" Power Amp Distortion " => is this why the Kemper *cant* profile Power-Amp Distortion ? ....if so, can this be "fixed" ?

  • Hey all


    In my quest to try and profile Ch 2 of my Matchless DC 30 [ Ceriatone clone ] cranked ..... I just read the following on the Kemper site here:-


    http://www.kemper-amps.com/pag…ling_Amplifier___FAQ.html

    " .....We spent considerable time researching the dynamic behavior of the tube. It was also necessary to study the interactions between the tube and surrounding circuits, which become very complex when the tube starts to distort. We were lucky to find a way to extract this exact tube behavior by analyzing the intermodulation products of crossing sine sweeps. The relation between the intermodulations and the unprocessed sine sweeps tell us the full story about the distortion shape and dynamic of the tube and the behavior of the surrounding circuit. It can even deliver the information about several distortion stages in a row, so long as there is only one stage significantly distorting. This measurement is independent of the frequency response of the amplifier. Once the distorting part has been analyzed, it can be separated from the transfer function. The frequency response of the cabinet is then easy to determine and separate.Aside from the ease of profiling the whole amp, there is another good reason not .. "


    I think this is the reason.


    Why does the Amp need to be cranked you say ?


    Well .... because that is where its glory lives .... it is the tone it is famous for ... imagine the Top Boost Channel of a classic AC30 with everything just about on full .. then take away the flubbyness and add in punch and clarity and buckets fo harmonic chime ......


    If I crank Ch 2 of the Amp it is a glorious mix of Pre-Amp [ EF86 ] and Power-Amp Stage [EL84] - it has to be heard to be appreciated :) Ch 2 Pre-Vol set to around 1.00pm and the MV set to around 11.00


    Bear in mind to it is only a 15w / 30w switchable amp.


    However .... no matter how I [studio] profile it - regardless of refining or not refining and regardless of mic's used the result is always the same .... TERRIBLE :(


    I can now only assume (?) the explanation above [ in red ] is the reason why.


    If so .... can the Profiling process be imporved to capture [correctly] pre and power amp saturation ?


    Ben

  • Judging from two of the three "Similar Threads" listed at the bottom of the page it seems we've been here before with the general thrust being a) the profiling algorithm isn't optimal for more than one "significantly distorting" stage (which might include pedals) and that b) power amp distortion is overrated, and not much to crow about.


    Now, I'm in the second camp (to which I'll also add that speaker distortion is also not worth crowing about, but that doesn't mean that some software amps don't try.) If it was such a wonderful thing we'd see negative feedback circuits in guitar amps disappear in favor of increased power-amp distortion and pentodes being used for preamp purposes except that your DC-30's Ch 2 EF86 appear to be doing just that!


    Personally, I'd like to hear some examples of the glorious tone you're trying to reproduce (ideally, live & profiled with pedals off at several different master volume levels) just to get a sense of what the power amp is or is not contributing vs. the Kemper's failure to reproduce it. For curiosity's sake, there's another DC30 Ch. 2 rig in the Rig Exchange... how does that one compare to your rig with its Master Volume set to a modest level?

  • In my opinion, power amp distortion is important and not overrated. Compared to the tube amps, I just don't hear enough power amp distortion in Kemper, but the feel of power amp does exist in some Kemper profiles (for example in Guido's JCM800 profiles). In those profiles, you can sense the amp has been profiled really loud. However, if I record myself playing the profile and listen to the result, I don't really hear the power amp distortion (nor speaker distortion), at least not as much as I feel it when playing the profile.


    There is a glimpse of power amp distortion in some Kemper profiles, but not as much as in real-life tube amps. In fact, you can hear the difference in here (unfortunately in Finnish only, but with English subtitles): https://www.youtube.com/watch?v=QwDXJDZfKnQ&#t=337


    Couple of years ago when I tested Fractal Audio Axe-Fx II, I heard nothing but preamp distortion. The firmware was version 9 back then, so nowadays things may be different. My comparision point was Kemper and of course all the tube amps I had played, using different volume levels and also attenuators.


    My number one reference for the power amp distortion is a classic one: Malcolm Young live (Mal is on left channel, his tone is cleanish but his amp is LOUD): https://www.youtube.com/watch?v=iEX4E9gGY0Y


    Here is "a challenge for profilers" I already mentioned in Guido's profiles thread. I quote myself by saying that I haven't heard this kind of power tube distortion on any profile yet (but I would love to): https://www.youtube.com/watch?v=LUf551mWkrk


    Thus said, I still think that Kemper is the best solution in digital market for authentic tube amp tone. After all, most of modern tube amp tones are all about preamp distortion. And my personal opinion is that speaker distortion is ugly and overrated.


    Just my two cents.


    -Jari