On a previous post, I posted a schematic of a passive direct box using Jensen Transformers
I have a ROLLS DB25 passive direct box in my studio so I decided to open it up to see it's "guts".
The ROLLS DB25 is an inexpensive direct box using all passive components. That's right, no need for a 9V battery or wall wart to use this thing. Plus, it's got a transformer inside that takes care of converting from an unbalanced Hi-Z connection (from a guitar) to a balanced Lo-Z connection for connection to your mixer or preamp via XLR jacks.
In addition, it has a -20dB and -40dB pad, and a ground lift switch for "stubborn hum" reduction.
This DI box is very inexpensive at less than $30 per unit.
Input impedance is 50Kohms, with an output impedance of 600ohms. Max Output level is +4dBm (loaded). Frequency response is 50Hz to 15Khz +/- 3dB. Okay, I know what you're thinking... only 50Hz? Only 15Khz?
Before you get crazy, this unit's application is for electric/bass guitars. You don't need 20Khz response or down to 20hz response for this application.
So let's crack open this thing and see what makes it tick.
The unit's case is made of steel. This gives you strength and it's small size is perfect for the cramped stage (or recording studio).
Here, you can see the -20dB/-40dB pad switch and the ground lift switch. You can also see the XLR male output jacks.
And these are the guts inside the unit. I've labeled them for easy identification. If you buy the unit, there is a schematic included so I won't bother posting it here.
This is a nice unit featuring transformer-based isolation. Additional features like pads and ground lift switches makes this a versatile unit. You should have at least one in your studio! Come on... it's cheap at less than $30. Click here to BUY this DI Box.