Radial Engineering JDI vs Radial Engineering Pro DI

Discussion in 'Amps and Cabs [BG]' started by SleazyB, Sep 25, 2016.


  1. SleazyB

    SleazyB

    Sep 25, 2016
    Frankfurt a.M.
    Guten Tag,
    Ich habe mir vor kurzem einen Tube-Amp zugelegt und habe jetzt das Problem mit dem DI-Out. Zwar werde ich live zwar meistens mit einem Mic vor der Box versorgt, ich will mir aber trotzdem sicherheitshalber noch eine DI-Box zwischen den Amp und die Box schließen, falls sich der Tonmann mal querstellt. Nach einigem lesen bin ich auf die eben genannte Möglichkeit gestoßen und auf verschiedene Modelle von Radial Engineering, kann mir jemand sagen was der Unterschied zwischen den ganzen Modellen ist und welche von denen "am Besten" ist ?
     
  2. Ubersetzung bitte ......
    Willkommen zu T.B. :)
     
  3. SleazyB

    SleazyB

    Sep 25, 2016
    Frankfurt a.M.
    I recently got myself a tube-amp, with no DI-Out. I asked myself how I could solve this problem. After doing some research, I found that one option is putting a passive DI-Box between the Amp-Head and the Cab. But since there are a ton of different Radial Engineering DI-Boxes on the market, I need some help in choosing.
     
  4. 10cc

    10cc Inactive

    Oct 28, 2013
    JDI
     
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  5. Be very careful with what you place between the head and cab. The JDI connects to the second input jack on your cabinet - if there is one - and there MUST be a speaker connected to the amp. The JDI isn't a load box and there will be catastrophic results if you don't follow the directions.
    An alternative is the Countryman 85 that works under the same principal.
     
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  6. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    Personally I find the Radial JDI or Cuntryman 85 to be excellent and recommend them highly. I do not think the Pro DI, while excellent as well, will work on the speaker output side.

    Both the Radial JDI and Countryman work well between any instrument and an amp as well as via a parallel "speaker out" from the back of a speaker cabinet or an amplifier. However, you must have a speaker cabinet connected when you use them on the speaker output side. It's also very important that you do not run the signal to the speaker though either box as has also been said.

    Viel Glück!
     
    Last edited: Sep 25, 2016
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  7. Jamesmidders

    Jamesmidders

    Sep 16, 2013
    UK
    I have the ProDI (ProD2, same but extra channel). Can't use it for in between the amp and cab though, get the JDI for that.
     
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  8. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The ProDI is a stripped down, more economical version of the JDI.

    You want the JDI, it has a Jensen tranformer, the ProDI does not. The ProDI can not be connected to parallel the the speaker cabinet like the JDI can. This is something that you said that you want to do with your tube amp.

    The features of the JDI are better.
     
    Last edited: Sep 26, 2016
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Do not connect any of these to the output of a bridged amp or you can short 1/2 of the output bridge to the signal ground of the XLR device that is connected to it (if it is ground referenced). Most class D amps these days are internally bridged, and can deliver enough current into a shorted load to damage the connected device (and possible itself).
     
  10. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    Really good to know - thanks Andy! I've never used a DI with a speaker output signal, although I own two that are set up to do that. I was never completely comfortable going the speaker out route and with all the other choices for getting a good signal to a mixing desk, I never felt the need to try it. I'm now feeling a lot better about my anxiety actually being good intuition. :)
     
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    It's not generally a problem with tube amps, or most ground referenced amps (though there can be issues with unintentional ground loops between grounds that never were intended to connect together) but it is a very real problem where the amplifier uses a BTL type output stage. With BTL, the negative terminal (which would correspond to the sleeve on the 1/4" connector) is not at ground but is driven opposite of the positive terminal. When this is connected to the DI, the sleeve, which is also connected to pin 1 of the XLR connector feeding the console or recording interface forms a short circuit back to the console where pin 1 ties to the ground bus (usually through traces nowhere near heavy enough to handle the short circuit currents) and directly to safety ground. The amp is also connected to safety ground, as is the high current ground path to the amp's power supply. The current travels from the amp - to the sleeve of the DI which is connected to pin 1, which travels down the snake (or mic cable on a smaller stage with no FOH mix) and into the console through small traces to the ground bus and then to the same safety ground reference that the power supply is referenced to inside the amp.

    Now, in theory, lifting the pin 1 ground connection on the DI should be ok BUT many DI's that operate using phantom power do not fully (or really) open pin 1. The other problem is that many of the networks inside the DI are not rated for the output voltage these amps can deliver.
     
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  12. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    I was always pretty confident that with the older full tube amps the problem was less likely, but as a bass player in "the modern age", hybrid and solid state (including Class D) is all I own. I always exercise extreme caution with any bridged amp and try to never put something in a bridge operational mode unless it's a necessity. However, I never thought about the class D approach utilizing a type of internal bridging and presenting a problem that some other solid state classes of amps might not.

