Hi guys. I'm new to the forum so I hope I am posting in the right place. Anyway, right now I have a mesa dual rectifier going through a fender fm412 cab with a boss gt100 in the fx loop. The clean channel sounds great and my channel 2 and 3 sound good on raw or vintage. But when I switch over to modern it sounds like there is a chorus effect on (which there isnt. I have check several times on my gt100). When I turn the loop off it sounds like how it's supposed to. Im not sure what the problem could be. I think its something to do with the fx loop. If anyone has any idea what the problem is and how I can fix it please let me know. Thanks.
These amps are known for not having the greatest loops. Especially given the 'Rev' or year. If it is an older amp and you need it for recording or gigging and you like it otherwise - consider getting it modded (like fja mods dot com).

Now, that said, I'm not so certain I would run a Boss GT100 (or similar) into the loop of a Dual Rec. What do you use it for? Have you tried it out front? Have you messed with the Loop 'Mix' knob?
311ZOSOVHJH Thanks for the reply. The amp was made in 2012 so i wouldnt say its an older amp. I use the gt100 just for the effects via the '4 cable method'. Im not sure what the loop mix knob is. I have one of my knobs set at 'bypass loop'. That might be it.
I havent tried it in front of the amp yet. Would be worth a go.
Last edited by nstrelic at May 7, 2017,
I see.

Not sure why you would get a 'chorus' sound only on the modern setting. Is this a 2 channel or 3 channel Rec? And so if the Loop is bypassed the modern setting sounds fine? But with the loop engaged the modern setting sounds chorusy while the other settings still sound fine? Is the chorus subtle? Is it more of a warble or is it clearly chorus? Try messing with the FX Send Level. Try just a single pedal in the loop and also just 'patch' the loop with a short cable, or any cable, and see if the problem persists.

(From the mesa web site for reference)

Fully Buffered Series FX Loop w/Send Level Control - Footswitchable, Channel Assignable or True Bypassable - See True-Bypass Options below for more information
I'd say A/B it with and without the GT-100. I run a GT-10 same way on Mesa Mini Rectifier and it does color the sound somewhat. It is not bad but you'd have some small difference. You can play around with the placement of the S/R in the signal chain on the GT-100 and make sure all effects are truly disabled, as well as the amp sims. Also make sure you've picked the right output type in the GT-100, usually "Stack" or "Stack return" for output choice.