REL subs with Rowland Amplifiers

Al,
Is there a logical reason why when both subs are connected through the high-level input with the REL supplied speakon cable no hum is audible,  but when  I use the Signal speakon cables the hum is clearly audible?  This is with no RCA cable  connected to the RELs LFE inputs and into my preamps outputs. Of course connecting RCA cables to the LFE inputs and my preamp's output eliminates the hum when the REL supplied speakon cables or Signal speakon cables are used. 

Richard, were you or were you not connecting your RCA ic to your preamp from your REL at the low level connection (LFE connection)? Because if you were, you are now activating your low level connect ( pushing signal as well as establishing a ground), I do NOT believe you can have both a high level and a low level at the same time...as I was told that if you do this, the low level takes precedence.

daveyf,

You do realize that the .1/LFE and low-level inputs are different? Although I didn't use .1/LFE I thought it was understood I wasn't referring to the low-level input. Since you won't listen to me, I have attached emails that I received directly from REL.

DIRECTLY FROM REL:

Richard,

You had been running the RELs low level. Instead of finding a place to connect the BLACK wire to the chassis, you can use RCA cables to make the signal ground connection.
I would connect between the pre-amp and the LFE RCA input of the RELs. The collar of the RCAs will provide the same connection that the BLACK wire if the high level cable would make.
Simply leave the .1/LFE Level control at minimum.

When you have a component system like this, all the components need to share the same ground reference. This is typically the signal ground of the system and is shared by both the pre-amp and the amplifier.
What I am instructing you to do is access the signal ground by connecting the PRE-AMP to the REL.

Yes, you can use make the RCA to RCA connection while still using the high level connection.

There are two input channels to the RELs.
1) the high level/ low level channel and
2) the LFE channel.

Each has it’s own level control.
The ground connections for both the these channels are connected internally to the REL. So connecting the RCA collar is like connecting the BLACK wire of the high level cable to the signal ground at the pre-amp.

Interesting Richard. I got the exact same advice from REL and then on a subsequent call was told that the LFE.1 channel takes precedence ( same as the low level connection). If it is connected via an RCA cable. The second adviser told me that i should just run a wire from the preamp to the REL chassis to establish just a ground and not an RCA cable...i did neither. No question that attaching the RCA CABLE TO THE PREAMP AND TO THE REL CREATES A GROUND.

I've already sent Rowland an email requesting the cost of adding an external ground screw. Hopefully they will respond tomorrow and I will ship my amplifier to them before the end of the week.