I see that it's a TVC passive preamp. I've never tried one but I've seen where many people love them.
I came across a designer/brand named Promitheus Audio that seems to specialize in TVC volume control for reasonable prices. They had some other components that interested me as well.. but I had a hard time finding any current owners or user reviews. Their stuff looks good to me though.
I did recently purchase a relay controlled attenuator off eBay from Ukraine. The same ones used in Phast preamps.. another Ukraine based designer. I bought the simple 2 channel unit just to try out & I'll admit that I was impressed. I liked it better than my GoldPoint stepped when I directly compared the 2 in the same circuit. Better sound & stage perceptions. There could be a little bias towards the relay attenuator because it has a remote.. but I think it sounds great. I replaced an Alps remote with it in my SP13 & the difference was grand.
I ended up making a passive out of the relay control with a wood enclosure I grabbed off Amazon for $30 bucks. Pulled the volume control completely out of the SP13 & used it as a tube buffer in my patio system with the relay passive controlling the volume. The buffer helped with its added gain
A transformer based volume control will still be superior. How it handles current, filters noise, & transforms voltage cant be matched by the usual suspects of attenuators. If you go that route I hope you share your experiences somewhere in the forum. I like the relay attenuator because it was cheap in comparison to other quality attenuators, I didn't lose anything when pulling out my stepped attenuators, & it has remote control.
The passive is a little sloppy as it was a quick build to see if I would like it. My photos came out sideways again..not sure how to correct it.

