DI-boxes suitable to create Direct Amplifier Profiles

  • I was given, then repaired a broken Live Wire Solutions SPDI Direct Box. This is a passive DI box, but after acquiring the schematic I determined it can be used for direct profiling within power limits and attenuation settings. The attached spreadsheet and schematic list the resistor voltages and the power ratings are based on the attenuator setting at 0, -20 and -40db for 4 and 8 ohm loads at output wattages at 25, 50, 100, 200 and up.


    I checked the math against scope measurements into a dummy load. They are correct


    For a 0 - 25 W amp MAXIMUM, a 0 dB setting is acceptable.
    For a 0 - < 400W amp -20 dB setting is acceptable, 0 dB is unacceptable (@ 400w into an 8 ohm load the wattage is exceeded on R2 10k ohm unless it is increased to a 1W resistor..)
    @ a -40dB setting the attenuation is sufficient to use the DI box but the signal may be too attenuated at lower wattages.

  • The chart is correct and measured the voltages across R1, R2, and R3 while testing the DI box using a dummy 4 and 8 ohm load. The DI box was tested up to 50 W with a dummy load. However, the 0dB setting is really intended to be used as a passive DI box for signals only.


    So to avoid any damage to the DI, the attenuator switch must never be set to 0dB for any load greater than 20W conservatively.


    The IN and OUT jacks on the schematic were drawn incorrectly. The are not shorting jacks, just paralleled open end jacks.


    I have currently direct profiled 9 amps using this method.

  • I want use the Avalon U5 as well. Can you tell me how you wired your setup? From the amp speaker out into the U5 and then back to the Kemper? Thanks ^^

    This is from the Avalon website.


    Q: How do you use the speaker input on the back of the U5?
    A: The set up is as follows:
    1. Connect your instrument to the input on your instrument amplifier.
    2. Connect your amplifier speaker output to your speaker for normal operation
    3. Connect a secondary speaker output from your amp or your speaker cabinet to the SPEAKER INPUT on the rear of the U5.
    4. Press in the SPEAKER to INPUT on the front of the U5
    5. Connect the line output on the U5 to the recording device or mixing console.


    Now I use the DBX db-10 for my di-profiles. This can be hooked up between amp and cab witch the Avalon can not. works great.

  • Do you still use ths for your profiles and if so what’s the set up i.e. do you use speaker cables from kemper to the di and di to the cab or instrument cables. Plus do you have amp/instrument and flat/filter selected?
    Cheers

    no i dont use it no longer . head to unit (xlr) / unit to cab (speaker) and then normal lead for guitar input . I think thats what i did, its been along time sorry.

  • Yes, DLS...
    That’s what I understand also, it’s very simplified… Which could be a good thing… But I have talked to a few people in studios and they all say that the countryman is the most transparent DI box they have ever used and they swear by it, so… I will try both and see if I can get some half decent direct profiles

    how did these go? Sound the same, different? Which did you keep?

  • I kept the countryman type 85… It’s my favourite out of the eight that I’ve tried so far, I never did get a chance to try the actual Kemper DI yet, obviously it should be good…


  • Hi Burkhard, I don't know which manual are you checking, in the PDI-03 manual available on Palmer's site, page 8, paragraph 2 (explaining the four rear Line Out connectors) it says: " The outputs 1, 2, 3 and 4 provide an unfiltered line level signal, i.e. without speaker simulation, for using the amplifier as a dedicated preamp to feed effect units separately. The ooutput can also be tracked for re-amping"
    So don't worry, the speaker simulation is not involved in those outputs, and i can confirm that by my direct experience!


    I’m trying with a Palmer PDI-03 and getting awful results. My reference amp signal is great but the profile is terrible. Sounds like it’s being overloaded.


    Any thoughts? It doesn’t have a pad but it has a level knob, which I’ve had most of the way down, once it was even so low that Kemper didn’t hear it. Came out the same :/


    I’ve even added a direct box between the Palmer’s direct out and the Kemper’s return to take it down even further.

  • Hi Dickjones,
    I did not have any good results with any of the speaker simulator/ DI rack units such as the Palmer, In fact, I had terrible results. I actually got better results even using the cheap Behringer ultra GI 100
    But the best results I have gotten so far are with the countryman type 85 DI box. I have tried eight different DI boxes and this one is the very best.
    You might want to take the Palmer out of the equation completely and just try the DI box alone.
    Keith

  • Hi Dickjones,
    I did not have any good results with any of the speaker simulator/ DI rack units such as the Palmer, In fact, I had terrible results. I actually got better results even using the cheap Behringer ultra GI 100
    But the best results I have gotten so far are with the countryman type 85 DI box. I have tried eight different DI boxes and this one is the very best.
    You might want to take the Palmer out of the equation completely and just try the DI box alone.
    Keith


    Thanks Keith. I may have to. I don’t get it.


    Side note: I just tried a profile using the cab simulated outputs (as my cab) and deselecting the “No cabinet” option and it worked perfectly.


    (?) So weird. Why would a direct profile be any different? Levels are apparently not the issue.

  • Just last week I experimented with a super simple homemade circuit for direct profiling, and had the best tonal success ever. First, a story on how it came to be.


    There are pictures available on the internet of the inside of the Kemper direct profile interface, in which it appears to be a few resistors and capacitors, and no active components or transformer. This implies that the interface does not provide any isolation or differential drive for a balanced cable. The entire reason for a direct box is to provide signal attenuation as well as balanced drive capability, along with earth isolation if needed. But the Kemper box does not provide balanced capability, and the Kemper is only a few feet away from the amp, and the grounds of Kemper and the amp are interconnected at the input, so is a balanced circuit (along with the active circuitry or passive transformer) actually needed? All that circuitry in a standard active or passive direct box will affect the tone to some degree, and less expensive transformers will not sound good. Maybe it's best to get all that stuff out of there if it's not needed.


