Is an unbalanced preamp a bad thing?

I have a Herron Audio VTSP-360.  Keith doesn't put XLR connections on any of his gear.  It sounds fantastic.  Before that I had a Modwright LS 100.  While it had XLR connectors, it was not "balanced".  It did however also sound great. 

How does your system sound?  Another preamp might sound better than the one you have, but whether it is balanced or not is probably not going to be the reason it sounds better.

Op - "I am borrowing a Conrad Johnson preamplifiper and it sounds very nice but to my surprise I couldn’t use XLR cables"

Seems like you knew this last year when you started the below thread 8/2021

@facten

i take this poster’s comments with large, very large grains o’ salt

either a very dull pencil, or a professional chain jerker... (or both)...

I think OP has a big question mark in his brain and that  let him to ask again. Very similar with me.

On this forum, people said it again and again ,it is the better choice to use XLR input, but why there is so many RCA  pre or amplifier on the market, especially for some main Street brand like CJ.

In my personal experience, RCA connection bring very good experience, even better than XLR.

All in all, it goes down to the design of the amplifier, the connection won't decide the sound in large percentage.

@runwell

+1.

Don’t worry about the connections. It’s all about the component. I would take a Conrad Johnson component using an single ended connection over a Mark Levinson, Naim, Macintosh, or any number of brands any day.