audible hum from the BHK 300 Mono's


#1

Hi all,

How silent should the 300 mono’s be? I can hear a hum from each unit that is audible to me from my listening seat 3m away. It is low level but always there - I may just happen to be susceptible to this frequency range.

The 1st thought was DC induced hum (even though my other amplifier which has a larger transformer than each mono unit that amp doesn’t hum) so I purchased a DC Blocker, no change.

Cable dressing hum is not an issue as the speakers are quiet.

The set-up is as follows;

3 Dedicated AC lines for hifi.

PS Audio P10 (either direct from wall socket or with DC Blocker from wall socket and P10 plugged in to that) feeding the S300’s (and also the Quad2905’s).

Separate AC cct powering;

PS Audio BHK Pre, DS-DAC, PWT. All interconnects are XLR-XLR.

Ambient noise level at listening seat is 35dB (using Iphone Decibel 10th app)

Iphone at rear of S300 (1cm away from access/vent grill for tubes);

No power to amp = app reading is 35/6dB

Power via P10, S300 power switch on (I) = app reading is 41/42dB

Power via P10, S300 power switch on (I) + initialised (S300 front blue light continuously on) = app reading is 41/42dB

Result is exactly same if P10 power is supplied via DC Blocker.

Result is same if speakers connected or not and if signal leads are connected or not.

Any thoughts? I don’t like hearing a continuous, low level hum when the room is quiet so I’d like to eliminate this if at all possible…


#2

Have a hum issue with my BHK 250. Have to pull the ground on the power cord. I bought a PS power cord just for this purpose. Keep getting told it’s a ground loop but don’t believe it (I’m pretty good at trouble shooting: I’ve checked all the obvious stuff). I do use unbalanced interconnects but still…


#3

If pulling the ground removes the hum, you have a difference in ground voltage potential a/k/a ground loop. Tracking it down can be an incredible bother.


#4

I also tried removing the ground pin from the power cord to the P10 and the result is the same, except I ruined a cord in the cause.


#5
frank7036 said Hi all,

How silent should the 300 mono’s be? I can hear a hum from each unit that is audible to me from my listening seat 3m away. It is low level but always there - I may just happen to be susceptible to this frequency range.

The 1st thought was DC induced hum (even though my other amplifier which has a larger transformer than each mono unit that amp doesn’t hum) so I purchased a DC Blocker, no change.

Cable dressing hum is not an issue as the speakers are quiet.

The set-up is as follows;

3 Dedicated AC lines for hifi.

PS Audio P10 (either direct from wall socket or with DC Blocker from wall socket and P10 plugged in to that) feeding the S300’s (and also the Quad2905’s).

Separate AC cct powering;

PS Audio BHK Pre, DS-DAC, PWT. All interconnects are XLR-XLR.

Ambient noise level at listening seat is 35dB (using Iphone Decibel 10th app)

Iphone at rear of S300 (1cm away from access/vent grill for tubes);

No power to amp = app reading is 35/6dB

Power via P10, S300 power switch on (I) = app reading is 41/42dB

Power via P10, S300 power switch on (I) + initialised (S300 front blue light continuously on) = app reading is 41/42dB

Result is exactly same if P10 power is supplied via DC Blocker.

Result is same if speakers connected or not and if signal leads are connected or not.

Any thoughts? I don’t like hearing a continuous, low level hum when the room is quiet so I’d like to eliminate this if at all possible…

It sounds like the hum is coming from the units and not the speakers, since when you disconnect the speakers the hum remains. Is that right? And if that is right and you verify that, and a DC blocker has been applied yet doesn't do anything, then it might be the intrinsic hum of the internal transformers. I never hear that and so it's never bothered me, though the amps are many feet from me. Besides, if you're running the P10, then there's no need for a blocker since the P10 will do that for you.

I would start by narrowing down exactly where the hum is coming from - be a good sleuth and then report back.


DC offset/humming/P10/P15
#6

My guess would be you have a bit of DC on the line causing the transformers to hum, but you have a DC blocker.


#7

Yes, I have ruled out DC and I believe I have ruled out induced hum from cables or voltage imbalance so it leaves the units themselves. I believe I have demonstrated with the dB meter that the units do hum, it is a question of how loud is acceptable?

My listening position is ~3m from the amplifiers and it is audible.

I have a audio friend coming over today to listen to the new setup (pre + amps) so he will be able to provide a 2nd opinion. I will report back. It is more audible from the rear.

Thank you to everyone’s input.

Cheers Frank


#8

Most transformers hum a bit, but audible at three meters strikes me as excessive.

Do they make an equal amount of noise? If it is the same and are audible at an equal distance I suspect something other than the amps as both cannot be flawed. Yet, maybe they are just noisy enough and your space is sufficiently quiet.

I would guess power as I understand voltage can vary a great deal in Australia, but you have a P10.


#9

Elk it is the amps.


#10

That certainly appears to be the case. The question is why.


#11

I haven’t been able to identify exactly where in the units hum is emanating from - I think I’d need a stethascope (jut putting my ear to the unit doesn’t cut it) or take the casing off. I’ll have another listen tonight.

On another note - whilst comparing the sound quality with and with out the BHK pre-amplifier in my system I had the left channel S300 drop ~4dB in volume at the speaker.

I was testing the sound quality of the DS/BHK-pre/S300’s or DS - direct to S300’s.

After swapping once or twice (by putting source & pre into stand-by, swapping over XLR interconnects, then beginning listening again) I noticed that the imaging was a bit off and to check it wasn’t my hearing I ran the Chesky Records Stereo set-up test CD, Track9 / Left & Right channels alternating a reference pink noise burst.

Measuring each speaker @1m with a tripod mounted SPL meter the left channel was down -4dB on the right speaker.

Just in case I had inadvertently messed with balance settings in the sources (both pre or Dac) I put the DS in standby, swapped the interconnects over, left - to - right and right - to - left) , so the DS was connected direct to the S300’s and replayed the test track. Same result. Left channel was down compared to right.

I then powered off the left S300 (both front and back switches) and hard restarted - everything back to normal.

Is there a protection circuit in the S300’s that somehow I tripped that would cause this?

Cheers Frank


#12

Boy, that’s an odd one. No, haven’t heard of anything like this nor are there protection circuits that only partially turn it down. Weird. I always now look on the preamp display to make sure the little (and hard to notice) triangle to the right of the display isn’t active. That indicates a balance control adjustment has been made. It seems to happen easily - and I might be pushing a balance button inadvertently. Might have been that, but if it was, that shouldn’t have corrected itself.


#13

Coming back to the question of hum - it hasn’t gone away and I’ve lived with it. However, if I want to track it down is there a tutorial on the web on how to dismantle the casing of the BHK300 or is it simply undo all the screws and carefully remove panels? Are there any tips/tricks I should follow?

Thank you in advance

Frank