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When I plug my electric guitar into a multi-effects pedal and from the pedal into my amp, it works perfectly. But, when I use the same guitar, pedal, and cords that were just functioning correctly, but connect to a PA instead of an amp, the volume fluctuates - almost like a tremolo, but not at any particular tempo.

To be clear, these strange fluctuations happen regardless of the effect I choose, but none of the other instruments/vocals through the PA are affected. I can't figure out what this could be, especially considering that the exact same setup works fine through an amp. Thoughts?

  • What kind of PA? Normally guitar signals won't work well plugged right into a PA or mixer unless it has a high impedance input. Or you can use a DI box. A guitar amp and a PA input are very different. – Todd Wilcox Feb 2 '18 at 22:45
  • Though, a digital multi-effect pedal should normally work fine into a mixer's low-impedance line input. – leftaroundabout Feb 3 '18 at 23:40
  • @ToddWilcox - Mixer is a Mackie 2404 VLZ4 to powered Mackie Thumps. I might try a DI like I use for my keyboardist, but that still leaves me confused. I know a PA and amp are very different, but another guitarist uses her multi effects pedal without any problem, and my acoustic pedal works well, too. No high impedance input needed for those.... Thoughts? Thanks in advance. – Nikki J Feb 5 '18 at 15:26
  • @leftaroundabout That's what I thought, too. I don't know why other pedals are working but mine's not. Especially when it was fine through an amp. Same guitar, pedal, cords, etc. – Nikki J Feb 5 '18 at 15:27
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Is there a compressor on the mixer? I wonder if you are hearing the pumping of a compressor. If your signal is overly compressed, you may hear some strange volume changes. I suppose it could sound like a wonky tremolo.

  • Again, apologies for not getting back sooner, and thanks for trying to help. Notifications were coming to my inbox, and then randomly started going to spam. Turns out the pedal "went bad" suddenly and with no indication until it was connected to the PA. Go figure. – Nikki J Mar 27 '18 at 15:14
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I had the same situation when plugged into a Fender Passport. As it happened, the system had a feature called priority, controlled by a single knob, which would permit the first channel to override the other channels when sound was picked up by the first channel, resulting in automatic decrease in volume in the secondary channels. Supposedly designed to enable use of the system in situations where announcements are made during a performance, the whole idea caused us nothing but headaches for us during our performance just because that single knob was improperly set, I don't know about your set-up but it might be worth checking into.

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    Thanks for the help! For some reason the email with this notification went to spam so...excuse the delay. It turns out the volume fluctuations were caused by the pedal itself. It was so strange... The pedal worked through the amp, then in the ten feet between the amp and the PA, it went bad. I tested all the cables and used another guitar to confirm. Plugged back into the amp and the problems from the PA were there. No idea what I did in that short trip across the room. – Nikki J Mar 27 '18 at 15:11

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