Posts by EdwardArnold

    So the cable you’re given on-stage is already 1/4” TRS or 1/8” TRS jack socket on the end of it carrying headphone level signal? I.e. driven from a headphone amp somewhere?


    Or is it an XLR/TRS jack that you plug into your own headphone amp/level control box or wireless IEM transmitter?


    Forgive me for not knowing if you’re well versed in audio TLAs or not - if the above doesn’t mean much to you let me know.


    You can do what you’re suggesting with the correct cable adapter(s) connecting to the Aux input (Return 1 for mono) on the Kemper.

    You would need to mute the guitar signal being sent from the desk (or just pull the send down on the iPad app if no mute button) and set the aux input to mono on the Kemper. You’d still have most of your signal in the middle though - mono to a stereo output isn’t going to suddenly become a lot wider. The guitar would be in stereo, yes, but most of it is still centred unless you pan it around (panorama control on the Kemper rig settings). You won’t be able to pan the desk mix, but you can connect it to one side of the aux return in stereo mode I suppose, and pan the guitar to the other side (hard pan). I know some people who play like this, but I find it awful personally.

    I still think a mono Kemper aux setup could work though, with the following considerations:

    1. With the ‘rest of band’ mix now separate from your guitar foldback, you can be more liberal with the foldback/aux EQ (or your engineer can). I suspect that there just a lot going on in the midrange and it is making it difficult for you to define your guitar at times. Just increasing the level of the guitar will risk damaging your ears, so instead try cutting out a chunk of the mid frequency range from the band mix to give it more space to occupy on its own. As it’s a digital desk, it is bound to have Aux EQ for this.
    2. Make sure you don’t unintentionally unbalance the signal coming from the desk by using a TS jack cable, as it will pick up interference. The Toaster and Rack have an XLR Return (as well as the TRS) so that would be ideal as it is balanced+robust and easy for live sound venues as there should be XLR cables aplenty. The Stage has TRS returns only, which are also balanced connections and compatible with XLR, using the correct cable.
    3. Using the 1/8” headphone out on the Kemper will sound great; better than any wireless IEM system, for example, and most headphone outs period from what I’ve found, but it’s not robust if someone trips on your cable. It’s a real shame this isn’t a 1/4” output, it hey.. Just make sure you secure the cable to take the strain relief.
      Also remember “Space” might be enabled on the headphone out so enable/disable as required.

    Lastly, depending on the size of your band and the size of the desk, there might actually be scope to provide a stereo foldback mix if you can convince the engineer that you need and deserve it ?. They might just have a working practice of mono foldback despite having more capacity. Worth a conversation with them. Have you already explained the issues you’re having? While handing out personal monitor mixing on iPads solves a LOT of challenges and saves a lot of time for an engineer while empowering the talent, it shouldn’t absolve them of their monitor mixing duties entirely.


    Let me know how you get on and if the mono
    EQ solution does anything for you, and if any of the above doesn’t make sense please let me know.
    -Ed



    Yes, you could connect a Bluetooth receiver to the returns and use them as Aux input. If you have a Stage you would use Return 1 (L) and 2 (R), or Rack/Toaster Return 1 (L) and Alternative Input (R).


    You would not need to connect the sends to anything. For the example you’ve linked, you’d require a stereo RCA/phono to (unbalances) TS 1/4” Jack cable.


    If it’s for home use, no problem. If you’re considering this for live use, be aware that Bluetooth signal ranges are compromised by interference from lots of other devices. It’s also likely that the audio quality takes a bit of a nosedive on cheaper Bluetooth devices as you’re relying on their DAC stage. The direct iPhone DAC is actually really good.


    I have a similar setup, where I can wirelessly stream audio to my studio monitors if I want to. However, I bought a secondhand Apple AirPort Express 2 (found one for £30!) and configured it to join my home WiFi network to use AirPlay. It has a very high quality audio output compared to BT and being WiFi, I don’t have to worry about pairing or signal range. It would also fair slightly better in live use.

    Testing, testing, 1... 2... BLAT!!! ARGH!!!



