Split the Stack

  • Quote

    KEMPER PROFILER Main Manual 5.5

    • A PROFILE of a guitar amp, tapped at its effect-loop send jack, representing the preamp section of this amp. This

      Direct Preamp PROFILE can then be played back into the effect-loop return of the guitar amp, and further through its power amp section and a guitar cabinet. The following graphic illustrates this configuration for information only - we don’t recommend this setup.


    It is unclear why the manual doesn't recommend creating preamp profiles. I suspect that Kemper believes that the results are usually sub-optimal.


    There is no supported way to profile a power amp by itself. The signal must first come through a preamp. However, it would be possible with a split stack. You can already use cabs from other profiles which are part of the stack. Why not have the same ability for the preamp and power amp sections? If split stacks were possible, you could create a DAP, then split its pre and power amp sections for use as individual components in a stack the way that cabs are selected.


    Here are some examples of split stack uses and benefits.


    You could make DAP profiles of an amp covering all of its multiple wattage and configurations. Take the Mesa Boogie 5:25 or 5:50 Express Plus amps for example. From the manual:


    Quote

    Each power mode has it’s own tone-spawning operating class and wiring configuration! Choose the full power mode of either amp (25W in 5:25+ or 50W in 5:50+ ) for Class AB running in a Push-Pull configuration for punch, authority and headroom. Or, kick down to 15 watts (25 watts on the 5:50+ ) for Class A Pentode for a more silky, vintage voice with enhanced clip potential. And for the ultimate in low wattage power expression knock it down to the 5 watt mode... now you’re running one tube in Class A Pentode wired in a Single-Ended configuration.

    These are in effect three totally different power amps. The idea is to get profiles of all of the circuit configurations of the power amps. I'd make three or four profiles with varying gain levels from the preamp to cover gain level input of each power amp circuit. Note that the preamp's only contribution to the power amp's profile would be gain output at the power amp input. Once you have made these DAPs, you could use a totally different preamp profile assuming split stacks were available.


    Now you could place a Vox AC30/6 Top Boost preamp profile in front of a Class A 5 watt Single Ended Mesa with a single EL84 tube. Or try a Fender 5F4 Super preamp profile with the 15 watt 2 X EL84 tube Class A Mesa power section profile.


    Sure, you could profile these amps with their own preamps, but the ability to mix and match and preamp profile with any power amp profile would greatly increase available tone pallets. Also, these classic amps had no effects loops. That means they can't mix and match pre and power amp sections without hardware modification. That would greatly drop their value.


    Not so with Split Stacks. With Split Stacks, any vintage amp without a hardware loop can have one. No mods needed.


    I like to use multiple Preamp profiles with a hardware amp and cab. I can do that now by loading a preamp profile on my Kemper, sending the signal to my Mesa 20/20 power amp. The 20/20 uses two EL 84 tubes.


    But what if I had a Synergy Syn 2 hardware system and I want to match the Marshall Plexi module with EL34 tubes, like the actual Plexi amp? The effects loop on my Marshall JCM-2000 DSL 401 combo is parallel, and feeds the dry preamp into the effects return. So I can't feed the power amp section with the Syn 2. With Split Stacks, I could profile the DSL and just use the power amp section.


    The Kemper currently has 4 mono stomp slots, the stack, and then four stereo effect slots. With Split Stacks, you could potentially place effects between the preamp and power amp sections instead of after the stack. That would be a more traditional placement for effects.


    You could also potentially run a hardware multi effects unit between the pre and power amp sections if the X slot could be placed there . This scenario would require that that the hardware effects be mono. However, potentially Kemper could make the redesign allow for a stereo return from the X slot into the power amp section of a split stack. There might be enough DSP to handle a dual mono (parallel) amp section. Or possibly, since effects DSP load could be lightened by using an external hardware multi effects unit, limiting the use of on board effects could make enough DSP could be made available to make this possible.


