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Power Amplifier
Tenor Audio 175S

Price: 155 000 zł

Polish distribution: SoundClub

ul. Skrzetuskiego 42, 02-726 Warszawa

tel.: 22 586 32 70
fax: 22 586 32 71


WWW: Tenor Audio

Text: Wojciech Pacuła
Translation: Krzysztof Kalinkowski
Photographs: Tenor Audio, autor

Tenor Audio is a brand no so known in Poland, if at all. Although I wrote about it a few times, but only in the context of the High End Show in Munich (for example in 2008 – report HERE). Their amplifiers played in systems prepared by the German distributor of the company Kharma. And it was the first time that I heard, that those loudspeakers can play at all – all previous presentations were absolutely not satisfying, bright, mechanical and lifeless. And with the Canadian amplifiers, one per channel, everything sounded fine. The amplifiers I listened to were stereophonic power amplifiers, if I am not mistaken, the 175S – big, powerful units, weighting 54kg (67kg with packaging), built in hybrid technology – all voltage stages use tubes as amplifying elements, and the current stage is a classic solid state circuit.

And Tenor did not start from transistors, and the new products, like the tested 175S, but also the monoblocks 350M, came to life as an effect of an evolution. And this evolution went along the path I follow, since some time, so is known to me. The goal was to create a high power amplifier, able to work with full band (please do not confuse with ‘wideband’ – this is the description of loudspeakers utilizing one driver covering the whole sound spectrum), big loudspeakers. This is nicely summarized by the company motto: “Power. Performance. Pasion”. And then: „Ultimate Audio Amplification”. And according to Tenor, they can speak of “ultimate” amplification only recently. The company started its adventure with “power” from OTL tube amplifiers. Those are tube amplifiers without output transformers (Output Transformer Less). In the beginning of the 21st century the company developed a proprietary OTL circuit, which they call “Tenor OTL”. This circuit was so successful, that – according to company materials – after 10 years those amplifiers can be purchased second hand with a price 50% higher, than the original one. But like I say, since the very beginning, Tenor was focused on delivering high power. The OTL amplifiers offered by the company brought 75W per channel, what is really a lot – for a tube. But this was also not enough – the company built some prototypes of even more powerful amplifiers, but their sheer size and the amount of heat generated, as well as problems with delivering the right protection to the users and loudspeakers, resulted in the project being dropped. So creating a hybrid amplifier was a natural next step.

A hybrid amplifier, is one, that has one (or more) amplification stages built with tubes, and a second (or different one/ones) built with transistors. Almost always it is a construction, that has tubes on input, and the control and power stage are solid state or ICs (the latter for example in the series Magnum 50/100 from Synthesis, or in iTube Carbon 2 from FatMan). Rarely, but still those exist, there are devices with solid state technology in the input section, and tubes in the output section. This is for example the KR Audio (test of the Kronzilla SXI-S HERE) and in the amplifiers of the Polish company Linear Audio Research (test IA-45 HERE). But because 99% of those constructions are tube-transistors, let us stay with that. The main argument is, and Tenor follows that path, that the best place to use a tube is the voltage amplification stage, where the currents are not so high. This uses the splendid linearity of the tubes, their resistance to clipping and working with high voltages (this is also the path the company SPL follows in their studio gear, which use transistors working at 120V). On the other hand transistors are best used in current sections, where high current reserve is needed. Combining this two technologies created the tube-solid state hybrid amplifier.

I know devices of that type, I listened to many of them, I even built some myself, and really – it is a very good base to create a nicely, warm sounding amplifier. But despite what you can sometimes hear, this is not an ideal solution. Almost 100% of the hybrid amplifiers I know sounds too warm, too mudded. They do also have limited resolution. It is like the worst would be taken from those two technologies, and not the best. I know, that this can be found appealing – the sound is really nice, in low and medium price ranges – but in hi-end this is rather not acceptable. This is why Tenor Audio prepared their own version of this technology. According to Jim Fairhead, the CEO of the company, the Canadian engineers started from the OTL concept, and it was the base to create the input stage. In fact, this is an A class OTL amplifier, working with high operating voltage, which has at output a big solid state circuit, working in unity-gain mode, without voltage amplification. This section is designed to provide current only, the whole amplification is the domain of the tubes. A really interesting approach.

later amended with the stereophonic hp150 (those numbers represent power). The output stage employed MOS-FET transistors. In 2006 a new generation of the amplifier was presented – the monoblocks 350M and stereo version 175S, the first ones went into production in 2007, and were first shown in Denver, on the Rocky Mountains Audiofest, the second ones were shown one year later, during the Las Vegas CES 2008.


