Pete's guide to fx loops

[Twisteramps]

The simplest type of fx loop is basically just a 'hole' between preamp and poweramp that you can put your effects in. The reason why fx loops even came out to begin with is because you can get a cleaner tone by adding effects *after* your amp's overdrive. If you put a delay pedal into the front of an amp, you're going to overdrive/distort the original sound AND the delays, which makes them sound very blurred. Choruses, flangers, etc are affected the same way.

More intricate fx loops have circuitry to allow better tone with effects in the loop. Some are tube, some are solid state. Since you're going to be putting solid state effects in the loop anyways, I wouldn't buy an amp just because it had a tube loop, or avoid an amp just because it had a SS loop. Here are a few options you may see:

1) parallel vs series. Parallel loops allow you to mix your dry, unaffected signal with the effect. This way, you're not putting all of your signal into the effect, and it can work well. However, some effects will give you a out of phase tone - because the effected tone's signal is slightly delayed from going through the effect. Literally, only a few milliseconds will cause this. I hate it, and it's one of the reasons I sold my mesa racktifiers. I couldn't put anything in the parallel loop that wouldn't get that out of phase sound. Series effects loops put the entire preamp signal into the effect. All your amp's tone is going to go through the loop and the effects you have there. This avoids the phase issues.

2) line vs pedal level - the early effects loops were pretty much line level only, depending on how hot the signal was from the amp's send. So, pedals wouldn't work well - there was an incompatibility with levels. Depending on the type of loop you have, you can have a mismatch with effects. This can give you either distorted output because the amp's send level was too hot, overdriving the effect or hissy low volume issues because the signal from the amp was too low. Some amp manufacturers have a switch that allows you to change your loop to pedal or line level.

3) send/return levels. Some amps also have a return level, or send level knob, or both - this is a way of making sure that anything in the loop isn't too loud or too soft volume wise.

So how should you run your effects? If you can, don't use pedals in a line level loop or line level gear in a pedal level loop. You're screwed from the start if you try this.

Some effects won't work well at all in a parallel loop - anything like a whammy effect, EQ, BBE, etc are going to work better in series. If you have a parallel loop and get that annoying phase tone with your effects, you're pretty much screwed then too.

Some effects aren't usually used in the loop at all either. Boost pedals and wahs especially. Some can go either way - an EQ pedal can be used to shape the tone in the loop (where it will have much more effect) or going into the amp. Some people prefer the tone of a phase or flanger in the front, where it's not quite so 'studio sounding' as in the loop. If you need a volume boost for live playing, putting an EQ in the loop is a great idea.

What I like doing is setting my effects so that when the loop is off or on, the volume level is the same. One can also turn all the effects off, and see how much 'tone suck' is being generated by comparing the loop being off or on.

I've heard of a few devices that will change the level of a signal from pedal to line level, or vice versa - this could help if you had a mismatch and an amp that had a fixed level loop.

Pete

[dannyr]

Great info! Thanks.

[beachjammer]

Hey Pete,
Thanks a bunch for this explanation! VERY informative! I'm having the trouble you mentioned with the parallel loop on my Rectoverb combo. Mainly on the delay sounds. I found the best way to run it was to come out of the slave out and into another amp or power source to strictly run the effects but that's just too much gear to carry around. Currently I'm using a Boss ME-50 and it's doing a decent job overall but still not exactly what I'm looking for. Before you sold your Ractifiers, what did you find that worked best for delays?

[Twisteramps]

Effects sounded so bad in the loop of my racktifiers that I got rid of them instead of try to band-aid it. I've heard there is a parallel to series mod for them, but I heard about it too late. Don't know what the mod entails either, but I think it's just pretty simple.

Pete

[Spivonious]

Great info! Someone make this a sticky!

[beachjammer]

Effects sounded so bad in the loop of my racktifiers that I got rid of them instead of try to band-aid it. I've heard there is a parallel to series mod for them, but I heard about it too late. Don't know what the mod entails either, but I think it's just pretty simple.

Pete

If you find out anything on this mod then please let me know. Thanks again for all the info!

I second the motion to make this a stickey

[GodWentPUNK]

Pete: Great post.

regarding loop suckage. I'll hook up a single cable to the send/receive loop jacks. I'll then swtich back and forther between loop/no loop to see how much of the loop is effecting my over all sound.

+1 sticky

joe...

[fritzreiser]

Pete,

What is the purpose of having an FX loop in a rack preamp?

[hippietim]

Pete,

What is the purpose of having an FX loop in a rack preamp?

If it's at the end of the output stage of the preamp then it's useful if you don't have a switcher and want to be able to have a direct path to the power amp with no effects in the way at all. Or if you happen to like the quality of the loop for it's tonal characteristics - some of them have buffers that folks like.

Some preamps offer loops that are before the preamp but usually after a buffer. This is useful for putting stompboxes in your rig ahead of the preamp but still in your rack.

If you have a switcher like a GCX or a Switchblade, it's doubtful that you'd ever need a loop on a preamp.

[Twisteramps]

What the hippie said. Plus you can have a little more control usually with the fx loop on a preamp - like being able to footswitch it, etc. If you run effects from the preamp out to a poweramp in, then the volume of your preamp is the 'send' volume to your fx. It won't hurt anything to try it both ways, see what works best for you.

Pete

[donvandam]

what kind of loop does the JSX have?

[Twisteramps]

what kind of loop does the JSX have?

Series, with send and return levels. Works great IMHO with pedals and rack mount gear.

Pete

[usrname]

If you find out anything on this mod then please let me know.

I believe it involves moving a wire or two around. I was going to do it to my F-30, but I sold it. Try searching the Boogie forum:

http://forum.grailtone.com/

[toejam]

I believe it involves moving a wire or two around. I was going to do it to my F-30, but I sold it.

What was wrong with the F-30 loop? I had one for a couple years, loved it. I didn't use the loop all that much, but I thought it was excellent and had no problems whatsoever when I did use it.

[horns666]

Yay..I support anything involving "holes"...

[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.