From what I’ve read, getting tubes is becoming more of a problem, and it’s only going to get worse.
An FX loop is a way to patch pedals in between the pre-amp and power amp sections of your guitar amp.
If you weren’t aware, guitar amplifiers (and most other audio amplifiers) have two amplifiers within them which are chained together:
input —> pre-amp —> power amp —> speaker
The pre-amp takes the tiny signal from the guitar pickups (or microphone, or turntable, depending on type of amp) and boosts it to a higher level. On a conventional guitar amp, most of the overdriven/distorted tone of the amp comes from over-driving the pre-amp.
This signal is then fed into the power amp whose job it is to create the high electrical power needed to physically move the speaker cone. Generally, the power amp is designed to be fairly neutral and doesn’t add much tone, but there are some exceptions to this.
An effects loop (or FX loop) breaks the connection between the pre-amp and the power amp so that you can insert one or more effect pedals:
input —> pre-amp —> (FX loop send) → Effects → (FX loop return) → power amp —> speaker
The reason for this on conventional guitar amps is that some effects are felt (by some people) to sound better when placed after the pre-amp. Typically, these are time-based effects like delay and reverb.
FX loops can be useful for loopers too, if you like to use the overdrive of your amp. Placing the looper in the FX loop after the pre-amp lets you (as a typical example) record the sound of your amp with a clean tone, and then play back that loop whilst soloing over it with an overdriven tone. If you try this with the looper into the amp input, then when you turn up the gain to get the overdriven tone, it will effect the recorded loop too.
With looper pedals, the general rule is the loop should record the effects (including the overdrive effect of your amplifier if you are using it). If you are using a modelling amp with built-in effects, the only practical way to use an external looper with the onboard effects is by putting the looper into some sort of FX loop.
Note there are some workarounds on some amps to support loopers on amps without specific FX loop capability. These workarounds are, effectively, still doing the same thing as an FX loop.
Cheers,
Keith
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Very interesting and informative, Keith! Thanks for the explanation!
One other question though… if there’s no headphone jack but there’s a second speaker output or line out, can headphones be safely plugged into either of those jacks?
That’s the setup on the Harmony H605. No dedicated headphones jack.
Tod
Speaker out is completely different from line out and, if you plug anything into it other than a speaker cabinet (or load box) of the correct impedance (usually 4 Ω to 16 Ω) then you are likely to damage something. If you plug headphones into this, you’ll probably damage the headphones.
You certainly won’t damage anything by connecting headphones to a line out and it may be worth a try. However, it’s probably not going to be useful for you. Line out is normally a fairly low-level signal designed to be amplified, so it is likely to be very low volume and a fixed level. Also, unlike a dedicated headphone output, plugging in the headphones probably won’t mute the speaker
Your best option for headphone use is to use the line-out with a dedicated headphone amplifier, which will amplify the sound as well as giving you volume control. Of course, that won’t mute the amp speaker, but you should be able to turn down the amp volume (or maybe put it into standby) and still get a signal on line-out into your headphone amp.
Bear in mind that the line-out on almost every guitar amp, including all-tube amps like the H605, have some degree of emulation. This is because this signal is bypassing the power amp and the speaker and cabinet. The power amp (as I described above) probably won’t make much difference to the tone, especially if it’s not fully cranked, but the speaker and cabinet are a HUGE part of the sound of the amplifier.
The bottom line is: the sound you get through line-out is not going to be the lovely tones you get from the amp speaker. They might sound OK (if the speaker and cab emulation is decent) but they won’t sound the same.
It’s entirely likely that you find using the Harmony with headphones isn’t any better or, possibly, is actually worse, than using the Katana on headphones.
Cheers,
Keith
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@Majik Thanks for the clarification and great explanation of what an FX loop is and what it does. That’s probably the clearest explanation I’ve read about it so far!
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We’ve been down this FX loop path a few times:
Don’t rule out how cool it can be to put a preamp pedal in the FX loop.
