Tubes versus Solid State
One of the oldest debates in high end audio is between the proponents of tube equipment and those committed to solid state designs.  There are arguments to support each position.

Solid state equipment is hassle-free—there's no need to replace tubes at periodic intervals; warm up time until reasonable performance is briefer than it is for tubes; and the component can be left on for long periods of time (and oddly, this will improve performance) without exhausting the finite life expectancy of tubes.  More significant in terms of performance, solid state equipment has better S/N figures than can usually be achieved by tube equipment, in part because of the inherent residual noise level of tubes.  Solid state equipment produces crisper edges, and thus sharper transients, because solid state IC's and transistors have a faster decay time than tubes.  Finally, far lower Harmonic Distortion figures can be reached with solid state equipment than can be reached by tube equipment, again in part because of the residual higher distortion levels of tubes.  There are other areas, such as Dynamic Range   where solid state equipment again usually excels over tube equipment, but the first three produce the greatest challenge for tube designers.

At first glance, this is an impressive list of advantages, whose sonic effects would weigh in favor of solid state designs.  But there are certain advantages that tube designs have over solid state designs that make the choice more complex.  

Tubes produce a rounder, fuller sound than do solid state components.  For many this adds a pleasing warmth and body to the music not easily achievable with solid state equipment.  In addition, tubes are better able to capture those higher order harmonics that distinguish the reedy quality of an oboe from that of a clarinet, the resinous quality of a string bass from that of a drum bass, and the sound of a soprano's breathy vocal chords better than solid state equipment.  For tube aficionados, this too is a big plus.  Finally, tubes, because of their inherently slower decay times, are better able to capture the musical rise and fall and ebb and flow of live music, which does not turn on and off the way solid state component parts do but instead flows imperceptibly from one rising or falling phrase into another. For many listeners, this slower decay time of tubes enhances the listener's experience of the music—that is, the music sounds more musical and involving when played over tube equipment.

Must one choose between these two opposing excellences?  The answer is no.  If the designer is insightful and creative enough, he can minimize the shortcomings of tube equipment while still preserving their excellences.  In effect, he can narrow and almost eliminate the advantages unique to solid state equipment. 

Since Signal-to-Noise is among the two or three most critical parameters of sonic excellence—one can't hear any micro-detail below the noise floor--a tube designer must first attempt to bridge the gap between solid state designs and tube designs in this critical area.  Many tube designers achieve this narrowing by elaborate feedback circuits.  While the use of feedback does lower the noise floor, the elaborate circuits required to do so complicate the signal path and thus introduce signal compression.  Thus while they gain in reducing S/N, they lose in sonic openness and transparency.  Joseph Chow avoids feedback entirely. But by virtue of his deep insight into materials and circuits he is able with his tube designs to achieve S/N levels that would do many solid state designers proud.  For example the S/N for the Audio Horizons TD 3.0 is -100dBv.

As further illustration of Joseph's ability to virtually eliminate this key sonic advantage of solid state designs, one need only compare the S/N figures of the Audio Horizons solid state DAC, the DAC 2a (-105 dBv) with these of the TD 3.0.   These differences are superb for a tube DAC when one realizes that a well known tube DAC with separate power supply costing over $12,000 is only -108 dbv.  Frequently, the S/N levels are reported using higher than 1 volt output ratings (usually signaled by the abbreviation dBv), say 2 volts or 3 volts, but the S/N at 3 volts, for example, will be about -10 dB better than at 1 volt.  Thus by using 3 volts output, the manufacturer is able to use a -10 dB lower S/N figure than he would if he used the generally agreed upon 1 volt standard.  Some manufacturers call this marketing.  In addition, sometimes the S/N figures on tube equipment are so poor they are not indicated in the website spec sheet.

By virtue of avoiding feedback and using a philosophy of classic design, Joseph is able to achieve the clear edges and fine transients characteristic of solid state designs.  And by designing balanced geometry interconnects with carefully designed capacitance, whether using RCA or XLR jacks, Joseph  is able to create tube designs that have clean but soft edges, that in a word, preserve all the excellences of tube design while achieving those common to solid state designs.

Finally, while Joseph can not overcome the residual higher distortion common to tubes, at 0.05 % THD he has achieved superb specs, where only the most rarified ear can hear the difference.  The same is true for his specs for Dynamic Range (better than 105 dB) and crosstalk or channel separation (98 dB @ 20-20kHz).  These are outstanding specs for a tube component and approach or exceed the specs of excellent high end solid state designs.

In essence, Joseph has created a tube DAC that weds the virtues of solid state design to those of tube design to create a superbly transparent sounding DAC.  

Introduction
The Audio Horizons TP 2.1 Stereo Preamplifier is a high end tube preamplifier boasting specifications found only in preamplifiers costing two to five times as much, such as razor straight linear frequency from 10Hz to 50kHz +1/-2 dB, THD guaranteed not to exceed 0.05% from 20Hz to 20kHz, dynamic range of  90 dB, signal to noise guaranteed to be in excess of 110 dBv, A weighted, and channel separation (crosstalk) better than  90 dB at 1kHz.   Individual TP 2.1 specifications come with each unit, and units typically exceed these specifications.

We invite you to compare these confirmed specifications with those published by other manufacturers of high end tube preamplifiers.  Then we invite you to audition the TP 2.1.

