Geek Pulse Audio: High-Rez Desktop Sound System

A performance audio system dreamed up by us, made real by you, and celebrated by audiophiles.
Gavin Fish
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Pulse Audio System


Pulse Headphone Amplifier (Back to Top)

You've gone and done it. You've spent a good amount of money on a set of headphones. You've spent time with them and you think they sound great. But can they do better? You know, you'll never realize the full potential of your headphones without proper amplification. You just won't.

Two Configurations

Pulse Headphone Amplifier is built using a 100% solid state topology. It features a fully balanced, dual mono design that rejects noise and wraps the listener in a precise and musical presentation.

Pulse Tube Headphone Amplifier is built with a hybrid solid state/tube topology with dual 6922/6DJ8 tubes in the voltage amplification stage, with a constant current source to make it more linear.

Pulse Headphone Amplifier Q&A with Larry Ho

Amplifier Component Exchange (ACX)

The Amplifier Component Exchange is a module that inserts into Pulse Headphone Amplifier that allows you to swap out its active components (transistors and OpAmps). Basically, it's tube rolling... except it's with active components instead of tubes. All you have to do is follow a simple procedure that we provide you with, and you can swap in your favorite active components anytime without affecting your warranty.

The core value of ACX is simple. A lot of audiophiles buy different amplifiers just because they want to find the best sound characteristics to fit with their headphones, or vice versa. Larry and Gavin do this all the time, too. Tube rollers do the same thing looking for audio nirvana. ACX enables you fine tune the sound without buying any NEW amplifiers. Too good to be true? No. No, it isn’t.

We feel very strongly about ACX, and have decided to add it to every HPA. It increases our cost, but it adds so much additional value, that we think it’s worth it. Don’t worry, this addition doesn't affect your price. Each HPA will come with a pair of ACX #1 modules installed by default, and you have option to get other ACX modules.

  • Future Upgradeable
    With ACX, your Pulse HPA is completely upgradeable. If you don't want to commit to additional modules now, you can do it later. The only risk is that the price for each module will be higher later.
  • User Serviceable
    ACX modules are easily swapped in and out. All you have to do is “Read the manual first”! And power down your Pulse HPA, pop the top, remove two screws, pull out one module, insert another, replace the two screws, stick the top back on, and power up.

Remember, you’re not forced to buy only ONE. You can pick as many as you like. Have fun with it! You could even trade them with your Geek Force friends.

Technical Details
There are two types of ACX modules. The first, ACX-V, works in the voltage amplification stage of the solid-state Pulse HPA. The second, ACX-I, works in the input buffer stage of either the solid-state Pulse HPA or Pulse Tube HPA. Remember, the function of these two stages is different, you cannot plug ACX-I into ACX-V’s slot or vise versa. Don’t worry, the pin-out for each type of module is different so you don’t accidentally cause damage to your HPA.

Please note: These ACX modules are not waterproof. You should not throw it into the fire. If you sit on it, it will break. Hand with care.

Five ACX-I Options

  • ACX-I #1: Included
    This input module comes standard in your Pulse HPA. In features quad JFET transistors plus dual OPA1652 OpAmps biased to pure Class A. This is the structure when we want to have the best bang for the bucks.
  • ACX-I #2: $79
    This input module features quad JFET transistors plus dual OPA2604 OpAmps biased to pure Class A. These are the same OpAmps that we use in our first prototype Geek Out. To our taste, they have a traditional “Burr-Brown” sound. They’re a little bit dark, and a little laid back. Classic!
  • ACX-I #3: $99
    This input module features quad JFET transistors plus quad AD797 OpAmps biased in pure Class A. These OpAmps are famous for their transparency and clarity. If you’re a “clinician” (like Gavin in happy mode), this module is for you.
  • ACX-I #4: $119
    This input module features ultra low noise quad JFET transistors plus dual OPA1612 OpAmps biased in pure Class A. These are the same OpAmps we use in the IV stage of Pulse X Fi DAC. They’re very detailed, but still organic sounding. This combination is Larry’s personal favorite for classical music out of the five options we offer.
  • ACX-I #5: $159
    This input module features ultra low noise quad JFET transistors plus dual famous AD8620 OpAmps biased in pure Class A. Of all our options, these OpAmps are the most precise, the most technically perfect, high speed and low noise.

