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Do you record active pickups with active DI boxes?

Discussion in 'F.O.H.' started by blue_fAng, Feb 8, 2013.

  1. blue_fAng

    blue_fAng Member

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    I've read a lot that you should use active DI boxes for guitars with passive pickups and use passive DI for guitars with active pickups. Is there somehing wrong with using active di + active pups? I ask this because I currently own a Countryman T 85 and I really want to get a Schecter Hellraiser C1 with EMG's and want to know if getting also a passive di like these radials in the 200 bucks range is worth it, or stick with my current di box or just plug the guitar into my focusrite saffire pro 40. I know that some guys in other forums have recorded their EMG's into countrymans and it sounds ok, but I'd like to hear your opinions about this you guys since you have good ear.
     
  2. Trevoire520

    Trevoire520 Member

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    There's nothing wrong with using active and active. It's just one of those daft things that's become "accepted knowledge" for no reason.

    Basically you need a DI with an input impedance of at least 10 times the output impedance of the source you're recording.
    So for an EMG 81 (10K output impedance) a Radial JDI (140K input impedance) will be fine.
    But a passive equipped guitar that could have an output impedance of something like 16-30K you'll need something higher in order to capture the full frequency response of the pickups. And typically DI's with very high input impedance are active models (normally around 1M)

    As far as I'm aware (someone correct me if I'm wrong!) there's no such thing as too high an input impedance for a DI, so a active pickup will work perfectly fine with a active DI box.
     
  3. TheWinterSnow

    TheWinterSnow Den Mørke Natt

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    Simply like Treviore said, active pickups are more capable of handling a passive DI then passive pickups are. While it is better for passive pickups to be loaded with an active DI, active pickups also get additional benefit.

    Somewhat true. In most cases, yes really high can be a good thing. However in some cases where a lots of gain is essential, higher impedance, mostly passive resistance will create more noise. This is why the input impedance of most mic preamps are usually in the 1K to 4.7K area considering the average mic pre has a gain of 60+dB. Guitar amps are noisy by default and the resistors in the amp in most cases be much louder than any active impedance noise (and small amounts of transformer noise) that would be amplified by an amp so realistically as long as you don't have more than 1M of passive resistance on the guitar before the amp, all should be good.
     
  4. blue_fAng

    blue_fAng Member

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    Great, thanks guys!
    My countryman has 10M input impedance, isn't it extremly high for the actives?
     
  5. blue_fAng

    blue_fAng Member

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    I'm sorry, I am cofused. 140k is a little more that ten times the output of the EMG 81 and that's fine, but I researched the radial jdi input impedance and it says it is 10k ??? Am I missing something?
     
  6. deLuther

    deLuther Member

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  7. Trevoire520

    Trevoire520 Member

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    ???
     
  8. blue_fAng

    blue_fAng Member

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    I read this
    http://www.radialeng.com/di-jdi-features.htm
    " The JDI input features a high 10kOhm input impedance for minimal loading. "
    Im not sure what this means Im new to all this.

    I actually didnt do proper research (fail), my phone wont let me enter some sites or open pdf sorry about that haha so yeah its clear that the jdi input has 140k. Now my countryman has 10M , reading TheWinterSnow's post I wonder if this input is too high for the emgs. What do you think?
     
  9. blue_fAng

    blue_fAng Member

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  10. JakeAC5253

    JakeAC5253 Frozen Sun Audio

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    The Type 85 is literally the best sounding DI box made. It's got JFETs and JFETs are awesome. An EMG 81 actually has an output z of around 25k, and a passive pickup will have an output z of 500k. These are measured by the typical volume pot values seeing as how this is what the driven device needs to work in parallel with.

    When you input into a device with an excessively high input impedance, a few things happen: a. the bass response is increased b. the amount of current drawn from the source is lessened c. the noise level is raised. None of these are really a problem for an EMG pickup though.
     
  11. JakeAC5253

    JakeAC5253 Frozen Sun Audio

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    The noise is only one of the factors to consider when determining why mic preamp input impedances are lower than guitar amps or DI boxes. A microphone of the dynamic or ribbon transducer type typically has an output impedance that is measurable in the range of ohms while a guitar has an output impedance typically measured in hundreds of kilohms. They're incomparable really. Yes increasing the input z of a mic pre would have a linear effect on the amount of noise but don't disregard that this would also have an effect on the tone of the mic pre in the same linear way. Mic pres are designed to perform one job while a guitar amp is designed to do a different job and the same can be said for a DI box.

    10M is not too high because all that matters really is getting the signal to the DAW in the most transparent way. A 10M input z may well be too high for certain circuits that can't handle the voltage swing on input, but the Type 85 has JFETs and JFETs are awesome, it can handle it. Your reamp box drives the actual amp and that will convert the impedance seen by the amp to a more normal range that the amp needs to see, that's the largest link in the chain that has any effect on the amount of noise in this case.
     
  12. deLuther

    deLuther Member

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    I`m thinking that Radial has mistakes on older version of it`s site, you should refer to recent info.

    Another example of mistakes in Radial`s info:
    http://www.radialeng.com/r2011/prormp-specs.php
    ProRMP does not have Merge or Speaker filter at all as well as pad :)
    Impedances also wrong, DC resistance of transformer used is larger than mentioned impedances :)
    Measured impedances of transformer is 10k (for input).
    http://www.schematicsforfree.com/ar...ytone/YT-12243's approval sheet(20021003).pdf
     
  13. Trevoire520

    Trevoire520 Member

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    Wait so, if the output of a guitar is 500k due to the vol/tone pots then should we technically be having to use DI boxes with 5M ohm inputs or greater for passive equipped guitars? In order to get the 1/10 ratio from output to input happening?

    Confused.com
     
  14. JakeAC5253

    JakeAC5253 Frozen Sun Audio

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    Yes, that gives even more of a reason to need a DI box. That 500k pot does a pretty good job of providing a load for the pickup in and of itself, but when you plug the guitar into something it will drag the pot down and reduce its effective value by a concept known as impedance. If you were to plug your guitar into something like a mic pre which has an input impedance of 1k for instance, then the 500k pot disappears and the total network impedance will be 1k. Network impedance always favors the weakest link.

    When the 500k pot is adjusted, there is quite a bit of series resistance added to the signal, in the hundreds of kilohms. What this means is that the load that it is producing into needs to be many times larger than the series resistance so as not to ground out a majority of the signal or dull the tone considerably. At half pot value on a 500k pot (this is about 67-86% of the way up on an audio taper pot) the series resistance is 250k, which means that to minimize losses at this setting, the load it produces into needs to be at least 10x its value, or 2500k, or 2.5M. Realize also that at this same setting, the parallel shunt value of the pot to ground is now also 250k, it's not 500k anymore, which necessitates the same 2.5M load. The load itself is calculated by the shunt value of the pot as well as all other loads as well, which in this case means the 250k value dialed on the pot as well as the 2.5M load resistor. Now since the paragraph above, we know that the 250k shunt value on the pot will win, so that's the network impedance that the pickup and 250k series resistance is producing into. You could take a different setting of 400k series and 100k parallel, and this is just further padding down the sound. If something down the chain is pulling the shunt impedance down further then you get more padding effect because of the ratio of series/parallel resistance, which is acting as a signal divider in this case. You will never get a perfectly unloaded guitar pickup when the volume pot is at any setting other than full up because as you turn down the volume knob the network impedance is changing and this has a "tuning" effect on the sound of the pickup changing what frequency it resonates at. The best that we can try to do is keep the guitar as unloaded as possible when the volume is in its full up position.

    I'm confusing you more than you need to be... Sorry.
     

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