# Using a DI Box in reverse



## techietim (Dec 15, 2013)

Hi all,

Just to be clear in this thread I'm *not *talking about re-amping.

The floor wedges at our church take a 1/4" input but come out of the mix console as XLRs.

Is it possible to put the 1/4" output into a passive *or *active DI box to go *from *XLR to 1/4"?
Got to use a DI as somebody has helpfully laid the mains cables right next to them and they cannot be moved! (I know these ideally need to be moved).

Thanks for your help!


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## headcrab (Dec 15, 2013)

Are your wedges active or passive?


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## carproelsofly (Dec 15, 2013)

Ha! I was just writing the same thing!

Are your wedges active? (Are the amps built in?) If so, then your solution could be a simple adapter or a DI, depending on whether the console output is mic level or line level, and whether there is a pad on the wedge that you can engage.

If your wedges are passive, which is far more common (and likely if you see a 1/4" jack), then you'll need an amplifier in there somewhere. That would normally be where you'd convert from the XLR (input; probably mic level) to the 1/4" cable (much heavier gauge, typically 2-conductor) which carries the amplified signal to the speaker.


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## techietim (Dec 15, 2013)

headcrab said:


> Are your wedges active or passive?



Wedges are active!


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## techietim (Dec 15, 2013)

carproelsofly said:


> Ha! I was just writing the same thing!
> 
> Are your wedges active? (Are the amps built in?) If so, then your solution could be a simple adapter or a DI, depending on whether the console output is mic level or line level, and whether there is a pad on the wedge that you can engage.
> 
> If your wedges are passive, which is far more common (and likely if you see a 1/4" jack), then you'll need an amplifier in there somewhere. That would normally be where you'd convert from the XLR (input; probably mic level) to the 1/4" cable (much heavier gauge, typically 2-conductor) which carries the amplified signal to the speaker.



We have some adaptors now but they're not great, bit faulty (DI Adaptors).

We're using the Behringer XL3200 console. Think it's probably line level out.


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## headcrab (Dec 15, 2013)

Your wedges are active, and if your mixer outs are balanced (manual will say), you shouldn't need a DI in between; a simple wire adapter should suffice. Adapters are neither hard to make nor expensive.


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## techietim (Dec 15, 2013)

headcrab said:


> Your wedges are active, and if your mixer outs are balanced (manual will say), you shouldn't need a DI in between; a simple wire adapter should suffice. Adapters are neither hard to make nor expensive.



Problem is that the monitor feed cable runs right alongside two/three mains feeds (for various stuff), means the monitor feeds are therefore quite noisy without a DI..


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## chausman (Dec 15, 2013)

A DI will perform the same function regardless of the connector. So you need to adapt to 1/4" TRS to go in the DI, then from 1/4" TRS to XLR to come back out of the DI.


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## FMEng (Dec 15, 2013)

Hold on there. A _passive_ DI can work in reverse, but an _active_ DI will not. Even then, a passive DI may compromise the sound quality because the transformer inside will be operating at line level instead of mic level, a much greater signal level than it is designed for. A passive DI also makes an impedance conversion, which would step up the signal voltage to the monitor, which may cause clipping of the input stage. Please tell us what kind of monitors you have, so we can determine whether they have TRS balanced inputs or TS unbalanced inputs. From there, we can come up with a proper fix.


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## museav (Dec 15, 2013)

FMEng said:


> Hold on there. A _passive_ DI can work in reverse, but an _active_ DI will not. Even then, a passive DI may compromise the sound quality because the transformer inside will be operating at line level instead of mic level, a much greater signal level than it is designed for. A passive DI also makes an impedance conversion, which would step up the signal voltage to the monitor, which may cause clipping of the input stage. Please tell us what kind of monitors you have, so we can determine whether they have TRS balanced inputs or TS unbalanced inputs. From there, we can come up with a proper fix.


+1, there is more to a DI box than simply different input and output connectors. Keep in mind that one thing a DI box does is to take a line level signal and drop it down to microphone level, used backward you are essentially applying that change in level in reverse and thus would be feeding the DI a signal greater than it normally sees on the 'output' side and also having a greater output level to the speaker than is coming from the mixer.

