Differences between DI Boxes
Old 18th February 2012
  #1
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Differences between DI Boxes

Hello
I guess this questio nmight have been asked a couple of times already, but i still haven't found it...
I have a mixer and some hardware effects which causes hum, and i guess that a DI box might fix that issue (before asking, yes, i have spent a lot of time trying to spot the troublesome gear, and i try to use balanced cables as much as possible).
My question then is : is there a lot of difference between DI Boxes ?
I really don't have much money to spend on it, but on the other hand i don't want to mess up my audio signal flow with a crappy DI.

I am planning to use it on the output of a cheap mixer (which i am using to mix drum machines with multi-outs), and also on some analogue synths used for basses, so my main interest is in getting a DI box which will keep the bass and transient alive.
I won't use it on acoustic devices, guitars, microphones, etc.

Any advice will be appreciated, thanks
Old 18th February 2012
  #2
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I've got some cheaper 30 dollar ones and a 100 dollar radial, I bought the radial because I read it had a nice saturation running through it's jensen transformer, I do notice a difference. 70 dollars isn't a huge difference in money IMO if you're just picking up one DI, but it's not a make or break by annnny means. Hope that helps.
Old 18th February 2012
  #3
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Zes, thank you.
Is there a risk that a very cheap one may mess up the audio ?
And is there a chance that the DI will solve the hum issue ?
Old 18th February 2012
  #4
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A $100 radial DI does not have a Jensen transformer.
I also have a $35 Rapco DI and a JDI.
There is a great deal of difference between a $30 DI and a Radial JDI with the Jensen transformer.
I don't think it will solve your mixer/effect noise though.
It might help a bit.
Old 18th February 2012
  #5
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Depending on the source of your hum problem, the ground lift on a DI may help.

As for the sound, anything you run signal through will change the sound to some degree. To what degree is up to your perception. If you have the opportunity to directly compare two DI's you may have a preference.
Old 18th February 2012
  #6
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Thank you for your replies.

Quote:
Originally Posted by CompEq View Post
Depending on the source of your hum problem, the ground lift on a DI may help.
Yes, i hope so. The mixer is nothing fancy, but shouldn't be über crap either (it is an old Boss mixer from the 80s).
The issue is that it "hums" since i plug it into my amp or into another mixer desk, even if no synth or drum machine is plugged into it.
I tried on 2 different mains, and it keeps on humming.
(but i don't hear hum on phones).
Old 19th February 2012
  #7
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Quote:
but i don't hear hum on phones
I'm not a tech, but based on what you mentioned, I would guess there's a grounding problem in the mains output of your mixer. Maybe you cna borrow a mixer to see if the problem manifests on a different piece of gear and then decide if it's worth it to repair or replace.
Old 19th February 2012
  #8
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Would a cheap DI be able to smear the transients, or muffle the sound (cutting the low range or the high range to an audbile extent) ?

(Quite a noob question, i know, but i used to work with line levels only for years, so never had to deal with DI boxes )
Old 19th February 2012
  #9
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The difference in the transformer-based models is the transformer. Cheap small transformers are easier to saturate, messing up the audio. The difference in the electronic models is akin to the differences between a cheap console and an expensive one... design, parts choice, signal path, grounding....

The DI of choice for 25 or 30 years was the Countryman. (Though Urie had a nice one, and there were several specialty DIs which had their proponents but which never widely "caught on".) The Countryman was upstaged by the BSS and Radial offerings. I've used most of them, and if I was buying today it would be one of the Radial choices (there are several) or the BSS, but I'd not cry about a Countryman.
Old 19th February 2012
  #10
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If you are using an "Old Boss mixer from the 80's" I would suggest that it is most likely the problem. When you say your mixer shouldn't be "uber crap" you may only be half right.
A new inexpensive Soundcraft, Mackie, or even Behringer mixer would probably represent a considerable upgrade.
Old 19th February 2012
  #11
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You don't want a DI on the output of a mixer, you want an isolation transformer. Check this out: Isoblox.

A DI changes from high impedance to low impedance, and from instrument to mic level (to be boosted by a preamp to line level). The output of your mixer is already low impedance and line level.
Old 19th February 2012
  #12
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Quote:
Originally Posted by ears2thesky View Post
If you are using an "Old Boss mixer from the 80's" I would suggest that it is most likely the problem. When you say your mixer shouldn't be "uber crap" you may only be half right.
A new inexpensive Soundcraft, Mackie, or even Behringer mixer would probably represent a considerable upgrade.
Well, of course it is not my main mixer (which is indeed a new Soundcraft).
I needed something simple and straightforward to gather the various outputs of some drum machines with multi-outs, so that Boss KM-600 should have been what i was after.