Five ACX-V Options (For solid-state HPA only; Pulse Tube HPA uses dual 6922 tubes in its voltage amplification stage)

  • ACX-V #1: Included
    This voltage amplification stage module comes standard with your Pulse HPA and features quad JFET transistors plus dual LM4562 OpAmps biased in pure Class A. These are the OpAmps that we use in the Pulse DAC too.
  • ACX-V #2: $80
    This voltage amplification stage module features quad JFET transistors plus dual OPA2604 OpAmps biased in pure Class A. These are the same OpAmps that we use in our first prototype Geek Out. In our opinion, they have a all the signatures of a “Burr-Brown” sound. They’re a little bit on the warm side, and sound a little laid back. Classic.
  • ACX-V #3: $100
    This voltage amplification stage module features quad JFET transistors plus quad AD797 OpAmps biased in pure Class A. Again these OpAmps are famous for their transparency and clarity. If you’re into a more clinical sound (like Gavin in happy mode), you should give this module a drive.
  • ACX-V #4: $120
    This voltage amplification stage module features quad ultra low noise JFET transistors plus quad LME49990 OpAmps biased in pure Class A. These OpAmps present the listener with a bit warm sound and a lot of dynamic range. They’re very strong. One of Gavin’s favorites too.
  • ACX-V #5: $160
    This voltage amplification stage module features ultra low noise quad JFET transistors plus quad OPA827 OpAmps biased in pure Class A. This OpAmp is Larry’s personal choice in the VAS on single-ended output in his prototypes. A discrete ultra low noise JFET plus a famous JFET input OpAmp equals one of the best JFET sounds in the world.
Circuit Topology

Pulse Headphone Amp's voltage amplification stage works directly with its analog volume control circuit. By doing it this way, it won't attenuate your music in the first buffer stage of headphone amp like other devices (which decreases the SNR performance). It's the best variable gain design available, maintaining a good noise floor and signal to noise ratio.

We know the importance of slew rate, which is defined as the rate at which voltage can change within the amp over time. Our current feedback structure is placed at the output, keeping Pulse Headphone Amp's slew rate above 2000V and preventing odd order distortion anomalies. Many of our competitor's slew rates clock in at only 20 to 100V.

To address the issue of power reserve, Pulse Headphone Amp's output stage keeps twice its rated power in reserve just in case you want the cannons in Tchaikovsky's 1812 Overture to feel like they're taking aim right at you.

Features as Unique as Our Backers
  • Ultra-wide bandwidth for high-resolution listening
  • The most versatile headphone amplifier on the market, outputting 100 mW from the 3.5mm output (perfect for IEM's) all the way up to 10,000 mW (for hard-to-drive cans).
  • No gain switch needed. Each output connector is optimized for the proper power output of what will be connected to it.
  • Fully-balanced analog volume control.
  • Fully-balanced precision DC servo on each output.
  • Instant Power and Current Feed technologies. You'll get the punch you need when you need it.
Technical Specs

The History of Pulse Headphone Amplifier

Back in 2009, Larry was on a quest to promote the importance of high-resolution audio. He had been building the first 32 bit/384 kHz bit perfect resistor ladder DAC, and so he was traveling to speak who anyone who would listen, which included a visit to Intel, one of his first investors, and International CES in Las Vegas.

At the time, he was demonstrating his DAC using a headphone rig. He'd chose the HD800 over-ear headphones from Sennheiser as his reference, but he couldn't find a headphone amp with a wide enough bandwidth to reveal the beautiful nuances of 384 kHz digital music; nor could he find an amp with enough power to effortlessly drive his big cans. He needed a fully-balanced, dual-mono amp with a DC coupled, non-negative feedback output. And since he was demoing 384 kHz music, he needed a bandwidth of at least 200 kHz.

He couldn't find such a beast, so he built it himself.

The feedback he received from his demonstrations was remarkable. Interestingly, he found that even people who didn't self-identify as audiophiles were touched by the music they heard through his rig.

After this experience, he went to work and finished the development of Da Vinci DAC. The headphone amp, sadly, has only been enjoyed by a very few people since. Now six years after its first development, we're excited to offer you the improved version of his last (but not first) headphone amplifier: Pulse Headphone Amp.

