Santor Stereo Power Amplifier and Sarod Preamplifier
Two beauties from AcousticPlan of Germany
Review By Dick Olsher
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  AcousticPlan's founder, Claus Jäckle, tells me that music reproduction and its associated technology have fascinated him since childhood. He recalls tinkering with old tube radios and experimenting with electronic kits. After receiving a technical degree in electronics, he worked at several companies as an industrial electronics engineer. Fueled by his love of classical music and many years of research into novel ideas of music reproduction, he decided to launch AcousticPlan in 1996. His vision was to combine German engineering and craftsmanship into a perfectionist pursuit of unique audio products. I find it extremely reassuring that at its core this company is guided by the premise of audio serving the music. I can recall several instances in the high-end arena of designers whose entire design process was strictly based on measurements; listening tests being deemed irrelevant. Sometimes they got lucky, but more often than not they simply missed the boat. At AcousticPlan, designers do pay attention to parameters other than those that just yield superior technical data.

A deeper understanding of the man and his philosophy can be gleaned from his take on the prime aim of high-fidelity audio. The problem, as Claus see it, is that reproducing faithfully what's on the recording hardly guarantees fidelity with respect to the original performance. Claus is right to point an accusatory finger at the recording engineer. Microphone feeds are routinely equalized and blended in a mixing console to produce what in the final analysis is the engineer's artistic take on the original performance (or isolated takes in the case of most multi-track pop recordings). He posits the following question: "Does it make sense to reproduce the result of a recording engineer?" He ultimately came to the conclusion that it was far more important to focus on the emotional essence of the musical performance. After all, he says, "who gave the recording studios and engineers the authority to manipulate while the claim to a home system is to work [as] accurately as possible?"  In his opinion, and I do agree with him, current practice tends to manipulate recordings to obtain an overly detailed and analytic character, which is unnatural and foreign to the concert hall experience.

It should therefore come as no surprise that AcousticPlan components are optimized for the reproduction of the midrange – a frequency band that is home to vocals as well as the power range of an orchestra. It's a question of tonal balance, of framing the midrange to the exclusion of excessive treble or bass emphasis. Harmonic sweetness and freedom from dissonant distortions are also design priorities, as is the ability to perceive the spatiality of the soundstage in a stable manner with believable depth and width perspectives. A minimalist design with the least possible number of active stages is preferred over complex feedback designs.

Technical Details

Santor
In a gesture, very much in keeping with the company's vision, products are named after Indian musical instruments. The amplifier's namesake is a dulcimer-like Indian stringed instrument. It is a hybrid design meant to incorporate the best features of both tube and transistor amplification. It features a triode-based gain stage (6922/E88CC) followed by a driver stage using a new dual triode type (ECC99) manufactured by Tesla/JJ and specifically intended for driver applications. The output stage uses six MOSFETs per channel in push-pull operation biased for extended Class A operation. The output stage acts as a high-current impedance converter capable of sinking significant current into low-impedance loads. Neither overall feedback nor differential amplification are employed. Both balanced as well as unbalanced inputs are transformer coupled to the first gain stage. This achieves DC blocking without the use of a capacitor and also facilitates handling of balanced inputs.

The AC mains transformer is housed in a separate enclosure that connects to the main chassis via an umbilical cord. The Santorcan easily be configured as mono power amp in bridged operation for even higher output power. For example, a pair of Santors in bridged mono can deliver 200 wpc into 8 Ohms relative to only 50 wpc for a single stereo amplifier. And did I mention that the aluminum chassis are precision milled and beautifully finished?

Sarod
The Indian Sarod is a smaller than the sitar, but apparently no less demanding a musical instrument. And this is really an appropriate name for a device that sits at the head of the amplification chain and is responsible for taking care of low-level voltage signals. This is truly an all vacuum preamplifier. Not only that, but it goes to heroic lengths – no expense spared - to make the Sarod sing sweetly. Think tube rectification (6CA4/EZ810) followed by a cap-choke-cap pi filter. And then throw in a sophisticated all-tube high-voltage regulator circuit which uses three pentodes – 2 ea. 6CW5/EL86, 1 ea. 6BX6/EF80, and 1 ea. 75C1 voltage reference tube. All tubes, even those in the phono stage, are AC heated to avoid use of semiconductor rectifiers.

A line-level stage is standard, while an internal phono stage is optional and takes up one of the four available line inputs. Coupling transformers are used everywhere; there literally are no capacitors in the signal path. Not only is the balanced input transformer coupled, but so are the outputs of the line stage. All signal transformers are said to be designed in-house.

