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Author Topic: Active DI Boxes?  (Read 12225 times)

Steve M Smith

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Re: Active DI Boxes?
« Reply #20 on: June 29, 2016, 02:48:22 AM »

If ground lift isn't a requirement, and for many applications there is no need for ground lift, then an active DI like this one is, as you note, not rocket science.  And this "simple" DI will have better sound quality than any DI based on a transformer, because transformers are always bad things, with the only remaining question being the scale of money required to minimize "bad".

And that is quite an elegant design.

Thank you.

Unless a DI has a transformer isolated power supply such as the BSS133, then an active DI cannot have a true earth lift as there would be no return path for the power supply.  In practice, a 10R resistor and a 0.1uF capacitor is usually enough to stop an earth loop.

I like the simplicity of this circuit.  Gain isn't required as it connects to an input optimized for microphone levels.  Also, it will happily work with a PNP transistor - just put the collector to the ground side.

Here is my Hi Z design intend for piezo pickups (but works fine with everything else).  It has a 5M input impedance which is enough to preserve the low end of a double bass.

The circuit is based on the Schoepes microphone circuit with a high impedance FET input stage.




Steve.
« Last Edit: June 29, 2016, 02:52:12 AM by Steve M Smith »
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Ivan Beaver

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Re: Active DI Boxes?
« Reply #21 on: June 29, 2016, 06:44:29 AM »


As for the amps that blew, not sure exactly what happened there but the amps were 15 year old crest amps that we knew had some problems (we often had to go in and solder in a new power cable because they would over heat and melt the wires together.)
There is something very wrong with this statement.

Either the repair was done very poorly. Or the description of the repair was wrong, or the understanding of the repair was wrong.

Power cables that are melting is simply NOT a normal issue.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Don T. Williams

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Re: Active DI Boxes?
« Reply #22 on: June 29, 2016, 11:58:21 AM »

There is something very wrong with this whole situation.  The "powers that be" really don't want to solve the problem.  Surgery is needed.  A band-aid won't solve the problems.  Robert, sometimes you just need to walk away!
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Chrysander 'C.R.' Young

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Re: Active DI Boxes?
« Reply #23 on: June 29, 2016, 01:42:02 PM »

OP,

Where are you located?  There are some folks here that may be able to assist, even if it is just reinforce what you already have tried to tell the folks in charge at your church.

I have been in your position and had to finally just walk away and use my skills to serve other ministries.  The defects you describe are borderline frightening and I personally would not want my fingerprints on that mess.  Find another place to serve and share your gifts.
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David Buckley

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Re: Active DI Boxes?
« Reply #24 on: June 29, 2016, 05:14:51 PM »

Transformers are wonderful things.  They solve a multitude of problems. Good ones like Jensen have lots of headroom before any distortion. They are simple and work in a number of dicey situations. They protect phones and MP-3 players ETC from phantom power. and nothing isolates a analog signal like a transformer.

All true.  But it doesn't alter the fact that transformers - even good ones - bend audio.  That's why you need a "good" transformer, because it will will do less audio damage than a $1 transformer.  Otherwise all transformer-isolated DIs would have $1 transformers in them, rather than an expensive transformer.

A DI box with a Jensen in it will sound good, no doubt, about as good as a $5 home made active DI.  If you need a transformer, then you need a transformer, end of story.  Some of the time, you don't, and a simple active DI will do very nicely.
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Frank DeWitt

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Re: Active DI Boxes?
« Reply #25 on: June 29, 2016, 10:46:42 PM »

All true.  But it doesn't alter the fact that transformers - even good ones - bend audio.  That's why you need a "good" transformer, because it will will do less audio damage than a $1 transformer.  Otherwise all transformer-isolated DIs would have $1 transformers in them, rather than an expensive transformer.

A DI box with a Jensen in it will sound good, no doubt, about as good as a $5 home made active DI.  If you need a transformer, then you need a transformer, end of story.  Some of the time, you don't, and a simple active DI will do very nicely.

