Setting up my first serious SO2R station with K3 twins and MK2R+. Everything seemed to work fine during initial testing, but I'm having intermittent audio issues during contests. The headphone split randomly switches back to combined audio while I'm in the middle of copying an exchange on radio 2. This only seems to happen when radio 1 is transmitting, and the switching won't reverse until I stop the CQ.

I've tested all cable connections and they appear solid. Has anyone experienced similar issues with SO2R controllers? I'm wondering if this could be an RF issue from the amplifier feedback, or possibly a timing problem in the control logic. Any diagnostics I should try before the next contest weekend?

I had the exact same problem with my MK2R+ setup last year. The SO2R controller started randomly switching split headphones back to combined, then would not switch back until the transmitting radio stopped. Very frustrating when about to copy a serial number. In my case it turned out to be RFI from the AL-1500 getting into the control lines. Adding ferrite cores on all the audio cables between the controller and radios solved it completely.

Check your grounding scheme first - I've seen this behavior when the SO2R box doesn't have a solid RF ground reference. Also verify the firmware version on your MK2R+, there was a known bug in earlier versions that caused audio switching glitches under high RF conditions.

This is exactly why I started with a simple manual A/B switch before investing in fancy SO2R gear! But seriously, have you tried operating with reduced power to isolate whether it's RF-related? Also check that your headphone impedance matches the controller specifications - some units are sensitive to load mismatches.