We expect to begin accepting contributions for Pulse Headphone Amplifier on February 23rd. If you have any questions, please head on over to the Force Forum and ask them there.

Power Supply

Pulse Headphone Amplifier comes with low noise 12VDC switching power supply. And we recommend you use Pulse HPA and Pulse Tube HPA with our Pulse LPS4. Pulse HPA needs one 1.2A 12V output from LPS4 (or LPS). And Pulse Tube HPA needs one 1.2A 12V, one 500mA 12V output from LPS4.

Again, HPA works with Pulse LPS or LPS4. Tube HPA needs LPS4 to provide one 500mA 12V (for Tube heater), and one 1.2A 12V supply (for the rest of the circuit)

Pulse Headphone Amp FAQ's

Is the Pulse HPA fully discrete and op amp based? Would that make it similar to the Pulse DAC headphone out except with a lot more power?
Pulse HPA is an opamp/discrete hybrid. Pulse Tube HPA is an opamp/discrete + solid state/tube hybrid. "More power" is one difference, but there are at least three other major differences:

  1. Pulse HPA has THREE dedicated headphone output circuits, optimized for IEM's, standard headphone, and hard-to-drive cans. While Pulse DAC uses a gain switch (similar to other popular headphone amps), Pulse HPA uses separate, dedicated circuits.
  2. Pulse HPA features an optimized analog volume control. If you use Pulse DAC is concert with your Pulse HPA, you have a combination of digital and analog volume controls. We'll publish an article on our blog about this soon.
  3. Pulse HPA has no digital circuitry. It's pure analog!

Has it been confirmed anywhere if a single LPS4 can look after both the Pulse and HPA (of either type). I assume it uses one of the 12v rails?
Yes. Please see the updated power supply area for a description.

If I commit to an HPA perk now and a better bundle one comes along, can we get an "add-on" perk to bring us to parity?
Yes. That will happen soon.

Is it required to purchase separate tubes for Tube HPA?
Yes. We offer a pair of JJ E88CC/6922 Tubes here on the campaign for $49.

What is the maximum power output on 1/4'' and 3.5mm headphone output? 
On 1/4'' headphone output, HPA could output 1000mW @ 16 Ohm load. And on 3.5mm output, it could output 150mW @ 16 Ohm.

Pulse Tube Preamplifier (Back to Top)

Put Analog Back Into Your Music
For so many of us, the drawback to listening to digital music is that is sounds too, well, digital. Pulse DAC does a great job delivering both precision and warmth to your stereo, but if you really want to put analog back into your music, Pulse Tube Preamplifier is a must. It uses 6922/6DJ8 tubes to give you a very wide bandwidth, and a low noise floor. With its warm and charming characteristics, prepare to spend a lot more time listening to your music!

Pulse Tube Preamplifier is designed to be the center of your desktop audio system. Use it to choose your source, whether it's Pulse DAC or something else!

Pulse Tube Preamplifer features two analog inputs: one balanced and one single-ended. Choose between the inputs easily by pushing the volume knob in. There are two outputs: one balanced, and one single ended. Volume attenuation is controlled by a large, comfortable knob on the front panel.

Circuit Topology

Technical Specs

Pulse DAC (Back to Top)

Pulse DAC is an audio digital-to-analog converter and headphone amplifier that was crowd-designed and crowd-funded here on Indiegogo! Since we launched the campaign, word has spread quickly and Pulse DAC has become 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.

What does Pulse DAC do?

Many people don't know this, but our human ears can't actually hear digital audio.

Digital data has to be converted into analog before we can hear it. To do this, we use digital-to-analog converters, also known as DACs.

DACs are everywhere: in our phones, in our cable boxes, in our computers. Seriously. They're everywhere. The problem with the DACs that we find in all of our devices is simple: they're made to do the job with the least amount of effort and the lowest cost to build.

Pulse DAC is designed to differently. Instead of just barely getting the job done, it goes the extra mile to get the job done well. Very well. So well that there's no other DAC that can do what it does without having to pay three times the price.

Three different configurations.

Pulse DAC: This is what others might call a base model, but we prefer to think of it as where awesome starts.

Pulse DAC X: This is a fully-balanced, dual mono version of Pulse DAC. On the front, in addition to the 1/4" stereo headphone jack, you get a four-pin balanced headphone output. On the back, there's another way for your stereo: a pair of balanced XLR outputs.

