t was hard for us to make an appointment with Wiktor for him to deliver the amplifier for test, even though we live in the same city within a few kilometers. When finally came at 9 a.m. rushing immediately out for a rehearsal, I saw myself in him, the homo running. Wiktor is primarily a musician, he plays contrabassoon, trying to finish his doctorate on the Krakow Academy of Music, and only then he is also a designer and owner of Haiku-Audio. And a frequent attendee of Krakow Sonic Society.

The proportions between all these activities begin to change, and the designer's passion starts to take over. His company is constantly developing. From a completely unknown company offering amplifier kits, it became a recognizable brand, and Wiktor had to start thinking about employing yet another person. Currently he makes only the flagship amplifier iovita by himself.

Haiku-Audio has earned its reputation with their hybrid amplifiers, with tube input-stages and transistors in the output. At the same time, a full range of tube amplifiers was offered featuring the significant name of Hommage á Williamson. Wiktor started his audio adventure in 2003 with tube amplifiers. As he old us in A few simple words for Haiku Bright Mk3 review, these were OTL amplifiers, but later he gave up this type of circuit because:

Only the experiments with hybrid circuits gave satisfactory results. The solution was simple and innovative. It turned out that instead of building a hybrid design by adding a single tube to the output stage of a solid-state amplifier, it was a better idea to add a single solid-state stage operating as a sort of a “super-output transformer” to a complete single-ended triode amplifier.

More HERE, „High Fidelity”, No. 131, 2015

WIKTOR KRZAK
Owner, designer

Every tube lover knows or at least should know the D.T.N. Williamson name. Countless contemporary amplifiers refer in some way to his projects. Careful study of Williamson's works reveals a general thesis he postulated:

Of all the available system solutions, one should choose the ones that using the available most up-to-date components present the most objective advantages in particular application.

What our amplifier has to do with Williamson's original work is the overall topology. It is a frame that allows to build a device evoking the vintage sound.

There are also several differences between the original and our approach, but all aim to match the capabilities of the amplifier to contemporary conditions while preserving the original sound signature. These differences include for example:

• Ultra-linear mode. Originally Williamson used a triode power tubes, but for most modern speakers 10-15W output range is simply not enough. The ultra-linear mode preserves practically all the advantages of triode mode, but delivering twice the output.
• Application of 6CA7 tubes. Initially, the Williamson's amplifier featured KT66 tubes, and later the EL34s were extremely popular, because they seemed to be tailored for this particular amp. Contemporary 6CA7 is theoretically an equivalent to EL34, but in many respects it outperforms it. It is slightly larger, features a more rigid structure and an anode with a larger surface, so it can withstand higher loads without a risk of damage and without losing the fantastic sound quality of EL34 lamps.
• Semiconductor power supplies with stabilization. The available technologies and components that have been used for power supplies have significantly changed over the years. The low-noise , high-efficiency power supplies made today are capable of bringing the older circuits to even higher levels.
• Components: Ohmite resistors, Wima capacitors, metallized precise resistors – these are all components that were not available at Williamson's time. Skillfully used they ensure reproducibility of the amplifier and even better parameters. They also allow designer to simplify the amplifier's circuit by omitting compensating circuits,

In addition, we have adopted a few assumptions beyond the original project from the past:

• Power output of 30 W, for better match to modern speakers, that are usually much more difficult to drive than the old models.
• Single output. User does not have to wonder if his speakers' impedance is 4, 8 or maybe 6 Ω. The amplifier has one output that accepts the full impedance range of modern speakers. There is no bias adjustment, operating mode switches, etc. Everything is automatic, so replacing the tubes is very simple - remove the old ones, inserts the new ones and you're ready to go. You do not need to mark the order or remember any settings.

The Hommage á Williamson amplifier has been offered for the past three years as a Custom model built upon order. Each was slightly different, tailored to the specific system and user's preferences. This allowed us to gather the experience, which was used to create a serial, universal, user-friendly tube amplifier that offers the sound of the past and very modern parameters.

Hommage á Williamson 6CA7 Ultralinear

The tested version of the Hommage-Williamson amplifier is the first for Haiku-Audio, which uses the 6CA7 output tubes. This is an American version of the EL34 power pentode, which differs slightly from the Philips design, with a number of different operating characteristics, mainly in the lower voltage range of the first grid (-20 V). It can also be fed using higher anode voltage, resulting in higher voltages. Although nominally 6CA7 and EL34 are substitutes, in this particular case it is not recommended to replace one with the other.

The device has typical Haiku-Audio appearance, which includes a distinctive front panel. The device features four unbalanced RCA inputs and single speaker terminals. Usually tube amplifiers sport two sets of outputs (except for Manley products) for 4 and 8 ohm loadings. The appearance of the device is characteristic for this type of product, i.e. with tubes and transformers placed on top of the chassis. There are four 6SN7 EH made by Russian company Electro-Harmonix. The same company also produced four 6CA7 tubes.

