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Author Topic: Building DI Box  (Read 5027 times)

fezzle

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Building DI Box
« on: May 16, 2011, 05:35:19 pm »

Hi people,
               I'm just writing to anyone who might be able to help me with a a small project I want to do, to build my own DI box.  I have a DAW setup at home , and want to build a standard style box that has a Hi Z input and a 600Ohm output for my Mic Pre's. BUT also was wondering if its possible to have a line level input and output in the box too.  I have spotted a rare UTC transformer I want to use because apparently they sound excellent,  which is high Z to low Z , but is it possible to run line level in and out of it to get the same isolation and characteristics, or would I need another transformer?  I am very new to all of this sort of stuff , and dont really know what else I would need,  any thoughts or advice would be greatly appreciated!! I kind of want the box to have some moderate colour i guess from the design

Cheers!!  Dave
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Barry Hufker

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Re: Building DI Box
« Reply #1 on: May 26, 2011, 11:42:12 pm »

Hi Dave,

I can't answer all your questions, but I can help a little bit.  My students recently built D.I. boxes based on different transformers.  This meant creating a "look" for the box, a layout and then building/testing them.  The parts used were the Cinemag CM-DBX, the Jensen JT-DB-E, the Lundahl 1530, the Lundahl 1935 and the Sowter 4243 transformers.  You can see and hear the results here.  http://prorecordingworkshop.lefora.com/2011/05/24/di-boxes/#post2

The audio examples should give you a pretty good idea about the "color" of each transformer.  The photo may not be completely revealed without clicking on it.

Barry
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klett

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Re: Building DI Box
« Reply #2 on: May 29, 2011, 10:52:37 am »

transformer is easiest

I'd suggest a 200 ohm output as most all mic pre's are fine with the lower source impedance and some pre's like TAB V76 and V72 modules MUST be sourced from 200 ohms (or as close is possible)

you can look for 10K:200 (or 200:10K and use it backwards)

a lot transformers use a two windings to make 600 ohms in series and 150 ohms in parallel so you can go with that...  150 ohms works fine going into V76's et al

Sowter makes some 200:10K mic input that you can use backwards

a lot of winders make 10K split to 600 split
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John Roberts {JR}

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Re: Building DI Box
« Reply #3 on: May 29, 2011, 12:46:51 pm »

Hi people,
               I'm just writing to anyone who might be able to help me with a a small project I want to do, to build my own DI box.  I have a DAW setup at home , and want to build a standard style box that has a Hi Z input and a 600Ohm output for my Mic Pre's. BUT also was wondering if its possible to have a line level input and output in the box too.  I have spotted a rare UTC transformer I want to use because apparently they sound excellent,  which is high Z to low Z , but is it possible to run line level in and out of it to get the same isolation and characteristics, or would I need another transformer?  I am very new to all of this sort of stuff , and dont really know what else I would need,  any thoughts or advice would be greatly appreciated!! I kind of want the box to have some moderate colour i guess from the design

Cheers!!  Dave

Unless you want to make this more difficult than it need be, all you need is a simple resistive pad to send a line level to a mic input, while some better mic preamps have pads built in. For the amount of pad attenuation involved it should be easy to come up with good termination impedances for both (all three) ends.

While some might question the merit of not just using a line input.

There are some good general purpose transformer based direct box designs published in old Jensen app notes. Likewise opamp or discrete based DI can be made much cheaper and arguably more linear than transformer based DI, if that is important to you.

 Perhaps you could be more specific about what qualities of a DI you want to realize.

JR
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