Even run with the power lines the monitor feeds should not necessarily be noisy if you use balanced audio signals run over properly wired shielded, twisted pair audio cable. The Main and Aux/Mon sends from your mixer are electronically balanced signals with XLR connectors. If the powered monitors have balanced TRS line level inputs then may be that an adapter is all that is needed. If they have microphone level inputs available then maybe you could use a DI or pad at the speakers with the mic level output from the DI to the speakers. If the monitors only have unbalanced, line level inputs then you may need a custom wired adapter or or perhaps a 1:1 isolation transformer at the speaker input. But until we know what inputs are actually available on the powered monitors we'd be guesssing at what may be appropriate.


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## carproelsofly (Dec 15, 2013)

museav said:


> perhaps a 1:1 isolation transformer



Yep.

Also, since your wedges are active, check your AC path. Is there noise in them when they're turned on, without signal attached? All of the noise you're hearing might not be coming down the signal cable....

Jen


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## howlingwolf487 (Dec 16, 2013)

techietim said:


> Problem is that the monitor feed cable runs right alongside two/three mains feeds (for various stuff), means the monitor feeds are therefore quite noisy without a DI..


Until you find out where the noise is coming from, you'll never truly fix the problem - only BandAid it.

Starting from the active monitor(s) that you hear the noise from, work your way upstream towards the mixing console. Unplug each signal cable and check to see if the noise remains.

If you can't eliminate the noise for some reason, a high-quality isolation transformer (Jensen, preferably) should do the job. It is similar to a passive DI in that it uses transformer isolation to physically decouple the signal grounds from each other (eliminating ground loop and the noises that come with them), but the turns ratio is 1:1 versus the step-down type found in instrument DIs.

You'll pay for it...but it will be money well spent - I'm looking to buy one in the next year. About $200USD or so for a Jensen seems right...


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## FMEng (Dec 16, 2013)

A good isolation transformer is a bullet proof fix when nothing else works, but it should be the last thing to try rather than the first. Let's find out if the cabling is properly shielded and wired all the way through, and whether the speaker has a balanced input. It's easy to hook something like that up with a guitar cable, or even worse, a speaker cable, and wind up with hum because it isn't balanced.


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## FMEng (Dec 16, 2013)

carproelsofly said:


> Yep.
> 
> Also, since your wedges are active, check your AC path. Is there noise in them when they're turned on, without signal attached? All of the noise you're hearing might not be coming down the signal cable....
> 
> Jen



This is a myth that I would like to put to rest. Audio hums and buzzes are not the result of "dirty power" or "bad grounds." Leave the surge suppressors, AC filters, and pin lifters in the junk pile. It's a matter of the simple physics of current flow, resistance/voltage drop, induction, common mode rejection, etc., sneaking noise into the signal line. It's possible to connect two pieces of audio gear together, run them on perfect power with text book installation of the building's AC wiring, and wind up with hum. It's also a simple matter to solve much of the time. Google Neil Muncy and the "pin 1 problem." He did more to educate on this topic than anyone before or since.

Consider that virtually every piece of audio gear has a power supply that takes AC power and rectifies it to DC, filters the ripple to smooth DC, and regulates to stable voltages for use by the circuitry. It is nearly impossible for junk on the AC line to get past all of that and affect the audio stages.


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## carproelsofly (Dec 20, 2013)

FMEng said:


> Consider that virtually every piece of audio gear has a power supply that takes AC power and rectifies it to DC, filters the ripple to smooth DC, and regulates to stable voltages for use by the circuitry. It is nearly impossible for junk on the AC line to get past all of that and affect the audio stages.



Thanks for the info, FMEng.

For the record, I wasn't suggesting a suicide ground lift or other cockamamie solution. Glad to hear that the electronics in active speakers serves to solve the other AC issues (shared power with dimmers and inductance are the ones I seem to fight with most often in older/smaller systems).


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## museav (Dec 21, 2013)

Just a reminder to the OP that their providing the specific model of speakers involved or details about the available inputs on the speakers, as well as any details on the wiring between the mixer and speaker, would really help people be able to offer more specific recommendations.


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## techietim (Dec 28, 2013)

Hi All,

Thank you all very much for your help! I've been pretty busy with a show at the theatre at present but will look at the wedges as soon as I can and post them here.

I'll also read your replies more carefully when at the computer.

Sorry for the late replies 

Tim


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