I'm stumped, please help me figure out what's wrong here

Installed head unit, amp, sub. Wasn't my first time so I know I did it all right. Everything sounded great, until recently when I decided to add a bass knob. Now, the sub hums.

The knob intercepts the rca cables from the head unit then goes to the amp. turned all the way down, there's no hum. Turned all the way up, there's no hum. As you turn it up it gets worse until the middle then starts dropping off until full blast when there's no hum.

What the hell is going on here?!

 

Did you try to turn the gain down on the amplifier?

 

where is the wire ran as compared to your other power and rcas

 

Double check the connections on your knob. (Insert Butt-head snicker). There might be a stray little wire creating a short somewhere. Use a DMM to check for continuity between the terminals on the knob, especially where there shouldn't be any.

 

Ran it under the cup holders but pretty sure it's away from all wires and metal (I feel like I'd notice that). I'll open everything up again tomorrow and maybe wrap all connections with electrical tape

 

Since the noise is introduced in the middle of the boosts range, I would suspect a bad booster. If it were signal related it would be consistent with the amount of boost you are feeding it.

Also, I have not seen a boost that wires onto the RCA inputs, is this an aftermarket/universal device?

 

^^This.

 

yep universal

 

Is it powered? A bad ground might cause this, but if it's passive, I would say the knob is faulty.

 

Just a couple of further thoughts:

- post a link, maybe someone else has used one
- do you have a friend where you could hook this up and see if the problem follows
- have you removed it to make sure it is the booster