Thoughts after going through my amp FX loop

  • I thought I'd try putting the KPA in the FX loop of my amp just to see how it sounded today, especially after all the talk of how glorious the KPA sounds through a real guitar cab, and I'll be honest it was an eye opening experience, but not for the right reasons.


    Some background - my rig for this was a Mesa Express 5:25 Combo amp, this offers a standard straight FX loop without the usual Mesa Mix parameter that only has a 90% throw, I know this amp pretty well and before trying the KPA had spent a half an hour or so just noodling on it, then I set it to a very clean sound with tone controls at midday before putting the KPA in it's loop (I used the KPA's monitor output for the loop). The profiles I tried included the Andertons profiles, several of the standard profiles that come with the unit some of Andy's and of course my own of this very amp, I tried with and without the cabinet section enabled on most amps and various EQ settings just to be sure of the results.


    First up noise floor. Can you say holy crap that's a lot of noise? This is known to be a "noisy" Mesa amp to begin with, but this was as loud as a vacuum in the room with me. I tried the various lifts and volume adjustments to little joy, though I may go back and try again to see if i can trouble shoot this because it was just obscene.


    Second problem, aliasing. Something that's just not very apparent through studio monitors is apparently amplified (if you'll pardon the pun) when being driven by a real tube power amp through a real guitar speaker. I have to apologize to Radley as maybe this is how he's been hearing this all along. But notes that are usually silky smooth on the amp are just full of the most horrific atonal harmonics and ghost notes, the thing is after I've heard them so prominently once I went back to playing through the studio monitors I could really hear them as compared to playing through my real amp and it's kinda spoilt the fun.


    Third is feel, the KPA just wasn't as spongy. Now bear in mind that the KPA is basically replacing the amps own preamp and we're still using the amps power section, this was like I'd slammed a limiter inbetween the pre and power amps. Playing through studio monitors doesn't exhibit this problem, the sound is much more lively, but through the amp while the sound was still passable it just lost that liveliness completely and felt like an old solid state amp. No amount of fiddling with gain or levels could bring this back.


    Fourth was sound. As was expected most of the profiles sounded pretty alike through the guitar cab, but even with a profile of the this very amp the sound was out, far too much treble/presence a really biting sound even when I dialed that far down on the KPA (the input and output lLED's were all green in case you were wondering), the distortion far less rich and complex. Again when I went back to the studio monitor with the KPA the result was much closer to the real amps sound and complexity, but through the amp itself somehow it turned into a much too smooth fuzz style distortion.


    TBH I'm pretty disappointed, I'd expected a better showing, but this just didn't feel any better than any other amp sim in that situation and worse when it came to the so called aliasing (which I should point out started to be very noticeable at well below the 12th fret on the upper strings). Of course it was just a quick test and I need to do a lot more, but I was surprised at just how extreme some of the issues were, they weren't subtle problems at all when compared to the amps real tone or the KPA through studio monitors.


    Anyhow, there is always the possibility that I did something horribly wrong, but I checked everything twice and all the components involves are working fine and the settings should be good, I'll have to try it again another day when I have more time maybe in a different configuration (any suggestions?). If this is just the way things are then I'm not expecting much to be done about this, and please don't think I'm bashing the unit because I do love my KPA, but I'm just feeling a little glum about the outcome of this particular experiment this time :/ On the other hand I don't need to use the KPA in this configuration I can carry on using it through the studio monitors and be happy (apart from really noticing the artifacts now, and the extreme treble/upper mids transient peaks). But hey you've gotta try these things out at least, right?

  • Quote

    I set it to a very clean sound with tone controls at midday before putting the KPA in it's loop

    I may be wrong, but the tone controls shouldn't be working if you're going into the FX loop of your amp, you should only be using the poweramp?

  • then I set it to a very clean sound with tone controls at midday before putting the KPA in it's loop (I used the KPA's monitor output for the loop).


    When you say "in the loop" you ofcourse mean you plugged the KPA output to the return of Mesa's loop and your guitar straight into KPA's input (and not to the input of Mesa and the loop send of Mesa to the input of KPA)?


    Because if the KPA would be literally "in the loop" of Mesa you would have two preamps in the signal path (the Mesas and KPAs) which could explain the noisefloor etc. But I'm sure you are well aware of this.


