In need of a GOOD 3:1/4:1 passive input selector

I have two turntables and will be adding a 3rd to my main system. It will be used to screen records purchased from less than ideal locales (goodwill, garage sale, etc). I have a 4:1 passive ’preamp’ (sic) that I use with my primary turntables on my Bryston 1B-MC. The problem I hear is a audible low-frequency hum over the speakers at around 70 hz regardless of the input I select. Both tables are grounded. If I select one table over the other and connect directly to the back of the preamp, the hum goes away. This tells me that the selector i have is, well, a cheap POS.

Is there a solid 2:1 or 4:1 passive selector that filters out the hum?

(NOTE: worst case, I could create a filter that filters out the hum. but seeing as it is the 70hz and below region, I will cut-off some low frequency information.)