Product Review

ONIX H6550 Integrated Tube Amplifier

May, 2007

Piero Gabucci



● Power: 50 Watts RMS x 2 into 8
   Ohms or 4 Ohms (Transformer Taps)
● Tubes: Two 12AX7, Four 6SN7, Four
● THD+N: 1%
● Input Impedance: 250 kOhms
● S/N: 90 dB
● Dimensions: 7.4" H x 17" W x 15" D
● Weight: 74 Pounds
● MSRP: $1,995 USA



Following a product as revered and successful as the SP3 integrated amplifier, ONIX steps up and produces the new H6550. How could I possibly resist the temptation to request one for review? The good people at AV123 graciously offered to send it to me.

Anyone who reads Secrets on a regular basis cannot avoid the likes of AV123, lead by Mark L. Schifter, owner and founder of the ever evolving group. Along with the wildly popular Rocket speakers, you'll find their electronics lines including Emotiva and ONIX.

ONIX is the branch of Mark's stable of companies specifically for the two-channel audiophile. I had the pleasure of reviewing the SP3 integrated tube amp Mark affectionately refers to as "our little friend". I ended up making the SP3 review unit a permanent fixture in my system, and why not, it's an outstanding value. It offers two inputs and 38 watts per channel. Not bad when it comes to tube amplifiers, but Schifter and company did not rest, and the new four-input H6550 was developed.

The Design

Unpacking all AV123 products is an event in itself; you become part of the club once you place those white gloves on your hands (really meant to aid in handling delicate tubes that don't appreciate oily fingers, but don't panic, we all have them). Lifting the 74 pound unit is a challenge, but don't despair, quite worth the effort.

Whereas the SP3 is glossy gray, the H6550 is liquid piano black. Gone from the design of the H6550 are those curved elements that gave the SP3 unusual styling. The newer version is larger and much boxier, almost shouting how much more serious it wants to be taken.

But oh that finish is stunning!

The H6550 sits on three sturdy legs, giving good isolation from its stand.

On the face of the H6550 you'll find three control knobs. A centered volume control is flanked by power on/off and an input selection knob. With four RCA input options, ONIX labels them Tape/CD/Aux/Tuner.

Turntables have become popular again, very much like vacuum tube amplifiers themselves. I happen to plug my iPod into one of those inputs, but that experience comes later.

The H6550 is a class A/B push-pull design, which means among other things, it idles in a lower current, thereby allowing it to produce more power under demand.

On the rear you'll find four sets of RCA jacks for those inputs, sturdy gold-plated right and left speaker binding posts for both 4 and 8 ohm speakers, a removable power cord, and a fuse replacement location.

The sides have small holes for a small screwdriver, which is for bias adjustment. ONIX ships the tubes in place and with the bias properly set (2 volts).

The main set of tubes is covered by a removable cage cover, easily popped off for tube replacement or just to watch the tubes glow. Keep it on if you have a cat or small children, they run quite hot. Take the cage off if you like to see the tube filaments glowing.

The high quality compliment of tubes includes 10 (similar in quantity to the SP3), and although they share only one tube type, a pair of common preamp high gain 12AX7s, the similarities end there. Completing the array of tubes includes four medium gain preamp 6SN7s and the power-generating 6550s, each channel having a pair. The 6550 output tubes are known for their reliability and produce an impressive 50 watts per channel.

Having a look "under the hood" you'll discover craftsmanship and quality, and neatness counts. Notice that probably 95% of the circuit is hard wired, rather than PC boards. This is one of the features that tube lovers love.


When I reviewed the SP3, I was fortunate that the excellent XCD-88 CD player was sent along with it; my regret is I didn't have the upgraded CD-3 CD player from ONIX to partner up with the H6550.

For those interested, I used primarily for review my reference Krix Symphonix speakers, a Denon DVD-2910, and Ethereal cables throughout. I did swap the stock power cord with a new Wireworld "5-squared" unit. This setup is right in line with the sub-$2k ONIX. I've had the H6550 so long (thank you, Mark), that I was able to review a McCormack universal player and a pair of unique Onkyo speakers (the D-TK10) all with the Melody.

