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What is an effects loop?

If there’s one question that I get more than any others, it’s “Are you Tom Green?” But the second most popular question is about effects (fx) loops in amplifiers. What is an effects loop? What does it do? Can it hurt me? Am I still a Christian if I use one? These are all great questions.

Here’s the general idea of an effects loop. I would argue that the better amps in the world are tube/valve based amplifiers. Amplifiers are comprised of two internal sections: the preamp section and the power amp section. (*I’m oversimplifying an amp, but if you want to know specific details about how amps work, there are a good deal of other sites out there.) The preamp section is where the grindy distortion and overdrive is created and the power amp section is there just to create a louder version of whatever character the preamp is creating. When people talk about a “master volume” amplifier, they are talking about an amp that has a volume for both the preamp section and the power amp section. A master volume allows you to turn up the preamp section and get lots of cool overdrive and turn the master volume, or overall output volume, down to a comfortable listening level.

Guitar Effects loops

Guitar Effects loops explained

The need for an effects loop comes when you want to use effects like delay and modulation (chorus, tremelo, phaser, flanger) but you’re also using an amp that has some onboard distortion or overdrive. The order of your effects will make a huge difference on how your guitar tone sounds. Delay and Modulation effects sound splatty and uncontrollable when they are in front of the overdrive section. An effects loop allows you to insert some effects in between those two internal parts of the amplifier (preamp and power amp). Now you can run volume pedals, fuzz, overdrive, distortion, and compressors up front (or into the front end/ input of the amp) and then you can run the more refined and sophisticated effects through that effects loop so that they come after your distortion and overdrive.

Also, you’ll notice that people will refer to two different kinds of fx loops, a “serial” fx loop and a “parallel” fx loop. Many companies will offer a serial loop while some of the more elaborate amps out there offer the ability to switch between serial and parallel or they’ll over both kinds of loop in the same amp. The difference lies in how the amp routes the guitar tone. Serial fx loops will run the effects in line, as if everything is in a row. Guitar tone goes into the input, through the preamp section, through the delays and modulations, through the power amp section and then out the speaker in the form of facemelting rawk. A parallel loop splits the guitar tone off into two signals in the loop section so that you’re mixing in the delayed and modulated sound with the pure unaffected tone from the amp itself.

Effects loops explained: serial vs. parallel

serial vs. parallel fx loops

Not every amp has an effects loop and not every player requires the sonic benefits that an fx loop provides. The Edge from U2 has been running delay pedals into the front of a Vox AC30 amp for much of his career with great results. It’s important to note that there are some guidelines for guitar tones- but never any hard and fast rules. I particularly like the sound of some modulation effects going into the preamp section because they sound goopy and chocolatey. As always, experiment on your own and figure out what your ears want to eat.

{ 30 comments… add one }
  • matt July 8, 2010, 10:18 pm

    hey wondering if you know of someone who makes like a junction box type thing? i cant really explain it. i know they are out there just dont know who makes them. i could probably get one from loopmaster but dont wanna wait haha. my pedal board is crowded and i need my nova delay somewhere that is easy to reach but then i have a hard time runing out to my amps cause i cant reach the left and right outs. not sure if that makes sense

  • el jefe de la cucina July 15, 2010, 2:52 pm

    Hi Matt,
    There are a couple of places. I know that AnalogMan.com makes some. There’s always Loopmaster, like you said. You could also to a “Wanted To Buy” post on The Gear Page and see who has one that might be less expensive. My favorite one is from a guy named Dan who runs This 1 is mine. He makes high quality pedalboard accessories and is a great guy to work with. Good luck!

  • TheLastDon November 12, 2010, 2:27 pm

    Hey there tone chef. I’m using a 2 channel amp for cleans/drives, and run delay/mod through the loop and wah/boosts/drives through the front of the amp – as described in your article. However, if I ever add a multi-effect unit such as Line6 M9, and run it through my effects loop so I can still use the amp distortion… will this have an adverse effect on M9 effects that typically would run through the front of the amp? For example, Line6 drives and Wahs? In other words, right now I can run some pedals through an effects loop and some through the front of the amp. If one unit controls all effects (like M9), do you just throw the whole thing in the effects loop? Are there choices/sacrifices to make? Thanks!

  • el jefe de la cucina November 12, 2010, 4:45 pm

    The problem you’ll face is that the power section of any tube amp is more akin to a hi-fi home stereo. If you run boosts and distortions through the loop, it bypasses the preamp section (as you know). The problem there is that the preamp section is where most of the squish happens and that squish works to smooth the harshness of the overdrives, distortions and boosts. In a pinch, I would sggest running everything through the front end and then running the amp cleaner so that your delays and modulations don’t get funky because they’re going into an overdriven amp. OR, you could save up and upgrade the M9 to the M13 which allows you to choose which effects go into the front end of your amp and which ones go through the fx loop.

