BHK 300 Mono Volume Difference Due to Tubes?

I am noticing a slight tilt in volume or balance to the right in my system that I didn’t notice a month ago. Adjusting the speaker balance in Roon it looks like a 1.5 dB difference. After swapping various things around I’m guessing that this problem could be coming from my BHK 300’s, the speakers, or perhaps some change in my hearing or room configuration. As far as I can tell it has nothing to do with my BHK preamp or R26 DAC. Speakers are Magnepan 3.7s.

Because of the position of the monoblocks and the length of my cables it wouldn’t be easy to isolate the cause of the problem further. So my question is whether the tubes in the BHK 300’s could be aging at different rates resulting in some imbalance in gain that translates into the small imbalance I am hearing?

I am playing a lot more vinyl so adjusting the speaker levels in Roon won’t work for vinyl and as far as I can tell the BHK preamp doesn’t have a balance adjustment? Is there a cheapish but high quality balance control I could add to my system if it turns out the problem is ears or room related?

The BHK pre does have a balance adjustment but may not have a fine enough increment to fully correct your approx 1.5 db difference; however it’s easy enough to try.

Less easy is to switch the 300’s and see if the imbalance follows. If so you could then switch tubes around.

Coincidentally I also have 300’s and an imbalance (to the left). In my case I’m pretty sure it’s eustachian tube blockage since it’s better or worse at different times and I can “balance” the soundstage by pulling my right earlobe.

If you find the problem please let us know.


Did you swap the Pre output cables to see if the problem moves?

Thanks for that tip. I had no idea the BHK pre had a balance control. I had googled it before but all the hits were about the balanced inputs and outputs. Now that I have found the balance control that does mostly solve the problem. It is a bit coarse, ideally there would be half steps, but setting the balance +2 to the left is a big improvement.

I am still curious about the cause of the problem and whether different rates of aging in the tubes can cause a volume difference. I had my hearing tested a couple of months ago but I suppose even a low level infection could effect that.

Yes, I did switch the preamp cables. The problem isn’t in the preamp or DAC.

I’d suggest:

  • swapping right/left tubes on BHK Pre
  • swapping right/left BHK monos
  • swapping right/left speakers

If the low level follows the right/left exchange you have found the culprit. Otherwise you need to investigate deeper (room or hearing)

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Yep, day to day sinus variation has an effect for me.

Another possibility is room changes even minor ones. One time I had a soundstage shift and was frustrated trying to fix it until I noticed someone had moved bass traps about a foot out of the corner. Another time I forgot to close the listening room door.

I think the aging tubes/volume diff might be hard to answer. As the tubes age more anomalies will likely occur confounding the issue. To me the best shot is to replace the tubes now. If there is no change just use the old tubes until they need replacement. No financial loss and the replacements are there when needed.

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This might sound bizarre, but since you mentioned hearing, have you turned yourself 180 degrees to see if the volume difference stays with the same speaker?
I have done this at times when i sometimes hear one speaker louder than the other, as ear wax buildup does affect me from time to time.

That is a reasonable suggestion. It is a bit tricky to implement because of the room layout but I’ll see if I can give it a try.

No equipment. Just you.