The Audion Silver Night PX-25 Stereo Power Amplifier
By Dick Olsher
Since its inception in 1987, Audion has stayed true to a simple guiding principle: open a doorway into the world of high-end audio without forcing customers to sacrifice their home, first-born child, or bank balance. What a refreshing attitude and a clear break from the greed and excess epitomized by the kilo buck pricing of speaker cable and interconnects.
The Silver Night line launched in 1993 has exemplified that philosophy: good build quality, exceptional looks, and delicious tube sound at a price that the working man can afford. The PX-25 is built on the same chassis as the 300B Silver Night stereo amp; the only external difference being the output tube. Please see my review of the Art Audio PX-25 for background information on this tube. I was originally led to believe that the amp was outfitted with Chinese Golden Dragon PX-25s. This is most definitely false. As it turns out, no true PX25 type is being manufactured in China, and all current production of this tube in fact originates with KR Enterprise in the Czech Republic. So how did I, as well as Audion, come to believe in a Chinese PX25? For starters, there's that prominent Golden Dragon logo on the glass envelope. Furthermore, I was informed by Audion that when they originally purchased the PX-25 from England they were supplied in Golden Dragon boxes and that they were led to believe that the tubes were of Chinese origin. When this review first aired on the Enjoy the Music site, both Audion and I received angry emails from Dr. Riccardo Kron, KR Enterprises, seeking to set the record straight. Apparently a production lot of some 200 KR PX-25 tubes were sold to PM Components in the UK. Audion corroborated Kron's allegations and stated that they have recently established that these tubes were indeed manufactured by KR and were later re-branded in the UK under PM Components' "Golden Dragon" brand. Regarding PM Components role in all of this, all I can say is: what a devious sleight of hand! This is a great looking tube, which uses the original British style base. Beware of imitations: every KR Enterprise tube is manufactured with a number code inside the glass envelope. This code certifies the authenticity of the tube. Dr. Kron tells me that there are imitations floating around, branded as a PX-25, but with the innards of a 300B.
When I asked Audion for a copy of the Silver Night schematic, my request was honored quickly and professionally. There was no attempt to cloak the design in secrecy, no smoke and mirrors in presenting the product. In contrast, most of the designer-label manufacturers are reluctant to expose the truth that they are charging uncommon prices for very common circuits.
Because in the crazy world of high-end exotica, the Silver Night asking price qualifies as a semi bargain, Audion had to make some tough circuit and part choices. Looking over the schematic, I was left with impression of a conventional, keep-it-simple, single-ended triode (SET) design, executed with a large dose of sound engineering and common sense. The input stage uses one half of a 6922 twin triode, while the driver stage is built around one half of a 5687 dual triode. The operating points of these tubes were chosen with due care and they are well decoupled from the power supply. No global feedback is used and local feedback is also avoided , presumably in order to maximize the overall gain. As a result, the sensitivity is high at around 200 mV for full output. My review sample was outfitted with a stereo volume control (50K ohm log pot), which would allow a CD player or even an FM tuner to be input directly - without the need for an intermediate line stage or preamp.
The power supply is all solid-state. DC filament supplies are used to light up the filaments of the PX-25 output tubes, which are cathode-biased to minimize the effects of tube aging and to ensure soft clipping characteristics. Hum and noise are low, really excellent for a SET, making the Silver Night eminently compatible with high-efficiency (96 dB plus) speakers, which is the sort of load any 6 wpc amp ultimately hopes and prays for. Speaking of compatible speakers, don't be tempted to mate this amp with low-efficiency speakers, unless you basically listen to FM radio at low volumes. This amp will clip and clip often unless your speakers are sufficiently sensitive. Since only 8-ohm output taps are provided, I would recommend that you stick with 8-ohm nominal loads and avoid current-hungry 4-ohm loads.
The Input Stage: Tube Rolling
The Silver Night's design places a large burden of responsibility on the shoulders of the 6922 input tube. To a large extent, the sound of the amp is dominated by the sonics of the input stage. Its sonics live and die by the hands of the 6922 input stage. My review sample was outfitted with a Tesla NOS 6922. This tube sounded mellow and harmonically rich out of the box – good things in my book - but it also placed a veil over the soundstage and fuzzed up image outlines. I found myself straining to make out the inner recesses of the soundstage, while lack of image focus didn't make me a happy camper either. It may not be fair to characterize this tube as factory stock, as no cache of NOS tubes is typically large enough to keep up with production demands. What was puzzling, however, is that my sample - presumably the very same unit that I auditioned at the Winter CES in Las Vegas in January of 2002 - did not sound that way at the Show.