Design Features
A number of impressive design features in the Audio Horizons TP 2.1 contribute to its superb performance.  They include:

• The power supply uses a 10 times larger VA than needed in order to insure a stable soundstage.
• A capacitor bank comprising 12,000 uf on the DC filament.
• Independent channels each with a pure DC filament supply to reduce crosstalk between channels.
• Thirteen stages of regulation on high voltage provide better ripple regulation, which results in quieter noise levels.
• The use of a low ESR capacitor bank, with an extremely high 2,860 uf of storage in the HV section, to provide extra reserves when sudden instant sonic demands are made.
• In addition, the use of a cascode section increases the system's dynamic range, linearity, and responsiveness, thereby producing a punchier sound.
• The low output of the line out transformer design permits the use of long interconnects with minimal sonic degradation.
• All inner wiring uses Teflon silver coated wiring to provide optimum performance for many years, and to protect those who live in environments with high humidity. 
• 30 second delay after power is turned on to insure low start up noise and pop.
• RF shielded balance/XLR connectors eliminate contact impedance, insuring the lowest possible noise floor.
• All gold plated Teflon RCA jacks insure low connector loss and insure high signal transfer.

But while this extensive list describes some of the features that contribute to the TP 2.1's superb performance, they do not fully explain it.  Too truly understand how Joseph Chow has managed to achieve spectacular performance at a relatively modest cost, we have to spend a moment explaining how Joseph Chow's classic design philosophy differs from typical audio design philosophy.

Most of us are aware of the well-known division among audiophile designers between those who prefer solid state designs and those who prefer tube designs, but few are aware of other deep divisions.  The most important of these is between two audio electronic design philosophies--between those who seek to prune away as severely as possible the materials and circuitry used (who, for example, when designing a preamplifier have as their ideal, “a straight line with gain”).

Opposed to these minimalist designers are those who seek to overcome the inherent limitations of the materials used by elaborating circuits and feedback.  These designers seem wed to complex circuitries.  For purposes of this discussion, we will call designs of severe simplicity, the school of simple design.  The second group, which attempts to perfect designs via circuit complexity, we will call the school of exotic design.  Most designers fall somewhere in between, but within the parameters of one or the other of these ruling philosophies.

Joseph Chow has chosen a third way of design, one neither simple nor exotic, but one which seeks instead to look deeply into the circuit function, the materials used in it, and the sonic goals to be achieved.  By analyzing these, especially the inherent sonic characteristics of the materials and components at every stage, Joseph Chow seeks neither to eliminate components, as those in the simple design school do, nor to compensate for them, as those in the exotic design school do.  Instead, he seeks to harmonize the inherent characteristics of materials with the circuit design itself.  This search for harmony between the materials used and their function within the overall architecture is what defines and distinguishes Audio Horizon design.  The focus is always on the sound characteristics inherent in the materials themselves and, given their characteristics, to achieve at an affordable price the highest quality sound possible.   

The Audio Horizons designer looks as deeply as possible into the circuit path, and into the sound characteristics of the materials and components used, and he does this at the smallest level possible.  His search for distortion and noise at the minutest circuit and material level begins, first, with a desire to eliminate all spurious noise and, second, with a respect for the importance of Q [defined as the “quality factor of an inductor or capacitor.  It is the ratio of a component's reactance ... to its effective series resistance” Dictionary of Electronics].”  

We seek to lower noise because only by lowering noise are the sonic characteristics of individual components revealed.   No designer, no matter how fine his ear, can improve a design below the noise level, for at that level he cannot hear the difference between one component make or value and another, one circuit modification and another.  Low noise permits the designer to hear more clearly the very fine sonic differences small component changes and slight circuit modifications make.

Typical of Audio Horizon's attention to the smallest detail, the designer has specified that the input jacks be Teflon insulated because the Teflon reduces signal loss, and because it has a high Q.

In addition to a focus on high Q, Audio Horizons' classic design leads it to eliminate all spurious, little used features, ones that may add glamorous complexity and the appearance of quality to the product, but yield no sonic improvement and in fact present design problems of their own.  This is in keeping with Audio Horizons' desire to keep distortion, the noise level, and costs as low as possible at every stage.  Thus, as part of his desire for a classic line, at every stage the Audio Horizons designer seeks to keep the signal as clean as possible with the minimum number of parts.  If three parts, however, will yield a cleaner signal than one part, without altering or degrading the signal, then three parts is both theoretically and sonically the minimum number of parts required. 

Concern with a clean signal begins as soon as the power enters the circuit system, which is why the TP 2.1 has a filter in the line immediately after the AC power input, and has separate power supplies for digital and analog functions.  Throughout the circuit, noise and distortion are reduced by providing clean, high Q signal paths that make the signal timing more accurate and lifelike.

UPGRADE VERSIONS
The TP 2.1 is available in a number of upgrade versions.  Upgrade versions may be purchased new or if a buyer wishes to adopt a more measured approach, upgrades may be added at any time for the same upgrade price.  Each upgraded version comes with a slightly different designation which is noted on the Serial Number sticker.  See the Price List for prices of each upgrade.  Upgrade items may naturally be combined in many upgrade combinations.

The TP 2.1n adds additional shielding and isolation to further reduce the noise floor, and upgrades the tube capacitors by upgrading them to premium Properity capacitors. 

The TP 2.1B adds larger premium output line balancing transformers instead of high quality line balancing output transformers.  It uses the same high quality input transformers.

TP 2.1 R adds remote function version. As a convenience, Audio Horizons  maintains a supply of new low noise Siemens tubes, which customers may buy if they so choose.

Current Pricing
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