Grace Design m303s High Performance Active Stereo DI

Two channels of Grace Design’s transparent active DI, with custom Lundahl transformers, full galvanic isolation, and phantom power operation.

The m303s puts two channels of Grace Design’s m303 active DI into one chassis. It comes from Grace Design of Lyons, Colorado, and it is built in the USA. Each channel takes a 1/4" instrument or line signal and converts it to a low-impedance balanced signal on XLR, ready for a mixer, stage box, or recording interface.

The design goal is transparency, and the numbers support it. Each input is a FET stage with 1M ohm impedance, high enough that passive pickups keep their full tone. Each output passes through a custom-wound Lundahl transformer from Sweden, with a high-nickel core for headroom and a mu-metal shield against hum from nearby gear. Bandwidth runs from 20 Hz to 80 kHz, and output noise is -118 dBu A-weighted. In practice that means a direct signal with solid low end and natural top end that takes EQ and compression well later.

Two channels open up a lot of uses: a stereo pedalboard going straight to the house, keyboards, a dual-source acoustic pickup system, a laptop, or two separate instruments for a player who doubles. Each channel has its own input, Thru jack, pad, and XLR output. The two inputs share a common ground, which is worth knowing if you plan to run two unrelated rigs through it.

The control set is short on purpose. A 13 dB pad on each channel raises the maximum input from +14 dBu to +27 dBu for active pickups and keyboards, and a red peak LED warns you 3 dB before clipping. The Thru jacks are wired in parallel with the inputs to feed a stage amp. A GND-ISO switch separates input ground from output ground for full galvanic isolation when a ground loop shows up.

Power comes entirely from 48V phantom, at 4 mA maximum, through either XLR. Grace recommends supplying phantom to both outputs when you are using both channels. All of it sits in an extruded aluminum chassis with 1/4" walls, recessed connectors, and gold-contact toggle switches.