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Equipment Review

December 1999

Harmonic Technology Pro-Silway Mk II Interconnects, Pro-9 Plus Speaker Cables and Pro-AC11 CL3 Power Cords

by Jeff Fritz


Review Summary
Sound "The treble range was most notably affected…the nuances of fine recordings were better exposed and presented"; "midrange clarity was improved…the clarity with which vocals were presented draws you in"; "very good in the lower registers," but not the best Jeff has heard in this regard.
Features Patented casting process produces 99.999997% purity and low crystallization.
Use Harmonic Technology offers an array of cables, so choosing based on budget or sound quality is easy.
Value "When considering the extreme price tag on many of the state-of-the-art cable contenders, the Harmonic Technology cables offer unrivaled bang for the buck."

It makes sense to review products that are of interest to our readers. That is, after all, our reason for being in existence. The SoundStage! team attempts to provide articles that are interesting and informative based on components that are claimed to have good sound. Of course, all high-end companies make this claim for their products, so there’s no surprise there. However, when the audiophile community emanates a buzz based on a particular component or company, we at SoundStage! listen (to you and the component) and report our findings.

Harmonic Technology is a prime example of this occurrence. I first heard of this company and their cables in late 1998 when several of our reviewers had positive results with the line. Greg Weaver, in particular, raved about Harmonic Technology’s products in his December 1998 "Synergizing" column. In addition to this, it seems that many of the newsgroups and message boards (including our own Talk Online) have fielded discussions about these California cables. As of late 1999, people are still talking, so we’re still reporting.


I was asked to review formally a complete Harmonic Technology system that was chosen by the company to mate well with my components. The individual cables that make up the top-of-line Harmonic Technology package include the Pro-9 Plus speaker cable, Pro-Silway Mk II interconnects and the Pro-AC11 CL3 power cords. This trio replaced a horde of Transparent Audio Super XL cables that have served me well for some time. Once the swap was complete, I let my system play continually for five days, logging in 120 break-in hours before any critical listening took place.

My impressions were formed by auditioning the Harmonic Technology combination in its entirety. This was done to oust completely the effects of the Transparent networks and remove any potential compatibility problems between a networked cable and its "naked" counterpart. Toward the end of the review period I replaced individual Harmonic Technology cables with budget-priced substitutes in order to subtract (and thereby identify) individual cable signatures. Only one cable set was out of the system at any given time. This methodology was chosen primarily to hear the Harmonic Technology system without the signal being filtered through any device other than the associated components. It also allowed the Harmonic Technology cables to burn in together and "settle in" with the system.

Review system

My review system includes a Pioneer 606D DVD player as the primary source. This player has bettered several expensive CD players (in my system as well as others’) and to my ears is hard to fault at the price or many times higher. Speakers were the Wilson Audio X-1 Grand SLAMM Series IIs. A Levinson 335 and a Coda 04R line-stage preamp provided power and control functions respectively. A dedicated 30-amp line supplied the power amplifier while all other components used their own 20-amp version. No power-conditioning equipment was used, and the review system did not change (other than the aforementioned cable substitutions) for the entire period.

Technical description

The entire Harmonic Technology line shares some important design similarities that separate it from other cables. Although many companies use copper for the conductor material, Harmonic Technology has patented a casting process that achieves a claimed purity level of 99.999997 %. This is accomplished by using a preheated machine that prevents the massive crystallization that occurs when copper cools too fast. Harmonic Technology provides photographs taken from an electron microscope showing the huge number of crystal barriers found in normal wire and, of course, a comparison photo of a Harmonic Technology model. The purity of the OCC copper is said to remove the crystal barriers, which lowers distortion and improves sound quality. Harmonic technology also pays equal attention to insulation material and winding geometry to produce an overall well-engineered cable.

For those wishing for more technical information, I would refer you to Greg Weaver’s "Synergizing" column. Here you’ll find a more detailed description of the Harmonic Technology cables’ construction process and why it’s important. His column is an appropriate preface to this review as you will find many similarities (and some important differences) in our observations. As they say, two heads are better than one, especially with audio reviews.


Consistent with Greg’s findings, the treble range of my system was most notably affected by the Harmonic Technology cable system. Resolution of fine detail was enhanced with a deeper look into the upper harmonic structure. This does not imply that tonality was altered in any way, but that the nuances of fine recordings were better exposed and presented. More "air" seemed present around individual notes, creating a more transparent, lifelike presentation. I definitely felt that I could hear further into the music than ever before. This effect aided low-level, late-night listening sessions in that my system sounded fully "alive" even at lower-than-optimum volume settings.