    My digital console looked a bit unloved, so I decided to use it as a fancy signal generator to do some testing with the Kemper Stage. I made a video of my methods and observations in case it is interesting to anyone from a technical standpoint. Some of it just helps *visualise* what's happening to signals rather than giving out numbers. I accept that some of this may be known already or buried in the manuals and that I've also taken some liberty with my assumptions!


    I'm interested to keep the technical conversations going for my own learning, so if there is something flawed in my test methods - [entirely possible] - and/or you're getting wildly different results, please let me know and I will try, try again...

    Here are the video 'chapters' if you just want to skip through:


    0:05 SSL Live test rig explanation

    1:10 +14dB of gain measured from inst. input to line output

    2:00 -12dB switch is two -6dB stages

    2:30 Different gain stages in the signal path

    3:00 Bug in latest 7.4.1 release regarding -6 dB switch for Git+Processing

    4:40 1kHz tone stack harmonics test

    5:00 Pink Noise Stack test

    5:30 Phase cancellation test - nice and flat

    6:50 Latency measured = 2.5 ms

    8:10 Constant latency mode = 4.9 ms

    9:30 Essential cheesey outro


    Notes in addition to commentary, the phase-cancellation test did factor in the latency of the return signal, delaying the reference, I just didn't mention it. It made no significant difference to the result. I could get absolute cancellation of the 1kHz sine wave signal when aligned, but also didn't show this.


    All the best,

    Ed

    Haha. Not sure that any of us who’ve spunked over £2k on a Kemper rig can justify crowdfunding support ?

    I’d be up for it, but the rule would be that it has to come from wish.com. That would get some amusing results in about 12 weeks - a UDA Alpopo or something for only £7.

    ...how many dB do I need to boost the signal into my audio interface from one of my Stage units to exactly match what I have currently with the toaster?

    For the Balanced XLR outputs, the published specs suggest the Stage is 7dB lower than the others so that there isn’t a level difference between XLR and TS outputs. As you have access to both are you able to prove this for us? You would use a flat profile on each and a constant test tone as the source, looking at your DAW input meters.


    If you’re recording at another studio though, there are surely other factors that will change the input level, even if you take your toaster. Different A/D converters for example have different operating levels, so the same level of analogue signal lines up to different dBFS meter values if they are not using the same standard. What equipment are you using in each case so I can look up the specs?

    What headphones are you using and are they your only option? It sounds like they are very low impedance and also efficient drivers, therefore very loud. For the sake of protecting your hearing, it might be worth investing in a pair that take a bit more to drive them.

    In v7.1.x I had a complete software freeze whenever I left the tuner on for around 30mins (to mute the guitar), while also connected via USB to RM.

    Kemper Support sorted me out in no time with a beta that resolved it, plus they got the log files and explained what they saw. I’d highly recommend getting in touch with them, as it will at least inform them of bug fixes for future releases.

    Converters to/from coaxial SPDIF to optical TOSLINK are certainly available. The Stage has the advantage over the Toaster and Rack in that it can be either clock master or slave. I would run it in slave mode to avoid your interface having to re-clock upon connection of the Kemper.


    Something to look out for would be the latency of the converter (see if you can find published specs for one). It’s unlikely to be significant but worth confirming.

    The Apollo twin has a nice feature that the optical input can be either SPDIF or ADAT format, so you’re good on that front.


    The Kemper analogue outputs and Apollo inputs are both class-leading, so you’d miss out on all that groovy preamp modelling in offer, but if you’re re-amping etc. Back from your DAW it makes a lot of sense.

    ...The XLR outs on the Kemper measure that same output impedance as the ART DI Box I have to hand (both are 220ohm on my multi meter across two pins. By comparison the bridge pickup on my PRS DGT measures 8.6k. Am I measuring wrong?

    Thinking about this a little more, this isn't measuring impedance. Your multimeter will use a small DC voltage to measure resistance, which isn't the same as calculating/measuring the impedance of the op-amp used as the output driver. I don't know how much difference there is between the DC resistance measurement and the actual impedance - it might not be significant.
    As far as I know, you'd use a 1 kHz sine and load the output to do it properly. I'll have a think about how this can be done. The alternative is to lift the lid on the Kemper and see what op-amp device is being used, then look up the specs for that. I'll let you go first hah!

