Direct box question

[Super 8]

Can someone tell me the difference between a direct box, and one of those little 1/4 inch to XLR thingies that they sell at Radio Shack?

 

I've talked with people who seem to think there is no difference. I don't believe it, but I lack the technical understanding to set them straight on the issue.

 

Thanks

[greendoor]

A 1/4" to XLR thingy may or may not be a DI box. If it's a cable, then it wouldn't be. If it's a box, and it has a transformer or an active circuit in it, it probably is. Whether it's a Good DI box is another thing.

 

The term 'DI box' has different meanings for different things. At it's most basic, it is a passive transformer that converts a Hi-z input (e.g bass or guitar) to a low-z XLR to enable a long run of cable to a low-z mic input on a mixer or preamp.

 

Cheap transformers sound cheap. The great sounding transformers are not cheap. They don't hiss, and they can be used backwards (e.g. to re-amp a track).

 

There are active boxes that do the same thing, without an expensive transformer. They tend to hiss, due to the electronics, and they can't be used backwards.

 

Usually a DI doesn't add gain or eq. But some do - usually specific to an instrument.

[Scodiddly]

A "real" DI can handle more signal level. Those little Radio Shack barrel transformers do work, but they overload easily and aren't especially flat in the frequency response.

[60hurts]

Some cheap direct boxes are exactly like the Radio Shack thingies. They just put the cheap little transformer in a box!

Usually the box has an unbalanced in AND out though, and maybe a ground lift.

[fantasticsound]

In theory they are identical, but reversed.

 

The RS unit you described is low impedance in, high impedance out, with XLRf on one end and 1/4"m on the other.

 

Its' most common use is for plugging "pro" mics into high impedance inputs on instrument amplifiers or inexpensive mixers, etc. (The latter being less common these days, with the advent of cheap mixers with XLR inputs feeding mic preamps.)

 

Direct boxes are most commonly used to direct inject (hence the term, DI) low level, high impedance outputs of guitar, bass and other instruments with high impedance pickups into mic pre's, etc. Most can accept line levels as well, for use with keyboards, drum machines, etc. Many DI's can be used in reverse for re-amping, too. The reason some will not work in this way is you're driving the DI with a line level signal. The typical connections are one or two 1/4"f jacks (one input, one through to amplifier) to XLRm.

 

Some can even accept speaker level from instrument amps and transform it down to a low level signal for input to a mixer. The speaker still needs to be plugged in through the DI, however, so as to present the proper load to the amplifier. Otherwise you risk blowing up the power output section of the amplifier. Consult the manufacturer's instructions before using their DI with the output from an instrument amplifier.

 

A bump box is designed to raise a consumer line level (-10dBv) up to pro-line level (+4dBv) or vice versa.

 

Of course, DI's have developed over the years. Many guitar effects manufacturers have developed DI's with speaker simulation, EQ and other features. Many instrument amplifiers come with DI outputs built into the amp circuit. And let's not forget tube driven DI's. There's a plethora of DI's on the market today.

[MrKnobs]

 

Originally posted by fantasticsound In theory they are identical, but reversed. The RS unit you described is low impedance in, high impedance out, with XLRf on one end and 1/4"m on the other.

 

 

RS makes both kinds. You can get the 1/4" in to XLR which is essentially a little direct box without the ground lift.

 

They don't sound terrible, but they don't sound great either. I have about 12 of them in my studio, sometimes they get put to work on V-Drum outputs.

 

Terry D.

[fantasticsound]

Oops! You got me, Mr. Knobs. Forgot to mention the inline DI's as you described.

 

BTW - As long as we're getting into a bit of the esoteric, I've seen cables with the equivalent of the RS low imp. to high imp. built right into an XLRf to 1/4"m cable. Shure used to make one, IIRC. I don't know if anyone's manufactured a DI into a 1/4" to XLRm cable.

[TimmyP]

Nice post from fantasticsound. Pretty well tells the tale.

 

Mr. Knobs, you don't need those cheezy transformers on the VDrums. I can say from experience that the VDrum outputs are quite capable of feeding either the line inputs or the mic inputs (if they can handle the signal level) through very long lines. I think this will sound better than those transformers, which I expect are saturating most of the time.

 

The job of a DI is mostly to change the signal level of the source to match that of the load. In the case of say a bass with passive pickups or an acoustic with a piezo pickup but no preamp, the DI does also act as a buffer so that the instrument does not see such a low load impedance, but it's still a lot lower than the instrument sees when it's feeding a guitar amp. Most guitar amps are at least 250k Ohms. A passive DI will usually be no more than 50k Ohms. An active DI will usually be at least 100k Ohms.

 

http://www.padrick.net/LiveSound/Interfacing.htm

[MrKnobs]

 

Originally posted by TimmyP Mr. Knobs, you don't need those cheezy transformers on the VDrums. I can say from experience that the VDrum outputs are quite capable of feeding either the line inputs or the mic inputs (if they can handle the signal level) through very long lines. I think this will sound better than those transformers, which I expect are saturating most of the time.

 

 

Nope, tried it both ways. With an adapter (sans transformer) and with the Radio Shack thingie. Definitely sounds better with the transformer.

 

Terry D.

[Anderton]

What a lot of people don't realize is that like tubes, transformers are signal processors. They exhibit a "ringing" in the midrange (easy to see on an oscilloscope) that adds some warmth to the sound. I know quite a few people who use transformers not to do anything related to impedance, but to color the sound.