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Thanks for the topic link Clint. I’ve browsed through it, and while most of it is a bit advanced for me currently, I’ve saved it for future reference, especially now that I’m considering the Mustang GTX instead which does have built-in effects and an FX loop.
As a general update, I managed to find a guitar store in Camden (guitar guitar if anyone’s curious) that had the Fender Tone Master Princeton Reverb in the store to try. They were kind enough to setup me up with a Fender Strat and the amp in a demo room to fiddle with it at my own luxury. My limited experience with it is as follows:
- The amp is really light for the size!
- The attenuator option is great! Playing at 0.75W was plenty loud for home practice levels.
- The amp sound is really Fender clean but the reverb didn’t sound as good as the effects on my Mustang Micro (probably because that has a combination of FX not just reverb).
- I couldn’t get a crunch tone out of it even with turning it down to 0.3W (lowest setting) and cranking both the amp and guitar volumes up.
Conclusion:
I’m really glad that I found the amp in-store to try, but I wasn’t wowed by the sound I could produce from it as I thought I would be. Keep in mind, that’s not a judgement of the amp sound/capability itself, but rather an issue of my own expectations, currently limited playing abilities and lack of pedals plugged into it (the first two being the major factors).
So I’m shelving the Tone Master idea for now, until my playing is better and I have more experience and specific need with pedals/multi-fx units.
That being said, I still love the Fender tones so I’m reconsidering the Mustang GTX amps since:
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I love the amp and FX simulations on my Mustang Micro (especially the Fender and Vox amps). So it makes sense to go for the regular amp version of the same modeling technology.
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It has a lot of great features, some that I can use now: bluetooth audio streaming, wifi connectivity for updates, community presets, mobile app for editing presets, preset set lists, footswitch, AUX-in, headphone jack, XLR line-out if I can use it for direct input into my audio interface).
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It has some features I can use in the future as I progress: FX loop, editing FX pedals and the order in which they’re placed, enough power to jam with others (both the 50/100W models).
Some questions to any current Fender Mustang GTX users (@jkahn or others):
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Is the lack of an attenuation option an issue for home practice? Can you still get good sounds out of it at low master volume? There’s always the headphone option, but I prefer to practice without them when I can and I’m lucky enough to have an office on the other side of the house so I don’t bother my wife or kids while I’m practicing at night).
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Have you used the XLR line-out (just one of them, not both stereo outputs) to plug-it in directly to an audio interface for recording? Or is only intended for connecting to a PA system? Is the quality of the sound as good as what you hear from the speaker or of noticeably lower quality?
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PS @jkahn I’ve been watching your rock songbook AVOYPs and I’m loving your tones with the GTX (not to mention great playing skill)
So, now my next mission is to find a place that has one of these in-store to try (guitar guitar didn’t), so I’m planning on checking PMT London in the next few days.
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You can set the GTX-100 to very quiet for home use, its not a problem.
What is is that all the different presets have different levels (obv not master level but) so changing between them can change volume a lot, this tbh is a feature rather than a fault but not so 3am bedroom friendly!
The XLR output I have not used yet I should give it a go now I can, but its supposed to be 100% the same as the actual sound (I guess minus some speaker colouring). Unlike the USB output wich is supposed to be poor.
Headphones work great with it too, though if thats the primary focus then there are probably better options.
The GTX-100 comes with the foot switch, if you are buying that anyhow then the GTX-50 doesnt make sense unless you find it (and the footswitch?) on sale
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Thanks for the detailed and helpful feedback Rob.
I noticed the same thing with my Marshall Code (presets volume level), it’s made me jump in my chair a few times 
That’s why I like the idea of the preset set list on the GTX, I can switch between my preferred and selected presets without any surprises.
Yeah I’d like to use the XLR for recording as it’s less of a hassle than setting up the mic and much better quality than USB.
Good to know the headphone output is good, although I prefer not practicing with them if I can.