    If you wanted to keep the M9 dedicated to the loop, I’d stay away from anything in Yellow and Pink effects sections (Distortions and Filters) and then try to to grab a cheap-but-good sounding OD (like Digitech’s Bad Monkey) and run that up front.

    I hope that helps. If you have any more questions, serve them up!

  • Cameron Gardner October 15, 2011, 4:27 pm

    Hey there tone chef,
    I use a Peavey vk100 head and the effects loop makes the tone sound digital and processed when it’s used. Is there a way to upgrade the loop to a parallel loop or would the whole amp have to be rewire? I have tried different pedals and cables and it results in the same crappy tone.

  • el jefe de la cucina October 15, 2011, 4:53 pm

    Hi Cameron,
    hmmmm… not sure what the issue is. Since the ValveKing has a tube-buffered effects loop, one would think that it should be less harsh. It could be that one of the 12ax7’s (preamp tubes) might need to be replaced, namely the one that buffers the fx loop.

    And, yeah, rewiring a loop to change it from serial to parallel (or vice versa) is major surgery. You would be better off selling that guy and buying something that gave you the loop configuration (and the sound) you’re after.

    Are there specific pedals that sounds really terrible- or is it just the loop in general? Maybe we can figure this out.

  • Sean Drummond November 11, 2011, 5:49 am

    Hey there tone chef. I have a Crate BV 120H which is awesome. I run a BBE maximizer through the effects loop and a chorus and sometimes delay pedals out the front. A few questions…

    1. Should I be running the pedals in the chain with the Maximizer?
    2. Do u suggest a certain Maximizer or Aural Exciter?
    3. And this is the most important question….

    My effects loop decided to stop working. There is a manual on/off switch on the front. If this is on which means the loop is active, the guitar volume will fade. If I play around with the volume knobs on the amp, it might blast back on for a second. The amp now only seems to work with the loop switch off. Is there a preamp tube that if bad will affect the loop? There are 3 12ax7’s off by themselves and one away from the other three. People have told me yes and no. I found this site and wanted to ask you before I try and swap tubes.

    Thank you so much!!

  • el jefe de la cucina November 23, 2011, 3:36 pm

    Hi Sean,
    I personally like the sound of delay and chorus in the loop since they keep them clean (they come AFTER the drive section). The BBE can really go anywhere. You’ll have to season to taste. I’ve heard them in the loop which is good and I also used to run one at the front of my chain. The BBE is the one I have had experience with and I thought it was great. If it ain’t broke, don’t replace it!

    On the fx loop question, that’s a tough one. If it’s a tube-driven/buffered loop then you could have a failing 12ax7 in there. Try moving those three tubes around to see if the problem persists. If it does, then you may be able to rule out a tube issue and the amp will need to go in for repair. Tube amps are finicky and it’s probably not something you wanna try to tackle on your own (since they contain lethal voltages within).

    Good luck, Sean. Lemme know what you find out.

  • Keith March 13, 2012, 11:28 pm

    Great stuff man! Very informative and succinct!

  • Caleb March 20, 2012, 6:11 pm

    Hey tone chef!

    I have a B-52 AT-100 amp head that has been having some problems as of late. My Line 6 DL-4 delay, Hardwire reverb, and boost pedal all go through my effects loop. Recently my delay pedal when engaged squashes my tone and muddies up, and my boost pedal completely destroys any distinguishable guitar sound coming from the amplifier. It sounds like it is going to blow up. The weird part is that this happens slowly and gradually as I play my guitar. Maybe for a half hour it is fine but then BAM!! Explosion sounds….haha..I also just replaced my tubes (all of them) a month ago. Any help would be sweet! Thanks!

  • tonepot April 20, 2012, 9:06 pm

    Hey, another question for you. My amp, a Fender Deville, has 2 channels (clean and drive). When I get my M13, should I go through the clean channel, or the drive channel? Just wondering…


  • el jefe de la cucina April 26, 2012, 2:49 pm

    I think you’d be best served going into the clean channel. Normally, delay effects don’t sound very good if there is distortion after them and the dirty channel would put that distortion after the M13.
    Good Luck!

  • Mojo May 30, 2012, 8:01 pm

    Where is positioned the ampยดs reverb, before or after our modulations in the FX Loop?