Pulse DAC Xfi: This is Pulse DAC X on steroids. Remember that optional dual femto clock upgrade? This is where you get it. It also has upgraded passive components (capacitors and resistors) as well as upgraded active components (opamps and controllers).

Pulse LPS (Back to Top)

LPS stands for "linear power supply." If you really want to get the most out of Pulse DAC, PULSE LPS is a must.

Pulse LPS takes dirty AC power from the wall and delivers clean DC power to Pulse DAC. This clean DC power has very low noise, which improves the sonic quality of the music coming out of Geek Pulse. With clean power, you get more natural music.

As an added feature, Pulse LPS can be used to clean the noise off of the USB connection from your computer to Pulse DAC. Just connect your computer to Pulse LPS using a USB cable, then connect Pulse LPS to Pulse DAC (or any USB DAC, for that matter) using a second USB Cable. When you do this, Pulse LPS 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.

Special note: With USB 2.0, cable length is very important. You cannot go longer that five meters in total length and expect consistent results. Because Geek LPS does not incude a repeater or amplifier (due to noise concerns), the sum of the lengths of both the input and output USB cables cannot exceed five meters.

Two different configurations.

Pulse LPS: This is Pulse DAC's linear power supply buddy that we told you about earlier. It has one 120 or 240 volt AC input, one 12 volt DC output, one USB input, and one USB output.

Pulse LPS4: This is just like Pulse LPS, but it has four 12 volt DC outputs instead of just one. It's perfect for other audio gear you might have that uses 12V DC power.

Pulse Power Amplifier (Back to Top)

Amplifiers have a simple, but very important task. They take the audio signal from their input, amplify the signal by adding more "juice," then pass it along to your loudspeakers. It sounds easy, but it's actually quite difficult to make amplified audio sound "unamplified."

With this in mind, we we decided to attend to the amplification process, with a focus on a more efficient use of power. Ultimately, we developed four solutions that improve the sound quality, and ensure that everything can fit inside a very small footprint.

  • Multi-Zone Class A (MCA): With our innovative MCA Amplification, Pulse Power Amp automatically adjusts to the most efficient amplification level to fit your listening volume.
  • Bipolar Instant Power (BIP): With BIP Boost technology, Pulse Power Amp holds power in reserve for sonic events that have more "boom." Pulse Power Amp's bipolar power design will make the power output slew rate faster than ever. You need bass power, you got it, instantly.
  • Ultra-Wide Bandwidth: True to LH Labs' design philosophy, Pulse Power Amp has an extremely wide effective bandwidth.
  • Smart power management: With an automatic shut-off mode, Pulse Power Amp provides power when you need it and smart energy management when you don't.
Three Configurations

Accessories for your Pulse Audio Components (Back to Top)

We've created these little goodies that match up perfectly to your Pulse Source, Pulse DAC, or Pulse LPS.

LightSpeed 1G USB Cable: LightSpeed 1G is an affordable high-end USB cable that boasts more than twice the bandwidth of USB 2.0's Audio Specification standard. Due to its wide bandwidth, the USB controller inside your DAC isn't overburdened when jitter makes its way into the signal, making your DAC run optimally and signal noise-free.

LightSpeed 1G Micro USB Cable: With exactly the same topology as the standard LightSpeed 1G, this cable is fitted with a micro-USB connector allowing you to connect mobile devices to your DAC.

LightSpeed 2G USB Cable: This USB cable's bandwidth is four times USB 2.0's standard bandwidth of 480 MHz. Similar to LightSpeed 1G, the wide bandwidth of this cable ensures a low-jitter signal environment inside your DAC, giving you lifelike, bit-perfect music.

Technology breakdown. (Back to Top)

About LH Labs

LH Labs is an amalgamation of audio geeks and engineers who have partnered together with one sole purpose in mind: bringing the sound of high-end audio to the masses.

Based in Northern California, the epicenter of the high-end audio industry, LH Labs was founded on the principal that music lovers deserve something better than just the "usual." We've made it our mission to create the best products possible for both audiophiles and music enthusiasts.

