Speaker level ground wire?

[silver007]

First post!

Ok I have hooked up an older US Acoustics 2050 amp to my factory Ford radio (1996 cassette!) via the speaker level inputs.

I have the right + and left + wired to their inputs and the speaker level ground ran to the same ground as the amp's main groun (seat bracket).

I have line noise.

The instructions for the amp say:

If floating ground, run speaker ground to h/u chassis ground.
If common ground, run speaker ground to h/u chassis.

Anybody know what type ground this factory h/u has? It does have a + and - for each of the 4 speakers coming from the unit, but I don't know what's going on inside the unit.

Also, by 'chassis' do they mean the actual tin shell of the h/u?

What's the difference in this 'chassis' and the 'chassis ground'?

Confused.

[Perry Babin]

Do you have a multimeter?

Does the speaker level input on the amp have 3 or 4 terminals/wires?

[silver007]

Yes, I have a digital multimeter.

The inputs for the amp are R +, L + and ground. Three total.

[silver007]

Manual: http://pix.crutchfield.com/Manuals/235/235USX205B.PDF

[Perry Babin]

You will connect the black wire of the adapter to the head unit casing/chassis/tin shell.

Almost all late model OEM head units have floating grounds but I'm not sure about anything from 1996.

To determine if the head unit has a common or floating ground, switch the head unit off. Set the meter to ohms. Touch the black probe to the case of the head unit and the red probe to the negative speaker wires. If you read anything near 0 ohms, the head unit has a common ground.

If you power the head unit up and set the meter to DC volts and you read ~6v on each of the negative speaker wires, it has a floating ground (bridged output).

When checking the voltage with the head unit on, be absolutely sure that NONE of the speaker wires come in contact with any other speaker wires, ground or power wires. If they do, the head unit is likely to be instantly damaged.

If the head unit has a floating ground, you will need to insulated the negative speaker wires so they cannot come in contact with anything.

[ppia600]

+1 on what Perry said.

I'm kind of amazed that amp has a single ground high level input, you'd think they'd use totally seperate channel input for ground and positive. If the noise doesn't end by grounding the input ground to the headunit chassis, find a good line out converter with a built in ground loop isolator. That should solve the issue. There are a few decent brands.

[monoaural]

If it is a Taurus, hook it to the chassis ground of the factory "amp" in the trunk. Pretty sure it is not common ground. Ford stopped doing that in the late 80s, I believe.