    Hi Alan,

    Well those are some interesting results, and I wouldn't say my mind can't be changed :D I think we're seeing that the Kemper performs a lot of the functions of an active DI, but not all.


    1 - Impedance - ...both are 220ohm on my multi meter across two pins.... Am I measuring wrong?

    I doubt it - it sounds like it is me that is plain wrong here. I'll take that one on the chin; anything under 600 ohms would be fine. I'll get the multimeter out for my Stage and Radial DI boxes later as I'm curious how they compare. I've got an Art dpdB lurking somewhere as well.


    2 - Balanced signal - the Kemper XLR Out is a balanced XLR signal which is suitable for long cable runs.

    Sure, the XLR out is balanced, and this is one of the primary functions a DI performs, but balanced line outputs on professional gear is par for course.


    3 - Level - while the KPA is capable of sending up to +16db (Head/Toaster or +15db Stage) this can be reduced to - infinity by using the Output Volume. A DI Box pads the output with a fixed attenuation (usually 20 - 40db). Why is simply reducing the volume being sent from the KPA different to engaging a pad switch on the DI Box?


    It's this last bit that, for me at least, that means the Kemper output does not replace a DI box. The output of the Toaster/Rack is only +16dBu on the unbalanced TS outs. The balanced XLR outs max out at +22dBu. The additional 6dBu equates to twice the signal intensity (peak to trough being measured by a differential amp rather than just peak to 0V reference).

    The Stage must have an attenuator for the XLR outs so that there is no signal level change between XLR and TS (I actually rather like this approach, to prevent 'blatting' during setup - I think this was the reason cited by Kemper for doing this).


    But mic level is down in the -60dBu to -40dBu range, which equates to a few millivolts, so even with the -12dB attenuation switch on the Kemper output, you've got a lot of gain reduction needed before it becomes suitable for a mic input that could well have a minimum gain value of 20dB to consider (most live engineer workflows I've witnessed don't start with all mic inputs padded or set to Line/unity gain, for example).

    I don't think using it in this way would be a sustainable workflow, as the potential and penalties for it going wrong are high. An analogue mic pot will be log, and if you're having to use it on minimum gain it will be difficult to adjust by a small amount if you subsequently need to, plus the ends of the pot travel are where the pot is noisiest, as that's where all the crud from the wipers gets pushed to.

    I guess you could argue that any low impedance line level output with a level control could be reduced enough to feed a mic input, but there is an inherent noise floor in any system, and trimming down the output gain this much will surely take you closer to it, with the noise floor being amplified up with the audio signal at the mic input with this reduced ratio. The Stage might be easier to manage, as it has the same -12dB output pad as far , but is already lower in signal level with its max +15dBu output. With the output pad, you'll still be at up to +3dBu, which is over 1V. I'll have to have a play with this to be sure- I'm interested to know what the noise floor performance is like at minimum output. Could do with finding someone with a D-Scope at home, as I'm unable to go to the office for the foreseeable future.


    By comparison, engaging a PAD switch on a DI would result in the noise floor also being attenuated, preserving the signal to noise ratio of the Kemper output. It's possible Kemper could be working some voodoo magic that means signal to noise is better than expected even when the gain value is at its lowest, but I will reserve judgement until someone can scope it out. I'm also not sure if the Kemper output PAD is an analogue function or not. If so, it will indeed be switching in/out circuit components so that the gain range remains optimised. It might be that this is just moving the digital trim range before the DAC. If it was a -30dB or even -40dB analogue PAD function, it would serve much better as a DI output.


    Still, after all this, the functions of a passive DI that still remain are the transformer isolation that can be reassuring in certain live situations. I mentioned line isolating transformers in my first reply, so perhaps they are worth mentioning again, as one of these, with a PAD function, might be closer to what the OP actually wants than a DI box, given that the Kemper is partway there.