Microdynamics were improved, allowing me to track small dynamic shifts and gradations. Good recordings certainly benefited from the above characteristics. One such example is Rebecca Pidgeon’s The Raven [Chesky JD115]. This Chesky release allows you to hear a close approximation of the recording venue. "Seven Hours" in particular is quite realistic without any artificial highlighting. Oddly enough, the enhanced upper-range resolution did not approach bright, bleached or grainy territory. In fact, the entire treble region seemed silky smooth and had a naturalness that was very pleasing. Greg Weaver’s term "bronzy" is fitting, although I don’t know exactly why. There was no coloration that I could detect, but a bronze feel accompanied the sound nonetheless.

Midrange clarity was improved to a lesser extent than the upper range. Again, this was most noticeable on pure, closely miked recordings. The oft-used cliché that "a veil was lifted" from vocals seems quite accurate. At first it may actually seem that the Harmonic Technology cables are slightly forward in their presentation. I don’t believe this to be the case though. The clarity with which vocals were presented draws you in; it’s a more intimate portrayal, yet properly scaled and placed. Very little flavor or character is noticeable when listening to well-recorded piano such as Clara Ponty’s "Jeux d’Oiseaux" from her self-titled CD [Philips 314 536 155-2]. The transition in and out of the critical midrange is accomplished without smearing or congestion.

I suspect my observations about the low-bass performance of the Harmonic Technology cables are irrevocably colored by referencing a system filled with Transparent Audio cable (low bass is a well-documented strength of this line). The Harmonic Technology cables are very good in the lower registers, but not the best I’ve heard. It certainly could be argued that the networked cables emphasize (in terms of power) and over-damp (with respect to attack and decay) low-bass notes. In any respect, the Harmonic Technology cables seem a bit loose on certain recordings. They do not roll off the low frequencies, but they are just shy of the powerfully tight impact of the Transparent Super XLs.

Greg Weaver stated that he heard a "vivid, yet realistic soundstage and stable phantom image." I heard the very same characteristic in my system. In particular, the stability of the soundstage was a confidence-inspiring trait that prolonged my listening sessions late into the night. When the music locks in, it takes some stress off the imagination and allows you to connect with the artist. This was a most rewarding attribute. Listening to Airto Moreira and the Gods of Jazz jam session, Killer Bees [BW041], illustrated the Harmonic Technology cables’ ability to place, with precision, all the performers within the soundstage.


Substituting Apature silver cables was a fascinating exercise. With respect to the speaker cables, the difference in sound quality was equal to that of replacing (in this case, downgrading) a preamp or power amp. The treble character lost much of the magic originally present when the Harmonic Technology system was intact. Referencing the Rebecca Pidgeon CD again, I detected a loss of detail retrieval that masked this high-quality recording’s resolution. To a lesser degree, the same type of "masking" effect was heard when interconnects were substituted. This exercise tells me more about the importance of having high-quality cables in a system than it does about the Harmonic Technology cables’ relative strengths when compared with those of the competition. It does conclude for me that one weak link in the chain can counteract the cumulative strengths of several others.

Exchanging the power cords with the stock units did prove to be less noticeable. I heard some degradation when the Harmonic Technology cord was replaced on my Levinson 335. I am a little uncomfortable in trying to describe the switch though. I know I run the risk of being banished from the "my ears hear everything club," but I call ‘em as I hear ‘em. The same was true for the Coda line-stage preamp and its stock cord. Of course, having the choice, I would keep the Harmonic Technology system in tact for peace of mind.


In several very important areas, the Harmonic Technology cables are the best I’ve heard. In terms of midrange clarity, treble purity and air, and low overall coloration, they outperformed my long-term reference. If I had to pick nits, their low-bass control and impact aren’t state of the art, but even here they are very good. The speaker cables and interconnects improved the overall sound of my system significantly. The power cords did not dramatically alter sound quality, although it should be noted that several of my components offer some filtering/shielding in this area, plus I have dedicated lines. Your mileage may vary, and a home audition is advised.

Finally, I’d like to touch on an issue that Greg Weaver concluded with in his article: value. When considering the extreme price tag on many of the state-of-the-art cable contenders, the Harmonic Technology cables offer unrivaled bang for the buck. Build quality is excellent and the sound quality offered, at any price, is hard to fault. Review components come and go. Who knows what will synergistically fit my system with a source or amplification change? For now, though, add me to the list of music lovers singing the praises of Harmonic Technology.

...Jeff Fritz

Harmonic Technology Pro-Silway Mk II Interconnects, Pro-9 Plus Speaker Cables and Pro-AC11 CL3 Power Cords
Pro-9 Plus speaker cable: $888 USD per eight-foot pair; Pro-Silway Mk II interconnect: RCA, $399 per meter pair; XLR, $439 per meter pair; Pro-AC11 CL-3 power cord: $180 per two-meter cord.
Warranty: Lifetime to the original owner

Harmonic Technology
13100 Kirkham Way
Unit 212
Poway, CA 92064
Phone: (858) 486-8386
Fax: (858) 486-6633

E-mail: harmonic@san.rr.com
Website: www.harmonictech.com

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