    Anyway, interesting findings. I have not tried the KPA with a poweramp and guitar cab.

  • I may be wrong, but the tone controls shouldn't be working if you're going into the FX loop of your amp, you should only be using the poweramp?

    I was thinking the same. Are you sure that you connected it correctly? In fact you dont put the KPA inside the amps loop. You just use the FX Return of the amp to use the power amp. The tube amps preamp should completely be out of the signal chain.


    Guitar -> KPA in -> monitor out (cabs off) -> FX return


    From my own experience, i can tell that many poweramps of tube amp heads behave very differently from stand alone rack power amps. Many times the preamp signal of a tube head is very bright sounding, while the power amp section sounds very dull to compensate this (or vice versa).

  • So in reference to above posts by me, guitartone and tylerhb and to put your post into perspective:
    was the KPA in between Mesas pre and power amps or were you just using the fx return of Mesa and therefore only the power amp?

  • I owned a Mesa Dual Recto for about 5 years. At some point I purchased a Marshall JMP-1 with the idea I would use it in the loop of the Recto, so just using the power amp.


    It sounded absolutely horrid, trebly, no body, just the nastiest horrid distortion I ever heard. No amount of tweaking made it work well. Now I have heard the JMP-1 into a VHT power amp and it sounded glorious. Conclusion: mesa's effects loop return does not work well as a power amp under most circumstances.


    I highly suggest you move on as this chain will not sound good imo.

  • Yeah, i've not had a whole lot of luck with the mesa's lop it has to be said.


    BTW you guys were right, I had made use of the mesa pre before the loop in a traditional way (just set to an extremely clean value), I tried again today with just guitar->kpa->amp return, and while it's a little bit less noisy and the aliasing is less noticeable the same problems remain.


    It's not abysmal, but it just doesn't feel anywhere near as fluid and organic as the real amp pre. Like I said before it's almost like there's a limiter in place, and maybe those few tiny MS of latency with the KPA do make a difference even if it's too short of a time to be able to pinpoint under normal circumstances. Or it could just be the attack of the notes, trying with various profiles didn't seem to help, nor adjusting the pick attack which to me sounds very mechanical for some reason, it somehow just didn't have quite the same definition as the real amp does there.

  • Oh one thing that may have a bearing on the spongy lack of attack thing is that the Express 5:25 uses some sort of capacitor dump thing to punch up peak volume an extra few dB on attack/transients, and make the amp sound louder than it's rating would normally allow (because Mesa's are just such quiet amps of course and need all the help they can get :whistling: ). It's possible that this doesn't just all occur in the power section.


    I've had also difficulty in the past getting good profiles of this amp, even though it's an all tube Mesa, and that may be the reason. Any thoughts Christoph?

  • Not one of those problems do I have when using my VHT 2903 and fat bottom 4x12 cab... Sorry to hear that, but if you heard the KPA with my setup, you would think otherwise for sure... I tried the KPA through my Friends mark IV head, and it was extremely unappealing FWIW...

  • Im using a a matrix power amps and cab.
    Ive also tried using the fx return of a Marshall yjm and an evh 5153 and have had no such problems, it sounds/feels great. I dumped axe2 cos I didnt think it felt anywhere near as punchy or bold in this kind of setup.
    Maybe its the fx loop of the boogie?

  • All has been said. The poweramp section of your MESA is build to match the preamp section. It does not work with the KPA.
    I remember pluging my Axe-Fx into the return of a Fender SuperSonic and it was terrible.
    I'm lucky it works fine into the return of the Randall.
    I have not aliasing at all.

  • All has been said. The poweramp section of your MESA is build to match the preamp section. It does not work with the KPA.
    I remember pluging my Axe-Fx into the return of a Fender SuperSonic and it was terrible.
    I'm lucky it works fine into the return of the Randall.
    I have not aliasing at all.


    Yeah, you're absolutely correct. You're also mixing power amp profile and power amp... which is silly. I'm not quite sure what the point of all this would be when the KPA on it's own is so damn good. I'm not saying the Mesa isn't good, of course, but it's its own different thing. I can't imagine using the KPA with anything other than a good frfr monitor. Let it do the job it was designed to do.

