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NF Audio reamp box?

Discussion in 'Recording Gear and Equipment [BG]' started by Peter_00, Apr 25, 2010.

  1. Do you own a passive direct box?

    If so, all you need is one of these and you will have the exact same thing:

  2. Good call but doesn't correct the impedance, though. However, if you solder a resistor onto the hot pin of the jack that comes from the DI then you are most of the way there. Only difference is that different pickups have very different impedances so trying out a few resistors from 3k up may help you get different results.

    The impedance selector on re amp boxes does this but allows you to vary it and get the best sound in 'real time'. It doesn't REALLY simulate how a pickup behaves but it does help you get a lot of useable sounds! I'm sure you could easily wire up a potentiometer to a jack lead allowing you to get the same thing with the tried and tested DI method!
  3. Of course it does. The transformer in DI box doesn't care which way the signal is flowing.

    Line Out -> adapter -> DI box(in to the XLR, out the 1/4") -> amp
  4. Cool thanks for replies, will have a look into the modding my own and see what works best.
  5. ??? I never suggested it doesn't work, I know it does i use the method regularly!

    What I suggested was it does not switch the impedance of the signal, the high impedance of guitar pickups and how they react with the amps circuitary is an important part of how an amp sounds.

    The transformer in the passive DI isolates the two circuits when reamping which helps stop hmm's and buzz's, but isn't the ideal simulator of a pickup!

    Thats why I mention the technique with a resistor, if you read my post you'll see I mention to use it together WITH a passive DI and an attenuator! The resistor is not a perfect solution, nor is the pot on re-amp boxes, but it does help get a lot of useable sounds.

    As a side note, its not really the impedance of pickups that matters, or at least adding any kind of resistor will not make it behave the same as a pickup. The measurement that really matters is inductance, and that changes depending on a lot of factors including which string you are playing, where on the fretboard you are playing (it frequency dependant!) and how strong the magnets are etc. Using a resistor is kind of like using an impulse response for a reverb that changes over time, it will work and sound realistic but not be quite as complex as the real thing.

    Thats all academic though, If it sounds good, do it! Try the passive DI, attenuator, resistor method first and see if it gets the results you want!
  6. Of course it changes the impedance. What do you think the transformer in a direct box is for? Maybe they don't teach this stuff at Full Sail.

    A passive DI box is a transformer.

    Running through a transformer changes the impedance. In a DI box it is typically stepping it down from the few10K ohms of a guitar pickup to the several hundred ohms a micamp wants to see.

    Running through the transformer backwards steps the impedance up by the exact same ratio, from the couple hundred or so ohms of a console line out to the several 10's of thousands of ohms a guitar amp is expecting to see.

    This is literally how a Reamp box works. Not 'literally' in the figurative sense but literally, it's a step up transformer and a variable pad. Or a DI box wired in reverse.
  7. Whats gotten to you? Thats a bit unneeded and offensive, I have never been to full sail, nor am I completely sure what it is but I'm pretty sure I get the implication. I work at a big UK studio, where I learned under my boss who has recorded and worked with some of the biggest acts and albums of the last 16 years. I have learned this stuff from a practical, working point of view, while boosting my knowledge on electronics etc in my spare time. Anything I post here is from experience, not from learning something at some uni course that I have never tried out. My posts were polite and trying to be as informative as possible, if you think I am wrong then cool, I'm all up for being proved wrong if I learn something but there are better ways to discuss this than cheap insults.

    ANYWAY, back on topic, your posts have got me interested in researching this a bit more, and I think that we have both got it a bit wrong... On my part, I think the resistor is unnecessary for the DI setup. I think the trouble with using a DI in reverse is that the impedance is much HIGHER than a guitar normally is.

    So a typical guitar pickup of say 15k might be stepped down all the way to 40 ohms with a DI box, fine for going into a mic pre. On the way back the 600ohm or so output on an audio device gets stepped up, impedance wise to 225kOHm! Once the signal is recorded, it doesn't rememeber the impedance it was stepped down too, when it comes back out of the console or soundcard it is the output's impedance that matters, which, as you say is normally a few hundred ohms, 600 used to be standard but I'm not sure if thats changed these days. These numbers are from a jensen transformer used in lots of good DI boxes.

