Are there passive attenuators that don't zero volume and only offer one input ?

Just had a look @ OP Stereo Coffee LDR attenuator @ 
Stereo Coffee Passive LDR Preamplifier (wixsite.com)

Why an A/C supply when a DC wallwart would keep all hum outtadabox?

PCB looks like something a kid would have designed 40 years ago.

TRIM POTS?!?!?!? WTF? Trim pots are the bane of high fidelity.

"However, the real magic of the 2020 StereoCoffee is what happens after 40 to 50 minutes playing music."

If a passive is changing, it's not passive. The whole point, at least for me for 40+ years, is PASSIVES DO NOT CHANGE!!!

He a shyster ieales, and known all over other forums
All you have to do is see how he disowned his own name and product, in the proof I posted up.

This was the best one he tried to sell on ebay and diyaudio he called a "Pass Transistor opamps" https://ibb.co/Db3yj9s see the little smd transistor squashed under the opamp with the "snake oil" he tried on
https://www.head-fi.org/members/dbxrecord.192735/

Cheers George

Why an A/C supply when a DC wallwart would keep all hum outtadabox?

Because you then avoid the cheap rectification components inside wall warts, all avoided by using a AC 12v supply.  Rectification can then be achieved with thyristors, and jfets

https://www.stereo.net.au/forums/topic/113297-comparison-lightspeed-diy-ldr-pre-vs-stereo-coffee-diy...

See ieales BS baffles the gullible, that’s his game.

Cheers George

Rectification can then be achieved with thyristors, and jfets

¿Que?

Thyristor is a gated diode. What earthly advantage is there over a 1N400x diode?

High quality DC supplies are 10 a penny today.