    There is a lot of context dependancy here, for sure; playing level, the rig levels, the output trim, the Kemper model, the input stage of the mixer. If someone can bend it to their will and is happy with the audio results and the workflow without additional hardware, then ok :thumbup:





    While staying with Radial, there is another option in the ProD2 (link here). It doesn't have the premium Jensen transformer, but it is still a premium product and I think it is much better value. You'll feel less guilty about kicking it around the floor - I had a JDI that I subsequently sold to a studio owner I know, as I was too precious about it to take it to gigs! Also, I suspect no-one in the world is going to notice the difference between the JDI and the ProD2 at a live gig.

    Yes, the passive Radial JDI will lower your signal level. It takes your high level, high impedance signal down to a low level, low impedance mic signal.


    Kemper (line level) --> JDI = use the -15dB pad switch

    Passive electric guitar --> JDI = no input pad needed


    There are both mono and stereo versions of the JDI, if you need. The stereo version is also perfectly happy being used for two separate mono signals/instruments, not just stereo from a single source.

    I see it:

    “..uses active electronic circuitry to present a constant input impedance to the source (Kemper in this case)..”


    By this I meant, “The active DI presents a constant impedance to the source device feeding it, which in this example would be your Kemper.”


    Apologies for the confusion.

    If I only had the option of picking one DI to take to gigs, I would take my passive one, not an active one, despite some of its drawbacks. My reasons are based on my own experience of the advantages and disadvantages of active and passive. For example, a passive DI has helped save some of my gear from damage due to the transformer isolation and it’s also simpler as it doesn’t require phantom power. I’ve had a few gigs where the supplied XLR cables have dropped a pin 2 or 3 connection. With a passive DI audio will still pass, albeit unbalanced and 6dB down, but an active DI will no longer receive phantom power and you’ll have no signal (mine isn’t battery powered).
    If I’m recording somewhere though I’ll use the active Radial DI as the particular mode I own sounds better to me than my passive one.


    Lots to consider, hence I’m trying to shine a little light in the subject; there’s more to it than first meets the eye :)

    Keep your eyes peeled. They pop up on ebay facebook etc regularly.

    Someone may do you a turn.

    There have been record sales of audio interfaces these last two months as people have had the time to explore hobbies involving music and podcasting from home etc. I’m starting to see quite a lot of “Purchased this last month, did’t really need it..” posts on marketplace at least, so it’s a good time to buy 2nd hand!

    Not wishing to smother you with options, but for around the same price as a typical 2in/2out USB Focusrite audio interface, you could probably pick up a secondhand small analogue mixer with a built-in USB interface. This has a few advantages:

    1. The headphone output jack on your PC won’t be as high quality as audio over USB to balanced interface or mixer outputs.
    2. You don’t need your Kemper powered on just to listen to music.
    3. Your main workflow requirement seems to be mixing signals; a mixer has dedicated controls for level control and EQ etc.
    4. You’ll have some mic inputs to record from.
    5. Your mixer can do double-duty for small gigs.

    That said, a well-featured USB interface sounds like it will do the business. I’d try and get one that has monitor mix controls between the inputs (Kemper) and returns from the computer (PC output over USB) as just a simple hardware knob so that you don’t have to go into an application window to balance things up.

    No, the Kemper does not provide the functions of a DI box as it outputs line level signal rather than low impedance mic-level signal. The latter would be required to a) feed a mic input on a mixer and b) drive long mic cable distances without degradation. So, you often still need a DI box unless you have a mixer input with built-in mic/line switching or pad functions (these are actually quite common on stageboxes that accompany digital desks, and highly useful).
    You can use either active or passive DIs with the Kemper, just be aware of the pros and cons as outlined above. Radial make great examples of both. If I could carry only one it would be passive.


    If it’s a mixer with a separate TRS Line input (common) you can connect straight to that from the Kemper’s output, with an XLR>TRS cable for example. This is great until you need to drive long cable runs through a multicore back to the desk. That said, the Kemper line output drivers are good. Chances are onstage though that you’ll only be given a wall box that feeds mic inputs on an in-house mixer. I’ve found that asking a hired-in engineer to start re-patching to line ins is asking for trouble, so I much prefer the idea of presenting a pair of D.I. outputs they can pick up.


