Allen & Heath GR1 rack mount mixer

I’ve been needing a 1RU rack mount mixer with a few stereo inputs and have been watching Ashly mixers on eBay but recently I saw an Allen & Heath GR1 and thought I would give it a try.

Obviously before I put it into service I want to verify that it functions correctly. The GR1 is a rather complicated device in as much as there are a lot of configuration options available via internal jumpers.

Allen & Heath GR1 Brochure short form PDF
Allen & Heath GR1 Brochure long form PDF
Allen & Heath GR1 User Guide PDF

My measurements from the various inputs to outputs show that the signal path to the L/R outputs is golden but there is something terribly wrong with the Mono output. At first I couldn’t get a useful measurement. As if I was getting self generated noise. I unplugged my measurement rig and landed the Mono output on a Whirlwind Qbox (small self powered speaker). Sure enough, white noise coming from the Mono output with no input signal on the mixer. As a reference, I tried the same setup with L & R outputs. Clean. So something is wrong with the Mono output stage. It may be due to something being configured incorrectly inside the device. It may be from being damaged.