BHK Preamp Background Noise vs. Tube Gain


#1

Background:

  • I’ve slowly switched over from a dead silent, but poor sounding AV receiver, to a mostly full set PS audio components that sound significantly better, but that have increased the background noise on my extremely sensitive 101db/1m speakers.
  • Current Components: Panamax Power Conditioner —>PS DSJr —> PS BHK Pre—>PS M700 —> JTR 212RT Speakers. Interconnects are XLR

The M700’s alone with the preamp turned off or with the preamp set to volume 0 do produce white noise but it is not audible at the listening position, however this white noise does become audible within 2ft of the listening position so it is just barely below the noise floor of the room.

The M700’s directly connected to the DSJr without the Preamp adds a noticeable and listening position audible amount of background pure white noise. This noise is constant in relation to volume on the DSJr as one would expect.

Adding the BHK pre to the signal chain notably improved the overall sound but has had an adverse affect on my background noise situation and I want to check with the experts if this is normal or if I possibly have noisy tubes or some other issue in my setup that I need to investigate.

As soon as I switch the preamp from volume 0 to 1 I get a audible jump in background noise at the listening position. As I increase the volume step by step the background noise gets progressively louder until I reach the next major volume step. This noise sounds like a combination of signal gain white noise, which I’m assuming is coming from the adjustments in tube gain, and a less appealing “electricity” sound, not hum, but electricity. Some volumes have worse electricity sounds than others so therefore those sounds are not purely progressive like the signal gain white noise. By the time the preamp gets up near a major volume switch, such as volume 24 or 52 there is a lot of background noise, more than when running the DSJr directly into the amps. However, when you click over to the lowest volume of the next volume set, say 25 or 53, the tube gain noise drops significantly and all that remains is the “electricity” noise.

The quality of louder sound is very similar/identical between volume 24 and 25 or 52 and 53, however I can hear very different noise floor levels in these volumes and end up picking my volumes around low tube gain volumes. This tube background noise is not as pleasant sounding as the DSJr’s white noise, when I turn the BHK volume up to 80 to 100 (line level and above) I can hear the DSJr noise again like I could before the Preamp and it definitely has a different character than what I’m describing above.

Is this standard behavior of the BHK in the way that it utilizes tube gain for volume adjustments? Should there be noticble background noise differences immediately before and after the major volume steps?
Has anyone else noticed this background noise structure in their setup?
Any recommendations on what I could try to reduce this noise?


#2

There’s an excellent section on eliminating hum in the owner’s manual.


#3

I run a DS directly into Atma Sphere M60 OTLs ( tube amps ) via 25’ balanced cables with Avantgarde Duo Omega 107 dB sensitive horns.
I have to place my ear directly up to or into the horns in order to hear any system self noise.
It is possible that the tubes in the pre are contributing to the system noise, how many hours are on the pre?
Is it possible that you have a tube and internal jumper setting in the BHK set up incorrectly?
How many hours are on the entire system? If you already have 500 plus hours on the gear, run in is just about over.
If you don’t have many hours on the gear, that might be a small part of what you are hearing, but I doubt it is the total cause.
What are you feeding the DSjr?
Network noise could be contributing to what you are hearing, if you are connected to a network.
Try disconnecting all the source cabling from the DSjr and see if the noise floor lowers.
If it does, than you need to address that connected source noise floor.
You also might try taking the Panamax out of the system, just to see if it changes the noise floor.
I run a P300 on my source end and a P3 on my amps.


#4

The background noise I am describing from the BHK pre that builds and drops at each of the major volume steps is present even when nothing is feeding the BHK Pre (IE all inputs are disconnected). It does not sound like hum directly, it’s a combination of electric type noise like a light bulb might make that gradually gets louder between 1 and 100 and what sounds like gain noise from the tubes which is what accounts for the large SPL drops after the major volume steps.

No input signal background noise is very noticible at any tube gain above ~10% of minimum gain on each major step.

When I swap out the XLR’s between the Preamp and the M700’s to RCAs I get all sorts of hum and other sound gremlins coming out of the speakers and the volume chufs are much much worse (again no inputs into system, just the BHK pre to the M700’s.)

On a well isolated circuit should you be able to run RCAs without large amounts of hum? Is the large amounts of hum I’m hearing with RCAs an indicator of noisy electricity that if fixed may lower the noise floor when running XLRs?

Do I maybe need an amplifier with significantly less gain than the M700’s?


#5

The BHK preamp does not do well with unbalanced amp connections in terms of noises from changing volume. It does sound though like you might want to try another set of 12AU7 tubes and see if that helps. Icepower module based amps normally don’t have that high of an input sensitivity so the gain of the amps shouldn’t be the issue.


#6

Interestingly - my BHK Preamp exhibits the exact same traits… Background noise drops in level one click above the significant points - 25 and 53…I installed new tubes but it didn’t improve my situation, it’s still the same. I also experience a loud thump through the speakers if I drop the volume to 0 then turn to 1 and back to 0 ? My interconnects are balanced. I am currently playing music with my DS straight to BHK300s. I will have to get my BHK Preamp checked out.
Maybe Paul can shed light on what the issues might be ?


#7

Yeah I would like to know too as others said adding the BHK pre has such a positives effect on the music.

On my DirectStream DAC I had to press the Filter button to get rid of the hiss noise. I suppose this is similar to OP’s white noise?

But Paul is now in Chicago setting up Axpona so I guess he won’t be able to reply too quickly.


