DI-boxes suitable to create Direct Amplifier Profiles

  • Guys and Gals,


    FWIW, using a DI box is not much more than an attenuator in parallel with the speaker load. Isolation is also available via a coupling transformer on any decent model. However it is not necessarily required on an amp than 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 the resistor values in the voltage divider! Additionally if the voltage divider resistors are chosen wisely(in the 100s of Ohms range or more) then this voltage divider in parallel the speaker impedance (2, 4, 8, 16, etc.) has very little effect on the speaker load impedance. ie. it doesn’t matter, since the lowest value of resistor in a parallel circuit is the dominant Value that determines the total impedance. If you don’t believe me then do a product over sum of a 100 ohm resistor in parallel with an 8 ohm speaker (100 x 8) / (100 + 8) = 7.1 ohms!
    Additionally If the resistors in the voltage divider use Carbon Composition (CC) resistors then there is no appreciable coloring of the amp tone, since CC resistors have zero inductance properties. All that is needed is a little planning and the use of Ohms law. Have fun!

    That's what I found recently and posted about in a previous thread. As an attenuator, I actually used a 10k resistor in series with a 1k, but the amp I profiled (a cranked Dumble #103 clone set to 4 ohms, with a G12H-100 4 ohm speaker) still clipped the Kemper input, so I tacked a 220 ohm in parallel with the 1k, and that got the signal down enough to do the job. The direct profiles I got with the simple attenuator cable were the best I've gotten with a Kemper. I should have calculated the resistor values in the first place, but I got lazy that day. :)


    I strongly believe that the coloration you'd get using a cheap direct box (especially a passive one, good balanced transformers are NOT cheap) will far outweigh any benefits of using a direct box with a Kemper. You want that connection as simple as possible as any coloration or frequency response issues with a poor direct box would be transferred to the direct profile. But the direct box is the safest route if you do not know about the output stage of your source; a simple attenuator cable connected to a solid state amp with a modern Class D output stage could cause some circuit damage. You have to know what you are doing if you plan to use other than an amp's direct out or a direct box.

  • That's what I found recently and posted about in a previous thread. As an attenuator, I actually used a 10k resistor in series with a 1k, but the amp I profiled (a cranked Dumble #103 clone set to 4 ohms, with a G12H-100 4 ohm speaker) still clipped the Kemper input, so I tacked a 220 ohm in parallel with the 1k, and that got the signal down enough to do the job. The direct profiles I got with the simple attenuator cable were the best I've gotten with a Kemper. I should have calculated the resistor values in the first place, but I got lazy that day. :)
    I strongly believe that the coloration you'd get using a cheap direct box (especially a passive one, good balanced transformers are NOT cheap) will far outweigh any benefits of using a direct box with a Kemper. You want that connection as simple as possible as any coloration or frequency response issues with a poor direct box would be transferred to the direct profile. But the direct box is the safest route if you do not know about the output stage of your source; a simple attenuator cable connected to a solid state amp with a modern Class D output stage could cause some circuit damage. You have to know what you are doing if you plan to use other than an amp's direct out or a direct box.

    MKB, I agree. As a minimum the user would need to understand OHMs law, and the application and implication of it on each external component (including speakers) connected to the amp. As my side job for over 30+ yrs. away from being an EE, I repair amps, have kept logs of the repairs. I can't begin to tell you how many were repaired due to a fried OT, blown transistor outputs including Class Ds due to misuse or not understanding the implications of their connections. FWIW, I built a clone #124 back in 2007. :)

  • I am trying to make a profile of my marshall jcm 800 superbass with a behringer di100 and a mesa cab 2x12(only direct amp profile)
    How can i put the beringer di100 to make a better profile?(-20db,-40db atenuattion....9v battery or not...)
    I try to make one profile,but the volumen in the cab of the profiling noises where to loud,it seems that the 2x12 where in risk!thanks

  • See If you can use -20 DB, Put a fresh 9V battery in the Behringer…
    The 9V battery shuts off automatically only if you are using phantom power…
    Do you normally use this Mesa 2X12 cabinet with your JCM 800?

  • Hi Keith - none. I have borrowed a Behringer DI600P and the profiles I did where ok but I just thought I would try the one designed for the profiler. It’s a bit over priced but let’s wait and see.

  • Hi Keith - none. I have borrowed a Behringer DI600P and the profiles I did where ok but I just thought I would try the one designed for the profiler. It’s a bit over priced but let’s wait and see.

    Yes, it will be interesting to see how you like it compared to the Behringer, I’m sure it will be better…
    I have the countrymen type 85 and it was best out of all the DI boxes that I tried, but I never did get to try the kemper DI box…
    Does the kemper DI take a 9V battery?

  • Yes, it will be interesting to see how you like it compared to the Behringer, I’m sure it will be better…I have the countrymen type 85 and it was best out of all the DI boxes that I tried, but I never did get to try the kemper DI box…
    Does the kemper DI take a 9V battery?

    I didn’t look and now set off to sunnier climbs. I will check when I get home. I don’t think it takes a battery though.


    While I’m away try this review


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  • Hi all,


    I was wondering if i can do a direct amp profile (Preamp+Power amp) without using my 4x12 cabinet with a Loadbox ? If yes, can someone please suggest how to use it ? The reason I'm trying this way to see if the cabinet has anything to do with the drop of the mids after making the final profile which happens to every amp i profiled using Kemper DI box + 4x12 cabinet.

  • Hi all,


    I was wondering if i can do a direct amp profile (Preamp+Power amp) without using my 4x12 cabinet with a Loadbox ? If yes, can someone please suggest how to use it ? The reason I'm trying this way to see if the cabinet has anything to do with the drop of the mids after making the final profile which happens to every amp i profiled using Kemper DI box + 4x12 cabinet.



    You can do it with a load box. My experience so far has been that the cabinet sounded better. I did a set of profiles with the same settings and two ART DI boxes (one passive the other active) and the atwo Notes Torpedo reload. The Torpedo didn’t sound good to my ears. I put all three up on Rig Exchange to compare (can’t remember if they’re still there though) under author wheres the dug.


    The Two Notes is a reactive load box so it should be close to the real speaker. A simple resistive load boad should colour the sound more as a real speaker doesn’t have a fixed impedence but rather a curve that changes with frequency.

  • Yeah, the "through" will handle the amp to cabinet load. I've verified that.

    I guess I'll just try and see if it works without a pad switch at all. At worst, I'll have an unusable profile.

    I'll let you all know if it works when I get around to doing it.