    Also others have posted that they have used the recording output of some amps (non speaker emulated) to feed signal to the Kemper for direct profiling with some success. Such a circuit is often merely a level attenuator with a DC blocking cap, and the cap isn't really needed with most tube amps since the speaker output is transformer coupled anyway.


    So I took a 1\4" male TS to XLR unbalanced cable, added a simple resistive attenuator from the 1\4" male tip to ground (10k from tip to XLR hot, 220 ohm from XLR hot to ground), plugged it into the extension speaker out of a fairly loud 50W tube amp set to 4 ohms (the amp had its standard speaker plugged in as well), took a direct profile, and it worked perfectly. Made several direct profiles of the amp, and they all turned out spectacular. In fact, one profile I made of my Dumble #103 clone sounded a bit better than the original amp, when the Direct profile was paired with an Ownhammer IR of a 2X12 G12-65 cab (better speaker than I have in the original amp).


    I can't think of any reason such a thing wouldn't work fine, as long as the builder knows what he is doing so that he doesn't risk blowing up the Kemper with too hot an input signal. Also such an attenuator cable would not work with many solid state amps, especially ones with Class D outputs as the output grounds must float. So the builder must be very careful in regards to the amps he uses, and if its output ground can be interconnected with its input.

  • You are missing a very important aspect. In normal operation there is huge amount of interaction between the output transformer of the tube amp and the guitar speaker which acts as a reactive load. This means that the speaker itself has a big impact on the sound of the amp. This is why companies like Suhr or Two Notes produce rather complicated reactive load boxes. They behave similar to a real speaker and help produce the same sound without a speaker attached. A simple load resistor like in your setup may work but in many cases it will sound totally different to the sound with a real cab attached. This is why profiling with the cab conncted will be the preferred method in most cases. If you want a balanced DI signal, simply get a standard DI box. I used the Behringer GI-100 regularly and it worked for me. Make sure the DI signal has a signal attenuation.

  • You are missing a very important aspect. In normal operation there is huge amount of interaction between the output transformer of the tube amp and the guitar speaker which acts as a reactive load. This means that the speaker itself has a big impact on the sound of the amp. This is why companies like Suhr or Two Notes produce rather complicated reactive load boxes. They behave similar to a real speaker and help produce the same sound without a speaker attached. A simple load resistor like in your setup may work but in many cases it will sound totally different to the sound with a real cab attached. This is why profiling with the cab conncted will be the preferred method in most cases. If you want a balanced DI signal, simply get a standard DI box. I used the Behringer GI-100 regularly and it worked for me. Make sure the DI signal has a signal attenuation.

    Please note that I stated that the amp speaker was connected to the amp during profiling. Also the resistor values in the cable are clearly not for a transformer load, but for signal attenuation only. The cable is sampling the signal at the speaker terminals, and attenuating the signal to the proper level for the Kemper.

  • I have successfully created a Direct Amp Profile with a 100W tube amp and a Palmer PAN 01. It also refers to amplifier speaker outs in the manual, so it seems to be designed for it. Can we put a sticky post with a list of (somewhat) confirmed DI boxes somewhere?


  • How did it sound? My attempt made a terrible sounding DI profile, but i haven't had time to try anymore. I'm using an inexpensive DI box, someday i may have to order the one from Kemper if i do more

  • Quote from tylerhb

    You are missing a very important aspect. In normal operation there is huge amount of interaction between the output transformer of the tube amp and the guitar speaker which acts as a reactive load. This means that the speaker itself has a big impact on the sound of the amp. This is why companies like Suhr or Two Notes produce rather complicated reactive load boxes. They behave similar to a real speaker and help produce the same sound without a speaker attached. A simple load resistor like in your setup may work but in many cases it will sound totally different to the sound with a real cab attached. This is why profiling with the cab conncted will be the preferred method in most cases. If you want a balanced DI signal, simply get a standard DI box. I used the Behringer GI-100 regularly and it worked for me. Make sure the DI signal has a signal attenuation.

    ___________________________________


    FWIW, a DI box is not much more than an attenuator in parallel with the speaker load. Isolation may be available via a coupling transformer on any decent model, or a coupling capacitor, but it's not necessarily required on an amp that has an OT. Attenuating the amp output signal to an input signal level (into the Kemper) is usually a simple voltage divider. Some models may have switches to select the attenuation, but all this does is change resistor values in the voltage divider.


    This was the point MKB was making here.

    Also others have posted that they have used the recording output of some amps (non speaker emulated) to feed signal to the Kemper for direct profiling with some success. Such a circuit is often merely a level attenuator with a DC blocking cap, and the cap isn't really needed with most tube amps since the speaker output is transformer coupled anyway.

    If the attenuator resistors are chosen wisely (in the 100s of Ohms range or more), then this voltage divider will have a greater impedance than the speaker. The results are very little effect, if any on the speaker dynamics and load impedance.


    ie. the attenuator doesn’t matter if it is connected to a real cab, and here's the reason. Per the math of Ohms law, the lowest impedance here, (the dominant value that determines the total impedance), with the DI box and speaker in parallel in this case IS the speaker not the attenuator.


    This is also the approach that Kemper used in designing their DI box. Nothing active and nothing reactive, just a straight forward design that does not interfere with the tonal characteristics of the amp to be profiled.


    All that is needed to build an attenuator for this case is a little planning and the use of Ohms law. Have fun!