Discs used for testing:

  • Feel the Difference of the Blu-spec CD. Jazz Selection, Sony Music Japan, SICP-20050-1, Blu-spec CD + CD; opis HERE.
  • HiQualityCD. Jazz Selection, EMI Music Japan, TOCJ-90010, HQCD + CD; opis HERE.
  • Musik wie von einem anderen Stern, Manger Products, MANG-2010, 2 x 180 g LP.
  • Bill Evans Trio, Waltz For Debby, Riverside/Analogue Productions, 9399, No. 773, 2 x 45 rpm LP.
  • Billie Holliday, Songs For Distingue Lovers, Verve/Classic Records, One-sided, 2 x 180 g, 45 rpm LP.
  • Chet Baker, Chet Baker Sings and Plays, Pacific Jazz/EMI Music Japan, TOCJ-90028, HQCD.
  • Clan of Xymox, Medusa, 4AD/Sonic, SON66, CD.
  • Clifford Brown and Max Roach, Study in Brown, EmArcy/Warner Music Japan, UCJU-9072, 180 g LP.
  • Depeche Mode, Playing The Angel, Mute, lcdstumm260, SACD/CD + DVD-A.
  • Diorama, Cubed Deluxe Edition, Acsession Records, A 114, 2 x CD; review HERE.
  • Dominic Miller, Fourth Wall, Q-rious Music, QRM 108-2; review HERE.
  • Hank Mobley, Soul Station, Blue Note/Audio Wave, AWMXR-0001, XRCD24; review HERE.
  • John Coltrane, Giant Steps, Atlantic/Rhino, R1 512581, 2 x 45 rpm LP.
  • Julie London, Julie Is Her Name. Vol. 1, Liberty, LRP 3006, LP.
  • Julie London, Julie Is Her Name. Vol. 1, Liberty/EMI Music Japan, TOCJ-90014, HQCD.
  • June Christy, Something Cool, Capitol Records/EMI Music Japan, TOCJ-90033, HQCD.
  • Tomasz Stańko, 1970, 1975, 1984, 1986, 1988, Metal Mind Productions, MMP 5 CD BOX 006, 5 x CD.
  • Tomasz Stańko, Music for K, Polskie Nagrania, PNCD 922, Polish Jazz vol. 22, CD.
  • Wynton Kelly, Kelly Blue, Riverside/JVC, JVCXR-0050-2, XRCD2.

Japanese versions of the disc can be purchased on CD Japan

Besides the reference system, the Tenor worked also with the loudspeakers Avalon Ascendant, the turntable Avid Acutus Reference/SME Model IV/Air Tight PC-1 Supreme and the phonostage Avid Pulsare. Power cables – Acrolink Mexcel 7N-PC9100 and Acrolink Mexcel 7N-PC9300.

I already heard an amplifier with a similar sound signature. I did not need to think long to remember, which one it was – the Flight 100 from the Italian company Audia. It is probably not a coincidence, that Audia based their amplifiers on the unity-gain idea. The Flight 100 was also a big device, of the trans-impedance kind, using the transistors of the output stage as a kind of follower (in that particular case 16 pieces of selected Toshiba transistors, capable of delivering up to 160A). It is a similar idea, isn’t it? Tenor Audio goes in the same direction, only makes everything many times better. So good, that I can say, that this is the best transistor amplifier (thinking about output stage) I heard in my system, and one of the best amplifiers in general, regardless of technology. Because at the utmost top – although not fully, but about that later – are the two tube amplifiers Ancient Audio Silver Grand Mono and Reimyo PAT-777./p>

What makes a good amplifier? On the lowest level we have terms like tonal balance, dynamics, resolution, sound stage (holography). This is the basis. On higher level there is something that combines all those things and adds something else: the ability to differentiate. I share the viewpoint of people from “Enjoy the Music”, who made this their credo and no. 1 issue. Differentiation means the ability to show differences between the recordings, pressings, versions, or within one disc showing the timbres native to a given instrument, changing from recording to recording, or sometimes even within one track (if it was edited and glued together from many takes). The main role here is played by the resolution of the device, but without all the elements I mentioned earlier, it would mean nothing. And this is exactly the sound presented by the Tenor. The ability to look inside the tissue of the recordings, even into a certain structure of a recording session is incredible. To date (with a few exceptions – the top amplifiers from FM Acoustics, Spectral, Soulution and Vitus Audio) only tube based amplifiers, using the 300B, and especially the first two I mentioned, could do it in an equally convincing was as the 175S. This showed the things that make the HiQualityCD, Blu-spec CD and SHM-CD special in a beautiful, subtle and yet very unanimous. Smoothness, depth, coherence, right size of the instruments – I had everything within reach. It was heard best in direct comparison, on the samplers HiQualityCD. Jazz Selection and Feel the Difference of the Blu-spec CD. Jazz Selection, but the true magic began when I listened to whole discs like Something Cool June Christy, Julie is Her Name. Vol.1 Julie London, or Chet Baker Sings and Plays. The sound was full and intimate, close, slightly warm, saturated fully. But it was not like bringing everything to a common divider. Other nice amplifiers, like the ASR Emitter II, probably the cheapest so good (I mean absolutely hi-end) solid state amplifier, show such recordings in a fluent, passionate way, but they do that with all discs, regardless of what those discs are. Even my Luxman M-800A, which I love unconditionally, “evened” the sound, although in a different direction – it enhanced things. The Tenor goes further, it does the same thing, the 300B tubes do, every voice, every instrument are separate “beings”, separate existences, but are shown together, form the same recording.