    What can catch people out is on the back of the Rack and Toaster, you have a ‘Direct Output’ but this is an unbalanced 1/4” TS jack, and its level varies depending on where you choose to feed it from in the signal path, but it will never be low impedance mic level or balanced as that is not its purpose.


    I’m wondering if I confused things by putting “..(the Kemper in this case)...” ? I was referring to the Kemper being the source connected to the input of the active DI, not it being the active DI itself.


    If this doesn’t clear things up still let me know and I’ll give it another crack.

    Hi, have you updated to current firmware to rule out a problem in that earlier release? The other possibility, rather than software, is that the switch activation/deactivation is not being read correctly. This seemed to affect a large number of Stage users early on, myself included, but subsequent firmware releases resolved it for most. I still had some mechanical issues, but found that it was just because the switches were new, and needed to self-lubricate or similar. I 'exercised' them, say, 100 times and I haven't had any problems since. Beyond this, drop Kemper Support a line and I am sure they will sort you out.

    Happened to be reading back through this thread, and while the OP has found a suitable solution (a phantom power blocker) I thought it might be useful for others reading to clear up some information on different devices:

    1. Phantom power blocker - contains DC blocking caps that prevent damage to sensitive mics and equipment such as ribbon mics.
    2. Passive DI box - contains a transformer, which can usually be tapped at various points so that it can be 1:1, or step down with attenuation switches marked e.g. 0dB (unity) -20dB and -40dB although this is impacting upon impedance and may be sub-optimal; input and output impedances are also dependent on what is connected to the DI box, so you're not going to find a perfect 'one-box-solution' for mic, instrument, line and speaker level sources. Unless a high quality (=expensive) transformer is used, it is likely to add harmonic distortion particularly at low frequencies, especially when driven beyond the parameters it was optimised for. A linear frequency response is also unlikely on more affordable units, but this isn't always an issue for guitar as it is most likely to be a drop-off at either end of the frequency spectrum.
      Passive DIs have the advantage that there is physical isolation of lines, adding more protection against wayward voltage under certain failure conditions. You have to be careful where you place a passive DI though; if it is near a mains transformer it will induce hum.
    3. Active DI box - no transformer - uses active electronic circuitry to present a constant input impedance to the source (Kemper in this case) and a constant output impedance to the destination (mixer). Given that it is already an active unit, you can often find models that also incorporate further active processing such as EQ or pre-amplification. This is where 'active' gets confused with meaning 'preamp'. An active preamp doesn't mean that it will amplify the signal; a 'basic' active DI has all the same applications source-wise as a passive, except that it may well have a more linear frequency response and be less prone to harmonic distortion due to the design of the circuit, and the cost is likely to reflect this. The active circuit can also provide the -20dB, -40dB etc. to attenuate input levels without it also affecting the impedance, so the efficient voltage transfer that you require for your signal to pass unencumbered can happen. No physical isolation, requires either battery or phantom power to operate. I think the 'active = larger signal' association comes from active guitar pickup systems, where the pickup system contains a preamp as part of its active electronics. It wouldn't be the first time the guitar world has blurred our definitions a little (I'm looking at you, tremolo arm!).
    4. Line Isolating Transformer - contains a 1:1 transformer, and is very much the same as a passive D.I. in concept but the impedance values based on transformer windings are suitable or line level sources and destinations. While mic level signals are typically less than 1V, line level can be up to around 8V, driven by a source impedance of less than 100 ohms, with the output connected to a mixer or active speaker input (for example) that will typically be 10k ohms. The impedance of a 'mic level DI' with a step-down ration will be wildly inappropriate for line level sources, hence, these are different devices.
      Also provides isolation from voltage shorts through connected equipment. Usually features ground lift in addition to isolation through transformer to help solve a number of issues with humming monitors, speakers etc.

    Happy to discuss any of the above if I've missed something.
    All the best