Anyone having issues with a noisy channel on the BHK preamp

SDL, ,

Your last paragraph sums it up in my opinion.

Kevin Deal at Upscale audio thought so much of the Tungsram tubes 7dj8 that he included them with all preamps he sold. read my comments above. my 2 day experience with an expensive set of 6dj8’s was not good and they went back to Brent Jesse.

It may be that most of the issues we are all having here are from running NOS tubes that are not 12 volts.
With regards to keeping the unit? DO IT, DO IT, DO IT. it is a great sounding unit with great functionality. Since mine went back to PS I have been using the DSD DAC as the preamp, and it really sounds good. But, there really is no comparison in that the preamp adds so much beauty and richness to the sound that i could not really ever choose to not have it. There are some really fine units on the market, but almost any unit that will sound as good will be more expensive and not have the value of “made in the USA” and the support of a great CS dept.

1 Like

So my Preamp just developed the dreaded scratchy noise in the left channel. Of course I have been running Amperex 7308 and Tungsram 7DJ8 both platinum grade and cryo from Upscale. Changing back to the stock tubes does fix the issue.

I did put in a service request but haven’t heard back at this time.

My unit has 10 days left on warranty and I’m wondering if my best bet is to only use 12v tubes from here on out and not bothering to send the unit in.

This condition is generally the result of mismatched tubes.

Yeah, there isn’t a whole lot our team is able to do. A lot of times when people send their pres in with the 7DJ8s, it measures terribly on the AP. I’d either stick with the 12AU7s or try out a new set of 7DJ8s.

hi, if going back to stock fixes the issue then it is the tubes. did you swap them from left to right to see what happened. also if you have a set of headphones, test with those and see what happens just to make sure it is not the amp

I tested both pairs of the Tungsram and Amperex. The noise is always the left channel with all 4 tubes: I also swapped the outputs to the amps and the problem moved to the other amp, eliminating the cables and amps as culprit.
I purchased the Tungsrams after reading the statements from BHK. I’ve only used matched high grade tubes in the unit as I’ve heard others have had problems with mismatched tubes.
I’m not understanding how it’s the tubes when 4 units all have the same result. If the BHK just really needs the 12au7 then I will save money/time and only utilize them.

Just for grins try pulling and reseating the two small daughter cards behind the tubes. One of them could have an pin that’s not making good contact. You can also swap them side for side if you want to see if the noise goes away or follows the card swap. I was having a noise using 6v tubes only and then it started with the 12v tubes too. Reseating the cards fixed it.

my understanding is that newer units do not allow us to pull those cards out. caution is in order here

that is so puzzling. when i had problems, it made no difference if it was stock tubes or NOS. they all did it. just make sure to change the jumpers when you switch between different types of tubes

I think a big part of this could be that folks automatically assume that NOS tubes are better. And considering their age, I would guess that quality is very inconsistent. Just my guess.

Agreed. The 12AU7s that are in there as stock are actually great tubes. Are there better ones out there? Sure (it’s so subjective though). But I do like to inform folks that the stock tubes are fantastic.

1 Like

Never had an issue with the stock tubes in my BHK 250, BHK Preamp and/or BHK 300s. Can’t say that about the NOS tubes I tried.

1 Like

Hold on. What does the manual say is appropriate to use? Here is what I found in the on line manual:

“A unique self biasing constant current source and user selectable switch combination allows those who like to roll their own tube selections to place any acceptable 6, 7 or 12 series vacuum tubes inside the preamp.”

It seems to me that the preamp is likely to have a problem sooner or later when customers use 6 or 7 series tubes. Wouldn’t it be smart to change the manual and, in production, eliminate the voltage switch, so people only use the “acceptable” 12 series tubes? It would seem to be an act of negligence to not do so.


Mine was built in 2019 and does have plug in boards. If they are soldered in place then they would not be easily interchangeable. They required very little force to remove and replace.

Right. not sure when but they did change to permanent boards, or at least that was what i was told.
the problem i had was on the left board and they were able to repair it fine. no more problems at this point, even using NOS tubes.

1 Like

Glad I held off dabbling in rolling the tubes in my BHK pre. I’m still on the original set of tubes the pre came with, but thought I’d try something different on my next set, scratch that.

Gary, I only used the stock tubes and never dabbled with other types in my BHK preamp, 300’s & 2 x 250s. Now on my 3rd BHK preamp; all preamps replaced because of excessive hissing and other extraneous noises. 300s & 250s had tubes replaced then it was input boards - ‘then more input boards’ - due to the excessive hissing and/or banging noises through the speakers. Then the amplifiers were replaced, and replaced again, etc, etc…!

That’s very concerning.

wow that is a story. my amps have been trouble free but the preamp was the issue. but three preamps, that is amazing.

Dirk, someone mentioned going through a few BHK amps because of damage during shipping from PSA. Once had a UPS drive who damage numerous pieces of stereo equipment. Any chance your BHK issues stated during shipping.