Icon Audio HP8 MkII Triode Headphone Amplifier

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"Icon Audio's All-Tube HP8 MkII Is Glorious With Any Pair of Headphones:

Tube Smoothness and Excellent Detail Multiplied by a Powerful Headphone Amplifier Equals Astonishing Sound"

Highlights:
• Class A, all Triode circuit
• Point to point wiring, no printed circuit board to "color" the sound
• Japanese Blue ALPS volume pot
• High quality 2W metal film, & wire-wound resistors
• Polypropylene audio capacitors
• Silver TEFLON audio cable
• Japanese steel EI transformers with low oxygen copper
• Custom hand wound output transformers 
• Ceramic valve holders for minimum leakage
• Gold plated Input & speaker terminals

$1950 MSRP

SkyFi Notes:
• Slight hum with no input signal. Not affected by volume. Normal performance for this design.
• Tested and working as it should throughout.
• In very good physical condition with slight signs of use.

More from Icon Audio:
Built just like Icon Audio's magnificent tube amps, yet designed for the specific demands of 'cans, the HP8 MkII tube headphone amplifier is a love letter to headphone listeners. Flexible, powerful and rich sounding, the HP8 MkII delivers the sonic goods and is built to last.

Created by an audiophile for audiophiles, the HP8 MkII is chock full of sought after "sound goodies" from PTFE coated Silver internal wiring and an ALPS Blue volume pot to the heavy steel chassis and gold-plated RCA jacks. The circuit is simple; all point-to-point wiring, no circuit boards in the signal path, all tubes, all triode and as sonically pure as Icon could make it.

The execution is fabulous with large Japanese made EI core transformers, metal-film and wire-wound resistors, polypropylene capacitors. HP8 MkII truly stands in a class all by itself. Even the gorgeous copper plate over the top is as functional as it is aesthetically pleasing. Listen to your 'phones as they were intended to be heard, with tubes. HP8 MkII makes it easy no matter what headphones you own. Or will own.

To satisfy audiophile cravings, the all-tube gain stage is built around the much venerated 12AX7, a tube renowned for its smoothness, detail, and fluidity. Further back, a pair of 6SN7s do the heavy lifting, these tubes as linear and rock-solid as they come. A custom hand-wound multi-tap output transformer gives the HP8 MkII optimum load matching ability with a broad range of compatibility. Easily swap between your hardest to drive headphones and your easiest, with a flick of the front panel switch.

"The HP8 just flows like a gentle breeze on a summer day, never forceful but always welcome and refreshing. The sound quality is simply beguiling, with all the stereotypical benefits of a single ended triode design and very few of the drawbacks...." - John Grandberg, Inner Fidelity

In addition to building HP8 MkII with utmost care, Icon takes the worry out by providing a two-year parts-and-labor warranty as well as full service and support for the lifetime of the product. That's how it should be, and while most competitors don't go to such extremes, Icon is happy to do so.

Click below to add our recommended matching cables from Kimber Kable, all brand new as SkyFi is an official Kimber dealer.

Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - Power Cords - Better

The SkyFi Testing Process for Tube Amplifiers:

We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect resistors and other passive components for signs of overheating. If tube arcing has occurred in the past we can usually spot discoloration on the output tube sockets. On vintage units we often spot check select capacitors for value and ESR.

If the amplifier passes visual inspection, we move on to a full test of all of the tubes. We use an Amplitrex AT-1000 Tube Tester which is capable of testing both emission and Gm with a high degree of accuracy. We document the results of each tube and replace any weak or suspect tubes before proceeding. When we power on tube amplifiers for the first time we usually use a variac and current limited AC supply and slowly raise the voltage up to nominal mains level while monitoring plate, screen, filament, and negative bias supply voltages where applicable. If everything is in order we feed a low level test signal into the amplifier’s input and monitor its output on an oscilloscope across an 8 ohm dummy load. At this point we are just looking to verify basic function and confirm that the output transformers are not damaged. Once we have verified that the amplifier is safe to operate, we connected it to full mains power. For fixed bias amps we set the bias to manufacturer spec. For cathode biased amps we monitor the plate to cathode voltage to determine if the output tubes are operating in a safe range. Once the output section is verified we move onto bench evaluation.

We start by feeding the input of the amplifier with a low level 1KHz test signal, slowly increase its amplitude while monitoring the amplifier’s output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours. For tube amps we like to run this test at least twice. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when it has fully come up to temperature. We find this step to be essential, especially for vintage units.