I’ve found that my MixingLink needs to have the input gain turned up quite high to get unity gain through to a guitar amp.
Guitar>Inst In>To Amp>Amp
I’m not using the MixingLink FX loop or anything else (although I get the same issue if I do). The gain switch on the side is set to ‘low’. Setting it to ‘high’ results in way too much gain.
If I have the Input Gain and the Phone & Amp Level knobs set to 12 o’clock, the output signal is a lot quieter than just running a guitar straight into the amp. To make the level match, I have to turn the Input Gain up to 2 o’clock. This also introduces a small level of hiss.
Solved. The problem was a dodgy cable! The cable works fine in other pedals, but was causing problems when plugged into INST In on the MixingLink. I switched it for another one and the MixingLink works as it should, with unity gain at 12 o’clock and no hiss.