We've earned all kinds of awards, including a CES Innovations Honoree Award, A Publisher's Choice Award from TONEAudio, a Greatest Bits Award from Audio Stream, a Writer's Choice Award from Positive Feedback Online, and a Blue Moon Award from We've been featured in Forbes Magazine, Entrepreneur Magazine, The Wall Street Journal, The Los Angeles Times, The Street, Stereophile Magazine, The Absolute Sound, The Business Journals, and The Daily Swarm, among many other publications.

The LH Labs Team

Larry Ho, Electronics Engineering Lead
Always challenging the status quo. A die-hard tube, vinyl, high-definition music lover.

Gavin Fish, Marketing & Communications Lead
The nerdiestest marketer on the West Coast. Gavin is LH Lab's campaign architect and lead communicator.

Casey Hartwell, Online Media Lead
Social media enthusiast. Record Facebook session without going to the bathroom: 51 hours, 22 minutes. Recommended by 4 out of 5 people that recommend things.

Kayla Bejsovec, Industrial Design Lead
Kayla loves four things: bionic cats, Rock Band (in expert mode), Taylor Swift, and fresh industrial design. Not in that order.

Frequently Asked Questions

Besides 6922, what other tubes can I use in your Pulse tube gear?
6DJ8/ CCa / 6N11 /ECC88 / E88CC / E188CC / 7308 / 6N23P / 6H23 / CV2492 / CV2493 / 8223. Try to find a close match pairs. And don't mix them.

I've changed my mind. Can I get a refund?
Sorry, Indiegogo's policy is No Refunds. Unfortunately, there's nothing we can do about this. When your contribution is deposited into our PayPal account, it comes from Indiegogo, not from you. So if we were to refund your contribution, it wouldn't make it back to you. Please see Indiegogo's rules here.

What is the difference between Geek Out, Pulse DAC and Vi DAC?
Pulse DAC is a desktop version of Geek Out; the conversion and analog circuits are shared by both products. The difference between them is mostly in the power circuit. The USB bus powers Geek Out. A very clean DC power circuit powers Pulse DAC. Additionally, Pulse DAC has multiple digital inputs and has both a headphone output and a line stage output. Vi DAC is the home stereo version of Pulse DAC. It integrates the linear power supply of Pulse LPS and the digital and analog circuits of Pulse DAC into one chassis. It comes with an option tube output stage.

What kind of headphones can I use with Pulse DAC or Vi DAC?
We're including a gain setting switch in Pulse DAC/Vi DAC thanks to the suggestions of some of the backers of the campaign. With this switch, Pulse DAC and Vi DAC works well with 99% of the headphones that are on the market, including IEMs.

What kind of speakers can I use with Pulse DAC or Vi DAC?
You can connect Pulse DAC or Vi DAC to speakers in two different ways. First, you can use self-powered speakers— speakers with an amplifier built into them. Second, you can connect Pulse DAC or Vi DAC to a stereo amplifier, which in turn powers your speakers. Either way, it will sound great.

Can I get multiple perks?
Yes! You can back our campaign as many times as you want, choosing as many perks as you want.

Can I change my perk?
Unfortunately, not during the campaign. But before we send you your gear, we'll send you an email with a link to a system that will help you manage your perk, input your shipping information, and purchase add-ons if you choose.

When you ship, will you please declare a lesser value on the customs form?

Is the USB connection asynchronous?
Yes. Yes, it is.

How does volume control work on Pulse DAC or Vi DAC?
We handle volume attenuation in the digital domain using a 64 bit volume attenuation circuit.

What's the warranty?
Pulse audio components each come with a 1 year limited liability warranty that protects you against manufacturing defects.

How much is shipping?
It really depends on where you live and what shipping service you choose. Rather than include an average shipping cost in the perk price, we prefer to give you shipping weight and dimensions so you can get a shipping quote. When it's time to ship, we'll ask you to choose a carrier and will send you a PayPal invoice to cover our costs.

Shipping dimensions:

Pulse DAC: 14" width, 14" depth, 5" height, 8 lbs
Pulse DAC X: 14" width, 14" depth, 5" height, 9 lbs
Pulse DAC Xfi: 14" width, 14" depth, 5" height, 9 lbs
Pulse LPS: 14" width, 14" depth, 5" height, 9 lbs
Pulse LPS4: 14" width, 14" depth, 5" height, 11 lbs
Vi DAC: 20" width, 16" depth, 6" height, ~35 lbs

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total funds raised
Original campaign was 3,090% funded on December 27, 2013
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