After some more checking, it is actually a ground loop problem : Every plug in my studio was making the mixer humming, but when i tried in my garage, the output was quiet.
Then I found a Behringer HD400 (which i had forgotten about) in the bottom of a box full of stuff, tried it, and *voilà*, the humming were gone !
I also tried with a ground-lifter plug adapter : same, the humming was gone.


Quote:
You don't want a DI on the output of a mixer, you want an isolation transformer. Check this out: Isoblox.

A DI changes from high impedance to low impedance, and from instrument to mic level (to be boosted by a preamp to line level). The output of your mixer is already low impedance and line level.
I am aware about the DI being designed first to change the signal's impedance, but it seemed to me the cheapest (and most efficient ?) way to ground lift / isolate my humming signal

I will check those isolation transformers (i was only aware of DIY isolation transformers, or more expensive stuff like Furman).
In the meantime, i was browsing around for the Art DTI... Similar stuff i guess ?
Also, the Behringer HD400 should do the trick. I might buy one more

Thank you for the hints and avices !

(By the way, I think i will try to buy a cheap DI box anyway, just to use when feeding some pedal FX featuring rather sensitive inputs with synth/line level... It should be a good way to check in which way a DI can change/color/mess the signal).
Old 20th February 2012
  #13
GSF
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I've been involved in a test where we compared 7 or 8 di boxes, and the differences in sound between them were much greater than I would have expected. I would organize a few candidates for comparison and then make a decision from there...
Old 20th February 2012
  #14
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Yes, with pleasure, i'd be curious to hear that. THank you.
Old 20th February 2012
  #15
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Kragg: I think he meant you should make a short list yourself and compare different ones.

Seems silly to start from scratch when tests have been carried out already though.

GSF: Which DI's did you test and what were the results? I've been thinking about this too...
Old 20th February 2012
  #16
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Expensive vs Low cost direct boxes

There are a couple of big differences between direct boxes which can affect your tone.

Here are important factors:

Active Instrument or passive instrument

Active D.I. Box or Passive D.I. box

-------------------------------------

A passive D.I. box is typically just a transformer in a box.
Jensen is a 12:1 ratio.
Rapco-Horizon D.I. boxes are typically around 4:1 ratio.

The core material of the transformer laminations affects the tone. High nickel is very flat response (typical of Jensen). I don't know where Horizon gets their transformers now but their older units had excellent lamination material. I believe all the Horizon transformers now come from China and I have no idea about their content.

12:1 ratio will put less load on a passive instrument
Pro: less loading on passive instrument like Fender Bass, no power supply required
Con: very low output level, susceptible to noise

4:1 will put bigger load on a passive instrument
Con: rolls off high freq on Fender Bass, susceptible to noise
Pro: works great on keyboard instrument, no power supply required

An active Direct Box (like Countryman Fet 85) typically has a higher input impedance
Pro: very low loading on passive instruments like Fender Bass
Con: requires power supply like internal battery or phantom power

One of the biggest determining factors in D.I. box transformers is whether or not they are enclosed in a mu metal can for magnetic isolation from noise. An inexpensive transformer direct box can have excellent tone and if noise is not a problem with it, IMHO there is no reason to spend more.

In double blind listening tests we did not find significant differences between expensive and economical transformer D.I. boxes. An older Horizon D.I. box scored very well against our Jensen boxes when the level was perfectly matched between the devices.

Hope that all helps, best of luck to you.
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Old 20th February 2012
  #17
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Thank you for the techy reply.

I was thinking about a passive DI (as i do not plan to use any acoustic/electric bass/guitar or vocal, just synths and drum machines).

And as i do not plan to use it a lot (just for the ground lift feature, and when using some pedal designed for a more quiet signal than my usual synth level), i will not be a core gear in my studio, therefore i don't want to spend a lot of money in it
Old 21st February 2012
  #18
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Quote:
it is an old Boss mixer from the 80s
I had an 8-channel boss mixer (BX-8). It was my first! It's unbalanced and noisy. Very trashy sounding, I remember using piezo mics to trigger a practice pad kit through a drum machine into it. Direct to 4-track R-to-R!

I should have taken a cue from this:

Quote:
I have a mixer and some hardware effects which causes hum
Yeah, weakest link? Probably that. Otherwise, use it to make lo-fi goodness. Glad you tracked down the source of your hum!
Old 21st February 2012
  #19
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Quote:
Originally Posted by CompEq View Post
Yeah, weakest link? Probably that. Otherwise, use it to make lo-fi goodness.
Yes, i guess that's it
Old 21st February 2012
  #20
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If the only reason you are looking at DI box is because you have a hum at the frequency of the AC in your country, then you are looking at the wrong tool for the job!

If indeed what you need is a ground lift, how about doing it inside your cables?
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