Hum! - BHK Pre with BHK 300's

I’ve been plagued with issues for 3+ months now since I bought into psaudio.

Here is a bit of a recap on past issues

I am now on my 3rd set of equipment. This set thankfully has none of the weird issues like previous equipment, except for one. HUM, when running unbalanced.

When I run single ended, I have terrible hum from my speakers that can easily be heard 10+ feet away.

Balanced, this time around, quiets everything right up instead of making it worse like in the previous set of gear.

Sure, I could just run balanced out, but I don’t own a decent set of balanced cables, so in my opinion that is another cost I have to incur for no reason. The amplifiers support single ended so it should work properly, especially when spending this much on the equipment.

I have tried everything to eliminate the hum, and am throwing out a last hail mary for help with this.

All my testing is done with nothing more than just the preamp hooked up to the amps and then out to speakers. No source components hooked up.

I have tried

  • different speakers
  • different power bars/distribution blocks/basic splitter cords
  • different cables (speaker, interconnects, power)
  • I isolated my entire electrical panel, removed EVERY SINGLE circuit in the panelboard from the breaker/neutral/earth and unplugged every single device in my house so that the audio circuit is totally isolated with absolutely no potential for a ground loop from anything else in my home.
  • I ran extension cords to the neighbours
  • I removed the ground feeding my audio equipment circuit
  • I tried shorting pins 1/3 on the xlr connectors while using single ended

The only thing that has had any sort of success is putting either a cheater plug on the preamp or a cheater plug on the 2 monoblocks. And even this still doesn’t nicely solve the problem.

When I had the earth connection lifted from my panel to audio equipment I still got hum. So it definitely is not a grounding issue in the true sense of that third pin going back to a common point earth connection.

It was only when I added the cheater plugs that it helped (with and without ground lifted on the circuit).
This tells me that it is some sort of an issue when that third ground wire bonds all the equipment together back at the power bar or wherever equipment plugs in.
It makes no difference if that third wire actually goes back to earth or not. Just connecting the chassis of all three pieces through that third wire via power cords is doing something funny. I assume because the ground of the single ended is also connected to chassis?

Anyways, this is a plea for help. PSaudio has thrown in the towel and has no other recommendations except to just use balanced. I refuse to believe that I should just throw more money at this to buy a new balanced cable and ignore the fact that one of the available options, that I paid a lot of money for, does not work.

What am I missing? I feel like I’m going insane. I have spent an obscene amount of time troubleshooting and researching how to possible fix this. I’ve drove an insane amount of hours to pickup and return 3 sets of gear now. Somebody please help!

Have had ground loops in my system before and they are no fun. Currently have a BHK pre and 300 amps with no such problems.

Which sources do you have in your system? Phono. CD, TV, and/or Video? And, which speakers and/or subs are you using?

Can you post a few pictures of your basic set up and various connections? Also, is the hum typical of the sound of a ground loop or amplifier transformer? Can you record the hum and post an audio file here? Might help some of the would-be diagnosticians here. Finally, are you running any subwoofers? If yes, how are they hooked up? Good luck.

From the Fremer review in Stereophile over four years ago so well known.

" Though the BHK Signature 300s are fully balanced, I ran them single-ended, from my single-ended reference preamp, the darTZeel NHB-18NS. Everything was plugged in to my single, dedicated AC circuit, but I ran into a hum problem—which, in my system, happens only with some balanced amps that are being operated in single-ended mode: Keep that in mind if you run single-ended and are considering the BHKs. Cheater plugs took care of the hum, and I was subjected to only occasional lethal shocks (kidding)."

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Are you running balanced or single ended out to the amps?

This hum is with no sources hooked up.
If I hook sources up it make no difference.

No subs. I’ve tried with 2 sets of speakers a pair of 90db Sonus faber and 86db revel.

I’ll try and post the audio, need to host it somewhere.
The hum is no a transformer. It’s 100% coming from the tweeter. Volume on preamp makes no difference.
I have no subwoofers. This is at its most basic level. Amps, preamp, interconnect and speakers. Nothing else.

I’ve seen that. He was using a different preamp though. One would think having the matching preamp would not create this problem.

10-4. “Principles” aside. Have you listened extensively to the system with a cheap (or not) pair of balanced cables? If yes, is the sound mediocre, good or great? It is your prerogative, but if all is good with balanced cables and you are otherwise a happy camper, I would toss in the best set of balanced cables I could afford and call it a day.

For what its worth.

Again, good luck with the trouble shooting.

When does the hum first appear? If you have only the amp connected to the speakers, with nothing connected to the amp, is there a hum?

Then, do you get hum when the preamp is connected to the amp with nothing else connected to the preamp?

That is correct. Just amps powered up and connected to speakers it is just very slight white noise that I need to put ear close to speaker to hear.

If I connect interconnects from amp to preamp (with preamp off), I get hum coming from speakers that is audible from 3-4’.
Then the as soon as preamp warms up and clicks on… forget it. Can hear it right across the room.

Again, this is all without any sources hooked up to preamp. It actually makes no difference if there is a source connected or not. And makes no difference which input is selected on preamp.

I have only used XLRs with my BHKs. My previous groundloop issues were source related and removing the offending source fixed it. Yours sounds different.

Would it be too much to ask you to try running unbalanced cables from your pre to the amps if you have free time to see if you get any hum without sources connected. No big deal if you can’t.

Just would be nice to hear from somebody else that has bhk pre and bhk monos with single ended.

I have done it with two different preamps plus the BHK preamp and running unbalanced causes a hum with the BHK amps. A “good” set of balanced cables even used costs less than the time and gas money you have expended. Brand name on the preamp doesn’t matter.

When interconnects from amp to preamp and there is hum, the amp and the pre are plugged into the same outlet and there are no power cords or other sources of interference near the interconnects?

I am assuming yes and, if so, it appears balanced is the only way to go.

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Unless I’m missing something this indicates it is the pre. Perhaps try another unbalanced preamp if you have access to one.

I have the BHK pre and 300’s running balanced for mid/twt and also use the unbalanced out to a BHK 250 for bass. There is no hum in the bass drivers even up close and just a little hiss in the mid/twt’s.


Yup, plugged into same source of power, of which I’ve tried many. And I’ve made sure over all the testing to make sure the power cords are as far away as possible from interconnects.

I don’t think it’s the preamp. Like a previous poster just mentioned he had same thing with various preamps. In past testing I had same problem with a Cambridge audio preamp. I think it comes down to the amps. And the 250 may be designed slightly different than the 300s? So may be why you don’t get anything from your bass driver in terms of noise.

The two amps are not designed differently. He doesn’t get a hum from the sub because there is already a balanced connection to the preamp. This really is simple. It has nothing to do with other connected devices or your electrical system. It’s either cheater plugs on the amp like Fremer or a set of balanced cables.

Have you tested your outlet to make sure ground is actually wired.

Also, there is a possibility that neutral is jumped to ground at some place other than the main breaker box in some homes. That will cause ground loops.

Because of this, try other outlets around the home on different breakers.

Because balanced works, it’s showing that there is common mode noise riding on the negative in single ended which may be indicative of a miswired ground.


Excellent thinking.