That implied a problem with the stock 6922, so I began to experiment with various substitutions. I tried two samples of the Russian manufactured Sovtek brand and obtained nearly identical sonic results. The Sovtek sounded gutsy, full-bodied through the lower midrange, but also grainy and tonally skewed toward the lower octaves. I naturally tried both Phillips and Siemens 7308s and liked what I heard, but I was determined to offer our readers a top alternative that is readily available and not insanely priced. That turned out to be Richardson's Bugle Boy brand of 6922. This tube is VERY GOOD: extremely smooth sounding with excellent detail. I have received e-mail complaining that the Bugle Boy reissue is nothing more than a re-branding of NOS made-in-USA JAN Philips. Well, it's true that the Richardson Bugle Boys started life as JAN Philips – tubes originally manufactured to a strict Joint Army Navy (JAN) military specification. But don't get the idea that all you have to do to save bucks is to indiscriminately pick up the Philips JAN off an Internet tube reseller. It is important to understand, that even JAN spec tubes often feature as much as a factor of two or more variation in parameters. The only way to ensure tighter tolerances is to burn these tubes in, and then test and match for conformance. This is what Richardson does using original Philips test gear. Each set of Bugle Boys sold is accompanied by test data. In this case, you do get what you pay for. I don't, however, condone their advertising practice which does not clearly disclose the vintage of these tubes. Note that all of the sonic impressions that follow are based on auditions of the Silver Night PX-25 with the Richardson Bugle Boy 6922.
The Silver Night benefits from an extended initial break-in period. The Owner's Manual recommends a period of two weeks. Also, count on about a 15-minute warm up period, during which the sound of the amp tightens up considerably.
Despite its modest size and lack of heft, the Silver Night competes with the muscle boys of the SET universe. The big attraction (no surprise here) was the harmonic richness of the midrange. Although not nearly as suave sounding as the Art Audio PX-25, the Audion consistently managed to portray a believable impression of the music's harmonic tapestry. Lord, I wish that anyone contemplating the purchase of a solid-state amp be given the opportunity to the audition the Silver Night with a suitable high-efficiency loudspeaker. I deplore solid-state anorexia. Silicon-based amps (with apologies to a few select SE designs) are in my book aligned with the dark side of the Force. And much like Darth Vader, audiophiles may be seduced by bass power and overall muscle. But at what price? For me, a full-bodied lower midrange is essential in fleshing out the music's foundation. Getting that right is a high priority for me. It is after all the heart and soul of the musical experience. A case in point is the QUAD-57 electrostatic loudspeaker. My first exposure was at a friend's house many decades ago. I walked into his living room, when I heard a startlingly realistic voice behind me. After I completed a 360, I was shocked to discover that the voice was actually being reproduced by a speaker… the QUAD. I'm happy to report that the Audion gets it right. It is QUAD like in its ability to weave a magical midrange.
The corollary to the above discussion is DO's audio rule No. 2: man does not live by midrange alone. Tonal balance is also a priority and relates to how seamlessly the treble and bass ranges blend with the midrange. The upper octaves sounded subjectively open and extended, at least in terms of SET benchmarks. The Audion managed to adequately brighten up the treble, in stark contrast with the Cary Audio sound, which derives its dark, gothic perspective, from a limited frequency extension. The output transformer is often the limiting factor in SET designs. If you'd like to visualize what a -3 db at 17 kHz bandwidth does to the sound, imagine stage lighting that turns from a natural color temperature to a yellow-red hue. Textures turn overly liquid, the midrange warms up excessively, and the upper octaves lose brightness. Coupled to a bright speaker, such a balance makes for a more pleasant sound, but with a neutral speaker the resultant balance could prove to be musically depressing. Kudos to the Silver Night for maintaining a reasonable tonal perspective through the upper octaves. At the other frequency extreme, bass control was just OK with the BassZilla loudspeaker. In common with most SET amps, the output impedance is fairly high so expect only moderate cone damping and speaker dependent tonal balance variations. If speakers had a perfectly flat impedance magnitude this would not be an issue. However, real-world impedance magnitudes are far from flat, often varying by a factor of 10 from the minimum value. When driven by high-output impedance devices, the end result is an inevitable alteration of the speaker's frequency response. This highlights the need to partner and audition SET amps with prospective speakers.
The Silver Night's owner's manual should include instructions for buckling up and holding on for a roller coaster ride. Tonal conviction and harmonic bloom were coupled with excellent dynamic modulation. The music's emotional content resides in micro dynamic details. The feelings singers and instrumentalists inject into the music, their personal imprint, is embedded in subtle modulations of pitch and volume. The Silver Night delivered the goose bumps. Although I have no direct proof, I suspect that it spins the midrange more effectively than its 300B cousin. That also seems to be Audion's own in-house assessment, based on comments posted on their web site.
The cathode biased output stage clipped softly, and gave the impression of greater power than its modest 6 wpc. I had no trouble whatsoever in achieving realistic volume levels with only moderate levels of distortion, at least in the context of 96 db+ sensitive speakers.
The Audion Silver Night PX-25 sets a very high standard at its price point. It is a balanced performer with no major weaknesses. Its expressive midrange is hard to walk away from. It images well and can generate stupendous dynamics in the context of a high-efficiency speaker. Need proof? Spend an evening with the Silver Night. You'll be glad you did.
OS Services Audio
Web site: http://www.ossaudio.com/
Web site: http://www.audion.co.uk/
POWER OUTPUT RMS: 6 Watts into 8-OHMS Class-A at 240V AC
LINE SENSITIVITY (FULL OUTPUT): <200 mV RMS
DISTORTION: <0.5% @ 1KHz AT 3/4 Max power
FREQUENCY RESPONSE: 15 Hz - 40 KHz (+/- 3dB)
LINE POWER NOMINAL: 145W @ 240V AC