You can search   "Earthquake Sound ISO-200 Hum and Buzz Kleaner 600 Ohm Ground Loop Isolator with RCA to XLR Signal Conversion"   on Amazon.  They are $36.95.  I can't say that it will solve your hum problem because those can originate in many places and the source can often be difficult to pinpoint, but if it doesn't work you can always return it for a refund.  I hope this helps.  Best of luck.

Did you try lifting the ground on either unit with a cheater plug first to see if that eliminated the hum?  Not a permanent solution but a test point.  For XLR to SE conversion units look first to Jensen before car audio products.  Also reach out to Ralph and see what he recommends.  

@jackd yes, I am communication with Ralph.  He recommended lots of ideas which I tried.  His most recent suggestion is a Jensen transformer, but the specific model he recommended isn’t available.  That’s why I posted.

He recommended the Jensen PI-2XR.

I am wondering if the PC-2XR will work.

Maybe a longer-term solution, it seems a bit of a shame you’re running a fully-balanced preamp into a single-ended amp.  If I’m you I’d be saving up for a good fully-balanced amp from the likes of Atmasphere, ARC, VAC, etc.  Just my $0.02 FWIW.

@hifinut51 

If you're talking about this model then it looks to be the exact same thing and PE has them in stock.

I am wondering if the PC-2XR will work.

I think it should work and if you order from PE it comes with a 60 day no hassle return policy.

@jackd yes, I am communication with Ralph.  He recommended lots of ideas which I tried.  His most recent suggestion is a Jensen transformer, but the specific model he recommended isn’t available.  That’s why I posted.

He recommended the Jensen PI-2XR.

I am wondering if the PC-2XR will work.

You can call Jensen directly, they can answer your question, if Ralph doesn't do it first. When I called. they gave me a nice discount, too.

Bob

the specific model he recommended isn’t available.  That’s why I posted.

He recommended the Jensen PI-2XR.

@hifinut51 I know someone that bought that exact ISOMAX unit only 2 weeks ago. Did you talk to anyone at Jensen?

Jensen may make one give them a call .

why not just use a shure xlr to xlr iso xfmr they are use in profesional sound 

systems all the time I use them when i am mixing corporate shows to quickly isolate a channel as i don't have a lot of time for trouble shooting a system

when getting it up and going

or go to amazon foe sescom il19 plus other isolators

Whirlwind ISOXL Line-Level Isolation Transformer, 3-Pin XLR Male/Female Connectors at Amazon

Jesse at Pine tree makes a balanced to unbalanced converter. It is an amazing piece. I use it between my Lumin D2 and amplifier. 

Ground loop.
Power amp should have grounded AC.
Lift ground to the preamp.

Use only unbalanced RCA interconnects.
Unshielded twisted pair is best, by far.
Unless the system is balanced in and out, there is no advantage to a balance XLR cable. No need for a transformer or other performance robbing accessory.

K.I.S.S..

I have a device with dual jensen transformers—the expensive ones—works for hum, but really takes the slam out of drum hits and the like. Using a crown drivecore amp with balanced inputs—lots o slam! If one cant find the nice xfmr, jensen has a website last time I looked. That gadget that costs $450–those are the good xfmrs, but the cost might go towards an amp change. I like the balanced to run a 30 foot cable—zero noise of any kind.