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A few days ago I tried to plug my (OneOdio A71) headphones directly into my 9 V cheap mini Kokko overdrive. I was expecting to not hear anything, or almost anything, because it was my understanding that the output of the signal chain normally needs to be amplified to become powerful enough to drive speakers or headphones.

But, much to my surprise, it worked. Again, the following, works, I tried.

Humbuckers --> Overdrive pedal --> Passive mono to stereo adapter --> Stereo headphones

You can hear stuff, and it's pretty loud. But it does not sound great; it seems like the highs are too high, and there is some sort of harshness to it. I don't know exactly how to describe it. It's not necessarily a bad tone, but I don't like it for what I want to play.

So, the questions are:

  • Why does it sound so "meh"?
  • Is it an impedance problem?
  • Would a headphone amplifier improve the sound?
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1 Answer 1

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Guitar overdrives/fuzz boxes etc are designed to be fed to guitar amps.

This isn't even really a problem of impedance or even output voltage, it's one of EQ curve.
Guitar amps [& speakers] really strip the top off any signal going into them. A 'bright' guitar tone is nowhere near as bright as you might think, it tends to tail off from as low as 3kHz or so & be almost non-existent by 10kHz.
Because of this, a fuzz box doesn't have to care about how much fizzy high end it's sending, the amp will strip it.

Your headphones, on the other hand, will be good to 20kHz & you can now hear all that nasty high end, clear as day.
You can hear the same thing if you route one to a hifi, or your audio rig's line in. Nasty fizzy noise.
There was at one time a studio fashion to run a guitar straight into the desk - partly using the desk's own preamps to overdrive. The top end had to be rolled out quite heavily to make this work.

The desire to be able to practise using overdriven sounds at low volumes was partly what drove the popularity of such as the Line 6 Pod 20 years ago. It emulated the sound of a guitar amp [& speaker cab with a switch], so headphones or direct line in would sound 'right'.
You can pick up an original Pod on eBay these days for about $£€ 50.

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    There are lots of amp sim options now. Most multi-FX will do it. You can also get a range of purpose-built pedals, e.g the Flamma FS7 (which I haven't tried, but the Flamma range has had some good reviews on YouTube). Sep 9, 2022 at 0:55
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    The "studio fashion" of DI'd guitar is still good practise for the raw guitar signal and often for the post-FX signal too. The mixer/producer then has the option to put the guitar through whatever FX chain they think works best for the song, and also to use an amp sim if they want to shape the guitar sound differently. We're rarely limited on inputs these days, so recording a couple of extra DI'd inputs in case you need them is a no-brainer. It can also get you out of a hole if the amp turns out to be noisy - amp noise might not be an issue live, but it really jumps out in recording.
    – Graham
    Sep 9, 2022 at 11:09
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    @Graham - It wasn't really "DI" as such, it was literally plugging the guitar straight into the desk, no impedance matching or anything. Produces a recognisable, thin sound. I've done it myself back in the day. These days, though, I will often do as you suggest, though I'll use my pre-amp'sInstrument input, which doesn't thin it out in the same way - then I can amp/re-amp in such as Guitar Rig, to my heart's content. youtube.com/watch?v=9de6jeOevi8&t=80 - this is the kind of noise I mean. First one I could think of off the top of my head & not the best example.
    – Tetsujin
    Sep 9, 2022 at 11:23
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    @Graham - Ahh… I was basing this on my own practises back in the day & word of mouth from the time - long before we had the interwebz to look things up on. There is much discussion as to just who did it how, on what, from running it up through DI's/comps etc to some 'just straight in the board' . I found a list of great songs with variants on that theme - some I already knew did it, some a complete surprise - reverb.com/uk/news/… It includes one of my favourites of all time - the bizarre solo ending to Goodbye to Love.
    – Tetsujin
    Sep 9, 2022 at 15:30
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    @Tetsujin One other potential reason for a trebly pedal output is that it can help avoid ugly blocking distortion in the amplifier (especially at the power amp section). When it comes to "guitar/FX right into desk", this is my favorite example: youtube.com/watch?v=u84f2wdl6f4
    – Theodore
    Sep 9, 2022 at 20:54

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