I was initially looking at the GTX-50, but like you said, price wise the GTX-100 is only $40 - 50 more with the footswitch, and the size and weight difference is negligible so will be considering that one instead.
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The GTX-7 footswitch (that comes with the GTX 100) is awesome. It has three modes 1) Preset allows you to quickly move through different tones, 2) effect mode allows you to turn on or off specific effects in your chain, and 3) looper mode allows you to do multi-layer loops.
Once you have all of your presets set up, you don’t really need to use the app or the physical controls on the amp. You can do almost everything you need with the footswitch and the knobs and your guitar.
Another thing that I really like is that the footswitch doesn’t need power, so there are no extra cables or cords around. One plug from the amp to the wall for power. One cable from the amp to the footswitch. One cable from guitar to amp. This has ended up being a big one for me. Every time I think about adding an external pedal or looper, I’m reminded that I would need to deal with batteries or come up with an extra plug for power and, at least so far, I haven’t felt that external pedals would give me enough extra performance to offset the convenience of my current set up.
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Thanks for the input Rob, that’s really helpful. That does sound very convenient, and is my preferred way of interacting with the amp. Spend a couple of nights configuring presets using the apps, then just use the footswitch to move between them (or turn effects on/off) and use the amp knobs to tweak or experiment on the fly. Makes for less fiddling every day and more practice time, and like you said everything is streamlined cable-wise.
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I do believe you can also use the EXP-1 expression pedal too
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Firas, your experience with the Princeton makes sense - it’s just an amp, not a modeller, even though it’s a solid state imitating a tube amp. The fender amps were mostly known for their clean sounds rather than overdrive, so you’d need pedals etc.
Your questions, which Rob and Rob have also answered somewhat.
Attenuation is not an issue - attenuation is really a valve amp thing (or a modelling-as-valve thing). Volume & Gain control the modelled amps controls, master controls the speaker output itself independently. Yes it sounds good at low volume.
I use the XLR line out almost every day. It’s permanently hooked up to my Focusrite interface. In fact, I only use the amp either via its speakers or the focusrite. I might have plugged headphones directly into it a long time ago, although now if I use headphones it’s via my Focusrite. I haven’t used it’s USB out.
The XLR out uses speaker cabinet modelling. So it’s the sound of a miced amp, not the sound of a raw line out. Similar concept to what you’re hearing through the speaker, that’s also cab modelled.
Quality of XLR out is good, all my recordings have been via XLR out.
I used the bluetooth streaming for backing tracks a couple of times, but I find it more convenient to play backing tracks on my PC rather than via the amp.
Thanks dude, and cheers for the likes you gave me 
Yeah, the footswitch is awesome. I have one on my GTX-50, really only ended up with a GTX50 instead of 100 because I found one for sale lightly used on ebay pretty cheap, from an older gent that had bought it and then had to move into a retirement village.
Here is where we differ a bit, I use the footswitch & presets a lot, but I also am constantly tweaking and setting up new presets. 99% of the time I use the app for it rather than physical controls.
The only crap thing about the Mustang GTX is that the app is mobile & iPad only. So you can’t use your PC to configure the amp. I would find that more convenient.
Yep, sure can, I have that and used it for the dive bomb in my Lonely Boy cover. The EXP-1 is built like a tank. I don’t use it much though!
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Do you turn the master volume down completely whe using xlr out to the pc?
It’s also odd fender have a window desktop app but it only works with the other Mustang amps…
Yeah, I often turn the master volume down to zero when using the XLR out. Like if I’m using headphones on the PC.
Sometimes I leave it up though, there’s no noticeable delay.
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I’ll have to give it a go! See how it compares to my software amp solutions
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Hi Firas, you started an interesting thread, thanks for that. I can’t contribute but I’m highly interested and bookmarked the thread to follow.
Great insights from @jkahn and @Majik, who’s always giving us so much helpful advice! Thank you!