  • el jefe de la cucina June 1, 2012, 2:20 pm

    Usually it is after.

  • Stefan June 1, 2012, 2:28 pm

    Hello Tone Chef!

    You’ve given great answers to the questions that I’ve read above. Here’s my question: I’ve been thinking about getting a multi-channel true bypass switcher to prevent my pedalboard from sucking tone out of my signal. Originally I was just going to keep everything out in front of the amp, although I understood that placing my delay/modulators before the pre-amp might not be optimal. If I throw my delay/flanger/phaser into the effects loop, should I get a second bypass switcher to put in this loop? Or is tone degradation in the FX loop minimal compared with degradation out in front?

    If it’s advisable for me to use two switchers, I guess I lose some control over my rig because I now have to manage two floor controllers, not just one “master” controller.

    Thanks for your reply!!

  • el jefe de la cucina June 3, 2012, 3:27 pm

    Hi Stefan,
    You are correct in wanting to keep “tone sucking” pedals out of your signal chain. There are a few possible solutions. You could buy a second bypass switcher for just your fx loop pedals. You could also try the Pedal Switcher and Commander from Voodoo Lab which would allow a one-button push that would turn multiple pedals on and off at once. A similar option is the RJM Electronics Amp Gizmo, which essentially runs pedal switching from a midi-controller like the Ground Control Pro or something. It puts you dangerously close to a rack rig, but once you start getting into switching systems (even bypass loopers), your rig gets a little bit bigger and a little bit more like NASA’s Mission Control. ๐Ÿ™‚

    Good luck,

  • Stefan June 3, 2012, 10:10 pm

    Hi Corey,

    Your suggestions are much appreciated!


  • Bill November 1, 2012, 7:49 pm

    Tone Chef,
    Thank you very much for explaining the difference between Series vs Parallel FX loop. There’s not a lot of information on this and I have recently bought a Mike Fortin amp which has a series/parallel loop. I’ve never had an amp with this feature and this amp also has send/receive knobs for control and when switched to series this has a profound impact on the sound (tone, volume, gain). Running the loop in Series I can turn up the master (no preamp volume on this) and drive everything harder without it rumbling the walls and I can get a little extra gain and even change the overall tone of the amp. So my question. Is there a general “rule of thumb” for Series fx loop? Such as send level on 3, return level on 7, or both at 5. I’m guessing it’s set personal taste. Thanks again for taking the time.


  • el jefe de la cucina November 5, 2012, 9:03 pm

    Hi Bill,
    Good news and bad news. The good news is that there’s no rule of thumb. The bad news is that there’s no rule of thumb. ๐Ÿ™‚
    I would normally set the send and return levels to where they’re as loud as possible without any sort of negative effect on the tone. In some cases, you can activate the FX Loop via footswitch and depending on your levels, you could actually use the loop as a solo boost. I had this on my Mesa Boogie LoneStar Classic.

  • Rushi Ladani December 29, 2012, 5:56 am

    Heyy there tone chef…i have no question in particular but i just wanted to know what i hav learnt is correct or not… um so here’s wht ive learnt…
    – a guitar signal goes to effects like distortion, compressors or boosters which may or may not be in the amp.
    – Then it goes into the FX loop inside the amp which holds modulation effects like the chorus,flanger,delay,tremolo,etc.
    – this loop maintains an input( from extra-terrestrial inputs like pedals or stompboxes ) and an input(from these pedals) into the power amp section where it ONLY increases the amplitude of the sound.
    – and then from here it goes into the output or reverbs or whatever.

    but what does the FX loop ports function in pedals like M13, as in what is their need? cant we just put the FX loop OUTPUT in any pedals in series or parallel or any processor outside the amp and then carry their outputs to the FX INPUT in the amp and get on?

    and what was the tone sucking thing u mentioned above?
    Sorry to bother u with soo much but im just new to this concept. Any help would be great. Thankyou. ๐Ÿ™‚

  • el jefe de la cucina January 4, 2013, 6:08 pm

    Hi Rushi,
    You are correct in what you’ve learned. ๐Ÿ™‚

    The reason that something like the M13 would have an effects loop is so you can put other stompboxes in the signal path of the M13. To keep it simple, let’s say you’re going to use the M13 into the front end of a simple amp like an old Fender. Those don’t have an effects loop and the controls are simple. All of your pedalboard effects are meant to go between the guitar and the input of the amplifier. If you have a favorite overdrive stompbox, like a Way Huge Red Llama or a Klon Centaur, then you could place that in the effects loop of the M13.

