Mass test ‘plug in filters’ – an impression of the test setup

We are busy setting up a test setup for a big ‘plug in filter’ test. You probably know them: plugs that you put in the socket to combat noise on the mains. There are countless such plugs. In short: time to provide an overview and to separate the men from the sissies!

The applications are now complete. We have replies from everyone. Telos was out of stock and the question is how long that will take. But from all other parties we already have them or confirmation that they are on their way.

  • Kemp SNS Plug
  • Isotek Isoplug (EVO3)
  • Ansuz Sparkz (both models)
  • IFI AC Purifier and DC Blocker / GND Defender (the question is whether we can measure it)
  • Furutech NCF Clear Line
  • NordOst QV2
  • PS Audio noise harvester
  • Akiko Tuning stick

That’s a total of about ten products that we can include in this test.

The measurement set-up

At Alpha Audio we have adopted the policy of listening and measuring. The results of the test are based on both. You can decide for yourself what is leading for you; we always describe both sides of a product.

We’ve come a long way with the measurement setup, so we thought it would be nice to give a first impression. We are measuring the influence of the filter in a couple of ways. We had to solder together our own “measurement cable” for this test, because we like to have the plug in the signal path for certain tests. This allows us to map the filter behavior.

First of all, of course, we have the Prism dScope that can provide insight into the noise pattern of the mains (snapshot!). We do a measurement with and without the filter. So you can see where in the area of 5 – 96000 Hz something changes in the noise pattern. This is interesting because you are looking at the audible range. And so can see if the filter is doing anything there.

Besides the Prism, we have the Rigol scope and function generator to send signals through the filter to see what the filter is doing. We can let the function generator make all kinds of signals. And at frequencies up to 60 MHz. For example, if we send a square wave of 1 MHz through the plug, we can see on the scope what comes out. Noise with a bandwidth of 30 MHz? No problem. Really a handy device.

The combination with the Rigol scope and the Rigol Spectrum Analyzer (that one just came in!), shows what the filter removes. It also shows a bit more than the dScope. That works from 0 – 96000 Hz, the Rigol spectrum analyzer works from 9 kHz – 1.5 GHz. Not that we need to go that high, but up to about 10 mHz is interesting in itself to see what the filters do.


Of course we are also going to listen. After all, it is ultimately about what these filters can bring in terms of sound. We are very curious what the differences are and to what extent they add something to our system. For this we will have to take another socket, independend from the main system and independent of the filters we use – and make a choice for one source that shows the most. The reason we need to grab another socket is that the Titan and Aquarius have a direct impact: they already filter out a large portion of the noise, so the plug-in filters are less able to show their skills.

We estimate that we will use the Sonnet Pasithea and Metrum Acoustics Ambre for this test. To be continued!

1 Comment

  1. Hi from Spain

    I have / had a lot of problems with my very noisy grid. With DC Blockers + Schaffner RF/EMI filters + Würth 150 kHz ferrites… the sound is much better in my two audio systems.

    You do not need to spend a lot of money to solve the problems.

    – maty –

Leave a Reply