Project DI BOX

[Atk]

Hi Forum

I'd like to connect my "LINE OUT" of the amp to mixer but I hear a zzzzzzz.sound.. :x

I need a DI BOX...
I'd like to build it but I don't want use a trasformer inside. :wink:

Is it possible to biuld a DI BOX with some NPN or PNP or other Transistor? :?:

Have you got some schematics and layout to do it?

Bye


:wink:

Atk

[martinbertrand]

Hi,
I am working on something like that actually.

I plan to use the SSM2142 chip from analog devices.
There is a shematic in a german file that uses that device.
http://www.muziek-gg.com/koerier/koerier%203%2001.pdf

I got the chip free as a sample from the company http://www.analog.com/. They sent it free of charge by`UPS.  Ain't life good ?

The chip is a cheap alternative to the passive DI using a transformer. The transformers are pricey.

you can also check out Craig Anderton's DIY projects for guitarists. There is a Project called IGGY that is a Direct Injector. There is a layout available at General Guitar Gadgets. //www.generalguitargadgets.com

Keep us posted on your project.

[brett]

search the archives.  www.dse.com.au has a kit for AU$40 (US$30).  The kit was published by silicon chip magazime a couple of years ago.

cheers

[Mike Burgundy]

Be advised that it may also be a groundloop problem - a DI might not solve that!
If it's nice 50Hz or 100Hz (or 60/120 in the US) then it might very well be a groundloop.
A basic DI is just a device that produces a balanced signal (consisting of regular phase called "+", reversed phase called "-" and ground) out of a non-balanced signal (which is normal phase signal and ground)
That, and the ability to supply some current and drive a long line and cater for different in-and output impedances, and and.... Can be done with one opamp, or even one tranny, although there's some drawbacks to that. A simple one dual-opamp version should do you fine.
Do a forumsearch for DI and you'll get lots of ideas for DI's, with and without transformers.
If it still hums with a DI, you have some isolating to do - look for the ABY boxes on GEO for that. OR you build a DI with built-in groundlift, 'course!

[brett]

OR you build a DI with built-in groundlift, 'course

Mike's on the track here...ground loops are common and painful.
That kit and design I referred to include an earth lift switch.  Surely someone in the states and europe make such kits.

[llamma]

if you do build a DI Box using any of the above options (ssm2142 being the simplest altho it needs a bipolar power supply) then adding a ground lift is as simple as adding a spst switch on pin 1 of your xlr socket, all it does it literally lift the ground out of the circuit

i am still working on the ssm2142 circuits, i have built them into my bass preamp and acoustic preamp at the moment i am getting some hiss but i think i know the answer to that one, when i get the units back on sunday i'll have another go at them,

regards
Blair

[Mike Burgundy]

Although this does work, it might be troublesome if the noise comes from other sources, be dangerous if there is no grounding at all (then its you) and phantom feeding the circuit is right out.
If memory serves, this is often solved by not *disconnecting* ground, but connecting it through a small resistor (10 Ohms should be perfect) and 10n-1u cap, I think. That should take care of at least most loop hums.
hih