Step Down Powered Signal With A DI Box?

[Tekker]

Hi all,

Since there isn't a "live sound" forum here at the slutz, I figure this forum is the closest I can get.

So, my question is related to something that I heard recently that you can step down a powered level (for speakers) with a DI box to mic level and plug it into a mixer. Do you need a special type of DI box to do this or will any standard DI box (like for guitar) do this? If a standard DI box will work, do DI boxes have a wattage rating for how much they can handle before frying, or will that never be a problem? I've never tried doing something like that, but if a standard DI box would do this (without frying itself or the mixer) that would be great. Because I want to be able to use headphones at an upcoming gig, but we will only have floor wedges and I'd be great if I could simply unplug the monitor cable (which is powered) and plug the cable into a DI box so I can go into a small mixer for my headphones.

Thanks,
-tkr

[Mark A. Jay]

Originally Posted by Tekker

Hi all,

Since there isn't a "live sound" forum here at the slutz, I figure this forum is the closest I can get.

So, my question is related to something that I heard recently that you can step down a powered level (for speakers) with a DI box to mic level and plug it into a mixer. Do you need a special type of DI box to do this or will any standard DI box (like for guitar) do this? If a standard DI box will work, do DI boxes have a wattage rating for how much they can handle before frying, or will that never be a problem? I've never tried doing something like that, but if a standard DI box would do this (without frying itself or the mixer) that would be great. Because I want to be able to use headphones at an upcoming gig, but we will only have floor wedges and I'd be great if I could simply unplug the monitor cable (which is powered) and plug the cable into a DI box so I can go into a small mixer for my headphones.

Thanks,
-tkr

What you describe is called a voltage divider, and it's a simple passive (and linear) network that simply attenuates (via resistors) the voltage applied to the guitar speakers (while allowing the voltage to be delivered to the speakers), yet provides a small-scale version of that same signal that can then be used to drive an input of a console, recorder, etc. The slightly trickier part is turning it into a balanced signal, but that's only slightly more complicated.

By choosing the right resistor values you can achieve a divider that presents no singificant load to the amplifier and also is a low enough impedance to comfortably drive a low impedance input. It's pretty easy to do, but also should be very easy to find.

Some variants are a bit more 'live sound' friendly in that they employ things like isolation transformers (a great way to prevent mains (ground) loops). There are arguments on both sides as to the change in timbre that results from the isolation transformer (because of changes in frequency response borne of several factors - non-linearity of the core material in the transformer, hysterisis, impedance 'matching' and so on) and whether that is good or bad. Others employ a sort of hybrif approach where the voltage divider drives an op-amp / follower to provide some impedance buffering. All approaches have their advantages and disadvantages, and chances are one variant will be best for most of your uses as envisioned.

Anyway, those are the broader issues that you should look at. I know there are many more GS folks who are more current on the peripherals than I am, so I'll leave the model number / mfg. 'deets' to them.

[mixedupsteve]

Originally Posted by Tekker

Hi all,

Since there isn't a "live sound" forum here at the slutz, I figure this forum is the closest I can get.

So, my question is related to something that I heard recently that you can step down a powered level (for speakers) with a DI box to mic level and plug it into a mixer. Do you need a special type of DI box to do this or will any standard DI box (like for guitar) do this? If a standard DI box will work, do DI boxes have a wattage rating for how much they can handle before frying, or will that never be a problem? I've never tried doing something like that, but if a standard DI box would do this (without frying itself or the mixer) that would be great. Because I want to be able to use headphones at an upcoming gig, but we will only have floor wedges and I'd be great if I could simply unplug the monitor cable (which is powered) and plug the cable into a DI box so I can go into a small mixer for my headphones.

Thanks,
-tkr

I have a Countryman 85 DI that is designed to accept a speaker level input. I did a show once where a guitar player connected an inexpensive passive DI into the thru jack of a monitor and used an IEM device connected to a little mixer like you describe. That did however leave the speaker in the path also.

You say "monitor speaker cable which is powered" If it's a passive speaker then you do have a speaker level going to it. If you mean it's a powered speaker, then the cable going to it is a line level and it could be plugged into a line input of your mixer without a DI.

[Tekker]

Mark, thanks for the info. I didn't find much on a google search in terms of brands/models, so hopefully someone can chime in on a specific unit to look at.


mixedupsteve, the cable is powered so some kind of step-down device would be needed to plug it into the mixer.


We have several passive DI boxes that we can bring (they're not mine so I don't have the brand/models on hand, but can find out tonight). Would there be a way to tell from looking at the DI box whether or not it could be used in this situation, such as power ratings written somewhere on the DI box itself? Or would I just have to google the brand/model and read the specs?

