Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Dan Mortensen]

The active design allows you to design it to have no insersion loss, in fact you could even design it to have gain.

Yes, but are there any designed for general use that have gain instead of loss?

That seems like it wouldn't be what we think of as a D.I. but would be something else.

[Peter Morris]

Yes, but are there any designed for general use that have gain instead of loss?

That seems like it wouldn't be what we think of as a D.I. but would be something else.

Yes there are some with gain - http://www.avalondesign.com/pdfs/u5.pdf

Some such as the BSS AR-133 (and Behringer ultra DI) have selectable attenuation on the input of 0dB, -20dB or -40dB, making the box suitable for instrument, line or amplifier levels on inputs.

The clasic Radial J48 is 0dB with a 15dB pad to make it suitable for bass guitars and keyboards

[Dan Mortensen]

Yes there are some with gain - http://www.avalondesign.com/pdfs/u5.pdf

Some such as the BSS AR-133 (and Behringer ultra DI) have selectable attenuation on the input of 0dB, -20dB or -40dB, making the box suitable for instrument, line or amplifier levels on inputs.

The clasic Radial J48 is 0dB with a 15dB pad to make it suitable for bass guitars and keyboards

Thanks again, Peter.

That Avalon is a serious unit, and I note that they call it "Instrument DI - Preamp", which does indeed differentiate it from "DI". It' cool that it doesn't have a wall wart but instead has an IEC input, yet at 12 pounds shipping weight and Avalon price, I would not like to take 20 of those to a gig.

The BSS and Behringer do indeed have input attenuation where the lowest setting is "0", but neither of their documentation mentions insertion loss. I'm not yet ready to believe that 0 db attenuation translates to 0 db insertion loss.

Although the J48 Owner's Manual has quite a bit more interesting DI lore than the BSS and Behringer, it also does not show insertion loss.

Since we have variable gain on our consoles, none of this matters to us in use, but for the sake of this discussion I have to think that except for a special purpose box like the Avalon, the jury is still out on whether one is likely to always get insertion loss from using an active DI, with the understanding that it is possible to have no loss. Whereas, a passive DI will always have loss in the range of 20db. (The other DI's you linked spec'd -15 for their active to -22 dbu for their passive; when the attenuation is listed simply as "-20" or whatever on the box, is that dbu?)

And, again, there was no console involved in the original question, so narrowing this down keeps the discussion on track, albeit a narrow, tiny track.

When I get some idle time I intend to check the Countryman Active and Radial Passive DI's that I have for insertion loss, but that's going to be weeks if not months since, as noted, the answers make no difference in normal use.

Duh, I just checked the Countryman Type 85 active DI tech sheet, and it has a voltage gain of -10db, which I interpret as insertion loss, so there's that data point, too.

So there is a variable amount of insertion loss for active DI's, and probably around -20 for passive? Maybe that's the takeaway.

[Matthew Knischewsky]

Yes, but are there any designed for general use that have gain instead of loss?

That seems like it wouldn't be what we think of as a D.I. but would be something else.

That's called a preamp with a high impedance input. There's lots of them out there but they're often missing some of the features we expect in live audio applications: Parallel jacks and ground lift.

Dan, what problem exactly are you trying to solve? A DI box does impedance matching and level shift, while a 1:1 isolation box does not. 20dB or so of insertion loss is not necessarily a bad thing because it fits into our workflow and how the equipment is designed. I don't see a real need to reinvent the DI Box.

[Dan Mortensen]

Dan, what problem exactly are you trying to solve?

I'm trying to fully understand the situation presented in the first post of the thread, which involved two different understandings of what a DI box does and/or can do and the details of what happens when one is inserted in a signal chain.

There is no expectation of inventing anything, simply understanding the variabilities of the existing devices and thus being able to know what kinds of problems they are able to solve, and how they are doing it.

A DI box does impedance matching and level shift, while a 1:1 isolation box does not.

Quite true, and it's important to know which of those two different devices you have in front of you when you are trying to solve a problem. The people described in the OP were using the first one you described to try to get a result better obtained by use of the second one you described, although isolation was not relevant to the situation.

20dB or so of insertion loss is not necessarily a bad thing because it fits into our workflow and how the equipment is designed. 

