KH80 - transformer hum?

[Fingerbib2000]

Hi all,
Just received a new pair of neumann KH 80s and there is a very noticeable hum from them. It increases to a much louder level as I increase the output level switch to the loudest setting. The speakers have no audio source attached. Is this normal? It's very disappointing as I can hear the hum at a sitting distance of 1 meter with the output set to 100db. I will post a video example in the morning.

 

[somebodyelse]

As you'll see in the teardown thread there is no mains transformer, so that won't be the source of any hum. My guess is that it's the floating input that's the problem, and that if you short the input or attach a source the hum will disappear.

 

[Fingerbib2000]

Thanks, Good to rule out transformer.

FYI, there are no audio cables attached during my testing, it's just the speaker connected to mains.

See vid attached in link (you may need headphones to hear the"hum").

VID20220921124748.mp4

MP4 File

1drv.ms

Am I being too precious/unrealistic here and that this is just the way they are? I can hear the hum from 6m away when it's switched to 114db. at 100db, during the day, I can barely hear it from 1m away (but late at night when it's quiet I can clearly hear it).



Both speakers exhibit same behaviour so I guess it's in the design, but it's out unrealistic to expect them to be silent re: hum? High end hiss from the tweeter is one thing, and that is clearly called out in the marketing literature as being silent at 1m and I'm happy with that but I was not expecting the hum!

 

[somebodyelse]

By floating input I mean there's nothing connected - that's not a normal usage situation, and in combination with turning the sensitivity up you may hear some hum or pick up other interference. Normally you have a low impedance source connected and powered up like a DAC, audio interface or preamp, and the hum and interference will probably disappear, assuming you're using balanced interconnects. If the source is powered down then its output may be in a high impedance state and you may get hum/interference again. This is a general situation not something specific to the KH80s.

 

[HarmonicTHD]

Yes. Hook up an audio source via XLR or shorten the XLR pins. If the hum still persists then return the speakers.