The Sound

Let me get the iPod experience out of the way first. You purists don't need to chastise me for the experiment, I couldn't help myself, I needed to give it a try and I'm glad I did.

To my absolute surprise, the H6550 delivered such superb music from the iPod as a source that I left it plugged in for most of my background listening. I certainly won't pretend to compare the MP3 player with a quality CD player: bass was somewhat lacking, but acceptable, treble was pleasant especially with vocals, and the highs lacked some detail but were reasonably defined. I give full credit to the ONIX.

On the Bench: The H6550 delivered 18.97 volts into 8 ohms (each channel) at 1% THD+N (defined as clipping), which is 45 watts. At 5 volts into 8 ohms, and 1 kHz, THD+N was 0.32%. The measured frequency response was 20 Hz - 30 kHz ± 1 dB.

The H6550 is so quiet (no audible hum or hiss), I was astonished. It was dead silent when the volume was completely turned up (without a CD playing, of course).

Andrew Manze and The English Concert's Mozart 3 Violin Concertos is a wonderful recording, and I was very interested in the performance of the lighter strings. This disc is superbly emotional; the Melody sound grabs your senses and thoroughly engages the music. Track 5 "Andante cantabile" is sufficiently soft when the solo violin plays, yet robust with the full ensemble. Spatially, the H6550 holds the solo violin in its prominent position, center forward.

What the ONIX offers is a very controlled and neutral sound in the sense that it might appeal to a vast number of listeners. Don't expect extreme detail in the upper midrange. Do expect smoothness and effortless playback however.

Although cliché is to refer to a tube amplifier sound as "warm", the concern is warm turns into dark – this is not so with the H6550. I enjoy René Marie's voice, and her Serene Renegade is a reference CD for me. This recording is very live-sounding in that her voice seems unexpurgated by the digital process. Her lips puckering, her lungs filling with air before she bellows a note – the ONIX truly delivers her voice. Tonal quality is dead on and once again absolutely engaging.

I don't need much of an excuse to pull out the CD Miles Davis Kind of Blue. John Coltrane's tenor saxophone is so wonderfully isolated, the impression is he's playing in the room with the CD - breath and soundstage from the H6550 is chilling.

I was curious about Sting's new CD Songs from the Labyrinth – an interpretation of Elizabethan songwriter John Dowland, a 16th Century English composer. Although I don't quite understand Sting's need to express himself in this music, I did find some of the tracks extremely pleasant. The CD's centerpiece is the use of an Archlute – an Italian renaissance instrument with up to 14 strings, a second pegbox for additional bass strings. Track 7, "The Battle of Galliard", is an instrumental, and if you're a fan of stringed instruments, regardless of its Renaissance flavor, the music is purely magical. The ONIX reveals a deep richness to this instrument, and I was mesmerized by the warm wood resonance.


The appeal of the ONIX H6550 goes beyond sound - an effort was made to design an integrated amplifier that is reliable and to give its owner many years of elegant and trouble-free music. But also, this is an audiophile-grade product. As the ONIX will more than satisfy any seasoned tubeophile, it will yet provide a newbie an opportunity to show off something very different to his/her transistor friends.

Ironically it's almost too bad the H6550 came after the SP3 – I hope this brilliant integrated doesn't get lost as the descendant rather than a successor to the equally brilliant SP3. The superb look and feel of the H6550 drips with quality, and I'm dumbfounded to find anything unappealing from Melody either in build or performance. Mark's "little friend" has a grown up version.

If you're a tube roller, I'm sure you could tweak to your heart's content with the H6550 – I didn't for the very reason that the stock tubes offered what I would consider a superior and totally satisfying sound. If it is obvious in the review that the H6550 totally engaged me emotionally, then I say to you, "Mission accomplished."

- Piero Gabucci -

© Copyright 2007 Secrets of Home Theater & High Fidelity

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