Rear Input Quieter than the Front Input?

I'd check that again carefully with a test tone. Record the DI signal and look at the level.
With a 440Hz test tone and only shunt blocks, it's as you said.
https://www.dropbox.com/s/1dljw232j6kcx1z/440Hz test tone L+R Sum vs Left Only Shunt blocks.png?dl=0
With an amp and speaker block, the output appears normalized between the two. This should mean an increase in perceived gain from the left only setting as it's hitting the amp input with 6dB more signal, yes?
https://www.dropbox.com/s/og18pnv49ghpvtm/440Hz test tone Left Only vs L+R Sum amp and speaker blocks.png?dl=0

Interesting....

I'm still not sure my issue is the input pcb. There's only a small inductor/ferrite bead in series with the input and a zero ohm/100n ground float in series with the jack ground. I suppose the inductor/ferrite bead could have gone bad (maybe ESD punched through it). I have one on the way.

With no cable plugged into the front input I'm getting -65dB noise floor. Plexi 50 High 2 > factory cab 189 nothing else. Output 1 level @ 12%
 
That's not the case with my unit. The only thing that changes is the noise level, by ~6-7dB
Does that happen on clean sounds, too? I get a 6 dB reduction in input level when I switch from Left to L+R Sum. On distorted sounds, that translates to same output level but less gain.

IIRC, the level reduction happens in software, not in hardware. So if it's not happening for you, maybe it's a firmware issue.
 
Does that happen on clean sounds, too? I get a 6 dB reduction in input level when I switch from Left to L+R Sum. On distorted sounds, that translates to same output level but less gain.

IIRC, the level reduction happens in software, not in hardware. So if it's not happening for you, maybe it's a firmware issue.
I'll check this tomorrow and report back.
 
Does that happen on clean sounds, too? I get a 6 dB reduction in input level when I switch from Left to L+R Sum. On distorted sounds, that translates to same output level but less gain.

IIRC, the level reduction happens in software, not in hardware. So if it's not happening for you, maybe it's a firmware issue.
This is indeed the case. No software issue.
 
I'm not sure which way to read what you just said. :)
:)

Well I did try to make that as cryptic as possible. The 6dB reduction happens as it should when you switch from Left to L+R Sum.

LSS... I had a friend try my noise test on his XL+ and his front and rear Input 1 have roughly the same noise level with the guitar volume turned up. Mine has about a tenfold increase in noise from the front input to the rear and compared to his. I have ordered a new instrument input board from Fractal and should get it this week. I'll do some tests as I swap it out and them post my results.
 
Ah, now I get it. It does sound like a hardware issue at this point. I'm eager to hear your results with the new input board.
 
Ah, now I get it. It does sound like a hardware issue at this point. I'm eager to hear your results with the new input board.
Me too, as there really isn't much of anything significant on the input board. One series inductor for noise (which I suppose could have been damaged by ESD), a zero ohm resistor in series with signal ground and a 100n cap that floats the input ground. So it'll will be interesting to see if the board helps. I'll keep everyone posted.
 
:)

Well I did try to make that as cryptic as possible. The 6dB reduction happens as it should when you switch from Left to L+R Sum.

LSS... I had a friend try my noise test on his XL+ and his front and rear Input 1 have roughly the same noise level with the guitar volume turned up. Mine has about a tenfold increase in noise from the front input to the rear and compared to his. I have ordered a new instrument input board from Fractal and should get it this week. I'll do some tests as I swap it out and them post my results.
Bad ground on your front input board.
 
Ok test results, the instrument input board tested good for ground continuity installed in the axefx (I used a 1/4" male plug to test as in the video). Ground continuity tests good on the input board uninstalled in the axefx but still connected via the input jack cable. The input jack cable tested good for continuity. The input jack cable shield header pin on the main board tests good for ground continuity. So I must conclude that I dont have an obvious bad ground on the front input board. Here's a very brief vid clip I did after reinstalling the front input board with the same preset as before (noise gate off, amp block 50 watt plexi high 2, cab block factory 189), testing the noise difference between the front and rear input 1. Instrument In set to 36%, Input 1(rear) set to 50%.
The noise results are the same using both xlr output and usb.

The new front input board I ordered should arrive tomorrow. So I will give that a whirl just to eliminate my current board as a source of issue.

I have also attached the preset just in case
 

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