What changed compared to previous projects are output and power transformers left without housings. This is a comeback to the original design and it looks very cool - vintage, but interesting. The on/off switch is placed on the side of the amplifier that does not have a remote control. For a long time, Wiktor firmly refused to equip his products with a remote, arguing that it deteriorates sound quality. However, the demand from customers forced him to offer it as an option.

Williamson amplifier

“Williamson amplifier's” scheme, a reprint from „Wireless World” magazine, 1947

The choice of David Theodore Nelson Williamson's choice (also known as D.T.N. Williamson, 1923-1992) for a patron for an amplifier is not accidental. His series of articles, published in the Wireless World magazine in April and May 1947 is widely recognized as the beginning of the "high-fidelity" era (though, let's notice, that the term was defined already in 1934 by the Radio Manufacturer's Association ). The cycle was named Design for a High-quality Amplifier. For two years, the amplifier existed only on paper, as a blueprint, however, it quickly began to sell in the form of kit and many people, especially ex-military, used it to build their first audio amplifier. To this day it is a very popular project in DIY community.

The “Williamson amplifier” was a tube symmetric push-pull design using negative feedback and innovative ultra-linear mode. These solutions allowed designer to achieve a uniquely low (back then) distortion level of 0,1% at full power.

The original configuration featured KT66 ("Kinkless" Tetrode) in the output stage driven with the L63 (6J5) which is the electric equivalent of the 6SN7 double triode. The voltage was filtered in the U52 rectifier. The original project used Osram tubes manufactured by the M. O. Valve Company, for which Williamson worked until 1946. The second, modified version of the circuit was published in 1949. Over time, electronics and music lovers became more aware of its version with EL34 pentodes.

I placed the amplifier on the top shelf of my Finite Elemente Pagode Edition rack, on its own feet.

All cables, meaning power cord, speaker cables and interconnects came from Acoustic Revive Triple-C line (see HERE and HERE). My Ancient Audio Lektor AIR V-edition CD Player was the source of the signal and the reference amplifier Haiku was compared to was Ayon Audio Spheris III preamplifier and Soulution 710 power amp.

Recordings

• Alice Coltrane, Eternity, Warner Bros./Warner Bros. Japan 8122-79598-0, „Jazz Best Collection 1000 | No. 9”, CD (1976/2013);
• Annie Lennox, Medusa, BMG Ariola München/Sony Music Entertainment Hong Kong 430868021, No. 0123, K2HD Mastering CD (1995/2014)
• Art Farmer and Jim Hall, Big Blues, CTI/King Records KICJ-2186, „CTI Timeless Collection | No. 40”, CD (1978/2007)
• Depeche Mode, Going Backwards [Remixes], Columbia 5477452, SP CD (2017)
• John Coltrane Quartet, Ballads, Impulse!/Universal Music LLC (Japan) UCCU-40001, Platinum SHM-CD (1962/2013)
• Lisa Gerrard, The Silver Tree, Sonic Records SON212, CD (2006)
• Nat ‘King’ Cole, The Nat King Cole Love Songs, Master Tape Audio Lab AAD-245A, „Almost Analogue Digital”, Master CD-R (2015);
• Niccolò Paganini, 24 Caprices for solo violin. Op.1, wyk. Mayuko Kamio, BMG Japan BVCC 40003, „RCA Red Seal”, CD (2009/2012)
• Schubert, Song Cycles, wyk. Nathalie Stutzmann, Inger Södergren, Erato | Warner Classics 4623701, 3 x CD (2014)

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Japanese issues available at

In an interesting review of a new preamplifier by Shindo Laboratory Art Dudley, deputy editor in chief of Stereophile magazine, cites Ken Shindo, for whom the sound of music at its inception is so complex that the often very different sounding amplifiers that we use to play it back offer us one of billion of truths and at the same time each one of them is the RIGHT one (Art Dudley, Shindo Redux, „Stereophile”, Vol. 40, No. 9, September 2017, p. 27) .

It's hard to disagree. My version of this approach I explained using a mountain as an example, which can be climbed from many sides. But the point is the same in both examples - in audio there is no one right way, there is only the right direction. Therefore, any orthodox views or claims are suspicious and might be even dangerous. This came to my mind when I was listening to the Haiku-Audio tube amplifier. It so happened that this was my first contact with this type of design by Wiktor Krzak, so I did not know what to expect.

His hybrid and transistor amplifiers have several qualities, such as clarity, rhythm, resolution, dynamics, tonal balance. Among more ephemeral, but perhaps even more important, one should mention communicativeness, i.e. the ability to communicate with listener. And to do so, it is necessary to engage him in the created world, to attract his attention to music. There are several ways to do this, and Wiktor has chosen high resolution. So the more information the device communicates, the better it describes the musical world.

With his version of Williamson it is a bit different. It is also a very communicative presentation but it is achieved using other means. This is an amplifier with extremely soft, relaxed sound. It does not sound warm, meaning it does not suggest warmth, but it has a soft attack, a velvety transition between sounds, a velvety background - all this creates the sonic character of this device.

