To Doug Schneider,

I read your measurements of the Luxman M-900u amplifier and found the output noise values for the unbalanced and balanced inputs to be strange. The value for unbalanced was so much better than the balanced (up to -10dB). Was this a feature of the Luxman M-900u or did you mistype the values, and the values for the balanced and unbalanced inputs have been swapped?

Thank you,
Hieu Nguyen

It’s been a long time since the M-900u review was published (in April 2015) but the values are correct, as far as I can recall. While balanced connections and circuitry can have reduced noise compared to single-ended connections and circuits, that’s not always the case. It all depends on implementation. The M-900u isn’t the first product to show that behavior, and it definitely won’t be the last. It’s possible that the extra circuitry for balanced connection in the M-900u bumps up the noise. That doesn’t negate the benefits of a balanced connection, however—if common-mode noise is picked up on the cable coming into the amplifier, the balanced input will cancel it out while the unbalanced one won’t. So there still could be a benefit from using the amp’s balanced inputs.

Regardless, I wouldn’t allow that to deter you from buying the amplifier, even if you’re going to use a balanced connection. When I reviewed the M-900u amplifier, I used it with the companion C-900u preamplifier, which I also reviewed and wrote about the previous year. I used balanced interconnects to connect them and found the setup to be quiet, so whatever noise that exists in the balanced input is not significant. In fact, that’s still one of my favorite preamplifier and amplifier combinations. . . . Doug Schneider