Apollo Twin - Intense Hum when using Inputs 1 and 2 at same time

fresh1megpots

New Member
I am running into an issue that I have not seen before. Before I run out and spend more money on a DI with a ground lift, I am wondering if anyone else can confirm that they have experienced the same thing or if it is expected for some reason. Ideally I would also like to understand why this is happening.

I am simply trying to record 2 guitar signals at once - One from my amp, and the other a dry signal
Simple setup:
Guitar > Boss Tuner/ABY pedal > Output 1 > Amp > Sm57 > Twin Mic Input 2
Output 2 > Twin HiZ Line In 1 (tried with Twin mic input 1 as well)​

I plug in my XLR to mic2, as soon as i plug in the dry 1/4" to the HiZ1 input (or the line in on the back), the noise and hum is unbearable. It is much louder than the guitar signal itself.
Same thing happens if i plug things in in reverse order. No matter what, once both signals are plugged into the inputs, i get a harsh, loud hum. Either of the inputs alone through the apollo are not a problem.

I was able to find a workaround where i ran the dry signal into one of the inputs on my Octopre connected via ADAT, and the mic signal through the apollo. This seems hardly reasonable to me, so there must be a better way or something I am overlooking. I also don't understand how it is possible for a ground issue to arise only when two inputs are running to the apollo and not just one. If I didn't know any better, I would say it was acting more like it was completing a circuit internally - i.e. when two inputs plugged in, it creates crazy hum, and not otherwise.

Is this a ground issue? and thereby, would something like a radial DI with ground lift resolve the issue?

Any help is appreciated. Thanks.
 
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