HERRON AUDIO

Solid State and Tube Electronics
 

Though I've heard Herron gear a number of times in other systems, until recently I'd not had the opportunity to evaluate their equipment in a controlled environment. A good friend of mine (who now writes for a prominent webzine) was kind enough to send me his unit for a listen, and so I found myself one on one with the VTSP-1 tube line stage. Before I recount my experience, let me give you some background on Keith Herron the man and his philosophies on the subject of audio design.

            Mr. Herron is a degreed Electrical Engineer, an accomplished musician (drums, piano, and trumpet), recording engineer an audiophile (duh!) and has spent a good deal of time designing audio gear (duh, again). Unlike some with an engineering background (sorry, my classically trained friends, no offense intended), Keith is very open minded and perfectly willing to trust his ears as the consummate test and measurement device. Indeed, he’s found it necessary unlearn many of the traditional philosophies of audio design, freeing him to explore new directions.

            From the beginning Keith Herron focused on a primary goal: understand why a component sounds the way it does. Reverse engineering, of sorts. As Keith puts it - “Audio Pathology."

            His investigations uncovered many characteristics which he feels define ideal audio performance. Maybe the most important he terms “focus in time”. He writes: “If the beginnings and endings of events are clear and easy to decipher, then the highs and lows must be correct. When you have heard it done right, you will know immediately. With most capacitor, tube and circuit experiments, I do not even turn around and face the speakers. That clear focus in time is either there or it is not. There is nothing to agonize over. When the equipment has focus in time the music is easy to listen to, makes you want to tap your foot and provides both excitement and relaxation”.

The saying goes “the magic is in the details.” That statement is abundantly evident in the thoughtfulness and precision of Herron designs. A case in point is PC board layout. The way individual component parts (resistors, capacitors, etc.) are placed in relation to one another on the circuit board is recognized as an important facet of audio design. Even the layout of the traces on the board has an effect on performance. Herron products take that concept to dizzying heights. Keith has invested over 1000 hours per product optimizing the intricacies of board layout. 1000 hours! Such a monumental effort is testament to Mr. Herron’s fanatical attention to detail and pursuit of every last gram of performance.

            Herron designs are unique and often depart from convention. A good example is the design of the for volume control. Rather than the typical potentiometer, the VTSP-1 uses a 128 position electronic stepped attenuator - one for each channel (128 precision resistors and 128 electronic switches on one chip). The DC signal from the volume control commands a servo system (designed by Herron Audio) which dictates the positions of the two stepped attenuators in unison, providing much more accurate tracking than the typical volume pot. Herron Audio feels this circuit transcends the limitations and far surpasses the performance of conventional wiper or stepped switch attenuators. Ok, I can just see you analog guys rolling your eyes; this electronic approach can’t be good - must sound digital. Read on disbelievers.

The VTSP-1 and VTSP-2 have been designed with a high input impedance (100K nominal), which presents minimal loading to source components. It is known that third harmonic distortion increases when tube and solid state circuits are loaded below 100 times their output impedance, so keeping a high input impedance is very important. In an effort to lower crosstalk and improve high frequency response, many line stage preamps are designed with rather low input impedances. This design shortcut is used to improve measurable specifications but often sacrifices performance of the source equipment.

Accurate sound stage and lack of dynamic and frequency coloration are the result of careful selection and channel-to-channel matching of internal components with particular attention to accurate phase and flat frequency response. The human ear is extremely sensitive to frequency response variation, able to detect deviations in the range of millibels (1/100ths of a decibel). Matching component parts is a critical aspect of assembly. Herron Audio spends a great deal of time carefully matching circuit elements to minute tolerances, insuring optimal performance.

The term clarity sounds simple, but the way I use it here, is a multifaceted term. To have clarity a component must possess a number of traits. In my book clarity requires a low noise floor, good inter-transient silence, blackness of background and, as Keith Herron puts it, the ability to hear the beginning and end of each note.

A low noise floor is prerequisite to resolution of low level detail, and is one of the reasons Herron gear so carefully relays the subtleties and nuance of music. Those faint cues, often buried beneath a layer of muck, are critical in conveying music. The same low level details are required for the ear/brain to interpret dimension and space, recreating the soundstage.VTSP-2 has the lowest noise floor of any tube preamplifier I’ve heard.

                Regarding soundstage, Herron literature states: “VTPH-1, VTSP-1, and M150 have been designed to produce very accurate imaging and a sound stage having width, depth and layering, commensurate with the recording technique and venue. We chose not to artificially create a large "blooming" sound stage on all recordings since this would diminish the localization of instruments and vocalists. If the program material calls for a wide sound stage (as is often the case in stereo with spaced omni microphones in a reverberant concert hall), the sound stage will extend far outside the speakers. A monaural recording, on the other hand, will provide a sound which appears to emanate from a small space centered between the speakers. The voice of a singer should not be as big as the room".

On to the sound. After “wow,” the first word that came to mind was clarity. It only took seconds to realize that there was simply more information here than I’ve heard from almost any other preamp. And yet the information is not presented in a clinical or analytical way. It simply let's the music communicate. This preamp will draw you in more with whispers than with shouts.

As the company suggests, the soundstage is determined by the recording rather than being created or embellished by the component. Maybe it’s that the unit allows low level cues to be heard or the ability to define the commencement and termination of each musical note, I don’t know. What I do know is the soundstage is as believable and tangible as any preamp I know.

            From the practical side, Herron preamps are about the most user friendly pieces of tube gear you’ll find anywhere. No intensive tube matching, no need to anguish over expensive NOS rarities and forget about the need for frequent re-tubing are needed. Herron designs use the unglamorous Sovtek 6922 (tested/selected by Herron). The preamp has been optimized for this tube so tube rolling really isn’t necessary. Keith says many customers have experimented with other tubes and always come back to the plain vanilla Sovteks.

The tubes are used in an ultra conservative mode, running the tubes far, far below their rating. The 6922 is rated at up to 15mA, the Herron preamps operate the tube at 1mA or below. Tubes run so cool you can actually hold one in your hand that has just been plucked from the preamp. More importantly this conservative approach insures extremely long tube life. Keith tells me the tubes could last twenty years or more and there is no reason to replace tubes unless one becomes noisy.

So there you have it, a brief discourse on the VTSP-2, a truly wonderful preamp. You may not be in the market for a new preamp at the moment, but when you are, you'll be missing the boat if you don't audition this puppy.