Filter tweak for digital backwash?

As my system improves, it’s easier to hear anomalies. The search is now on for a tweak to filter only digital backwash in my AC. The culprit is the regulated transformer power supply (120vac/19vdc converter) to the dedicated laptop for streaming.

The balanced power conditioner has separate outlets for analog and digital. The digital outlets already have built-in filtration for backwash. They work well. But, I need even more. When the laptop is running on its internal battery, the music is very smooth. Unfortunately, the battery life is short. When the laptop is running on the power supply, there’s a slight stridency. When the power supply is plugged in anywhere else, there is huge stridency. So, I’m looking for some gizmo to clean up the digital backwash in-between the conditioner digital outlet and the power cord to the regulated power supply.

I’m not looking for an overall line purifier. The balanced power conditioner does a pretty good job already. Any suggestions?

Most laptop chargers are smp (switchmode) these days.
Try to get a linear charger for it, and your problems will be solved.

Cheers George 
Forgot to mention that my regulated power supply is linear.
Maybe it's a cheap noisy one?

Cheers George
Try another mains filter between your PC and the regulated power supply. Monster make some good ones less than $200. Also try to find out which device is picking up the backwash - is it the DAC or preamp? (Add the extra filter in be tween regulator and device you suspect is being affected)
The least expensive unit I recommend, based on a lot of research this one:

Series mode power surge suppression also includes noise reduction that works down to about 3kHz, and that noise reduction is bi-directional.  Most noise supression is too expensive, or doesn't work below 100kHz. These units are perfect for isolating a noise source. For $30 more this one adds their linear filtering technology, which works too, not sure you need it:

Of course, more expensive Furman units include multiple different filter banks. I haven't tried them for bank to bank isolation though.


OH! Almost forgot to mention, it has been shown that a lot of the noise from a laptop or PC isn't "noise" so much as a ground loop. Obviously, it looks like noise, but the fix is entirely different.

For these you need a ground loop isolator. Here is one designed for medical instruments, so it's a lot cheaper than audio-grade but works every bit as well. :)

I would try this first, then try a power supply strip like the Furman.


And, just a little rant.... Stereophile KNOWS this but still tests DAC's with battery powered laptops. Gahh!
Why aren't the engineers designing expensive audio gear dealing with these problems?

I thought it was pretty easy to deal with noise injection(?)
I thought it was pretty easy to deal with noise injection(?)
Not when smp is involved.

Cheers George
Georgelofi, smp meaning ' Symmetric multiprocessing', or am I missing something?
SMPS = switch mode power supplies.

Good question! :) I think in part it's because reviewers baby them during testing. :)

I thought it was pretty easy to deal with noise injection(?)
It was 10 years ago, we had relatively low levels of noise to deal with. Today now we have designers making new things, like Class-D, Delta Sigma converters and SMP(S) (sorry Bob), that introduce even more complex noise structures and with much higher output of those noises, now these have to be dealt with as well. Without effecting the core body of the fundamental that we hope should not change "the music and it’s harmonic structure".

Cheers George
Why aren't the engineers designing expensive audio gear dealing with these problems?

I thought it was pretty easy to deal with noise ...
I think working to reduce noise is a very tricky business, and I agree with georgelofi that there are more sources of complex noise than ever before. The problem is also compounded by the endless combinations of equipment that can be used with any given component.
Thx all for the excellent suggestions. I’ll update when I implement a ’fix’.

In the meantime, I’ve been swapping wire on a different linear ps (120vac/12vdc) that goes to my Empirical Audio Off-Ramp. From Ebay’s Tajacob’s - Jake’s Old Western Electric stuff, I’ve been sampling a variety of vintage WE 20 gauge wire - solid core tinned w/paper insulation, solid core un-tinned w/plastic insulation, solid core tinned with cloth insulation, etc. They each affect the sound considerably differently - sometimes, significantly. Crazy-making. Maybe taking up golf would be a good alternative.
When I see engineers post on various forums, they usually say it is trivial to design noise rejection into a circuit...

Dunno myself.

I'm sure there are more sources of complex noise than ever before but they are usually RF and often in the GHz range so should be even easier to filter out than other "historical" noise.

OTOH, I did see a recent white paper from Intel on USB-C showing significant noise down to DC.

Update: @shadorne Your suggestion worked - of putting a filter in the DC leg between the laptop and its power supply. I installed an ICT PCM-12 ADL, which is used for automotive electrical. Now, both the AC & DC legs are filtered. The laptop power supply is still plugged into the AC digital outlet of my balanced power conditioner. I like this filter so much, I’m going to get another one for the 12vdc power supply to my digital re-clocker. ICT has two versions: a PCM-12 ADL for 1-100vdc. and a SPM-12ADL for 0-17vdc.

My system has been fairly resolving for a while - now it's more so. It’s interesting to observe that digital noise offers the perception of ‘body’ to the music. When the noise is stripped away, the music can sound a bit ‘lean’. Then comes the challenge of adding weight back to it again - sans noise.


Noise is a very interesting phenomenon. You can think of it like the canvas of a painting. Just like a different canvas texture or tint could change the visual perception of a painting so too can noise with music or sound. 

Vinyl may be attractive because of the inherent high noise floor and listeners are able to use that background noise to advantage!

We can hear at least 15db below a noise floor!

Sometimes noise will help make some aspects of music more audible. 
Update: Added a 2nd ICT PCM-12ADL to my system. This time to the 12vdc linear power supply for the digital re-clocker. Wow! Clean, clear, beautiful music! If you have an Astron or similar linear power supply, I highly recommend this unit. A very inexpensive, yet very effective tweak a la Ebay.
Astron makes nice things, but I like meters, so they get more expensive! :)
Re the noise cause being a ground loop. Would it be a benefit to create a small extension cord for that digital outlet and drop the ground?
There are several ways to lift the ground - including a cheater plug. In my case, there was never a ground loop problem. To deal with the digital backwash, I mentioned previously that my linear power supply was plugged into a digitally filtered AC outlet of my balanced power conditioner. The ICT PCM-12ADL is so effective on the DC leg by itself, that I re-plugged the power supply into a non-filtered AC outlet. Much better dynamics.