Loud buzz with Marantz receiver preout to amp

Hi Team —

I’m trying to connect an amp to my Marantz 4270 via the preouts so I can control volume with the Marantz (the amp, an Ashly CFT-1800, has no volume controls). I’m getting loud buzz that gets louder with every gain dial increase on the amp, and there’s no music coming through from my phono or aux sources.

I can hear FM radio, but have to really crank the Marantz volume to get the FM loud enough over the buzz. Something’s not right. I don’t think it’s a ground loop issue because of the total lack of any phono or aux source audio. The RCA jacks from the Marantz preouts go to the Ashly’s screw terminal inputs (the RCA cable heads were cut off and the 4 wires run to both sides, channel 1 + and -, and channel 2 + and 1. The Ashly has two more screws between those channel inputs dedicated for additional grounds — input and chassis — both of which are empty in this case.

The Marantz uses shared jumpers in its preout and front main in jacks that must be removed to plug in an amp — which means the front main in jacks are then empty. The manual indicates that I should connect the main in jacks to the rear pre outs to get sound from front and rear speakers, but I don’t use rear speakers. I tried it though, to see if that made a needed connection that was missing, but it didn’t help. Same buzz. I should also say, the Marantz just came back from my tech, who specifically gave the preouts a clean bill of health, knowing I wanted to set this up.

Any ideas? Thanks very much!