Try a few more things:

1. Remove the RCA cable, turn the volume down and listen to the tone of the hum. Now raise the volume and put your finger on the RCA jack. Does the tone decrease in frequency (sound lower in pitch)?

2. Reverse the plug if not polarized. Does hum disappear?

3. Move the sub to another circuit. No need to plug RCA in. Does the hum disappear?

Last edited by Mojo; 03/06/21 02:12 PM.
House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated