Start a new topic

Audiostream Pulse XFI and LPS4 Review - July 23 2015



LH Labs Geek Pulse Xfi & Linear Power Supply 4 (LPS4)

By Michael Lavorgna • Posted: Jul 23, 2015

Share Tweet Email   Share



Geek Pulse Xfi
Device Type: DAC & Headphone Amplifier
Input: USB, Toslink, 2x Coax S/PDIF, AES/EBU
Output: balanced XLR pair, analog RCA pair, balanced XLR (Neutrik) headphone jack, 1/4" TRS headphone Jack
Dimensions: 8.25" D, 7.375" W, 3" H
Weight: 9 lbs (shipping weight)
Availability: Direct and through Authorized Dealers
Price: $2399.00

Linear Power Supply 4 (LPS4)
Device Type: External Power Supply
Input: USB Type-B, power
Output: 4x 12 volt DC outputs (2x 0.5A, 2x 1.2A), USB Type-A
Dimensions: 9.75" D, 7.375" W, 3" H
Weight: 9 lbs (shipping weight)
Availability: Direct and through Authorized Dealers
Price: $899.00

Crowds & Power
More than any other audio company, much-much-more, LH Labs has been exceedingly successful in utilizing crowdfunding for product development and sales. This model obviously shirks the traditional hi-fi approach in many ways but most importantly lots of people are buying audio gear without anyone having heard it. Reviews necessarily come after the initial wave of crowdfunding and crowd-designing enthusiasm has ebbed so at best we can create a second wave or tell people what they already know. I find LH Labs overall approach refreshing if a tad fresh.

The LH Labs Geek Pulse Indiegogo campaign, launched back in 2013, became "...the most successful crowd-designed high performance audio component in the world. 1,262 backers (who we lovingly call 'Geek Force') have contributed to its development, helping us to pre-sell over 9000 units." The campaign also raised a total of $2,906,692. That's $uccess. The Geek Pulse came in three versions; the Pulse, Pulse X ("a fully-balanced, dual mono version of Pulse"), and the Pulse Xfi (adds dual femto clocks, upgraded capacitors, resistors, opamps and controllers). We'll be putting the Xfi to the listening test.


The Geek Pulse supports up to 32-bit/384kHz PCM and DSD 128 (DoP or Native DSD which requires ASIO driver) using a pair of ESS9018K2M DACs. Prior to hitting those ESSs, the incoming data (via USB 2.0, Toslink, 2x Coax S/PDIF, or AES/EBU) is "converted to a 3L buffered [patent-pending] I2S signal". The Xfi includes both single-ended RCA and balanced XLR output pairs. I went balanced into my ADAM A3Xs.

Here's LH Labs on the importance of their 3L buffered approach which trickled down from parent company Light Harmonic:

"Our three layer buffer adds an additional step which decouples timing jitter that comes in with the original signal. By adding in the extra layer, noise is greatly reduced and proper timing is ensured. This is important in decoding streaming digital audio because, unlike other digital protocols, our DAC doesn't get re-tries. If it misses a piece of data, it has to guess at what it was."The Xfi also employs two Crystek Femto Clocks which have been specially customized for LH Labs. The dual mono 3000 mW headphone amplifier utilizes ultra low noise quad JFET transistors plus dual OPA1612 OpAmps biased in pure Class A. There are both a balanced XLR (Neutrik) headphone output and 1/4" single-ended jack both of which are front mounted and offer three user-selectable voltage and impedance settings (Balanced 3.5V/6V/13.8V, Single-ended 1.8V/3V/6.8V). Also up front is the volume/menu selector knob. Menu options include input selection, gain (low, mid, and high), digital filter (see below), and volume setting (knob or USB). The front panel display shows the incoming sample rate and volume level.

Here are the filter option descriptions from LH Labs but first a word from Larry Ho, founder and President of Light Harmonic/LH Labs, "Technically speaking, our TCM/FRM/FTM digital modes are more than just filters (including minimum phase and slow roll-off linear). Our digital modes involve different DPLL parameters, different clock distribution settings, and different even and odd harmonic distortion spectrum.":

TCM (Time Coherence Mode) – Uses LH Labs minimum phase digital filter and time optimization algorithm which removes all post ring from the original signal, and realigns the impulse response. This presents the listener with a more well- defined and natural soundstage.

FRM (Frequency Response Mode) – Uses LH Labs slow roll-off linear digital filter and frequency domain optimization algorithm to provide a smoother and clearer sound with even lower THD+N.

SSM (Stable Streaming Mode) – A digital filter to optimize audio from streaming sites such as Spotify and Tidal.

FTM (Femto Time Mode) – Uses an optimization algorithm that reduces time related distortion from the Femto Clock source, while providing better jitter performance. It also brings out the best of both TCM and FRM filter modes.


While the Xfi includes a low noise 12VDC switching power supply, LH Labs recommends upgrading to one of their external linear power supplies, the LPS ($599) or the LPS4 ($899). I have the LPS4 here for review. The LPS4 offers a total of four 12 volt DC outputs to deliver clean DC power to up to as many devices. There's also USB Type-A and Type-B inputs on the unit's backside so you can clean up the USB power leg coming from your computer and going to your USB DAC, "LPS4 disconnects the 5V power coming over the USB cable from the computer and replaces it with clean (under 6uV noise) 5V power coming from its super-regulated power circuits."

As you can see both units are your basic black on black and I appreciate their minimalist aesthetic. My one wish list item would be the ability to adjust the display brightness since I find the level a tad dim. Each unit also comes with LRF support (little rubber feet). The Geek Pulse runs on the very warm side so you'll want to let it breath. I sat both units on my desktop with the Xfi on top of the LPS4 and wired them up with two lengths of the LH Labs LightSpeed 1G USB cable ($99/1m). In addition to my desktop listening, I also spent some time listening through a loaner pair of Audeze LCD-X 'phones. I used Roon to control playback.


The Sound Of Clean
What does all of this cleaning, buffering, re-clocking and filtering get you? Big effortless rock solid sound. The Geek Pulse Xfi also digs way down into your recordings and comes up with as much nuance as there is to mine. There's a seemingly complete absence of grain or digital hash and music simply sounds like music with no additives or alterations. Nice.

I spent many weeks with the Xfi/LPS4 on my desk pumping tunes out of my ADAM A3Xs in every shape, size, and format. CD-quality either streamed from Tidal or on NAS, higher resolution PCM, and DSD. Santana, George Harrison, Lou Harrison, Karen Dalton, Miles, Trane, Alice Coltrane, PJ Harvey, Bach, Soler, and much much more. I put the Geek Pulse Xfi to the enjoyment torture test and it and I came up smiling. Of course this means I found that the Geek checked off all of the sonic checklist items; tight tuneful bass (check), a natural sense of timbre (check), great resolution (check), life-like dynamics (check), no edge or harshness to upper frequencies (check), and a compelling sound picture to get lost within (check).

Taking the LPS4 linear power supply out of the Geek Pulse picture resulted in many less-good sonic things. The sound image flattened out, things sounded more brittle, and generally music got less natural sounding and more digital sounding. I also wanted to immediately turn the volume down when I first made the switch suddenly feeling, "That's too loud!".

Just for kicks, I re-connected just the USB cable to the LPS4 leaving the Xfi running off of its switched mode power supply and some missing stuff came back. Things got less brittle, tone colors seemed to get richer, and we were that much closer to full music power. With the LPS4 completely back in the picture providing power and USB cleansing to the Xfi, the sound image opened up, subtlety returned, and music simply sounded more natural and whole.

Switching back to my reference Mytek Stereo192-DSD DAC showed the Mytek to be softer and less solid in comparison to the Xfi's iron grip on imaging and clean, clear, precise control of music's every move and texture. Of course I'm listening through the ADAM A3Xs so I'm really talking about how each DAC sounds through them. For my long term music loving tastes, the Mytek actually appeals to me more than the Xfi even though one could certainly argue the Xfi is providing a less colored version. I happen to like color in my music and the Mytek's fatter sound feels like a warm hug O music through the ADAMs. But I had a hunch...


I relocated the Geek pair to my big room rig, leashing the Pulse Xfi to my Pass INT-30A driving my DeVore Fidelity The Nines and all of the Geek's positive traits were amplified. Big, open, solid sound filled my listening room with a natural ease I could, and did, enjoy for hours on end. This suggests to me that I've found what I like in terms of a DAC for the ADAMs but the ADAMs may actually limit some of the Geek's stronger suits. Here, in-room, the Xfi sounded more relaxed and I was better able to appreciate its engaging way with music.

Since we're here a comparison to my reference Auralic Vega DAC is in order. The most noticeable difference I hear is with the upper registers where the Vega seems to flesh things out in a more convincing manner. Cymbal hits are more tactile with more light and sparkle through the Vega where the Xfi sounds ever so slightly soft in comparison. I'd give the edge to the Geek in terms of the overall sound image which is a bit more open than the Vega's. Of course the Vega does not get you the excellent sounding headphone amp that the Xfi throws into the mix so if you're a headphone person the Geek is the clear choice here.


I'm really no longer a headphone guy. There I said it. I can think of a lot of reasons why this is the case but one interesting anecdote is my blissful headphone listening immersion days seemed to coincide directly with my pot intake and Jimi Hendrix dancing through my ear goggles through my head. And those smoke-filled days are long gone. Besides, Tyll Hertsens over on our sister site Inner Fidelity has this headphone ground more than covered. However many devices come through AudioStream that offer 'phone fun and it would be remiss of me to ignore this important feature. So I dutifully clamped the Audeze LCD-X to my cranium and listened. I know, someone's got to do it.

Wow. Nice! Even on coffee. Everything I said so far applies here as well but what also sticks out is the Xfi's wonderful sense of drive. Music sounds powerful, where appropriate, and compelling. Some twiddling with the Xfi's digital filter options also had me leaning toward the FRM option where I was definitely enjoying FTM mode through my speakers. Filter options are good. While my headphone listening is as I said limited, there's nothing about the Geek's performance that I can see getting in between you and your music. With the Audezes, music reproduction sounds honest.


Clearly Geek
I consider the Geek Pulse Xfi/LPS4 combo to be paired at the hip, a truly dynamic duo, so my recommendation includes both. If you like your music delivered cleanly, clearly, and precisely with a wonderful sense of the place of the recording, whether in-room or in-ear, think Geek.

Associated Equipment

Also in-use during the Pulse Xfi review: Mytek Stereo-192DSD DAC




Login or Signup to post a comment