Thanks again,
-tkr

[mpdonahue]

We built this feature into our home made Jensen transformer DI boxes. It is actually in the Jensen DI application note.
The real issue is the impedance and how much heat the resistor needs to dissipate. We've actually got a switch that attenuates the signal to 3 different levels and we use 5w resistors.
All the best,
-mark

[Mark A. Jay]

Originally Posted by mpdonahue

We built this feature into our home made Jensen transformer DI boxes. It is actually in the Jensen DI application note.
The real issue is the impedance and how much heat the resistor needs to dissipate. We've actually got a switch that attenuates the signal to 3 different levels and we use 5w resistors.
All the best,
-mark

Mark's right about the resistor ratings (in terms of pwer dissipation). I mentioned the need to get the ratios correct (and that is oviously true) but the dissipation is quite important - both from a device 'survivability' standpoint as well as the fact that properly sized restors (in terms of power dissipation) ensures that resistnace value drift (due to temperature coefficient) is mitigated. Otherwise, as resistor values drift so too will the ratio of resistances and thus the apparent attenuation provided by the resistance network.

Transformers are a beautiful thing when well designed (i.e. for best frequency response as well as linearity (linearity and flat frequency response are not synonymous terms - they are related to one another, but people often (mistakenly) interchange the two terms)).

I say they are beautiful things because they do provide isolation (by their very nature), which can be very important when interfacing two pieces of gear in different locations, each having different ground references (as well as different potentials seen at ground).

The transformer approach also ensures that the driving side impedance (a function of the transformer) is low enough such that it can easily drive any input to which its output is attached. Again, in a transformerless approach, this can easily be accomplished by a follower, or by a simple op-amp based follower; their oputput impedance is typically around 25 Ohms or so, so they will easily drive pretty much any XLR/TRS differential input.

[Barnabas]

Some direct boxes have this feature as a switch that switches between a line-level signal and a speaker-level signal.

The switch might be labeled SPKR or PAD.

The Whirlwind Director has this feature, and I've used it several times with guitar amps that do not have a line-level output.

[hbphotoav]

This might be what you're looking for...

Whirlwind HOTBOX - Active Direct Box HOTBOX - B&H Photo Video

It's is an active direct box that operates with batteries or phantom power.

• 1/4" parallel wired in/out jacks
• Input switch selects between instrument/line or speaker level input signals
• Ground Lift switch to help eliminate hum and buzz
• LED indicates "ON" status

If you need more than a single channel, they also make it in a 4-up single rackspace unit.

Whirlwind HotBox Quad Direct Box HBQ - B&H Photo Video

HTH.

HB

[Mark A. Jay]

Originally Posted by hbphotoav

It's is an active direct box that operates with batteries or phantom power.

I love that you can source the operating power for this via phantom. Clever.

[hbphotoav]

Originally Posted by Mark A. Jay

I love that you can source the operating power for this via phantom. Clever.

All of my active DIs (Klark-Teknik, Radial, Samson and -urrp- rarely used Behringer) are phantom powered. I don't have one (of eight) that can be powered by battery. Fortunately, all my mixers (Mackie, Soundcraft) provide phantom, so it's not an issue.

[MichaelPatrick]

Building a step-down or pad box is quite easy.

The old Yamaha PM-1000 user manual has instructions, pictures, and precise component values if you want to make your own. Just Google "yamaha pm-1000 manual" and download it, then look at pages 24-27.

BTW, it doesn't make sense to step speaker level down to mic level unless you have to, since making up the lost gain just adds noise. I'd step down to something near line level.

[Tekker]

Thanks everyone. I'll find out what kind of DI's we have tonight and report back. If ours will work, then that would be awesome.

I don't think I'll be able to afford anything like the Hotbox, if it comes down to using a floor wedge or spending $100+ I'll go with the floor wedge. lol But I figured that if it was possibly only a simple matter of plugging it into a DI box, then it's worth asking about and getting more info on it since we already have some DI boxes.

Thanks again,
-Sean

[Tekker]

Hi again guys,

I got a chance to look at the DI boxes and they are called "Horizon Straightline Passive Direct Box".
Horizon - sl1 - Straightline Passive Direct Box The Horizon SL-1 Straightline Direct Box’s simple design offers reliable input jacks as well as a… Jacks Music Store

It doesn't sound like these will handle the powered signal, which is a bummer, but it sounds like the sound guy that will be running our show does have some that will work. I will have to talk to him about it and make sure.

At some point I would love to get one of these for myself to have for future gigs. The Hotbox sounds like a great unit, but does anyone know of anything cheaper than $130 that will also work?

Thanks,
-tkr