Jensen is also one of the few transformer companies that publishes the numbers for there products.  I don't think you will find enough bending to hear. 
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Robert Gerhardt

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Re: Active DI Boxes?
« Reply #26 on: June 29, 2016, 11:37:02 PM »

I agree that we have some MAJOR issues, but right now I can't get funding to fix them. C.R. I'm in Edmonton AB, Canada. I've been talking with the elder in charge of A/V and Worship and he is willing to work with me. I just took on the TD role a couple months ago (volunteer) and have not had a really good meeting with him until today. He admits that he knows nothing about A/V or worship, but is willing to work with me to find solutions for our problems. I have a few connections, so I'm trying to source some used gear right now to try and improve on a few of our issues. He's pushing for a much larger budget next year to fix many of our issues.

The problem with the power cable on the amps melting was due to a heat register right behind our amp rack (as I found out this afternoon). Looks like they were severely overheating so I moved the rack to the opposite side of the room, hopefully this will prevent any damage to our new amps.

Right now, I'm just hoping to build some DI's that will work to get us by for a year or two.
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Scott Holtzman

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Re: Active DI Boxes?
« Reply #27 on: June 30, 2016, 02:05:11 AM »

I agree that we have some MAJOR issues, but right now I can't get funding to fix them. C.R. I'm in Edmonton AB, Canada. I've been talking with the elder in charge of A/V and Worship and he is willing to work with me. I just took on the TD role a couple months ago (volunteer) and have not had a really good meeting with him until today. He admits that he knows nothing about A/V or worship, but is willing to work with me to find solutions for our problems. I have a few connections, so I'm trying to source some used gear right now to try and improve on a few of our issues. He's pushing for a much larger budget next year to fix many of our issues.

The problem with the power cable on the amps melting was due to a heat register right behind our amp rack (as I found out this afternoon). Looks like they were severely overheating so I moved the rack to the opposite side of the room, hopefully this will prevent any damage to our new amps.

Right now, I'm just hoping to build some DI's that will work to get us by for a year or two.

Someone already pointed you to a link at Audiopile with a decent DI that is in budget.  Don't build your own.  That just doesn't make sense. 

If you really have so much cable loss why don't you look for an 8 channel MIC preamp?  Here is a great Peavey from the Architectural Acoustic series.  The controls are recessed to keep grubby paws off.

http://www.ebay.com/itm/262497079127
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Scott AKA "Skyking" Holtzman

Ghost Audio Visual Solutions, LLC
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Chrysander 'C.R.' Young

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Re: Active DI Boxes?
« Reply #28 on: June 30, 2016, 09:23:22 AM »

I agree that we have some MAJOR issues, but right now I can't get funding to fix them. C.R. I'm in Edmonton AB, Canada. I've been talking with the elder in charge of A/V and Worship and he is willing to work with me. I just took on the TD role a couple months ago (volunteer) and have not had a really good meeting with him until today. He admits that he knows nothing about A/V or worship, but is willing to work with me to find solutions for our problems. I have a few connections, so I'm trying to source some used gear right now to try and improve on a few of our issues. He's pushing for a much larger budget next year to fix many of our issues.

The problem with the power cable on the amps melting was due to a heat register right behind our amp rack (as I found out this afternoon). Looks like they were severely overheating so I moved the rack to the opposite side of the room, hopefully this will prevent any damage to our new amps.

Right now, I'm just hoping to build some DI's that will work to get us by for a year or two.

OP, I totally feel your pain.  You seem be stuck between a rock and a hard place.  You and your church need to stop, define the goals of your sound system, and then pay someone to look at it as a whole system and prioritize what needs to be fixed.  Right now, I am seeing a classic case of "Well, the transmission won't shift out of 2nd gear and the engine runs rough, but we have the budget to get new seat covers, so let's do that." 
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Re: Active DI Boxes?
« Reply #28 on: June 30, 2016, 09:23:22 AM »


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