#8

The major clicks at 25 and 53 are normal. This is where the relay attenuator comes in and out, just part of the volume control. The control changes the actual gain of the tubebut that gain isn’t enough to cover the entire 70dB or so range needed for an effective volume control. So at those two points an attenuator is added or removed depending on which way you’re going with the control. The thump between zero and one says to me the preamp needs adjustment. It’s rare but happens on occassion. Can you get it to us? We can turn that around quickly with our sincere apologies.


#9

It does have an extremely positive effect n music and with the BHK preamp you don’t need the filter controlled attenuator on the DS. I am just getting ready to leave this morning. I still have an hour or two before the plane.


#10

Paul, thanks for info… I was aware of the volume setup as I’ve read threads on the forum and watched your videos… what I was trying to say (badly), the Preamp does something now that it has never done before, that differs from the aforementioned major click / volume description, etc. now there are various points in the volume setting range where there is quiet - silent backgrounds - one click above said major click points but, move on one more click or two above and the background noise reappears - I then find another point where there is silence but one click above and the noise returns, etc ? Apart from the series of faint clicks and the two major clicks – there was no background noise before whereas now I can control this evasive background noise…?
I thought this was down to faulty tubes because I have experienced similar with other equipment but on replacing the BHK tubes there is no difference !

I will speak to my dealer and make arrangements on getting the Preamp back to PSA…

Cheers.


#11

It’s not been a long time since I bought a pre. I get for goose skin and I sometimes cry over the nice sound it makes. There are a couple of tasks in my music life where i only use ds as pre amplifier. It kicks ass the pre


#12

I am hearing the same thing as you are describing. I’m not worried about the initial chuffs or major clicks when adjusting the volume, my question is about varying levels of steady state background noise based on the particular volume level and whether that is normal or abnormal? Should we be hearing a higher steady state noise floor just before the major volume clicks vs. just after?


#13

I hear a slight drop in noise when crossing the gain stage boundaries at 25 and 53, both are slightly lower than 24 and 52, respectively and nearly the same level as one another.

It’s simply not an issue with my relatively low 87dB speakers though. I can’t hear it from more than 2’ away.

Stock tubes, ~400 hours, M700s.


#14

Well, I bought my BHK Preamp in late July 2016 and I never experienced any varying levels of background noise whatsoever until the end of last year, which has since become progressively more noticeable and constant … I have another problem with the volume control; if I turn it to 0 then 1 and back to 0 there is a loud thump from speaker drivers - which is very disconcerting… I don’t know if both issues are related ?
I fitted new tubes but still I experience varying levels of background noise and the thumping noise.
I joined the in’ and out’ XLRs together and I am currently using the volume in the DS direct to the BHK300s…!
I will have to get my BHK Preamp back to PSA…


#15

You are not alone Dirk. In fact, you are at least the fifth person. My BHK Preamp is on the way back after 2 weeks in Boulder. Interesting, all the Preamps seem to have an issue with their main board.

Look at this link, scroll down to April 2017.


#16

Thank you for the info. Much appreciated. You said it seems to be an issue with the main board: …did PSA install a new board into your preamp ?
At post #7 Paul intimated my preamp just needs an adjustment !
I love the effortless musicality of the BHK amplifiers - in-fact all of my PSA equipment, but I have to say, I’ve been blighted by bad luck with all the kit bought … I’ve vented my spleen on the subject in another thread so I won’t say anymore other than I have a tipping point…


#17

The majority of these issues don’t require new boards. You sometimes see that ion the report because for expediency that’s what there techs do. The main cause of the clicks has been mismatched tubes, tubes different than what we provide, and the occasional misalignment of the on board servo which is the adjustment I referred to.


#18

Thanks, Paul. I installed new tubes gifted to me by Kevin Akam for the problems I encountered with the 250 front panel. The new tubes ( I assume ) are to P S Audio spec.? I might buy another pair and try them first before shipping the preamp over to Boulder . I am wary of rolling tubes for other types / makes because previously with other makes of equipment I have had issues with noises and channel imbalance, etc. after swapping tubes that were functioning perfectly… I now only change tubes when I really have to !


#19

Since a lot of folks roll tubes might be good to know how to match tubes to minimize noise in BHK products. I know there are several measurements that can be made, but which is important and how close a tolerance? While I’ve had no issues with my BHK pre I did have tube noise with my BHK 250, and they were the stock tubes. Some Tungsram’s solved that problem.


#20

I disconnected my main 101db/1w/1m speakers for a pair of “back room closet stock” 86db/1w/1m satellites that I had sitting around this morning. The noise floor differences I’m describing in this thread are still present with the 86db speakers but you have to have you head very near the speakers to hear them. This noise becomes completely inaudible just a foot or two away from the speaker so I can see where a vast majority of users would never notice or have need to be concerned by it.

I don’t think there is anything wrong with my BHK Preamp but I would like to verify with some other users with this simple test that their units behave the same as mine.

With no music playing start with your amplifiers turned on and your BHK Preamp set to volume 0/mute. With your head by your speakers you should be able to hear whatever level of idling noise your amplifiers are providing at this point.

Test Questions: Keep your head by your speakers for each step otherwise the desired observations will likely disappear into the noise floor of your room.

  1. When you turn the BHK from volume 0 to 1 can you hear a difference in the idling noise of the system?
  2. As you increase the volume one volume unit at a time can you hear the background idling noise progressively increase as you reach the top end of the tube gain stages?
  3. As the volume crosses the tube gain threshold steps (volume 25 and 53) do you hear a drop in background idling noise?

Again I think this behavior is normal and completely a non-issue for most people but I would like to verify that it is normal.