Dust cover up or down?

Some people have very strong opinions on this but mine is that, as is often the case, it depends. Not all dust covers are affixed to the turntable in the same way and left on during play some can transfer vibrations back to the phono cartridge. Others, such as the dustcover on my VPI TNT III, are completely independent of the plinth, so that's less likely to be an issue.

Back in the '80s, I had a Denon DP-80 turntable in a VPI HW-9 two-arm base. One problem I had with it (and that really took some sleuthing to resolve) was that static electricity from the dustcover was enough to decrease the VTF of either arm. So I always used that with the cover off.

Mine has not any hinges so it is one way, removed.

Back again not in use. Anyway i remember all my turntables to sound better when it was removed.

G

I remove mine - it sounds much crisper and cleaner

I only leave it on while it is NOT playing - it keeps the dust off👍

It's a really simple design that allows me to lift the cover off without having to undo any screws 

Regards - Steve

Theory is one thing:

dust covers can contain/reflect internal microphonics back onto the lp surface, ’corrupting’ what the stylus receives/transmits.

play in up position? double check the deck remains level when the cover’s weight is all on the back when open. The cover can transmit airborne vibration via the hinges to the deck, could be worse. Can be less than ideal visually as well.

lift off? have a designated location, perhaps some felt buttons on contact edges, that’s my preference.

play closed? protects from airborne dust if a potential problem.

Reality is another. Can you hear any difference/detriment either way?

Do it blind first: turn your back, have someone else play it up, repeat the track closed, jump around a bit up/dn? After that do it yourself facing properly, your ’expectation bias’ will be reduced some at that point.

Off, not up or down, but off. In this instance, go commando.

Dust covers are for keeping dust away, not to be on the turntable while playing a record. It's like putting a giant unwanted resonating badly tuned  (complex resonances) tuning fork on the side of a vibrational measurement device - called a turntable. Generally considered to be a bad idea.

Dust cover OFF. It acts like a vibration antenna in my opinion.

Yes. But in storage is better.