Sonic Improvements to the BHK Preamp

After reading some posts on the Forum regarding the sonic improvements EMI & RFI shielding can make, I decided to try it for myself and see what benefits it might give me. I have taken a couple of pictures to show what was involved and where I placed the “3M™ EMI Absorber AB7050HF” sheets. The company I purchased them from is called EIOM.COM “electronic inventory online” they are located in the Los Angeles area. Pricing on the sheets are $70.99 each. The sheet size is 8.5X11. It’s a peel and stick item so it is very easy to apply.

DIY part is that one needs to remove the black-top of the BHK pre which is held on with 4 small black screws on the underside of the unit. I have included a drawing from PSA showing the placement of the screws. I recommend that you stand the unit up on its side or just lay the unit on its top and remove the screws and carefully lift up the Preamp, and the top will be sitting there waiting for the installation of the 3M sheets. Also provided some pictures. I actually did not think that the complete coverage would take 2 sheets as I was thinking I would only cover the underside of the unit but after looking at the cover and its side sections, I decided to cover the sides as well. And that consumed both sheets. It is a straight forward job and after taking measurements to cut around the vent hole, it was easy peezy!

So what did I find out when everything was put back together?.. Drum Roll Please!!!
It really made a huge improvement to the sound. It is amazing and the other posters who commented on this Tweak are right on the mark! The first thing I noticed was how much smoother the sound was. And the reason I say that, is because all the ‘electronic’ noise which is mixed in with the sound was gone! The sound was less distorted. I am so pleased I spent the money and did the Tweak! I do not regret it one bit! The sound is so much more ‘transparent’ and open. I am so very pleased!!! And all for a small investment of $150 and a little DIY time.

I just wanted to share my findings and say thank you to those who previously mentioned it in passing. Unfortunately I can not find the thread where it was initially mentioned.
Screen Shot 2023-06-16 at 11.42.48 AM


I have to say that even with only a few hours, I am delighted! The music is much nicer! Less fatigue, bigger middle with deepth.

It make the sound more real!!

I believe you can get the same effect with much less material strategicly placed. The only digital circuits which could be a source of noise is the display and the digtal volume control.

1 Like

Yes, most likely however, not everyone including me, feels that way. But thanks for bringing it up.

1 Like

Makes me wonder why manufacturers aren’t doing this in the first place.

Cost to gains ratio too high.

1 Like

Do you have some specific locations that could improve the sonic quality? I have a sheet coming soon, and would to treat the BHK preamp. But, not a lot of information, and do not want to use two sheets to cover the whole case.

1 Like

It would leave nothing for the tweakers to do! :sunglasses:


I would place a piece on the underside of the tube access cover in the area where the high voltage warning is printed. On the underside of the top cover in the area of the display and volume control. Along the right side of the cover when the ribbon cable travels from the volume control to the circuitry. These are the areas where noise could be present.

1 Like

These are the areas that make the most sense to me.


To my way of thinking, if one only has 1 sheet to work with, then for me I would place it as I mentioned under the top cover. Only I did not want to block any of the venting / cooling and cut around it. Most of the sheet will cover the underside after the vent is cut out.

However, what I can reiterate is that doing this Tweak has made a profound improvement sonically to my system, for which I am delighted about!

If one only wants to use 1 sheet them by all means do so, as it will cover most of the top of the lid and do a good job. I happened to have purchased 2 sheets and felt that covering the whole inside might give me an even better improvement than only using 1 sheet. In the end it comes down to a personal matter of choice and any budget constraints that there might be!

With regards to more manufactures using the sheets, I can only surmise that for them its comes down to a cost priority or they just don’t know about using or are willing to try it in the first place.
Their attitude could also be that they think that their ‘product’ is so good that it does not need any such treatment or it just does not work!

Where is all this noise coming from?

I would suggest that it is generated by the electrical equipment in general and creates EMI and or RFI which our sensitive components both radiate and pick up depending on several factors.

Electromagnetic interference (EMI) is unwanted noise or interference in an electrical path or circuit caused by an outside source . It is also known as radio frequency interference. EMI can cause electronics to operate poorly, malfunction or stop working completely. EMI can be caused by natural or human-made sources.

Have you noticed a discernable improvement with this mod?

I have to do some more listening to determine the effect. The issue at hand is placebo. I made a change that I would think would suppress noise from the transformer and the digital circuits that control the volume. I can for sure say it did no harm. I feel at this early stage that it has opened up the sound a bit.

1 Like

Verendus, if your question is directed to sixpack1 then I guess its up to him to give you your answer however if you are asking is there a ‘discernible improvement’ with the mod then I whole heartily say YES and its very noticeable indeed! I am sure that if one were to stick a bit ‘here and there’ could give some improvement but I think the hit and miss approach has got to be marginal at best. To do it right, I think the top of the plate needs to be completely covered, bottom and sides of the top. And that requires 2 sheets. But again, each to their own… Good luck with what ever you try!

Vmax found that excessive application of the sheets had a deletrious effect on the sound quality. More is not always better. You are free to use as many as you choose. The preamp has no where near the amount of digital circuits generating noise than does a DAC. That is why I chose the selective application.


indeed, too much of it (or placed on wrong places) on DS DAC can suppress some (usually high/mid) frequencies


Thanks for the response. Yes, I am trying to find the correct location for the best enhancement. I’ve applied 3M absorber in different locations in the past and learned that more is not always better. I think the absorber by nature affects the digital side more than the analog. I was very obvious on the direct stream dac. But, even there, the Bridge and the screen really had the most detrimental effect, so I think 2 sheets will be overkill for the BHK. I could bite the bullet and order another sheet, but want to see if a few strategic placements will make a difference. Do you know of anyone who had a similar gain by covering the entire top plate?