...as I believe I have said in this thread a couple of times. However, 20 db of insertion loss is at least a mildly negative thing if you are expecting unity gain from the use of the DI box and you don't have make-up gain in the signal chain.

Clear enough now?

I feel like my initial big questions are answered, but nuances keep appearing (e.g., different gain losses/increases for different active DI's). IMO it's good to know the insertion loss for whatever DI you are using, since knowledge are good. 

[Steve M Smith]

That's called a preamp with a high impedance input. There's lots of them out there but they're often missing some of the features we expect in live audio applications: Parallel jacks and ground lift.

The high impedance DIs I make have those features.  Well, the ground lift is a 10 ohm resistor and 0.1uF capacitor to minimise ground loops.


Steve.

[Tim McCulloch]

I'm trying to fully understand the situation presented in the first post of the thread, which involved two different understandings of what a DI box does and/or can do and the details of what happens when one is inserted in a signal chain.

There is no expectation of inventing anything, simply understanding the variabilities of the existing devices and thus being able to know what kinds of problems they are able to solve, and how they are doing it.

Quite true, and it's important to know which of those two different devices you have in front of you when you are trying to solve a problem. The people described in the OP were using the first one you described to try to get a result better obtained by use of the second one you described, although isolation was not relevant to the situation.

...as I believe I have said in this thread a couple of times. However, 20 db of insertion loss is at least a mildly negative thing if you are expecting unity gain from the use of the DI box and you don't have make-up gain in the signal chain.

Clear enough now?

I feel like my initial big questions are answered, but nuances keep appearing (e.g., different gain losses/increases for different active DI's). IMO it's good to know the insertion loss for whatever DI you are using, since knowledge are good. 

Dan, the irony is that you answered your own question in that first post.

You were dealing with TechoDummies®.

[Scott Helmke]

...as I believe I have said in this thread a couple of times. However, 20 db of insertion loss is at least a mildly negative thing if you are expecting unity gain from the use of the DI box and you don't have make-up gain in the signal chain.

It's a little tricky to talk about things like "gain" in a transformer. I don't believe that insertion loss is the correct terminology, because that usually represents actual power* loss and tends to be a much smaller number.

What's going on in a DI transformer is that it does reduce voltage, based on the turns ratio, but very little power is ever lost.  What ends up happening is that the mic-level output side does have lower voltage, and therefore acts as though it is a weaker signal. But there's a lot more current available, which is not being used by a typical mic preamp.  If you use an XLR female turnaround and run the signal through two passive DI boxes, what comes back out of the second (run backwards) DI should be very close in both voltage and current to what went in to the first DI.

*power = potential X current, or watts = volts X amps.  A perfect transformer can change volts and amps around, but doesn't change the total power.

[John Roberts {JR}]

It's a little tricky to talk about things like "gain" in a transformer. I don't believe that insertion loss is the correct terminology, because that usually represents actual power* loss and tends to be a much smaller number.

What's going on in a DI transformer is that it does reduce voltage, based on the turns ratio, but very little power is ever lost.  What ends up happening is that the mic-level output side does have lower voltage, and therefore acts as though it is a weaker signal. But there's a lot more current available, which is not being used by a typical mic preamp.  If you use an XLR female turnaround and run the signal through two passive DI boxes, what comes back out of the second (run backwards) DI should be very close in both voltage and current to what went in to the first DI.

*power = potential X current, or watts = volts X amps.  A perfect transformer can change volts and amps around, but doesn't change the total power.

The signal gets "transformed",,,,

And this Nth DI thread reverts to form... There are different variant boxes that get called DIs often incorrectly. People just want a magic "fixer" box for sundry interface problems, and call that a DI.

JR

[Matthew Knischewsky]

<Snip> 20 db of insertion loss is at least a mildly negative thing if you are expecting unity gain from the use of the DI box and you don't have make-up gain in the signal chain.

If you're using a DI box in an application where there's no make up gain you're essentially in an off label application. A DI is designed to be used with a mic preamp, which has plenty of gain. In fact, a DI box with "unity" gain isn't necessarily considered a good thing- hot line level sources through an active DI can overload either the input stage of the DI or the mic preamp.

[ProSoundWeb Community]