    At present, I use my Kemper with my UA Apollo 8 interface to combine UA effects plugins with my Kemper. I use the X slot, placing the Apollo 8 there, connecting the two units via the analog send and the stereo returns on the Kemper. Having the fantastic sound quality and near zero latency of the UA effects is awesome.


    However, I haven't been able to figure out a way to connect via S/PDIF, placing the Apollo 8 into the X slot. (Anyone who can show me how to do that, please speak up.) I will say it now. There should be a way to use the S/PDIF ports as a routing option for the X slot hardware connection, even without Split Stacks.


    I have also used the Apollo 8 as a power amp section for a preamp profile. Some of the UA amp sims (Fuchs, Freidman, Suhr ) let you bypass the preamp or the power amp sections. So, I have profiled my Mesa Recto Recording Preamp , my AB763 clone (Fender Blackface), and the Preamp from my Marshall JCM 800 DSL, and I use the power amp sections of the Fuchs Train II, and Friedman BE-100 and DS-40 UA plugins.


    So what does this have to do with Split Stacks?


    With Split Stacks on the Kemper, I could use the UA effects and guitar pedal and amp sims in a totally flexible manner. The split Stack architecture would allow combination of any preamp, power amp, cab, or effect from either device to create a custom rig.


    Of course this would also work as well with Line 6 Helix, Fractal FX, Mooer, Boss, etc., hardware units.

  • Have you ever tried to play a tube preamp A for example via its fx send into the fx return of tube power amp B? And based on that experience is it worth the effort? Already today you could create a PROFILE of that setup, even a Direct PROFILE via a suitable DI box plugged between that power amp B and a guitar cabinet. The result would be a Direct PROFILE of preamp A combined with power amp B. I'm not aware anybody has ever done that.

  • However, I haven't been able to figure out a way to connect via S/PDIF, placing the Apollo 8 into the X slot. (Anyone who can show me how to do that, please speak up.) I will say it now. There should be a way to use the S/PDIF ports as a routing option for the X slot hardware connection, even without Split Stacks.


    Why are you so stuck on using SPDIF? Send a cable from your Kemper into an analog input of the Apollo. Then apply whatever FX. Then route that output back to the Kemper and create the required FX loop.


    This demand for SPDIF to be recognised as a loop is just wrong on so many levels and doesn't make sense at all.


    The profiling process that you describe otherwise might be possible with an amp that has a preamp out and a power amp in, so that you could profile each element of the chain. That said, do you know a lot of amps that have that? I can think of very few.


    You're basically making a case for a modeller, where you can mix and match components. The Kemper is definitely not that, it's more of a way to capture a specific tube amp's tone in conjunction with a specific power amp.


    And hey, if you have a preamp out, just send that signal to said power amp and cabinet combination and profile the result. Theoretically, you should be able to profile every combination of mix and match you desire.


    All this assuming that you have a preamp output on the desired amp and a power amp in on the desired power amp.

  • I’m definitely not an amp tech kind of guru but I suspect that the pre amp and poweramp parts of an amp interact with each other in the physical world in much the same way as the controls in the tone stack of a valve amp do and the power amp and speaker do. The reason you need to use the amp connected to a real speaker rather than dummy load when making Direct profiles is because of the interaction. I wonder if profiling Pre Amps and Power Amps separately would result in convincing combined profiles or if it would lose much of the mono because of the lack of downstream or upstream interaction from the other sections of the amp. I don’t know the answer for sure I am justhinking out loud.:/

  • Why are you so stuck on using SPDIF? Send a cable from your Kemper into an analog input of the Apollo. Then apply whatever FX. Then route that output back to the Kemper and create the required FX loop.

    Short answer:


    Staying in the digital domain lowers overall noise by eliminating redundant conversion steps. Further, using the same clock on both devices reduces jitter, which I find is the most detrimental cause of harshness in digital audio.


    I currently use a Strymon AA.1 in the X module to interface with my analog pedals. The Strymon AA.1 takes the line level send from the Kemper and attenuates it by 18 dB. That signal is connected to the input of my pedals. The output from my pedals goes back through the AA.1 which brings the signal back to unison by boosting it by 18 dB. Then the AA.1 stereo output goes to the return of the Kemper.


