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[Pat Semeraro]

If my opponent in the argument were right, why couldn't we then use DI's as 1:1 isolation transformer for situations requiring that?

Even if they were wrong like I think, why can't we have transformer DI boxes with 1/4" inputs and pass throughs as well as an XLR input so they can be used as iso transformers? Has there ever been such a thing? Or is it that impedance ratio thing that rules this out?

Probably a dumb question... but if the DIs were active, where was phantom coming from?

If you're looking to just solve grounding problems the Jensen isomax has almost no impact on audio quality as long as you don't ask the transformer to drive a long cable run.

For a passive hi-z to balanced lo-z an option that not many use but worked great is the Rane balance buddy.  Very high quality transformers and with the right console (quiet pres) can drive through an analog snake.  They were handy for stuff like keyboards with only a headphone output or super amateur DJ mixers, etc.

[Rob Spence]

Probably a dumb question... but if the DIs were active, where was phantom coming from?

If you're looking to just solve grounding problems the Jensen isomax has almost no impact on audio quality as long as you don't ask the transformer to drive a long cable run.

For a passive hi-z to balanced lo-z an option that not many use but worked great is the Rane balance buddy.  Very high quality transformers and with the right console (quiet pres) can drive through an analog snake.  They were handy for stuff like keyboards with only a headphone output or super amateur DJ mixers, etc.

There are active DIs with internal batteries. I don’t have any of them (actually I have 1 but no battery installed).



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[Chris Hindle]

There are active DIs with internal batteries. I don’t have any of them (actually I have 1 but no battery installed).

Active DI that will provide phantom?
Is that a "boutique" box Rob?

I supply phantom to my actives so I can do away with the batteries.

>or< I misunderstood completely where this conversation is going.
Carry on.
Chris.

[Rob Spence]

Active DI that will provide phantom?
Is that a "boutique" box Rob?

I supply phantom to my actives so I can do away with the batteries.

>or< I misunderstood completely where this conversation is going.
Carry on.
Chris.

A DI typically connects an unbalanced source to a mic input. They don’t provide phantom to their sources.

An active DI might require phantom from the mic input to power the active bits. It also might have a place for a battery for use when the mic input (mixer for example) cannot provide phantom power.


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[Chris Hindle]

A DI typically connects an unbalanced source to a mic input. They don’t provide phantom to their sources.

An active DI might require phantom from the mic input to power the active bits. It also might have a place for a battery for use when the mic input (mixer for example) cannot provide phantom power.


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Yes Rob. well aware of that.
I thought the conversation was heading to where a DI could PROVIDE phantom. Never run into that. (or seen the need)
Note: Remove the batteries from your 85's.
When they die, even with phantom supplied, the box dies. Got bit with that back in the 80's.
Chris.

[Peter Morris]

A friend of mine manufactures high-end DI's.  He has some useful info on his web site that may be of interest.

Passive
http://www.leonaudio.com.au/passive.htm

Active
http://www.leonaudio.com.au/active.htm

[Dan Mortensen]

A friend of mine manufactures high-end DI's.  He has some useful info on his web site that may be of interest.

Passive
http://www.leonaudio.com.au/passive.htm

Active
http://www.leonaudio.com.au/active.htm

Thanks, Peter, those websites specifically respond to the reason for creating this thread: Is there a level change when inserting a DI box into a signal path?

The passive box specifically uses the term "Insertion Loss" and says their box has a 22db Insertion Loss.

The active box is a little more coy and says the XLR output is -15dbu when driven with a 0dbu input, so a 15db Insertion Loss. The active box does not have a battery option, so it would not be relevant in the original situation of using a DI box to transform 1/4" unbalanced to XLR balanced (no phantom available).

I have not been motivated to do a comprehensive search or experimentation to see how much Insertion Loss is caused by various brands or topologies of DI boxes, but this seems like it gives a reasonable minimum range that a source output would be reduced by something in the vicinity of 20db by use of a DI box vs. going straight in.

In the original situation, I now know that the level would not have been reduced beyond audibility had all the bits been working correctly, but IMO looking at the use and placement of the DI's (which were transformer, not active) was a reasonable place to start to look when faced with no signal output at the end of the chain and the solution needing to be very quickly found.

Thanks to all who have posted.

[Scott Helmke]

Thanks, Peter, those websites specifically respond to the reason for creating this thread: Is there a level change when inserting a DI box into a signal path?

So... just how far down the rabbit hole do we want to go here?  Because it is an interesting but not at all obvious thing as to how a DI transformer "changes" the level.

[Mac Kerr]

So... just how far down the rabbit hole do we want to go here?  Because it is an interesting but not at all obvious thing as to how a DI transformer "changes" the level.

What's not obvious? It's a transformer. The turns ratio of the transformer is proportional to the voltage ratio between input and output.

Mac

[Peter Morris]

Thanks, Peter, those websites specifically respond to the reason for creating this thread: Is there a level change when inserting a DI box into a signal path?

The passive box specifically uses the term "Insertion Loss" and says their box has a 22db Insertion Loss.

The active box is a little more coy and says the XLR output is -15dbu when driven with a 0dbu input, so a 15db Insertion Loss. The active box does not have a battery option, so it would not be relevant in the original situation of using a DI box to transform 1/4" unbalanced to XLR balanced (no phantom available).

I have not been motivated to do a comprehensive search or experimentation to see how much Insertion Loss is caused by various brands or topologies of DI boxes, but this seems like it gives a reasonable minimum range that a source output would be reduced by something in the vicinity of 20db by use of a DI box vs. going straight in.

In the original situation, I now know that the level would not have been reduced beyond audibility had all the bits been working correctly, but IMO looking at the use and placement of the DI's (which were transformer, not active) was a reasonable place to start to look when faced with no signal output at the end of the chain and the solution needing to be very quickly found.

Thanks to all who have posted.

In the case of a passive DI you need to match a high impedance input such as a guitar to the low impedance input on your desk - say 20,000 ohm's to 200 ohm's so you need a transformer with a turns ratio of 10:1 hence the insertion  loss (20dB).

With an active DI the active circuit provides the impedance match. Typicall a FET or an IC using  FET input stage is used because of their high input impedance. The active design allows you to design it to have no insertion loss, in fact you could even design it to have gain.  In this case Ian designned it to have a nominal insertion loss of 15dB so that there was no need to put a pad on your desk or DI.

Being able to connect a high impedance source, and providing earth isolation when needed to the low imdedance balaced input of a mixing desk are the two main fuctions of a DI.

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