Hum connection two turntables with Rek-O-Kut switch

[Duane H]

I have two turntables that I want to hook to one amp. From some posts on Audiokarma, I was introduced to the Rek-O-Kut phone/aux switch. I bought it installed it paying close attention to the to the instructions, but I still have noise. Instructions from Rex-O-Kut mentions for amp line use you don't need the grounds from the turntables, "The ground terminal connection is not needed for line use and can be left unconnected."
Figuring something with ground was causing the problems, I then connect the grounds of the two turntables up to the back of the Rek-O-Kut and still same type and level of hum.
Connection each turntable to the phono jacks of the amp separately, both work fine with no noise.
What am I doing wrong?
Everything thing I have is older equipment. Amp is a 1978 MCS 3835 stereo integrated amp, one turntable is a Kenwood KD-2000, and the other turntable is a JVC L-A11

 

[safebet]

Signal level from a phono cartridge is particularly weak and also has not received the RIAA equalization curve which significantly boosts bass. Passive switchers generally work well with line/aux level signals.

 

[safebet]

if connected directly, do either of the turntables produce significant hum?

 

[Duane H]

sarebet, no, when connecting each turntable to the phono jacks of the amp separately, both work fine with no noise. The instructions, mention an alternative way to connect the Ret O Kut switch by using a preamp before the amp.