BHK Pre Humming After Plugging in Cables

Hi all, is it required to turn off the rocker switch on the back of the BHK Pre when plugging & unplugging interconnect cables? While playing with my TT earlier, I plugged in a set of RCA cables into Input 4 after only turning off the front switch (PS Audio logo). Once turned back on, there was a fairly loud transformer-like hum coming from the BHK Pre, and it wouldn’t go away until I turned off the rocker switch on the back and waited for a few mins. I was able to duplicate this with other input slots as well. Is this normal or something wrong worth checking it out?

It’s not actually off unless you turn off the rocker switch on the back only in standby with the tubes shut off.

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And it certainly is not necessary to turn off the rear panel rocker switch to swap cables. Just use the front panel standby button.

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Thanks. Looks like a call to the customer service is in order. For those interested, here is a video capturing the hum after I unplugged the interconnect cables while in standby mode.

The BHK’s manual says that is not correct.

“When in standby mode, all the internal solid state circuitry
such as the headphone amplifier, voltage regulators and high current output stage remain active, while
the input vacuum tubes are turned off, thus preserving their life.”

Better safe than sorry used to be common practice not convenience first.


The manual is correct though I am unclear where the disconnect his happening for you. Do you mean that because the power amp is still active it’s best to shut off the rear switch when changing interconnects or speaker cables?

If that makes you more comfortable then by all means do that. My point was it is not necessary. When in standby mode the bias is reduced, the input stage is off, there’s no danger to removing or connecting interconnects.

After being in this hobby for 50 years we will just have to agree to disagree. I would never encourage someone to change cables on a piece of audio gear that is still powered up in any manner which the BHK obviously still is per the manual. What is an extra couple of minutes to power it down versus a possible service call. And yes you don’t need to change any cable to any piece of gear with it powered up. The only exception I am aware of involves some gear allows “hot swapping” of USB cables but some like the newest Auralic streamers don’t allow that anymore. So no disconnect happening at all.


What was connected on the other end of the cables that you are connecting? It seems like there must be some kind of potential traveling on the cables from whatever is on the other end of those cables.


The other end is my phono stage.

Can’t say exactly what might be causing the hum. That said, call me a Nervous Nellie but I completely power down everthing before pulling or plugging in cables. All my source components are plugged into my power conditioner. I flip the master switch off.

It simply isn’t worth the risk of a fumble fingered blunder.