+1Radial bigshot aby.
Another +1.Radial bigshot aby. Ran my jcm800 and twin rig for 2 years. Rock solid.
I tried the Bigshot ABY. No luck. It introduced a massive amount of squeal, much louder than the guitar signal. Definitely not usable. Bummer.
Did you try all switch configurations?
Yup. Tried all the switches, tried different cables, tried with a power supply and without, tried not plugging in my guitar, still squealing. It’s very microphonic.
Sounds like a faulty unit. We ran 5 amps at once in many diy basements without the issue you describe.