One could similarly begin a review of some EL34 amplifier. And yet the 6CA7 is different, not only in terms of the design and I think that's why designer chose it. They are first of all faster and offer a better control of the speakers. They do not have the "magic midrange" of Jadis integrated, but it does not go in the direction of a very precise sound as the Linear Audio Research IA-30T Mk2 did. It's something in between.

The high (for this type of amplifier) output and good current efficiency translate into a very good bass extension. It goes lower than many transistor designs. It has no particularly precise leading edges, one should not expect it to be as selective in presentation of a bass guitar, as with good solid-states. Here all instruments play together, the sound is dense but rich with information and details and yet the atmosphere and “flow” are more important.

While this approach is something that many associate with EL34 based amplifiers, and often also with the KT88 ones, see McIntosh MA275 - a good bass extension combined with a very good control is something unusual for this price range. It requires a much higher output and consequently multiple parallel tubes, or powerful types such as KT150, to achieve a similar effect.

The opposite range extreme is sweet, nice and surprisingly resolving. Same as with the bass, treble is also not particularly selective though. But you've probably already figured out that this is not an amplifier that "x-rays" recordings, and will not let you study recording techniques. If you try to force it to do that you might get frustrated because it is not what it does.

This device invites you to a relaxing, soothing listening. It will play any music in an enjoyable way, so it's not about limiting power or dynamics. A soft attack, a gentle roll-off the treble, an emphasis on coherence at the expense of selectivity – these are elements associated with chamber music. In this case we can add powerful bass and surprising headroom that will allow you to have fun even with rock and electronic music. The amplifier delivers quite well-balanced performance, i.e. I have not found any coloration. But the presentation as a whole is slightly inclined towards the bass.

Summary

As usually in Wiktor's products case, the Hommage Williamson featuring 6CA7 tubes is a very well made device. It is also very quiet, i.e. there is no noise or hum - I had to put my ear against a driver to hear anything, but still at a very low level. From my listening spot I heard absolutely nothing. Just music. And this one is taken seriously, i.e. it has a proper dynamic and tonal structure. This is a dynamic device with a strong, “vigilant” but rather soft bass. The overall sound is rather soft, but like a cougar, not a sponge.

It takes a while to realize that it is a tube-based amplifier, because there is no emphasize in the midrange, and the foreground is not pushed forward. The resolution is really good, but you should know that the reverb is slightly shortened and direct sound are favored.

Haiku-Audio Hommage á Wiliamson 6CA7 Ultra-linear – that's the full name of the device under review, is an integrated tube amplifier. It features a classic design for this type of device, i.e. thee is a narrow front panel, and tubes and transformers are placed on the top. The chassis is made of solid, thick steel sheets, and it is placed on rubber feet. The finish is very nice and although it's definitely nothing fancy while you see it you know that somebody really thought it over.

The front is primarily an aluminum element with an acrylic plate fitted in it. On the sides there are two large knobs, the left one allows user to select inputs, the right one controls volume level. There are four unbalanced inputs featuring solid RCA sockets. The inputs are numbered from 1 to 4. Note that the input jacks in Haiku-Audio devices are marked differently – they use red for the left channel, and green for the right one. The speaker terminals also look good – there is one pair per channel. They are gold-plated but the connectors used inside to fix speaker wires to the socket are not gold-plated but tinned.

The tubes were mounted on top – in front the 6SN7 triodes and the power pentodes 6CA7 in the back. The triodes operate the input stage and they driver power tubes. The output operates in class A, in ultra-linear mode, originally developed by D. T. N. Williamson. All tubes are from the Russian company Electro-Harmonix production, so the names include letters "EH".

Unlike the original design where the anode voltage was rectified by a tube, here designer used a solid state rectifier. This amplifier features EI transformers, which make it different from all other model by Haiku-Audio that utilize toroidal transformers. The ones used here are made by Leszek Ogonowski.

Each unit is measured individually and the results are recorded on a piece of paper glued to the bottom of the chassis. Attached you will also find a complete schematic of the device. You can learn from it that the input signal goes from the input to the potentiometer, the blue Alps, and then to the grid of the half of the 6SN7 tube. The other half is coupled without any capacitor. The first polypropylene WIMA cap operates between the first 6SN7 tube and the second one that drives the output, and the other one between driver and power tube. Let's add that the first tube operates also as a phase splitter. Each channel has its own power supply.

The whole circuit system is assembled using the point-to-point method, which is the most time consuming and most expensive, but also the best one. The downside of this method may be smaller reproducibility and more chaotic layout. The Haiku-Audio amplifier can be a very good example of how it should be done.

Specifications (according to manufacturer):

Output (class A, 8Ω): 20W
Output (4Ω | 6Ω | 8Ω): 30W
Frequency range (-1dB, 1W / 8 Ω): 14 Hz-35kHz
Frequency range (-3dB, 1W / 8Ω): 7 Hz-51kHz
Input sensitivity: 500mV
THD (8Ω, 1kHz, 30W): <0.12%
Power consumption: 250W
Dimensions: 450 x 380 x 190mm
Weight: 15kg
Front panel color: black or silver