I mentioned resolution – for some time you may think, that the Canadian amplifier warms things a little. This is not the case, it is something different, but I needed some time to understand what I hear – actually it is something I did not hear with any other amplifier, except for the two tube ones I mentioned, and I did not think, that this is possible with a solid state device. The Tenor makes everything clear in the first minute of the recording. With analytical, resolving, but most of all analytical amplifiers, you need to work some time to combine everything we hear into one whole. Because we receive lots of information, but only loosely connected. Although we do not see it, our brain needs to work a lot, to make sense of it. This makes us tired with such a sound, sometimes even agitated. And the Tenor supplies a coherent whole, from which we need to extract the musicians, instruments, their relationships – reproduce a certain event. But – I think – this is how it works in reality, with live events – the tested power amplifier just tried to reproduce what we know from real life.

So we could nicely hear where the tape was glued in the piece Let’s Get Lost Chet Baker, and yet the intention of the sound engineer was clear – it was about having stronger percussion with the voice, and softer, when the trumpet played. And we can hear it clearly. And still this is one piece, maybe manipulated (within the boundaries of the technology and techniques available at time it was recorded), but still coherent. And the Tenor did not show it in a “microscopic” or “laser cut” way. This was not an X-ray, in the way that those things come later, are extracted by us from what we hear. And usually, solid state devices give those things for free immediately, and we need to put them all together, what is almost always not possible.

But this is really only the first level. In hi-end, and we talk about that here, on the top, other things are more important – something that is related to differentiation, resolution and other elements of the sound we talked about. It is about the ability to show each material in such a way, that extracts the best things from it. Not to extract everything, but only the best things. Please do not confuse it with making the sound homogenous and covering up the flaws and problems. Like I wanted to show, the Tenor can do it right from the start. But it makes it in a way far more refined, than all other transistor amplifiers, and most tube ones. Maybe I should have started the test with this paragraph, but I wanted to get to it in a well ordered way, so that it would not look like excitement, but like understanding, as it should be. So I’ll start. Since long I was tired listening to music at home. Everything was OK, nice, it was a system I always wanted to have, but music was no longer as pleasing as it used to be. And it was extremely tiring, as I listen a few hours a day, every day. Analytical and for pleasure. I know this state, I felt it many times before, and I know, that it means, that the possibilities the system offers have been exploited, and the expectations are higher. I just wanted more. I knew what I was looking for, and that what was lacking annoyed me most. This is why I liked more to listen to inexpensive, or even cheap gear, like the Pro-Ject tested last month, because with them everything snapped back into its place – expectations and results. With the Tenor I could listen again for hours. And that is good news, because I listen for my living…

The Canadian amplifier sounds slightly soft, and at the same absolutely precise. If we would reach as far inside as we could, then we should notice, that this is a slightly different presentation than with other top offerings, like amplifiers from Solution, Spectral or even Vitus Audio – although the last one would be very close to it. If I would have to find some match within tube amplifiers, then it would be closer to Reimyo than Ancient, although resolution would be close to the latter. And this is the best proof, that we deal with absolute hi-end here, as those are two postulates that commonly exclude themselves – resolution and striving to “goodness” in sound. And the first one is fulfilled on every possible level, and this can be seen best, when comparing different versions of the same disc. For example I have the original edition of the disc Julie is Her Name. Vol.1, maybe not in mint condition, but good enough to listen to it. Like I said, the HiQualityCD patent brings much good to the digital sound. But only comparing it to good vinyl shows, that there is still much to do. Surprisingly little, if we look at how CD players sounded a few years ago, but still enough to justify the return of music lovers to the vinyl disc. The 175S showed those differences brilliantly – with a deep, warm sound of the original, tending towards an underlined lower midrange, or even nasality, and the more precise, lighter sound of the digital version. And both versions were acceptable, although each for a different reason. I can tell the same, although the result of the comparison was different, about the disc Music for K Tomasz Stańko. I receives a new pack of this artist for my birthday, and it contains five discs from the years 1970-1988 (1970, 1975, 1984, 1986, 1988), where under the year ‘1970’ we find Music…. This was one of the discs from this box (individually numbered, mine has the number 0042), I had earlier, issued in the series Polish Jazz by Polskie Nagrania. Please listen to it, and you will hear, how you can destroy such an re-edition. I am talking about the boxed version. Music for K is simply tragic, and the Polskie Nagrania version wins heads over. In comparison you can hear the warm, full sound of the PN version, and the thin one of the Metal Mind Productions (box). Again – the Tenor showed it nicely, thoroughly, clearly, but I chose the PN version only in direct comparison. When I listened to the boxed version solo, I thought that it is OK, and that the recording was just made that way. And it turned out differently…

