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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
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
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