NAD C 389 preout hum and final thoughts

[Randolf]

After expiring the mediocre residual noise floor of the Class-D amplifier speaker output of the NAD C 389 and the distorted headphone output I finally tried to use the C 389 just as preamplifier for the Yamaha R-N803D. But even this setup is problematic, there is a small ground loop hum I wasn’t not able to fully eliminate. You can mitigate it by lowering the power amplifier volume/gain, however since no other device I ever connected to Yamaha R-N803D had such an issue I guess the root cause is in the C 389. Finally, I did an A/B comparison of 2 setups

• WiiM Pro->MiniDSP DDRC 24 (with DiracLive)->Yamaha R-N803->Lowther Fidelio
• NAD C 389 (with DiracLive)->Yamaha R-N803->Lowther Fidelio

Although I used 2 different DiracLive measurements and different Microphones (UMIK-1 vs. NAD) there was no meaningful difference. My hope was that the superior DAC in C 389 could make an audible difference (justifying to keep the C 389) but the DAC in the DDRC24 just seems to be good enough for this setup.

Luckily, I was able to resell the C 389+MDC2 BluOS-D module+DiracLive license for 1200 Euro. Since I bought it or a good price, I just lost 230 Euro (not counting all the trouble I had in 6 month and the environmental damage caused by sending the C 389 9 times via DHL). I informed the buyer about all the problems I found in C 389 but since he runs low sensitivity Spendor Speakers and uses no headphones he seems to be happy with the C 389.

Finally, I had an opportunity to test my Grado GS1000i headphone with a NAD C3050, the C 3050 seems to have the same headphone amplifier issue.

My conclusion on the NAD C 389 is:

• Poor residual noise floor of the power amplifier speaker output
• Distorted headphone output
• Ground loop hum issue on the preout
• No 2 independent speaker pairs
• Limited range of the tone controls
• Rather user-unfriendly operation
• Good streaming capabilities
• Excellent DiracLive

 

[Randolf]

From DALI GmbH I received the following response regarding ground loop hum, which I cannot test since the C 389 is sold:

"Regarding the ground loop with your Yamaha device: This most likely occurs because the Yamaha doesn't use a ground pin on its power connector, whereas the C 389 does. In such cases, it usually helps to establish a ground connection between the two devices. The C 389 has a "GND" connection for this purpose."

 

[peng]

From DALI GmbH I received the following response regarding ground loop hum, which I cannot test since the C 389 is sold:

"Regarding the ground loop with your Yamaha device: This most likely occurs because the Yamaha doesn't use a ground pin on its power connector, whereas the C 389 does. In such cases, it usually helps to establish a ground connection between the two devices. The C 389 has a "GND" connection for this purpose."

They (dealers and such..), and I guess lots of forum people would say that, but in my own experience, tying the grounds together wouldn't work, though of course it might help. Key words in such talks are "might", "usually", or "rarely" lol... The thing is, it has mostly to do with the designs, some designs/implementations are just more prone to form ground loop with other connected devices, though most combinations don't typically end up with issues that is audible from even just a few feet from the speakers. I remember years ago, quite a few users of Marantz AV7005 had reported issues with ground loops when connected to their other gear and were apparently tough to eliminate, but I owned one and it had no issues whatever even when I had tons of AV devices connected to it.

So, be happy that you sold it, that's excellent damage control imo, instead of trying different things, you can now just enjoy the music.