I did not write about the sound on purpose, although I usually start the test with that. But I said, that this is the hi-end kindergarten, and it does not matter in the end, because when there is something wrong there, then we cannot talk about high quality sound at all, and about hi-end in particular. But just to keep the compatibility with the other tests, I will do it now. The 175S plays with a warm, slightly soft sound. At least compared with other devices, which sound more unanimous, more edgy way. None is ideally equal to the live sound, and all are within the margin of error, all show their side of the world splendidly. This is also the case here. The treble is not softened, in the sense that it is withdrawn. It is strong and full – and if needed – expressive. There is even more of it than with my Luxman, which is also not veiled. But is nicer treble, richer in shades, warmer, but due to a higher amount of harmonics. And a treble that splendidly differentiates everything. We can say the same about the midrange, which is incredibly saturated and extremely energetic. This subrange is so rich, that it seems, that the diaphragms (in my Dobermann all are made from metal) seem to be heated form behind with a big oven. And bass is similar. Extremely low reaching, even lower than in my reference in that aspect, the Krell EVO402. But it has a softer attack, more physiological. But it works unnoticed, I mean it does not attract attention. Its timbre is very, very natural – the contrabass from Paul Chambers, from the disc Kelly Blue Wynton Kelly, and the electronic passages from Playing the Angel Depeche Mode had a distinct, individual sound, thorough, but not hardened. Just like it should be. And finally the sound stage. This is related to the flawless dynamics, because there is not cutout of planes and instruments, everything what is not part of the recording disappears. As if something would suck out the air in my room, and created a completely new universe there, with a different acoustics, different timbre, size. The way of presentation was almost holographic, and only the Ancient Audio Silver Grand Mono can create this better, not only push the shapes out of the black background. This is one of the things 300B do in an even more credible way. The instruments and voices are even more precise, but not due to higher detail, but through something deeper, due to such a high naturalness, that we are deceived for a moment, we believe that we hear something real. Despite the flaws of the recording, the medium, etc. With the Tenor we have it almost the whole time, and only from annalistic obligation, I must say, that the Silver Grand goes a step further. But only with small ensembles and in full symbiosis with the loudspeakers. The Tenor is much more universal, and will power any kind of speaker in any size of listening room. Ancient will not do that.


Tenor Audio 175S is a Canadian stereophonic power amplifier. The units are assembled manually in Quebec. Its power is quoted at modest 175W at 8Ω, 350W at 4Ω and 650W at 2Ω. Despite being big – 54 kilograms of weight. Its fascia is made from cherry wood, finished in high gloss varnish. Panels on top cover are also made from the same kind of wood. In the front there is a large round cutout with Tenor logo, which lights up red after power on, and after three minutes, when the circuit stabilizes, it changes to blue. The company mentions 60 minutes necessary for reaching full operational temperature. On the sides there are mighty heat sinks, covering the full length of the unit (over 700mm). But the top cover gets much warmer – there is a lot of tubes inside, working with high voltages, and they generate as much heat as a small oven. The back plate is crowded. We have there single loudspeaker terminals – the fantastic platinum plated WBT 0702 Signature. Next there are two pairs of inputs – RCA (WBT 0201 Topline) and XLR from Neutrik. Below we have a set of switches, which allow to choose one of many options of attaching the ground to the enclosure and the earth terminal in the mains plug. We can use it to optimize the sound in a certain system. Talking about mains, it is worth noticing, that the IEC socket in the Tenor is of the 20A, and not the usual 16A. We have to take it into account when buying a power cable. Above it there is a mechanical power switch. We have also a power on hours counter, which can be used to assess the remaining life of the tubes. They are good for 10000 hours of work, without degradation of the sound. Then they need to be replaced. There is a standby switch below the front panel, as well as a mute switch. It seems that the whole enclosure is made from thick, aluminum sheets.

