BHK Pre-Amp and Speaker Hiss

Hi All,

First let me start with my set-up: PC USB–>DSD Sr.–>BHK Pre–> Simaudio Moon Rocks–>B&W 800D3

I just purchased the DSD Sr. two weeks ago. My original plan was to run it directly into my power amps. Unfortunately there was an extremely loud hissing noise emanating from my speakers without the 20dB attenuation enabled on the DSD Sr. With the 20dB attenuation enabled the hiss was gone but now the max volume on the DSD Sr. was not enough for my taste.

I really loved the sound of the DSD Sr. so I wanted to keep it in my system, I figured the best path forward was to add the BHK Pre to my set-up to modulate the volume. I received my BHK Pre today, hooked everything up and the speakers were hissing. The hissing is not as loud as it was on the DSD Sr. w/o attenuation but is still audible over my desktop PC fan noise from my listening position which is unacceptable to me. The hissing occurs independent of volume of the BHK Pre/DSD Sr. and is still present even if I enable the attenuation on the DSD Sr.

There is absolutely no hiss when only my amps are connected to the speakers. I have never had a problem with hiss before, my previous dac/pre-amp was a Benchmark DAC3 and it was dead quiet in this exact same system.

Is there anything I can do or is the BHK Pre incompatible with my system?

I appreciate the input,


Ask the guys to send a new set of tubes. I had one stock set that was really bad.

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The hissing was there prior to the addition of the BHK Pre. New tubes won’t help here. I think that other users of SIM amps have had hissing. A search might identify what they did to help with the hissing. The other thing is that some speakers have a sensitivity issue and create some hiss.

I too don’t believe it is preamp or tube related.
I had hiss on my Sanders Magtech Monoblocks with matching Sanders pre, however it was low enough level to excuse. When I was doing my upgrades it happened in stages. The BHK Pre lowered the level of hiss, then changing the amplifiers(BHK 300S) eliminated the hiss entirely even with my ear right on my speakers(Magnepan 20.7’s). The last piece was the DSD dac, which hasn’t introduced any hiss at low or high level. I had Simaudio Moon-w5 in the past with various preamps from tubes to solid state and they had some hiss close to the speaker. My father had Moon-w10 monoblocks and his were the same, with matching P5 preamp.

If you’re up for it, I think it might be worth it to try out new tubes. Not a guaranteed fix, but it’s something easy we can do to narrow down the problem. Send me an email at and we can get that ball rolling.

One other thing, make sure you have the attenuator on the DSD Sr. enabled.

Also, are you using RCA or XLR cables in your system?

And last but not least, just a quick observation - your Moon Rocks are really high gain amps (33 dB - the norm for the industry is around 26 dB), so that is perhaps complicating things.

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The hissing did not occur until I added PS Audio gear to my set-up. My Benchmark DAC3 was dead silent with the same SIM amps and B&W 800D3 speakers, so I respectfully disagree with your assessment. I also had an ARCAM FMJ SR250 prior to the Benchmark, again no issue.

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Thank you, I will send an email shortly.

I am using XLR cables throughout.

Good luck! I hope wholeheartedly that you resolve your issue.

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Me too, I love my DSD and hope to restore the system to quiet with the BHK Pre.

I just don’t get where these hiss issues come from. i drive my amplifier directly with my Directstream DAC. My speakers are B&W 800 Matrix which are 93db per watt sensitive. I can walk up to the speaker and put my ear in front of the tweeter and the hiss level is barely perceptible! I am beginning to wonder if cables and interconnects have something to do with this problem. I do not use the pad and my listening levels can be fairly loud. Have never heard noise or hiss from my listening position either!

+1 @sixpack1

Is the hissing equal in both speakers? I had a bad tube when I received my BHK Preamp and have since swapped them. Even after swapping tubes the BHK Preamp is not silent, which I’m told is normal by others on this forum and PSA support. I wonder if you are hearing normal tube noise?

Also, do you hear it when the DS Sr. is off and the Preamp is on?

On the way home from work I picked up a cheater plug, the hiss still remains at the same level.

The hiss is present with the DSD completely removed.

Turning the BHK Pre into standby removes the hiss completely.

I have tried two different manufacturers’ XLR cables from the BHK Pre to my Sim amps, hiss still remains the same.

The right channel hiss is about 1.5x louder than the left.

Does anyone know what the gain is of the BHK Pre?

I appreciate the help,


I’ve also found cleaning the pins of the tubes reduces noise. 99% iso and a fresh scotchbrite (or similar) to lightly clean just the outer surfaces seems to do it.

10dB of gain for the BHK preamp.

My BHK makes some hiss but with careful selection of tubes it’s reduced to the point I can’t hear it unless I’m next to the tweeter but my speakers aren’t nearly as sensitive as yours.

We all have different states of hearing damage…yours may be less than average.

Mine acted the same way out of the box. One tube was noiser than the other. Service sent me a new pair of tubes and I also bought a pair of Amperex 7308’s which resolved the issue or I should say reduced the tube noise. I have Sopra 2’s with similar sensivity, 91dB which makes it more noticeable. I would call Service and get their opinion, that’s what I did and they confirmed tube noise is normal. I will say I had a Mc C2300 Preamp and it was silent so I was a little surprised with the noise of the BHK. With nothing playing turn the volume up and you will probably notice the noise is reduced at certain levels.

This thread/post helped me as well:

I don’t want to be a game changer here but what I don’t understand is that this is not tested before the equipment is shipped…! I mean, it’s all nice to “find a solution like nerds in a classroom” but we’re talking about expensive, new stuff…! I mean, if you would have read this up front, like at for instance you might have purchased something else…?

I couldn’t agree more, these things should be caught prior to shipment. The replacement tubes they sent me were almost as bad, one of them fluttered. I contacted PSA and asked if they test/match them and they assured me they do. I guess shipping could be part of the issue. They offered to send a 3rd set, I passed and bought the 7308’s which are much quieter.

Anything with fragile internal electronic parts (vacuum tubes in particular) do not like to ride up and down the rough highways we have here and I assume in other countries as well.
Even the best packaging cant protect them from visually undetectable shipping damage.
It may or may not be the issue in this case.
We regularly have to return DOA electromechanical components that are much more robust than these (but not stereo related) components.

Yep @Baldy, you indeed have a point there. I spent lots of time in the Lone Star State and they sure can use some highway upgrades. Don’t know how it is in Colorado though… But looking at @Paul 's video, where he’s riding his car, doesn’t look promising either…

I’m from the great pothole state of Michigan. I don’t even try to get my nice car out until June or July. Thats how long it takes the annual winter potholes to be filled. And then you still have to be very careful. One pothole snuck up on me a couple of years ago and bent both left side rims on my corvette. That was an expensive lapse in attention.