Focal Kanta No. 2 Speakers hum with speaker with speaker cable disconnected
Hi folks,
I'm a new member, and I couldn't find a solution for the specific issue I'm having on google. I'm thinking maybe someone here has any ideas on this weird issue.
As the title states I've stated noticing a hum emanating from the speaker's mid range woofer, specifically the left speaker. I only noticed it after upgrading my phono stage, which had a hum issue from the get go (not a ground loop or line hum evidently). Took about 2 months for my dealer and Pass Labs to send me a replacement unit. Long story short, same hum is still there, so it obviously wasn't the phono, though rotating the phono 90 degrees relative to the speaker reduced the hum. Did a bit of cleaning last week and noticed that the left speaker was humming at a very low volume, only noticeable when your ear is close to the woofer. The preamp, phono, power amp, and turntable are all turned off, yet I'm getting a hum that's unexplainable.
I disconnected almost all of my components' power and interconnect cables (Pre/Pro, Phono, DAC/Streamer, Turntable power supply) one by one hoping that any source of interference/hum could be identified. I also disconnected a separate power strip that powers the Router, TV, Philips Lights, and Apple TV with no change in the hum. For reference, my audio gear is fed by a Puritan Audio PSM 1512 mains purifier, pretty clean power.
For some reason I decided to disconnect the speaker cables to switch them around and there I noticed that the speaker is still humming very faintly with no speaker cable connected. My thinking at that stage that it might be some sort of wireless interference, so I unplugged anything that has bluetooth/wireless functionality. All of the audio components were disconnected from power as well. I noticed then that it's the exact same hum that the phono has been plagued wit all this time, but amplified at a much higher level. Maybe the phono cart is picking up this minute hum and sending it to the phono. I left the speaker for an hour to see if it discharged any of the crossover components that might be causing this, nope, still humming. 6 month old speakers so I'm thinking it's unlikely a bad cap, although possible.
I'm really out of ideas on how to sort this out. I did experiment with grounding wire paths, and ground lift adapters/DC blocking adapters when I thought the issue was with the phono stage, was not successful. Anyway any thoughts or ideas would be greatly appreciated.
Leave it shorted for 30 minutes. If the problem comes back after removing the short it’s EMF from somewhere, and also damn weird! If it vanishes and stays vanished it’s more likely to be a DC charge happening (could also be a combination of DC + wonky crossover). Since it doesn’t matter where in the house it is, or how it’s turned around it is unliekly to be EMF though. In any event, spend $40 on a multimeter and measure the DC on your amp outputs.
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OP:
I think you misunderstand me. DC on the AC input is very different. DC on the AC line causes mechanical transformer hum in the amp. DC on the amplifeir's output is caused by improper biasing or leaky coupling caps. Measure the amp's output terminals. DC should be near zero. Any significant DC could charge the crossover caps and cause oscilation when the input is removed. |
Moved speaker, same problem... shorted the outputs, problem gone. Other speaker is (and has been) quiet. Time to give Focal a call. Looking at their literature, they developed what they call a 'Neutral inductance Circuit" which does balancing act with the driver by making the magnetic field independent of the voice coil position, frequency or current. Something is not up to spec in that circuit and it's the surrounding emf couples a voltage to it enough to move. |
Thanks Erik for clearing up the mix-up. The measurements quoted above are the amp’s DC offset, I chose the right speaker binding posts but the left should be the same, no? I’ll try again when I get a new meter. Forgot to ask what’s an acceptable range of values for DC offset? I saw 100mV as the maximum acceptable value on the web, any truth to this? In the meantime, I’ll contact my dealer and Focal, and swap the right and left speakers to confirm it’s just the one speaker. Based on the what’s been mentioned above, it’s seems that there is definitely something wonky with the speaker’s crossover. Caused by their "Neutral inductance Circuit" not working as intended as @gs5556 has kindly brought up, or a malfunctioning component. So far I can’t find anything that leads me to suspect an environmentally induced hum. Quite the head-scratcher this had been. Again, thank you all for the help! Edit: Typo |