  • I have a very old Marshall keyboard amp, solid state 50W. It sounds f-ugly with keyboards, honestly, but with the KPA it's just glorious (shame is not loud enough for a normal stage, but for small gigs is perfect and light). I think is the combination of the Celestion G12P-75 with the tweeter that makes it work so well. Thinking about to get somebody to mod the power amp to get more volume (the speaker is rated 75W@4ohm and the amp is 50w@4ohm and is powering the tweeter too)...

    "Music is enough for a lifetime, but a lifetime is not enough for music" Serghei Rachmaninoff


  • I can't imagine using the KPA with anything other than a good frfr monitor. Let it do the job it was designed to do.

    I'm pretty sure the KPA is designed to effectively do both, depending on the user's preference. There's even a prototype Matrix power-amp being tested for use with the KPA and a cab, which is rumored to fit in the existing KPA back cavity. I can't speak for a Mesa Express amp, not exactly their best offering. But the KPA sounds excellent through my MarkIV poweramp and cab. :D

  • same experience here


    i tested my kemper with 3 power amps


    with my diezel it was a dream


    with my 2203 jcm 800 zakk wylde it was ok


    with my rectalfire it sounded horrible



    it seemed to me that only with the diezel there was a "real" seperation of pre and poweramp and that the loop return only went into the power amp.


    mybe thats the reason why fx always sounded the best with my diezel <3



    so dude, you always have to be careful talking bad about a product if you dont know how to use it right.

  • Thanks for the feedback guys, the KPA works great with studio monitors, but given the adulation it was getting from people using it in the loop of their guitar amps and through dedicated powered guitar cabs I figured I had to give it a shot.


    The Mesa Express actually is a great little amp, it's my preferred Mesa. It's unlike most of Mesa's other amps in that it's geared at warmer blues breakup tones, and in the 25watt version vintage British tones with it's little EL84's. It also has (unlike most of Mesa's amps) a series FX loop, most Mesa's offer parallel with a blend parameter, if you are having difficulty with your Mesa's FX loop you can usually trace the problem to this idiosyncrasy and the fact that the mix dial only goes as far as 90% pure FX signal. In the case of the Express that shouldn't be an issue, what comes in is 100% of the signal going to the power amp.


    With regards matching the pre to power amp, it's an idea but I'm not so sure that's an issue. Every amp out there is designed that way so it shouldn't be a specific thing to the Mesa unless there's some crossover between the circuits beyond the audio signal, it is a possibility though with the little boost on transient thing it's got going on, but seems unlikely. It's not as if the KPA can't output more than enough signal either, in fact too much. I had to dial it back quite a bit, so it should be purely down to the dynamic range of the resulting signal. Impedance shouldn't be an issue either, the KPA matches the standard specs of most kit that sits comfortably in any amps FX loop.


    Anyhow I guess the next step when I have time again will be to do a direct pre-amp only profile (I already have pre+power only profile from the THD hotplate, but this will have to be done from the FX send instead to just grab the pre, anyone tried this?) and if that still doesn't nail it match it up in Logic against the source and run few re-amp test signals to see if it's possible to identify exactly what's going on. The amplification process itself is a pretty basic thing so really this should just work straight up without any issue.

  • I've tried FRFR.


    I've tried high end self-powered monitors.


    I've tried Atomics.


    I've tried solid state power amps.


    But NOTHING sounds like a good tube power amp + a good 4x12, at least to me.


    I've been years using that configuration with the Axe while all the people were saying solid state poser amps or FRFR are the best option....since some months ago mostly experienced Axe Fx users I know are saying that, for amp in the room feeling, best option is tube poweramp+cab.


    Sure have pros and cons, but is the next best thing to a real amp that I've tried (sometimes even better)

    Proud Kemper+Axe FX II user.....yes, you can hook'em together, they WON'T explode.

  • It also has (unlike most of Mesa's amps) a series FX loop, most Mesa's offer parallel with a blend parameter, if you are having difficulty with your Mesa's FX loop you can usually trace the problem to this idiosyncrasy and the fact that the mix dial only goes as far as 90% pure FX signal. In the case of the Express that shouldn't be an issue, what comes in is 100% of the signal going to the power amp.


    FYI, these Mesa's all have series effects loops:


    -Lonestar


    -TransAtlantic


    -Mark III, IV, Mark V


    -Roadster


    -Road King


    -Stiletto


    -Royal Atlantic


    So actually, very few Mesa models have parallel effects loops. :S