NAD 375 hum

manyhobbies

manyhobbies

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Hi all. I just bought a new NAD 375bee. I have had an NAD 372 for several years. My question is about a slight hum in the transformer of the 375. It's more pronounced at startup, then gradually fades to a very low hum, or completely away. It's not audible more than about 2 feet from the amp and isn't heard over the music, even during quiet passages. Is this considered normal? I never noticed it with my 372. I know the transformer is much larger than the one in the 372, and the 375 outperforms the 372 in every respect. Should I return this one for another copy, or will it be the same. It's not bothersome, if it's the nature of the beast that's fine, but just don't know if I should exchange it. Any suggestions? Hopefully from other 375 owners.
 
I own the C356BEE and has zero hum, have heard the C375 and don't recall any humming even on very high efficient rated speakers....If still under warranty no harm in sending it in..
 
The hum isn't in the audio output at all. It's dead quiet, just like my 372. The hum I'm wondering about comes directly from the transformer. After hooking my 372 back up, and really listening, I realize it too, makes a low hum from the transformer, although barely audible. I'm thinking it's likely normal, but just looking for experience from other folks, with the 375.
 
So with no speakers connected, no source gear connected or on, just the amp on you hear a hum?
I would send NAD an email and ask them if this is normal
 
Put it on the floor and check, probably bad vibrations..
 
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I haven't tried it with nothing connected, but I will. It's definitely not coming from the speakers. I can crank the volume up all the way without any source input and it's dead quiet. I'm no electrical expert, by a long shot, but it sounds like it comes directly from the torrid transformer. Please don't misunderstand me, this is not an issue that degrades from the listening experience. I'd just like to know if it's normal operation for my $1500 dollars? Or is it some condition that will limit the life of the unit. Would really like to hear from others who own this unit. I don't always trust manufactures to fess up to their faults. But I will ask NAD if no one can shed some light on it.
 
Thanks so much for the link RH67. I did check my line for DC with a multimeter, per a suggestion from someone on one of these boards, and it showed about 8 volts. The DC filter is something I'm interested in, even before the 375. I will be ordering one asap.
 
I had the same deal with a vintage McIntosh power amp. It was in a rack on the bottom and I could hear it if I was standing near it. Really bugged me. I checked everything that I could inside it and didn't find anything wrong so I just gave up and let it hum.

A couple of months later I noticed that it had stopped humming. Although I never checked, I also assumed that it was from DC.

Just checked my 275BEE (brother to the 375BEE) and it's dead silent.

Murray
 
I have asked NAD through their product support e-mail. We'll see how long it takes for a response. thanks everyone.
 
Transformer lamination/winding noise is a common problem and in my opinion, on a new amplifier is COMPLETELY unacceptable. Honestly, it is slack QC and the transformer should be replaced under warranty or you should get another amplifier altogether. Consider it is one of their 'Holmgren' toroids and what's the point of having a fantastic S/N ratio if the transformer makes enough acoustic noise to mask low level detail?
I've come across many amps over the years with transformers I regard as sub-standard in that regard and many hundreds more that are perfect.
Do not accept it as being 'normal' - it is not. A tiny buzz when you put your ear on the case is normal- if you can hear it from 2 feet away, it's a junk transformer.
 
Just ordered the DC Filter RH67 linked for us. We'll see if that helps. Listening to some vinyl, John Mellencamp as I type this. Man this rig sounds awesome. This amp is only about a week old, hopefully the transformer is a non issue. After several hours of playing it makes only a tiny bit more hum than my 372. Can only hear it at a few inches away. Maybe it will settle in, it sure sounds out of this world.
 
manyhobbies said:
Just ordered the DC Filter RH67 linked for us. We'll see if that helps. Listening to some vinyl, John Mellencamp as I type this. Man this rig sounds awesome. This amp is only about a week old, hopefully the transformer is a non issue. After several hours of playing it makes only a tiny bit more hum than my 372. Can only hear it at a few inches away. Maybe it will settle in, it sure sounds out of this world.
Click to expand...

Cool, it sure worked to get the DC filtered with the LM amp. Let us know how it works with the NAD.:thmbsp:
 
Thanks so much for all the replies. Right now I'm keeping my fingers crossed, because I may have found the problem. I had an MIT Z power stabilizer hooked to the same outlet with my turntable and preamp plugged into it. I decided to unplug it and see if it helped. Well, it did, I hope. Now the 375 is dead quiet. I will try it again in the morning to see if it's still gone. I'm hoping this was it. The 372 didn't seem to mind the stabilizer, but the 375 looks to have a much larger transformer. We'll see.
 
^ Glad you found the problem...did not think to ask if you had any power conditioner stuff connected. Last night for shits and giggles I disconnected all my sources and speakers and only the C356BEE was powered on and I stuck my ear to the left side where the transformer is and I hear ZERO.
I do believe the C375 is a larger transformer but still...glad I hear nothing.

You can always put the MIT back in and see if the humming returns, if so there is your culprit.
Happy listening that is one beast of an amp!
 
Thanks so much for everyone's response. Taking out the MIT Z stabilizer seems to have solved the problem. NAD responded today. Not bad, within a day of the question. They said, "Slight hum is normal when you are close to the unit. Incoming AC power fluctuations can cause a slight mechanical noise in the transformer. If the hum was emanating from your speakers or headphones we would recommend it be serviced at your nearest NAD authorized repair center." An acceptable response I would say, just glad it's resolved. I'm off work today so I've been spinning vinyl for a big part of it. Turned the unit off and back on several times, and no hum. Happy, happy, happy. And this amp is by far the best I've ever owned.
 
hey manyhobbies - just saw this thread. I checked my NAD - it's plugged into a power conditioner -it's dead silent. Nothing. I put my ear right over the case and could hear nothing.

You're right - it's a great integrated amp. I recently just purchased and installed the MDC DAC 2 into her. Streaming music to it sounds almost as good as my McIntosh MVP 861 player.
 
KptKrunch said:
hey manyhobbies - just saw this thread. I checked my NAD - it's plugged into a power conditioner -it's dead silent. Nothing. I put my ear right over the case and could hear nothing.

You're right - it's a great integrated amp. I recently just purchased and installed the MDC DAC 2 into her. Streaming music to it sounds almost as good as my McIntosh MVP 861 player.
Click to expand...

Question on the DAC2.0.....what is the Phono switch for?
 
The phono switch is there because you can only use the one input on the amp. If you have both the PP375 and the MDC DAC installed, you need to put the switch to 'phono' to listen to your turntable thru the PP375, otherwise it will default to the DAC (with the disc/phono input selected on the amp).
 
KptKrunch said:
The phono switch is there because you can only use the one input on the amp. If you have both the PP375 and the MDC DAC installed, you need to put the switch to 'phono' to listen to your turntable thru the PP375, otherwise it will default to the DAC (with the disc/phono input selected on the amp).
Click to expand...

Ok thanks makes sense.....my C356BEE only has one MDC slot, so with two I see now.
 
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