    Circuits for impedance matching seem to use 'overkill' quite a lot, so that they can be sure that ANY input impedance will be succesfully reduced to an output impedance suitable for most line or mic inputs.

    And to be honest I'm still pretty sure this is oversimplifying, especially when you look at inductance and the way guitar pickups REALLY behave, but thats something even the best re-amp boxes don't really seem to have nailed, so I guess its not really something worth worrying about.

    When you look at the schematics of re-amp boxes they use transformers with a 1:1 turns ratio, and then adjust the impedance with a switch or pot, which is a bit more flexible than using a 12:1 transformer or similar. As I say, in reamp boxes the transformer is just doing the job of an isolator and 'un-balancing' circuit.

    On a practical level, I have reamped a lot, I just finished a months studio session where all the guitars and all the bass were re amped (very strange session..). For the most part they were ok, but not quite as good as using a real guitar, though to be honest a lot of that was probably how the guy recorded the tracks to re-amp in the first place!). We tried a few different methods, the just DI (no resistor) method sometimes was fine, and sometimes was a bit too skewed towards the low end. Sometimes a lead with a 10k resistor was fine (no DI), but most of the time some kind of isolation was needed, as it was a very 'high gain' kinda band and any little noises were gonna become massive after slamming into the dual rectifier!

    Anyway, I'm glad this came up becuase I now know I don't need my resistor cable when using a DI to reamp, but I still think a re-amp box is a little more flexible overall, they are very similar devices but not quite the same. You can build one for £30 or so, less if you use cheaper bits, its not hard and should be quite fun, I sense a project coming on :)

    Heres a schematic from the jensen website...

    EDIT - I'm very much in the beggining stages of learning electronics so I'm kinda expecting to be put right on some things :)

    Attached Files:

  8. Most equipment is designed to drive a minimum input impedance of 600 or so ohms. That's pretty standard.

    Typical output impedance from a console bus/insert/group/matrix/whatever out is something like a 10th to a 5th of that. The only hard numbers I have off the top of my head are for the equipment I use often: the older Soundcraft Spirit Live and LX7 boards and the Yamaha LS9's are 75 ohms. The Crest VCA boards are 100. Run that through a 133:1 transformer and you get 10 or 15K, which will happily drive a guitar amp's Hi-Z input all day long. Any for real equipment will have documentation with that number in it, look it up. If for some reason you have a mixer with a freakishly high output impedance you might need a different solution. But you will have the same problem with a regular passive reamp box.

    I'm not trying to be a dick here but the audio industry is rife with places you can spend money on solutions to problems which don't exist. There is nothing mysterious about an impedance matching transformer. If you own a passive direct box you already have one.
  9. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Well I gave that a whirl, then bought a Radial x-amp. Sound quality wise there is no comparison. The x-amp is worth the dough if you are serious about re-amping.
  10. Cool, yeah that makes sense, I'll keep on reading :)

    I agree that there are a huge number of products out there which are a massive waste of money. I think its always worth trying to build it yourself when it comes to lesser used but simple items like re amp boxes etc. That would certainly be my suggestion to the OP if he decides he does want to go with the dedicated re-amp box after all!

    I don't think you are being a dick, but the sail comment was a bit off.
  11. Thanks for the informative discussion guys, I think I need to brush up on my electronics knowledge a bit too. Nice to have such knowledgeable folks round here.
  12. Madcity Fats

    Madcity Fats Supporting Member

    May 28, 2008
    Madison, Wisconsin
    I seriously wouldn't categorize this as a problem that doesn't exist.

    As others have said, you CAN reamp with a reverse DI if you're willing to tackle what can be an impedance matching headache. Don't believe me that this can be a huge PITA? Just Google the terms "reamp" and "reverse di" and you'll find reams of evidence of folks banging their heads trying to cobble together a solution to this non-problem.

    +1. Can't speak for the Radial box, but the Reamp is a great tool. And yes, I've tried the reverse DI trick. I suppose you could say I got it to work, but never to my satisfaction.

    If you just want to experiment, go nuts. If you plan to incorporate a lot of reamping into your production, buy the right tool for the job.

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