Building a DI box

[tenchijin2]

So I'd like to build a nice DI box to go directly into my A/D converter (via XLR). I'm very new to this.

I currently don't own a DI box, all my preamps have DI inputs so it's not an issue. My goal is to plug the DI in without using one of my preamp channels to get more simultaneous inputs.

So far I've found plans for the "countryhick"
http://www.diyfactory.com/projects/countryhick/countryhick.htm

and a JLM DI
http://www.jlmaudio.com/JLMDI.htm

Edit: it would need an output level control (like a preamp) since it will be going directly to my A/D converter.

I'd like to power it with one or two 9v batteries. Preferably two, because I understand that improves headroom. Do I recalculate the resistors on the power input side to regulate the voltage?

I'm unclear whether I'll *need* an output transformer in either of these plans. I'm looking to do this with little cost, so I'm hoping not to need the transformer.

I realize these are like pre-school level questions, but I promise I'll learn if you help!

Thanks,

Aric

[scottso]

There is also this one:

http://sound.westhost.com/project35.htm

[tenchijin2]

Thanks Scottso!

Two problems with that one for me: I am still not able/willing to make my own PCB (which is not a deal killer but a dissuader for sure!), and that design doesn't have an output gain control, which I'll need if I'm going directly to my A/D converter.

Aric

[scottso]

Ah.. well you could always perfboard it.   Its a pretty small circuit.  I laid out a PCB for it and it was only 1.5 by 2.5 inches with a TON of space for fat traces.  You could probably easily fit it on one of those small RadioShack perfboards.

As for the output gain, you could always skip the switch for the input gain control and hardwire it to use the pot for the speaker input.

I don't think connecting right to your A/D converter with a DI Box is correct.  You want a preamp for that. A DI box is for hooking up to a preamp which is where you would control the gain.  The DI Box just converts an unbalanced input to a balanced output.  It isn't supposed to bring a signal to unity gain.  Thats what a preamp does.

[tenchijin2]

Yes, I understand that, but at least a couple "DI" units offer line level out. Sansamp Bass driver, for instance. In reality of course it's a DI and  preamp in one, with an amp simulator circuit.

So perhaps I should be asking: is there a simple schematic for a DI and Preamp in one that can run off of 9v batteries?

Eventually I'll be building some of JLMs baby animal kits, but that's more than I'm looking for right now.

[Pushtone]

You really don't want or need a DI for your application.

A DI is designed to convert unbalanced instrument-level signals to balanced mircrophone-level (-40dB) signals.
The purpose of a DI is to interface an instrument - through a snake - to the mic preamps of a console or other recording input device.
Thats how you get your acoustic guitar to the FOH console.

What you want is a instrument preamp with a balanced line-level output.

I would recommend you buy one,  but if your hell bent on building...

Circuits like the Fat Boostered and the English Channel would be OK for electric guitar sounds.
The problem with these is that their output is unbalanced and perhaps won't get you to line-level without some distortion.
Thats why I say they are OK for electric guitar sounds, unless your expecting super clean sound from it.

You can buy a 1:1 line bridging transformer from Jensen to balance the output of these circuits but you'll end up spending $80 for one.
Or you can build a balanced line driver circuit as an output stage but that will require a bipolar power supply.

To get that super clean sound the best way is to use a 12 or 15 volt bipolar power supply
because the power rails will set the input voltage point where your signal gets clipped.

Yes a single ended 12V power supply will get you more head room but it won't get you a balanced output line driver,
unless you use a passive bridging transformer to balance the output. Then you could use a single ended power supply.

Considering you can buy a mini mixer for $120.00 and be recording tomorrow, I don't see the point in building a circuit like this.

Find an older Roland, Rocktron, Sansamp, etc rackmount instrument preamp on ebay and get on with your recording.

[Pushtone]

The M-Audio Black box would be perfect for your application.

Balanced stereo out AND SPDIF digital too. $129.00

Anything you build with a bipolar PSU and balanced output would cost about $65 - $80 and would not have near the tonal control.

http://www.musiciansfriend.com/product/M-Audio-Black-Box-Guitar-Multi-Effects-Processor?sku=151083

Enough said.

[tenchijin2]

Point taken. Can't argue with that analysis.

Thanks!

[LOTUS]

Build the country hick, i'm sure you will be happy. active transformer di. Best of both worlds.

[tenchijin2]

I probably should build one, for the practice, anyway!