    I learn at least one new thing everyday, and on the days you're posting the count goes up in a one for one linear relationship. I'm always surprised at how little even some of us with technical backgrounds and education often really don't fully understand about many of the technologies we use every day. Having people like you share insights/information when you recognize that folks like me don't even know what we don't know, and really need to, is very much appreciated!
     
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    There are several reasons why class D amps have internally bridged architecture, one of the most important is that because of the non-linear nature of the output stage there can be a direct connection from opposite power supply rails through the load and under these conditions back EMF from the speaker and inductive reconstruction filters can cause the supply rails to rise above safe levels. Bridged switches allow this back EMF to charge the opposite rail at the instant it's being drawn down rather than charge a rail that is unloaded for a half-cycle. The reason why this is so important for bass guitar is the time period at 40Hz is 25mSec and 1/2 of that is 13mSec... the time the opposing rail remains vulnerable. That's a long time (relatively)

    This mechanism does not apply to linear amps (class AB/B/G/H) because the transistors do not act as hard switches and always (should) have degeneration resistors which together dissipate this same energy (minus the reconstruction filters) as heat. This is another way that class D amps can improve efficiency.
     
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  14. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    That's very interesting, as I always naively thought about class G and H as an efficiency improvement over A/B, and simply assumed that class D took those efficiency improving techniques to a much more advanced level. I've even heard some argue that class G and H are really just a variation/different implementation of class AB and not a legitimate new class. Class D at its foundation level always seemed to me to be simply taking the rail switching concept of class G and H to the extreme by actually shutting things off and turning them on as soon and rapidly as needed...sorry for oversimplifying something that I probably didn't get exactly right in the first place.

    When I've heard amp designers talk about some of the more significant challenges of making class D work it frequently seemed to be centered on stability of operation, especially at the extremes in the performance envelope. I suppose there are some fundamental/core challenges common to all amplifier design beyond just thermal management and safety. However, when you start shooting for efficiency as high as you can get with class D, my guess is that you end up with an order of magnitude more complexity in some areas, as well as a few new concerns that could have been dealt with on the margins in less efficient designs that didn't require the precise control.
     
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Correct Al, the complexity and attention to detail that's required in order to achieve the last few percent efficiency improvement is significant, but that's simply what it takes to do it right. Class D amps, as well as SMPS are specialties in the electrical engineering field. In fact, more and more areas are becoming so complex that we are being forced to become more specialized in order to advance the art. Not just the electrical design, but the mechanical design and layout. I have had to specialize a LOT more in layout and mechanical design. I went for 15 years without having to lay out my own PCBs, but things have become so tightly packaged and with focus on both safety and EMC control as well as manufacturing efficiencies, I just found it easier to step back into laying out my own designs. The newer engineering tools have really helped in this regard IMO.

    Class D is entirely different than AB/B/G/H in that the signal is voltage amplified via level shifted pluses, there's no linear representation of the signal in class D.

    Class AB and B are essentially the same (from a math perspective), G and H switch in and out a second (or more) rail(s) in a way that one of the two series transistors (per polarity) are in either saturation or cutoff but not both One is always operating in a linear fashion. In the US vernacular, class G has the lower tier essentially in saturation (it's actually a few volts below once the second tier begins to conduct) and in class H the higher tier is either in cutoff or saturation. I prefer class G myself because the turn-on and off characteristic of the upper tier transistor is softer and more like a level shifted version of the lower tier. It's a very clever and robust way to reduce waste heat.

    Note that any of these classes can utilize bridged architecture, but for different reasons.
     
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  16. BadExample

    BadExample

    Jan 21, 2016
    Injiana
    How the bridged outputs of a 2 channel class D amp can be bridged together to double the power (add the two channels power) to a single channel gives me a headache.
     
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Generally those amps are not internally bridged, though there are some esoteric floating techniques that can allow for bridging a bridged amp. This is the stuff that makes heads hurt!
     
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  18. BadExample

    BadExample

    Jan 21, 2016
    Injiana
    Mine has a separate bridged out speakon, in lovely Sheit brown. Thank God for if I ever bridge it for insane wattage.
     
  19. BAG

    BAG

    May 5, 2014
    New Zealand
    I'm not trying to be a smart arse but why wouldn't you go from your bass to the DI then through to the amp input and run the DI straight to the desk. Most amp DIs are pre EQ and Master so that any amp changes you make don't affect the FOH.
     
  20. Hallo Sleazy,
    das hier ist ein englischsprachiges Forum und die Mehrheit der Benutzer versteht absolut kein Deutsch.

    If you're looking for a DI box that can be connected between amp and cab, you should definitely check out the Rupert Neve DI.
    It can be used in the "normal" way (between bass and amp) or between amp and cab, which adds your amp's tone to the signal, and, based on your original post, this seems to be what you want.
    It's around 300 €, check thomann.de.


    Edit: you should check out www.bassic.ch. It's the biggest German speaking bass forum on the net.
     
    Last edited: Sep 26, 2016
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    Primary TB Assistant

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