    Of course, it would be optimal to have a second X module that could use the digital in/out to connect to devices like my Apollo at the same time.


    Have you ever tried to play a tube preamp A for example via its fx send into the fx return of tube power amp B? And based on that experience is it worth the effort? Already today you could create a PROFILE of that setup, even a Direct PROFILE via a suitable DI box plugged between that power amp B and a guitar cabinet. The result would be a Direct PROFILE of preamp A combined with power amp B. I'm not aware anybody has ever done that.


    I think I might not have fully gotten my main idea cross. Anyone with a Synergy, Egnator or Randall modular preamp system combines different flavors of preamps with either vintage or unconventional pairings of power amps all the time.


    The modular preamp concept is that most of the sound of a tube amp is generated by the preamp. So you can use different preamps with the same power amp and get to maybe 85 to 90 percent of the sound of a given tube amp with a different tube compliment and even circuit design.


    Look at the Synergy Syn 50 head, for example. It has two slots for 2 Synergy preamp modules with a 50 watt 6L6 tube amp. Say you have a Twin/DLX module and a Plexi module. The Fender preamp module matches perfectly. But what about the Plexi, which used a power amp section with EL34 tubes? There is definitely a difference, even if it is subtle.


    Next, consider that most vintage amps have no effects loop. You can't make a physical connection between a Vox AC 30/6 Top Boost preamp and a Marshall Plexi power amp section because neither have effects loops.


    But with Split Stack capability on the Kemper, these hardware limitations would be irrelevant. Make DAPs of the AC 30/6 and the the Plexi. Then simply use the AC 30/6 preamp merged with the Plexi's power amp section.


    Unless you can make a DAP, then split the stack into a preamp section and a power amp section, you can't get a profile of a power amp by itself. That limits your ability to mix and match vintage preamps and power amps the way you can use a DAP with any cab you want.


    To answer your question, "Is it worth the effort"? Absolutely.


    I have four tube preamps. Two are in combos, and two are stand alone. I regularly use two of them feeding my Mesa Boogie 20/20 (EL84) stereo power amp. The preamps are from a Marshall JCM 2000 DSL 401 combo, an Ampeg AX-70 combo, a Mesa Rectifier Recording Preamp and a Fender AB763 (Blackface) clone.


    I regularly take the send from the effects loop of a combo and connect it to the input of one side of my Mesa 20/20 . The DSL connected to the 20/20 is quite different from the EL34 tubes in the Marshall's power amp regardless of the cab I use. However, it sounds glorious.


    I cannot do the reverse, sending the output from my Mesa Boogie rectifier Recording Preamp into the Return on the Marshall. The Marshall's effect loop is parallel and sends at least 10% of it's preamp to the return of the effects loop. I am going to get it modified to make the effect loop mono with a 100% wet input at the return.


    The AX-70 is a hybrid. It has a tube preamp with a spring reverb and a solid state power amp. It does have preamp out and power amp in jacks. I plan to use the power amp section with DAPs to power various guitar cabs.


    I have not tried to make a DAP of the DSL --> 20/20 combo yet, though I plan on doing so. My Kemper DI box came just after I had to tear down my studio. I have since moved and am building custom furniture for the studio in its new room. Once I have the studio up and running, I plan to start profiling my amps.


    But Burkhard you did not comment on the Split Stack concept. Is it possible and if so, would you consider implementing it? Could an X module be placed between the stack's preamp and power amp sections?


    Also, is there any chance that the S/PDIF jacks could be used as a second effects loop with a second X module? As I said above, I use analog pedals now with the analog connections on the X module. I'd love to be able to do both analog pedals and digital effects on my Kemper.


    Thanks, Steven.

  • The 5.5 main manual says that modules X, MOD, DLY and REB are post cabinet:

    "You can add more built-in stereo effects to the signal, after it has passed through the amplifier and virtual cabinet, in the Modules X, MOD, DLY and REV";)