Pete's guide to fx loops

[Carbophos]

phase thing in parallel FX loop occur when you FX device is not capable of producing "wet" signal only.

Basically any chorus or flanger stompbox is not suitable for parallel FX loop. Reverb/Delay pedals should have separate effect (trails) level and MIX control (varuing from 100% dry to 100% wet, set at 100%) to be usable with parallel loop. Basicaly almost anything but rack unit with switchable dry path is not good for parallel loop.

[Twisteramps]

Interesting, I got the 'out of phase' problem with a G-Major set to full wet with my mesa rackmount head.

[toejam]

phase thing in parallel FX loop occur when you FX device is not capable of producing "wet" signal only.

Basically any chorus or flanger stompbox is not suitable for parallel FX loop. Reverb/Delay pedals should have separate effect (trails) level and MIX control (varying from 100% dry to 100% wet, set at 100%) to be usable with parallel loop. Basicaly almost anything but rack unit with switchable dry path is not good for parallel loop.

True, most of the time, the effect's level should be set to 100% wet for a parallel loop, but not always the case.
The thing you're overlooking is that those stomp boxes are more suitable for effects loops as long as the loop is intrument level and not line level. If it's line level, you'll need a rack processor instead of stomp boxes, otherwise the stomp boxes might not sound right and introduce unwanted distortion.

Stomp boxes = instrument level. Rack gear = line level.

[Carbophos]

Many modern amps have loop level switches or controls, but still most modulation effects pedals are not good for a parallel loop.

Interesting, I got the 'out of phase' problem with a G-Major set to full wet with my mesa rackmount head.

Well, the processing do add some latency like 1-2ms or so. But if you switch dry path off completely, it is can be corrected in your effect parameters. Moreover adding a couple of miliseconds latency to the delay (usually set at hundres of millesconds) would be barely audible. In case of chorus or flanger (1-10 ms delays are used) it may be an issue, but again, you set an effect parameters by ear while unit is plugged into the effect loops...

And effects like EQ, compression, to certain extent tremolo are not usable in parallel loop anyway.

I believe that the best FX loop is switchable (on/off) serial with separate send/return level controls.

[Carbophos]

BTW I know one more FX phasing issue.

Some amps for whatever reasons have double phase inversion in the FX loop. Phase in inverted before signal is going to send and is inverted again after entering return. So when you use this amp alone it's like phase is the same again.

But if you try to play stereo (using one amp preamp, then sending the signal to FX unit, then it goes to two returns) using different (not exactly the same model) amps you may face weird out-of-phase stereo effect.

[deflep]

Thank you so much. This was extremely helpful as my new amp has almost all of the options you mentioned: series vs parallel and a instrument level indicator as well as a return level.

[SydneyPC-1]

Hi Pete. Is it OK to run distortion pedals through the loop as well. I have a TC electronic flashback that I know should be run through the loop but what about the Ibanez tubescreamer which I use as a third channel or lead channel. Front end or loop. Thanks Paul

[leftykingv2]

Great post! Very informative!

[toejam]

Hi Pete. Is it OK to run distortion pedals through the loop as well. I have a TC electronic flashback that I know should be run through the loop but what about the Ibanez tubescreamer which I use as a third channel or lead channel. Front end or loop. Thanks Paul

You should never run a distortion pedal in a loop. It always goes in front of the amp.