Greetings. I just purchase a DM7 after reading Kal’s review. I’ve been waiting for a multi-channel DSD DAC at this price point for well over 10 years. I can finally abandon the compromised HDMI solutions I’ve been stuck with for playing multi-channel FLAC and DSD files.
One thread topic that caught my attention is connecting the DM7’s balanced ¼“ TRS outputs to a preamp with single end RCA inputs. It’s easy to do, but you must do it correctly. If you solder, it’s a simple cable build/modification. If you don't solder, you can have a company like HAVE, Inc build the cables for you.
A balanced audio line carries two signals over three conductors. One signal is the original and the second signal is identical except it is polarity inverted. The third conductor is the shared ground. At the balanced input, the inverted polarity signal is flipped back to positive and combined with the original signal. Any noise not in the original audio signal is now out of phase and gets cancelled.
For XLR balanced connections, pin 1 is ground, pin 2 is the original signal, and pin 3 is the polarity inverted signal. For ¼“ TRS balanced connections like the DM7, tip is the original signal, ring (the conductor band between tip and sleave) is the polarity inverted signal and sleave is ground.
To build a balanced to single end cable for the DM7, connect TRS tip to RCA center pin and TRS sleave to RCA sleave. That‘s it. TRS ring is not connected. Note: transformer balanced outputs to single end RCA inputs are handled differently but there’s no need to go into that here.
Here’s what you DO NOT want to do.
DO NOT connect TRS ring to the RCA connector at all. If you connect TRS ring to RCA center pin, you combine the original and inverted signals and the two cancel each other out. If you connect TRS ring to RCA sleave, you short the inverted signal to ground, significantly increasing distortion and potentially damaging the DAC’s output circuit.
DO NOT use a ¼“ TS plug (no ring conductor). A ¼“ TS plug will short the inverted signal to ground when inserted into the ¼“ TRS balanced output.
When the DM7 output is connected to a preamp with this cable, you get the original signal with no loss in fidelity. The output level will drop 6db since you don’t get the balanced input gain increase from combining the two signals. Not a big deal in most systems. You also lose the noise cancellation of a balanced to balanced connection so this is not recommended for long cable runs. But for connecting the DM7 to other gear in your rack, this is no different than any other RCA to RCA cable connection.
Russ