    So here is where it gets fun. Each scene on the M13 allows you to choose where you want that effects loop placed. So in scene 1, you could have Bank 1, then the effects loop, then Banks 2,3,4. But in scene 2, you could move all 4 banks to be before the overdrive stompbox. The reason you might want to do this is because it would allow you to have up to 4 M13 effects before the stompbox (like wah, compression, filters) or up to 4 M13 effects after the stompbox (like delay, modulation, reverb).

    And “tone suck” is a term that people use to describe the loss of volume or clarity when adding pedals into a signal chain. Try this: plug your guitar into your big pedalboard rig and play a few notes and a few chords. Then plug your guitar directly into the amplifier and see if you hear a difference. Many times, the direct guitar will sound brighter and louder and more clear. You have just experienced how a pedalboard can diminish the tone. The good news is that you can select a True Bypass or DSP bypass in the M13 and both sound great with little to no sound degradation at all. It’s a fantastic piece of gear.

    I hope that helps!

  • Rushi Ladani January 4, 2013, 9:02 pm

    WOW!! Well dats a beauty… :O thankyou very much!! ๐Ÿ˜€

  • Deep Dave January 19, 2013, 5:38 am


    Perfectly Explained.. And now I understand it perfectly well..

    Just 1 Question. I am using a Solid State Marshall HDFX Series Amp along with few mentioned pedals.

    1) Crybaby
    2) Electro Harmonix – Memory Man
    3) Krank Distortion
    4) MXR Dyna Comp

    Could you please guide me as to how to chain the Pedals with the Effects Loop?

    Thank You,


  • el jefe de la cucina February 15, 2013, 6:57 pm

    I would go wah > Dyna Comp > Krank > Memory Man.
    I think the comp and the distortion can trade places depending on how you choose to use the comp. As either a fattener or a boost.

  • Matthew Barr June 10, 2014, 9:21 pm

    Hi there. This is full of very useful information and you sound very knowledgeable. I have quite specific aims in that I am in a U2 tribute. I am rebuilding my rig as I think I had my delays in the wrong place. In any case I’m not happy with them and they are crucial to the U2 sound. I am trying to decide what to put into the send-return loop of my AC30 and where to put the delays. A number of U2 songs require two delays and I think the Edge runs two different delays to two amps (excuse my ignorance, is this what ‘in parallel’ means?). I do have facility to do this with a Fender Tweed second amp.

    To come to the point, most of what I have read here and elsewhere suggests that I should not put my delays before the overdrive pedals as this will drain the tone. However, I appear to be dealing with an exceptional case here as another site said : “The Edge from U2 has been running delay pedals into the front of a Vox AC30 amp for much of his career with great results.” So I’m very confused. Any idea what should be in the loop and what into the main AC30/Fender inputs? And, crucially, where is best for the delays? I have the following:
    Distortions – OD2, Big Muff, Ibanez tubescreamer
    Digitech Whammy
    Verbzilla (for shimmer)
    Compression – CS3
    Rack Delays – 2 x Korg SDD2000; Korg A3
    Pedal delay – Memory Man

    Many thanks indeed if you can clear the fog.

  • el jefe de la cucina June 11, 2014, 1:15 pm

    Hi Matthew, if you don’t mind, I’d like to answer your question in a new post… I’m writing it right now and will add the link below this response.

  • el jefe de la cucina June 11, 2014, 6:27 pm

    That post, Matthew, is right here…

  • Matt August 13, 2014, 2:17 am

    Quick question, well two:
    1) I tried the 4CM and was having some problems. The way I hooked it all up works, but I have no control over my amps volume. Its almost like the entire signal is running through the preamp. (I think) Is that normal. (amp: Fender Frontman 212r) Right now, I’m just running through both FX and front. with the entire M13 and other effects on the FX and distortion+wah in front of the amp. I have a Loop pedal that I had hooked up when I had my signal just running all the effects through the front of the amp, The looper being last so I could have whatever effect that i wanted on it, but where would you recommend I put that now? Thanks in advance!

  • el jefe de la cucina September 5, 2014, 6:27 pm

    It sounds like somehow the routing got funky and you have bypassed part of your amp. Try the routing again. Remember that it’s as if you’re running your guitar into the M13 first and acting as if you have put the amp’s preamp section into the loop of the M13 instead of thinking of it as if you have put the pedal into the amp’s FX loop. As for the looper pedal, now that could go first in line, before the M13 goes into the preamp, after it comes out of the preamp, or before the signal finally goes into the power amp. It depends on how much of your tone you want recorded in the loop, because the later it is, the more of your signal chain it’s going to capture. I hope that helps, Matt.

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