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Weird tone issue hooking Axe-Fx II up to 5150 with 4CM

jljesse

Member
Hi guys,
Long time lurker, first time poster. I'm struggling to configure my Axe-Fx II with my 5150 II head in 4CM. Following the instructions in the manual I was able to get a good level for my guitar at Input 1, and a matching level out of Output 2 and into the front of my amp by diming the Output 2 knob on the Axe-Fx front panel. I'm doing all of this using the factory Bypass preset 383 with an FX Loop block added. When I switch between this setup and plugged straight in to the amp I can't tell a difference.

When I complete the FX Loop connections from amp send -> Axe-Fx In 2 and Axe-Fx Out 1 -> amp return is where I have trouble. I'm able to get the levels balanced between In 2 and Out 1 but when I raise the Output 1 knob on the front of the Axe-Fx the tone coming out of the 5150 gets weird. There is a ton of missing low end and it sounds like there is some comb filtering or phase issue happening. I messed with the polarity of the Axe-Fx outputs in I/O and inverting output 1 did bring the low end back but made that hollow sounding issue worse. FWIW, I'm using regular TS cables to connect everything and this is with multiple guitars.

I've read the manual, watched every video on YouTube addressing the issue, and read each thread that has "4CM" in the title back to 2015 but I cannot find much info on this kind of issue. Thanks to any who read this novel for your time and help!
 

mr_fender

Fractal Fanatic
Make sure your FX Loop block is set to 100% wet. You don't want any dry signal passing through that block when running 4CM. Otherwise you'll get weird phase issues between the dry signal and the return signal from your amp's FX loop.
 

jljesse

Member
Thanks mr_fender! I checked the FX Loop block to make sure it is 100% wet. I also checked my amp's effects loop by connect the send/return with a patch cable - nothing concerning there. I'm still not sure why my amp sounds so different coming back into the effects loop return and am runnig out of ideas for trouble shooting. I may record a signal from the effects loop send into my DAW and compare it to what's coming out of the Axe-Fx's Output 1.
 

mr_fender

Fractal Fanatic
It's possible the FX Loop on the amp is wired in parallel. To test that, put a delay or reverb block after the FX Loop block and set it to 100% wet. If you still hear the dry amp signal from the speaker along with the reverb or delay, the loop is parallel. If you hear only the reverb or delay and no dry, it's series.

Parallel FX loops will cause phase issues with any dry signal that goes through that part of the Axe's signal chain.
 
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jljesse

Member
Apologies for the delayed response; health issues kept me away from guitar for a bit. I finally tested what mr_fender suggested and am dumbfounded by the results...

On the clean channel of a Peavey 5150 II head with the Axe-Fx II in 4CM and a preset containing only an FX Loop immediately followed by a delay block set to 100% wet I'll strike a chord and hear the delayed chord only. I never hear the chord as I strike it even with the clean channel volume set pretty loud.

However, on the lead channel when I do the same thing I hear the chord quietly as I strike it and then the delayed chord comes in as loud as I expect it to. Weird.

I reread the comments and realized that my FX Loop block does not have a setting for wet/dry; I'm on an Axe-Fx II MkII FWIW. Everything in it is zeroed out.

edit: some digging shows that the 5150 II's have serial/series effects loops and that the effects loop return is hi-z, which I don't think should cause any issues.
 
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mr_fender

Fractal Fanatic
Sounds like there might be something weird going on with the FX loop switching circuit in the amp. If you're hearing the dry signal a little on the lead channel, that means some of the preamp's dry signal is bleeding in past the fx loop. That's going to cause phase issues with signals that go through the loop.
 

jljesse

Member
After some searching I see a fair amount of other guitarists having similar issues with 5150's along with suggestions for which tubes best alleviate the issue of "loop bleed" on the lead channel. While the tube amp seems to me to have slightly more high and low end extension than the Fractal model the extra detail gets lost in a mix and they both wind up sounding great. Thanks for taking the time to help me troubleshoot this mr_fender! The 100% wet delay set to 2-3s really made the loop bleed obvious.
 
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