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Thanks for all the clarifications JK. I really appreciate it 
@Helen0609 You’re very welcome. If there’s one thing I’ve always been good at, it’s asking a lot of questions about anything new that I’m learning 
Lots of great answers and insights from everyone in the community here
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Ok I just tried this
GTX-100 to 2i2 via xls, and direct to headphone out + zero master volume
Its mono as expected but doesnt sound bad for that (you can do 2xXLR if you want stereo - the amp only has 2 speaker anyhow)
Some of the presets sounded a bit rough, most sounded decent and very like the amp
Good variety as expected
If I was just playing at the computer though Archetype Petrucci sounds a better. Its more limited (only 4 ‘amps’ and fewer pedals etc) but the modeling seems better and it can do stereo.
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Latest update:
I visited PMT London today and they had both the Fender Mustang GTX100 and the Boss Katana 100 MkII amps (I might as well test the Katana while I was there since everyone raves about them). The staff there were very friendly, they setup me up with a Fender Strat and gave me free reign to try out both. I spent around 40 mins. with both amps. Here’s what I felt about them (just my personal preferences and initial impressions, as this is nowhere close to being an in-depth review):
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The Fender has a very easy to use and intuitive interface with the physical knobs as well as the digital LCD screen. I could not only scroll between presets, but even customize them (tweak existing FX or add new ones) pretty easily without using the mobile app (I’ll still be using the mobile app, but this is good for quick on the fly tweaks and adjustments). That’s very convenient. I could also see all the FX and the levels they were configured with on this little LCD screen. It’s tiny but well laid out, has good resolution, and provides great feedback on the settings and any changes I made to them.
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The Katana in comparison, while simple to use and intuitive in terms of having straightforward knobs, preconfigured sounds/amp models (clean, crunch, etc.) but the lack of any kind of screen was a definite negative for me as I couldn’t see what FX were being used. Since this amp doesn’t have a mobile app, this would force me to use the PC app which is too cumbersome for me.
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As with most modeling amps, out of the 190 presets saved, I only liked a handful of them which is to be expected, maybe 10 of them at the most. That being said, the ones I liked, I loved. Most of them were Fender amp models: Twin, Deluxe, Blues Junior, Princeton not so much. I even liked some of the high gain ones, but keep in mind I only know the basic version of Zombie to test those out with. So I played around with the presets I liked, tweaking the EQ, gain, reverb and even adding some Overdrive FX to them. I loved the variety of sounds I could get with just those few amp models.
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Generally speaking, I liked the Fender tones much better. They sounded fuller than the Katana to me, and I especially liked the tones when I added Overdrive to them on the Katana more so than the Katana. Of course the cleans on the Fender were absolutely beautiful! Literal music to my ears (pun intended)
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I thought the attenuation levels/knob on the Katana would be a must for me, however, using both the Master Volume and Volume knobs on the Mustang worked better for me. I especially liked that the Volume knob adjusted the preset volume level as they each have different volumes (which was an annoying thing with my Marshall Code 25 as I had to edit those through the app and couldn’t do it using the physical knobs).
So overall, getting the chance to play around with both amps next to each other was a great experience that confirmed my choice of the Fender Mustang GTX100. Am I biased? Oh for sure! I’ve been practicing with Mustang Micro for the past 3 weeks, but I’m not reviewing these amps for other people just for me and my tastes and preferences. I’m sure that both amps can do a lot more once you get into their respective FX editing tools (Fender Tone & Boss Tone Studio), I just wanted to know which one sounded better out of the box for me.
Now unfortunately, PMT can’t ship directly to Kuwait if I order through their website. I’d have to order it here in London, and take it as extra luggage on my flight back to Kuwait which is a hassle and more expensive. Luckily, Thomann do offer door-to-door shipping directly to Kuwait via UPS Express, so I’m talking to them to place that order for me to hopefully receive it in a few weeks once I’m back home in Kuwait.
Thank you all again for your feedback and inputs, as it’s helped me narrow down the right amp for me that will hopefully carry me through the upcoming stages in my guitar learning journey