Review: Nordost QX4 AC filter

Category: Accessories

Here is a funny one...a phenomenal piece of equipment and really hard to describe. But i thought i would share this one because the Nordost QX4 would not necessarily jump out on many people's 'must have' lists. but it has been on mine since i first heard it, and now i am glad to say i own one.

i would not think of trying to enter into a debate on the technical merits of the technology that sits behind this. i know what i hear...that is all i am sharing. and frankly, that is what i care most about.

The Nordost Thor (QX1 inside) and this QX4 (which has 4 units inside) basically makes it much, much, much easier to understand musical passages. To my ear, this is not primarily due to greater clarity, or soundstaging, or detail retreival or lower noise floor...there are many products which DO actually perform these important things. And possibly better than the Qx4 which does do each of these things but it is not these things which makes the qx4 stand out in my mind.

What the QX4 DOES do is take multiple themes within any given piece...and suddenly when listening to understand it all much better.

Example: you find it easier to listen to the words in a song. normally, even without qx4 if you try, you can hear every word clearly...but normally you never bothered. With the Qx4, now suddenly, you could be typing emails...and it seems so easy to follow the words in the back of your mind without even trying.

Another example: take whisper-quiet taps or rhythms...whereas before they were just that...taps. With the Qx4, it becomes obvious that the composer was creating a secondary rhythm in the music.

Another example: say a violin is playing 1,3,5,7,9...and a piano is playing 2,4,6,8,10. Without Qx4 it sounds fine...2 instruments each playing their own thing. WITH the Qx4, it suddenly becomes obvious that the music is actually 1,2,3,4,5,6,7,8,9,10...just played by 2 instruments in a contrapuntal ensemble.

Somehow, this component delivers a greater understanding of musical patterns...musicality...naturalness and ease to listening to music through an approach that i have not come across ever before. again, i could find lower noise floors, or better detail retrieval elsewhere...but i have never found something which makes music more intelligible and enjoyable. weird.

Is it expensive? hey...such is a hobby like this one where the pursuit of music is endless.

Is it worth it? to me, is one of the few things you probably never see me sell/trade in. And i am blessed to have some pretty good components which i have managed to buy second hand.

Many thanks to Roy Gregory who first played one for me and who has been exceptionally responsive. And thanks to Arif at KJ West One who ordered and secured one for 24 hours and 2 days before Christmas!!! Talk about service!

Hope that is useful to someone who is interested in reading about this product.

Associated gear
Wilson Grand Slamm
Gryphon Antileon
Zanden DAC
Velodyne DD-18
Transparent Ref Power Conditioner
Transparent Ref IC/SC
PAD Dominus/Ann Contego PC

Similar products
PS Audio Powerplant Premier
PS Audio Quintet
Nordost Thor
Transparent Reference Power Conditioner
I have just bought my unit and I have to agree with everything you said. My niggle is the cost. In fact, I waited to get one of the rare second hand units that come. The fact they don't come up much, attests to their benefit.

I am afraid I really can't get my head round the retail cost. You are in the UK too and it's what, £1750 new. The origonal QRT units were a few hundred dollars, before Nordost bought them out. Now I know there are 4 QXT units in each QX4, but still, I think the cost is ridiculous, much though I admit how good it is. Sorry to moan about it, but there do tend to be so many things we have to pay through the nose for. I suppose this is symptomatic for the High End being a small and probably shrinking market
Hi David,

Yes, the cost of Audio has risen dramatically in certain cases (not all). And for many of us where the market is tough...that does not help.

I am glad the Nordost is working out for really is one of those pieces that does something to a system i've not found any other component to do...and so the QRT technology is staying! Enjoy your great system!
Hello Sir,
I too am running the Thor , how have you connected the QX4 ,veering away from the topic, I see that you have heard the Metronome Kalista, would you be having any experience with the new Calypso reference transport

Hi Boeing,

I run the QX4 from wall into the power conditioner, and also place the QX4 on top of the power conditioner (Transp Ref Isolation). I admit...i did not experiment a lot...i liked what i heard and left it, based on recommendation from manufacturer.

As for Kalista Ref transport...i have not heard the new Calypso. If i do, i will post...pls do same if you hear it! The Kalista Ref is quite different from the regular Kalista...the main benefit that i could hear was the 2-inch thick slab of methacrylate/clear base...really helped smooth things out. impressive.
Thanks Lloydelee .... Would you say that the PC attaching the QX4 , to the wall has any bearing on sound quality.

Also how would you compare active power conditioning like the Transparent to a passive unit like the Thor ?


Hello Again,
Would you happen to have any feedback ,on the reliability of the Kalista and other Metronome products in general.

I am informed that the Kalista range is to be shortly replaced by the Calypso. Only the Kalista Master Reference will remain in production , the Kalista Ref and the Kalista will be replaced by equivalent Calypso models.

Any sonic traits that you were able to ascertain , due course your auditioning of the Kalista ?

Reliability is one questionmark in my mind. Only based on what i have read...not as strong as Esoteric which are built to last. Again, only what i have read across the blogs.

As to sonic traits, Kalista Ref Transport has more detail in a more effortless (ie, unforced) delivery than i have come across (possibly exception Zanden/Stahl-Tek but those were different environment, so i shouldn't kid you about my ability to truly make a definitive statement).

It also delivered micro dynamic shadings very, very easily..but again, that isolation base is super-important. We started without it...and i said impressive but the frequency range felt a little uneven for some reason. They stuck it on, and bingo...there was no sense of any frequency imbalance, or anything...just music delivery.

The Kalista Ref with its DAC has a powerful, energetic delivery on virtually any music it plays. Zanden is not like this...some say softer...some say more nuanced. Personal opinion. I cannot think of another digital besides Stahl-Tek that brought me this close to effortless music delivery.

my two cents.
I have 2 Nordost QV2s plugged into mt Nordost QB8 power bar and I hear similar effects to what you are hearing. It really is hard to describe but it's an effect that is hard to live without after they've been in the system for a while! The other cool thing with the QV2s are they have a cumulative effect - the more you use, the greater the effect on the sound. The QV2s are also reasonably affordable compared to the QX4.

I look forward to giving the QX4 a go sometime in the future to see if it has a greater impact on the sound.
Hi Camb,

Thanks for your insights! Glad to read about your own experiences...i have only tried the Nordost Thor (1 Q module) and the QX4 which i still use every day. Enjoy! And i have equally read about a cumulative effect...perhaps someday i will try another QX4!!!
I own the QX4 and would describe it as you have. I think it is a great product that has become an integral part of my system.