How do you stop a sub woofer humming when connected to a BTL amplifier?

[CageyH]

How do you stop a sub woofer humming when connected to a BTL amplifier (via the speaker terminals) and the speaker outputs are floating?
I know one way would be to use a RCA cable from my pre amp, and use the low level input, but this is not convenient, as the headphone amp is connected there.
I have tried leaving the ground floating, and I have also connected it to the chassis ground.

With the sub connected, low volume listening is more pleasurable, which is why I want to keep it connected.

[Firebottle]

Positive input connected to one output of the BTL (can be pos or neg) and negative input to signal ground.

Perhaps the chassis of you amplifier isn't also signal ground, in which case try a temp connection to one of the input outer/negative/ground.

[Lawrence001]

Positive input connected to one output of the BTL (can be pos or neg) and negative input to signal ground.

Perhaps the chassis of you amplifier isn't also signal ground, in which case try a temp connection to one of the input outer/negative/ground.

Which input on the sub, and output on the BTL amp, do you mean though? it's not clear to me so may not be to the op.

[CageyH]

Positive input connected to one output of the BTL (can be pos or neg) and negative input to signal ground.

Perhaps the chassis of you amplifier isn't also signal ground, in which case try a temp connection to one of the input outer/negative/ground.

Thanks Alan. I shall have to check is the chassis has a signal ground, but that should be quick/easy to do.

[Mr.Ian]

If you knock up a long earth only rca lead you could connect it to any spare rca on the pre.

[Mr.Ian]

Out of my depth on the next chain of thought, but throw it into the mix for some one more knowledgabe to comment.

Some subs have a balanced high level input option. If available, is this a better option for BTL amps? assuming running one sub on each channel.

Probably still need the ground lead on the low level input though

[CageyH]

So connect the sub up using the Speakon connector connected as before, and add the earth only RCA?
Thanks, I will give it a try.

I have temporarily removed my headphone amp, and have it connected using the low level inputs. No problem with hum at the moment.

[Mr.Ian]

Cheap phonos and bell wire to any rca socket should work fine.