nside we see, that each section has a separate PCB. From the inputs the signal runs forward, to the input PCB, which has symmetrizing transformers for the RCA inputs – the amplifier circuitry is fully balanced. There is also a protection circuit there, which protects against all known failures. From there, using splendid professional connectors we go to the tube PCB. It is not bolted, but mounted on elastic elements. On the input we have two double triodes, 12AX7/ECC83 from Mullard (NOS), controlling four, very big, equipped with heat sinks and o-rings reducing microphone effect, ECC99 triodes from JJ. This is a proprietary tube from the Slovak factory, a tube which was designed to be similar to the super tubes 6H30. We have here four double triodes per channel, what gives a high output power and low output impedance (and high input impedance), what is the idea of an OTL design. Medium power triodes, even those like ECC99, are no power triodes, but in a circuit, where transistors take on them the role of the current source, this is absolutely sufficient. The company claims, that they output 10W in class A. More than Reimyo, and only 6W less than the Ancient Audio. Everywhere on the PCB we see the splendid resistors from Dale, polypropylene capacitors from Wima and Vishay. The power supply of this section is very worked out – it is bolted vertically, with the back to the power supply for the power stage, which shields this section from the transformer. And the latter is a small bucket with copper, shielded vibration damped and with a power of 1875W. So this is the reason, the IEC socket is rated for 20A. It has many secondary windings, separate for each section and voltage. Power supply for each channel is handled by vertical PCBs. Also vertical, bolted directly to the heat sinks, are the power transistors, the MOS-FETs from Toshiba, four complementary pairs 2SK1530 + 2SJ201 per channel. The signal goes from those directly to the loudspeaker terminals by means of flat tapes.

Like I say, attention is mainly drawn by an incredibly worked out power supply, with voltage stabilization everywhere where it is possible. The whole is really big, and nicely made. And as always the question returns – how much does it cost? But this is an academic question, we are not buying a bucket of nails here, but a product: the materials, workmanship, sound, brand, service, safety, etc. And this has a price. The unit is supplied in a splendid professional case, like stage devices.

Technical data (according to manufacturer):
Gain: 32dB RCA/30dB XLR
Power: 2, 4, 8Ω (1 kHz): 650, 350, 175W
Signal to noise ratio (10W*): -94dBA
Signal to noise ratio (full power*): -115dBA
Frequency response: 3-200 000Hz (± 3dB)
THD + N (5W/20-20kHz): < 0.10%
THD + N (10W): < 0.08%*
THD + N (175W): < 0.25%*
IMD SMPTE (10W): < 0.5%
Channel crosstalk (1kHz): < -100dB
Input impedance (1kHz; XLR/RCA): 20kΩ/33kΩ
Output impedance*: 0.16Ω
Damping factor*: 50
Working in class A: 13W *
Input sensitivity (175W, 8Ω, 1kHz): 1.3V XLR/1.5V RCA
Maximum power consumption: 1850W
Dimensions: 710 x 500 x 210mm
Weight: 53.5kg

*: @ 8 Ω, 1 kHz

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  • CD player: Ancient Audio Lektor Prime (tested HERE)
  • Phono preamp: RCM Audio Sensor Prelude IC (tested HERE)
  • Preamp: Leben RS-28CX (tested HERE; soon to be changed to Polaris II, tested HERE)
  • Power amp: Luxman M-800A (tested HERE)
  • Integrated amp: Leben CS300 (reviewed HERE)
  • Loudspeakers: Harpia Acoustics Dobermann (tested HERE)
  • headphones: AKG K701, Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro, 600 Ω version (reviewed HERE, HERE, and HERE)
  • interconnects: CD-preamp: Wireworld Gold Eclipse 52 (tested HERE; soon to be changed to Acrolink Mexcel 7N-DA6300, article HERE), preamp-power amp: Velum NF-G SE (tested HERE)
  • speaker cable: Velum LS-G (tested HERE)
  • power cables: Acrolink Mexcel 7N-PC9100 (CD; reviewed HERE) and 2 x Acrolink Mexcel 7N-PC7100 (preamp, power amp (reviewed HERE)
  • power conditioning: Gigawatt PF-2 Filtering Power Strip (reviewed HERE)
  • audio stand Base
  • resonance control: Finite Elemente Ceraball under the CD (article HERE ) Turntables change continuously, as do cartridges. My dream setup: SME 30 with Series V tone-arm and Air Tight PC-1 cartridge (also in the PC-1 Mono version).