar-emc.com/6220-1B.html

Here are some eBay ones.
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2053587.m570.l1311.R1.TR12.TRC2.A0.H0.XIsolat...

Cheers George

Step down transformers detrimental to SQ?

Just make sure the amperage rating is at least two times higher than the mains fuse on the amp this should keep the core from saturating even a little.
Also step down transformers can actually be better for mains born noise getting into the amp.

Cheers George