Volume control is normally accomplished via a high-quality 24-position stepped attenuator. However, my sample was outfitted with an optional remote volume control that works via relay-switched resistors. The relays are controlled by a micro-controller, which responds to the position of a motorized potentiometer. AcousticPlan notes that ultimate tube fanatics should rejoice in the fact that there are absolutely no semiconductors in the Sarod with manual volume control - the only exception being the blue LEDs on the front panel.

The design, however, is quite simple where it needs to be. For example, a single E288CC dual triode is used for line-level amplification. The optional phono stage uses two triode-connected pentodes (D3a) for amplification of MM cartridge signals. RIAA equalization is performed passively and step-up transformers provide additional gain for MC cartridge signals. Fit and finish are exceptional and similar to the standard set by the Santor, including a separate chassis for the AC mains transformer.

Sonic Impressions

The Santor
"An amplifier has got to know its limitations." That would be an audiophile version of Clint Eastwood's (as Dirty Harry) celebrated quip in Magnum Force – the movie. Applied to the world of tube and transistor amplifiers, it means that transistor designs typically have bass impact, transient speed, and high-current delivery into low impedance loads nailed down, but as hard as they might try, fail to deliver realistic harmonic colors and 3-D imaging. Tubes on the other hand deliver vivid, high saturation harmonic textures, palpable image outlines, but struggle when it comes to bass definition and bass slam. An obvious question presents itself: is it possible to combine the best of both worlds? That is, merge the best of tube and transistor characteristics in one amplifier. That in essence is the avowed goal of hybrid designs – an attempt at the elusive trick of having your cake and eating it too. The most sensible approach, as embodied by the Santor, is to use a tube front end and a solid-state output stage in an attempt to bestow tube flavor while maintaining current delivery. The reverse approach makes little sense to me and has been rarely seen. There is one potential problem with any hybrid approach, the danger being that the progeny of such a mixed union is neither fully tube nor transistor in character, and as such it may fail to appeal to either camp. I mean, if you're really into tube sound, a transitional sound, partly tube and partly solid-state is unlikely to impress. And, of course, the converse is likely to be true as well.

Initial impressions were obtained in a system context that included the Esoteric MG-20 loudspeakers, Esoteric SA-60 CD/SACD player, Concert Fidelity CF-080 line preamplifier, and FMS cable. Specifically, the Santor replaced the Silicon Arts Design ZL-120 monoblocks, an all solid-state design that has proven to be a synergistic match with the MG-20s – certainly no easy task. Well, I need not have worried. Relative to the ZL-120s, image outlines were more palpable, and vocals in particular took on a nearly 3-D presence. Harmonic textures were smoother and more refined, while instrumental colors were more vivid. And the soundstage depth perspective improved as well. All of these sonic gains are clearly tube virtues. On the other hand, I felt that some of the music's kinetic energy, speed, and resolution, were

being traded away for a mellower and more spacious sound. There was also the matter of bass impact. This was the only area where the Santor sounded like a low-power amplifier as it consistently failed to deliver the bass punch of the ZL-120s. All in all, however, a very promising start.

Later auditions firmly established an exceptionally low-grain, luxurious midrange imbued with pristine harmonic textures. Musical lines flowed naturally, making for a totally relaxed presentation. Most tube amps brush sonic makeup over musical textures, in effect prettying up the sound. The Santor proved relatively free from euphonic excess. Though on a recording such as Leonard Cohen's The Future (Columbia CK53226), whose goal was specifically a rough, mechanically raucous sonic flavor, it was clear that the Santor was actually smoothing over some of the rough edges.

The Santor turned out to be fairly load sensitive. For example, it was not totally comfortable driving the Final Sound 1000i electrostatics. The resultant midrange was very detailed, but it was unable to generate much in the way of bass impact. Matters improved considerably when the Santorwas mated with the Venture Audio Excellence III Signature speakers. Relative to the pair of Son of Ampzilla 2000 (SofA) it replaced, the midrange appeared slightly laid back; more so than with the MG-20s. But its tube signature shone right through, as the mids sounded slightly warm, sweet, and well nuanced. Here too image focus was excellent within a spacious soundstage. David Manley's recording of my Lesley (Jazz Me: BDM-78003) was reproduced with lovely harmonic colors and excellent image focus. There were, however, slight losses at the frequency extremes in terms of treble air and bass definition. In addition, a bit less dramatic tension was apparent relative to the SofA. In general, relative to the SofA, the Santor lacked kick-ass bass slam and full dynamic conviction when changing gears from loud to very loud.

When replaced by the Air Tight ATM-1S stereo tube amplifier in the above system, it became quite clear that the Santor lacked the lower midrange authority of the Air Tight. This big tone character, prized for guitar amplifier applications, may well be a function of the output power transformer. It's the sonic attribute most responsible for the suaveness of vintage tube amps, and one that keeps pulling me back to all-tube designs.

The Sarod
My first listen turned out to be a moving experience. I was immediately struck by its vibrant and rich harmonic colors. Lesley's rendition of "Summertime" (Jazz Me: BDM-78003) was richly colored and superbly faithful to the original studio experience. Remarkably, the Sarod seemed to excel at the frequency extremes. Acoustic bass lines were tightly defined while the treble range was intricately detailed. The music's drama and tension were given full scope of expression as microdynamic detail was allowed to bubble freely to the forefront of musical lines. Its strong boogie factor swept me off my feet. Metaphorically speaking, the Sarod's sympathetic strings were resonating big time with me.

It was time to get quantitative. First order of business was to pit the Sarod directly against the Concert Fidelity CF-080 – my current reference line preamplifier. It made for an interesting contrast in styles. First, in the context of the Esoteric MG-20 loudspeaker, the CF-080 evinced more transient speed, bass impact, treble extension and finesse, and superior soundstage transparency. The Sarod, on the other hand, sounded more euphonic with obvious midrange emphasis. But it layered the soundstage with an enhanced depth perspective and animated it with fully palpable image outlines. And at the end of the day, it was simply hard to resist its siren call, its trump cards of terrific sense of pace and kinetic energy. The Sarod propelled the music along with élan and rhythmic integrity. Now that, in my book, is a fantastic musical experience that's oh so hard to walk away from. Did I mind that its tonal center of gravity was firmly in the midrange? Not at all! Tonal colors were a bit more golden than the real thing, but it's all part of the AcousticPlan experience.

Similar impressions were obtained with the Venture Audio Excellence III Signatures. There was plenty of clarity to go along with sexy mids. The Sarod ensconced itself as the king of pace; musical tension never flagged! It was much the same story during vinyl playback. My analog front end currently consists of the Kuzma Reference turntable outfitted with Graham Engineering model 2.5 tonearm and Grado Reference cartridge, and Air Tight ATE-2 phono preamplifier. Setting the phono stage gain requires removal of the Sarod's top cover to access a couple of toggle switches. Two MC gain settings are available. At the MM setting, there was more than enough gain to accommodate the Grado. The midrange again was the star attraction, being really sweet sounding without obscuring low-level-detail. There was no trouble at all resolving massed voices and rendering violin overtones with natural sheen. In contrast, the Air Tight sounded a bit softer relative to the Sarod's phono stage and a tad less dynamic. Equally impressive was the spaciousness of the soundstage. But there was more to it that that. Returning to LPs after a long CD session really makes me appreciate the joys of analog. It's immediately obvious how much more stable image outlines are, to say nothing of natural harmonic textures free of digital brightness. With lesser tube gear I really have strain to accept the spatial illusion. With the Sarod it felt as though image outlines were nailed down, chiseled out of stone, totally stable and unwavering; it heightened the analog experience like never before.

Conclusion
On balance, the Santor strikes me as a successful hybrid design. Though it lacks an authoritative lower midrange in the mold of vintage tube gear, its tube virtues are numerous and should complement most conventional dynamic speakers. Its load sensitivity, however, merits a careful audition. The Sarod, on the other hand, qualifies for an enthusiastic and unqualified two thumbs up. It represents an all out effort to elevate musical reproduction in the home to a new emotional high. Configured either as a line preamplifier or a full-function preamplifier, its compelling musicality is impossible to ignore. Bravo, Claus! The Sarod truly lives up to its namesake which literally means "beautiful sound" in Persian.

Specifications
Santor:
Sensitivity: 1 V for full output
Power Output: 50 wpc/8 Ohm
100 wpc/4 Ohm
160 wpc/2 Ohm
mono: 200 Watt bridged/8 Ohm
mono: 320 Watt bridged/4 Ohm
Source impedance 250 Ohm 
Dimensions (W x H x D): 260 x 170 x 350 mm
Weight: 18 kg
Price: $11,000

Sarod:
Sensitivity (Line inputs): 500 mV/20 kOhm (inputs 1 and 2); 250 mV/50 kOhm
Phono: MM 3 mV/50 KOhm
MC (high gain): 0.2 mV/80 Ohm
MC (low gain): 0.4 mV/320 Ohm
Output: 1V/200 Ohm
S/N Ratio (A-weighted): Line: 95 dB
MC: 75 dB at 0.5 mV
MM: 80 dB at 5 mV
Dimensions (W x H x D): 260 x 170 x 350 mm
Weight: 18 kg
Price: $11,000 (line stage only) with manual volume control; $13,000 with remote volume control
$4,100 for optional phono stage.

Company Information
AcousticPlan
Oberstegle 1
D-78464 Konstanz
Germany

Website: www.acousticplan.de

US Distributor:
Tangram Audio
Tel.: (626) 689-8904
Web: www.tangramaudio.com