XRK971 Audio NHB Edition - Portable Amp Review

In all my years on many forums this is my very 1st review of audio gear. I admit it has been so long forthcoming. It was because I lacked the confidence of making one. I never knew how much goes into making one. I now can appreciate more all the energy you folks put into them.
My thanks go out to all of you who have helped me understand them.

My special thanks go out to Ian @Torq for his talents and help for giving me courage and providing tools and advice for this review.

This review is for all those who had to start somewhere. Where would we be without them? Many now known high quality equipment builders. They all started somewhere and many of them are the "unsung heroes” - Viet Nguyen is one of these people. Viet started started in 2017 with DIY projects wanted a better portable amp for his own listening enjoyment. In a shortly he began to build amps, speakers, and is building larger amplifiers in collaboration with Hugh Dean of Aspen Amplifiers He has become well respected on the audiophile forums. He is highly reviewed on all of his projects.

This is the story of how I got to know about and purchase his amp.

Although many reviewers indicated the FiiO X5 Gen 3 to be plenty strong to drive the Audeze LCD-2s, I did not agree. I then decided to try the FiiO X5 3rd Gen DAP with an amp. I tried the FiiO A5 amp hoping it would improve the sound. To my ears, I barely heard much difference. The bass sounded too muddy and there was no real separation of instruments.

So I set off on portable amp hunt that would work with my Fiio X5 gen 3 DAP and LCD-2. My FiiO has a 256GB sd card full of albums, most of which are HD or DSD files.

Then I stumbled upon a small startup company beginning to get noticed on many forums. After some research I decided to give it a spin. I’m sure glad I did.

Review of my "Pocket Class A Portable Headphone Amplifier NHB Edition", made custom by XRK 971 Audio - and let me tell you I had a great experience with this purchase.

I am using a FiiO X5 Gen 3 Dap and Audeze LCD-2 headphones with music described below.
This is my first and only review so far. I hope to learn and improve more reviews from our community.

This is one of those rare purchases where you get some of the man who built the product as well as this wonderful and magical amp.

This review is from my ears to their listening enjoyment.

This is with its clothes off:


Fairly simple and straightforward:

This is how it looks couple with my FiiO X5 3rd Gen:Short and sweet, these are my impressions. As always, I try to remember to listen to clean and well mastered recordings. In this case I listened to the DSD recording of Christian Mc Brides’ "Live at Village Vanguard". This would be a sure workout for the bass. I’m a fan of "Steve Hoffman" audio engineering. I listened to some of his "Dreamboat Annie", Pee Wee Russell and his clarinet - and others.

Please be aware, this amp is very unforgiving in its reproduction of poor music source. This is clear evidence of not trying to color the sound but to convey music as the artist intended.

I could not believe the musicality this magical amp would provide me with. Here’s how it was for me laying in my recliner listening to Lincoln Mayorga and Distinguished Gentlemen on the Sheffield label. "Lime house Blues" … toes are tapping relentlessly, shoulders rolling in and around and head rhythmically swaying side to side. All this from pocket amp.

I paid $395 for the fully loaded amp with upgrades. I was quite concerned about the price for a tin box. After receiving this I did well for the money. Materials included Panasonic OSCAR, Wilma film caps, Nichicon Ak Cap, Elma similar 2 cap. This is described by Viet (the designer/builder of the amp) as Single ended (SE) Class A portable amp. How’d they do that?
Although cost may seem a little on the high side, I can assure you it is well worth it. This amp easily will serve as a portable or desktop amp. It has plenty of power.

This is how it looks couple with my FiiO X5 3rd Gen:

All in all I think this is a gem of an amp and great value at that.

The man, the amp and the sound is what you get with HRK 971 Audio Company.

I would rate this product as:

Sound - 9. The HRK971 NHB edition added more realism to the soundstage than either the stock built-in amp of the FiiO X5 gen. 3 stock amp. With the FiiO A5 amp there was not very much improvement. Then with the HRK971 Amp it was exceptional compared to the others. It brought out the qualities of the LCD-2s. wider soundstage, more depth, and tighter bass.

The sound stage was very wide but does not have as much depth as I like. Most folks know LCD-2s are well known for bass. The bass this amp gave my setup was nothing less than articulate, and detailed. I am a big believer in "It’s not how low it goes. It’s how well it goes low". The speed of Mc Brides’ fingers up and down his bass is accurate. Who would ever believe this box could deliver so much bass. Instruments show distinct placement and not congested. Imaging and placement are very distinct in height, width and depth. However, vocals are more up front in my face than I prefer. This may be unfair since I have not listen to very many recordings with many female vocalists.

I found mid-range to be airy. The highs are accurate and warm with some sparkle -though not too much. as Being a tube lover probably accounts for my preference to be airy and more colorful

Build - 8.

The build is seven only because it is tin case. I would prefer to pay more for better case. The parts are very top quality - Panasonic OSCAR, Wilma film caps, Nichicon AK Cap, Elma similar 2 cap.

I am pleased to learn Viet is now a member of the Trade over at Head Fi and is currently building equipment that sells for $1000’s of dollars. Here’s to you Viet. One of the guys on the way due to people like you supporting their projects.



Great review Tom. It’s hard to believe it your first review. I hope you continue to post impressions and reviews. I really enjoyed reading it. Great pictures too.



Happy to help!

The first one is the hardest! Gets easier after that … (well, sort of …).

More than happy to play “editor” or “reviewer” for anyone that would like to review something but isn’t sure about it. Might just have to offer an interesting prize for the best review in the near future …


Thanks Ian. I tried following your review style as a template. It’s kind of you to offer your services. It’s a scary thing to do first time around. I have a new found appreciation of you guys who make it look so easy. It’s a lot harder than you’d think to be honest. Especially if you don’t write reports or such items in your working environment.


I’ll 2nd that. I have a new found appreciation for those who give of themselves to review for us.

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Well said Tom. I like your photography skills. Mine was just an iPhone 6. I also know next to nothing with regards to taking good pictures. It’s a particular rabbit hole I have never fallen down.


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It’s funny you say that. Mine were from an iphone x Typically , I’m horrible at pictures. The newer the phones get the easier it gets to take a better photo.


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Yes I can agree on that. Point and shoot is as hard as I want to get into. And to be honest phones are very good at what they do picture wise. To the untrained eye that is. And mine certainly isn’t.:slightly_smiling_face:.

On the other hand they also come packed with extra feature should you want to utilise them. And there’s a plethora of apps too. I will bet the photographers on this forum could take fantastic pictures on a phone. I won’t be buying a separate camera just for reviews. Although about 10 years ago I was given a Pentax something or other by my stepfather after he upgraded. It takes film though. Supposed to be a good one. It’s wasted on me. Nevermind. Wandering off topic again.


Phone cameras, especially iPhone, have come a long way. You can even shoot raw with them, which is awesome. The one area where their small sensor size still hold them back is in low light situations, but for product photography that shouldn’t be a big impediment.

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Thanks. I think some phones specialise in low light modes now and use this as a selling point. It’s probably more about who takes them rather than what they’re using when all said and done.:slightly_smiling_face: