Could you use a DI box as a headphone amp?

Discussion in 'Effects [BG]' started by bassman1185, May 16, 2002.

  1. I've already pretty much made up my mind that i'm going to get an MXR M-80, but i'm just kinda of curious whether or not I could use it to drive a pair of headphones. Anyone?
  2. No, that's very dangerous to the headphones, but you could run the direct signal into a headphone distribution amp and use it as a practice amp.
  3. john turner

    john turner You don't want to do that. Trust me. Staff Member Administrator

    Mar 14, 2000
    atlanta ga
    well, for starters, the output will be mono, which means you'll only hear it in one ear.

    i don't know about damaging to headphones, but it certainly wouldn't sound very good.
  4. Ok, thanks guys. I wasn't gonna get it as a headphone amp, but it would be cool if it would work. I am curious, though, why would using the preamp hurt the headphones?
  5. Because the outputs on the SABDDI are of a voltage high enough to drive amplifier inputs. This voltage is normally higher than a pair of headphones can take, so your sound could either be very distorted or you'll fry the wiring/speakers in the headphones.
  6. the SABDDI manual says mentions it, but doesn't say that it will ruin the headphones, although it says that it probably wont sound good.

    THe M-80 is based on the SansAmp, try both before you decide on one over the other
  7. malibu

    malibu Guest

    Dec 26, 2001
    isn't that just the pre-amplified "line level" signal into an amp input ?

    I'll guess - emphasize guess - it may have to do with impedance matching ? - headphones are 32 ohm and up I think.
  8. Well, the SABDDI can be used as a preamp, so it'll give enough output to drive a power amp too. That's quite a lot for headphones, considering my computer Line-Out drives headphones perfectly but wont make a peep when I plug it into the poweramp in of my amp.
  9. malibu

    malibu Guest

    Dec 26, 2001
    maybe a better way to say where I'm coming from would be . . .

    a DI is a "line level" signal - this is a step up from instrument level - it is the preamplified signal level.
    Also, so is an unbalanced line out or a preamp out or a send effects - all these need to be amplified to drive either speakers or headphones -
    using the appropriate impedance matching.
  10. BFunk

    BFunk Supporting Member

    I thought DI's were usually mic-level, about -40 Db. Line level is about +4Db. Instrument level is about -10Db. (Some DI's, like the one in the Kern per-amp is line-level, balanced 600 Ohm. Others, like the Aguilar is switchable, mic, instrument, or line.) Anyway, I think the impedence mismatch will give you very poor quality sound even if you could overcome the signal level and mono/stereo thing on the headphone.
  11. Here's the lowdown: There's no real reason why you couldn't do it. It probably wouldn't sound any good and it would be in mono, but that's beside the point. It won't do any damage to a pair of decent headphones. It can't put out enough current for that even into a relatively low impedence like 32 or 16 ohms. Let's say it can put out its power supply voltage, 9V, which would be the theoretical maximum (and it probably can't put out anything near that). The psu voltage will be converted to an AC waveform with absolute peak values of +/- 4.5V. Maximum RMS would be about 6.4V. 6.4V driving 32 ohms gives 0.2A (it's actually a bit more complicated than that, but that's good enough an approximation for this purpose). That's 1.28 W. Most headphones can dissipate that. The actual levels produced by the Di/preamp would probably be a fair bit lower than that. It can drive a power amp because most power amps only need 0.75-1.4V on their inputs to develop their full rated power. It won't sound very good because the DI's expecting to be plugged into a device with a high input impedence (2000 ohms or so). The impedence mismatch will probably do strange things to the output signal. So there it is. You probably won't damage your headphones, but it won't sound any good, so why bother. :D
  12. It's got a "line out" jack as well, that's probably nominally at +4.
    You're right, the XLR's probably between -40 to -10, depending on levels with 150-200 Ohms output impedence
  13. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Here's what you want.



    The PHA-1 is a professional unit that can be used as a headphone practice amp, versatile preamp, or to create your own mix in the studio. The PHA-1 will allow up to two players to plug in and practice together while monitoring their sound via the dual stereo headphone jacks.

    Using the patch chord provided, a stereo source (such as a portable CD player or cassette) can be blended into the overall sound. The left and right mix volumes adjust the levels of the external source, providing the ultimate environment for silent rehearsing, solo or with a fellow musician. Make sure you are in key by hooking up a tuner to the Auxiliary send. The sound of your instrument can be tailored using the 3 band EQ.

    Immediately noticable will be the sound quality, dynamic range and lack of annoying hiss. The PHA-1 will faithfully reproduce anything from a 5 string bass to the variety of sounds from a synthesizer.

    Are you done practicing and ready for the gig? The PHA-1 makes the ideal buffer between your instrument and amp. The high input impedance assures that ALL of you instruments tonal characteristics reach your audience. As well, the PHA-1 will provide additional gain and tone adjustments. The Auxiliary send and Stereo mix inputs can now act as a side chain effects loop. Being on a "side chain" insures the integrity of the natural sound of your instrument, while lowering the overall noise created by your effects unit. Use the Line Out to send the signal to your amplifier.

    The PHA-1 is powered by a pair of 9 volt batteries. Battery installation is easy using the battery compartment on the outside of the chassis. No "unassembly" is required. Battery life will be around 50 hours.

    Each unit comes with a 3 year guarantee against parts and workmanship.