REL B3 connecting to Linn Klimax Solo help...

First, the ear is extremely insensitive at 20 Hz. A tone at that frequency would be mostly felt rather than heard, apart from the possibility that harmonic distortion components that may be produced by the sub at higher frequencies (40 Hz, 60 Hz, etc.) in response to the 20 Hz input may be audible.

Regarding the connection arrangement, the ground connection ("earth" in your country) from the sub should go to a circuit ground point, as opposed to a chassis ground point, and preferably on the preamp. Depending on the design of the components, circuit ground and chassis ground may or may not be common (i.e., connected directly together). In the case of your components, I would guess that they are not.

If you have a multimeter, disconnect the preamp from everything else and check for continuity between the earth ground terminal it appears to have on the rear, and the ground sleeve of one of its RCA connectors (which WILL be common with circuit ground). If the resistance between those points is not zero ohms, or at most a tiny fraction of an ohm, they are not common.

In that case, or if you don't have a multimeter and can't perform the measurement, a good approach would be to purchase a simple RCA plug, similar to this one, and solder the ground wire from the sub to the ground sleeve of the plug (soldering the wire to the lengthy metal protrusion that appears towards the right side of the photo). Connect nothing to the center pin of the plug. Then insert that plug into an RCA jack on the preamp, and you will have provided the sub with a proper ground connection.

Hope that helps. Regards,
-- Al

Hi Al, my Source has a dedicated plug for ground on its rear. I am using that. Without the use of that, the unit hums. I have also tried using one of the negative speaker wires - that appears to work.

I think the unit may be faulty as I get little to no output on any setting in any connection method.
I also live in Australia where we have 3 prong power plugs

Thanks

My source has a dedicated plug for ground on its rear ....

Yes, but is that ground connected to chassis/AC safety ground, or to circuit ground, or to both. If it is only connected to chassis and AC safety ground, without being directly connected to circuit ground, that could be the problem. Especially if connecting to one of the negative speaker wires works with reasonable volume (not sure if that is what you meant when you said it appears to work that way).

Also, I would expect that using circuit ground on the source, or connecting the sub's ground to one of the negative speaker wires, would be less optimal sonically than connecting to circuit ground on the preamp.

Regards,
-- Al