⌈ OCTAVE AUDIO is a German company founded in 1968 by KARL HEINZ HOFMANN; initially it manufactured transformers. In 2000, his son, ANDREAS HOFMANN, took over the lead in the company, and since then it has been called OCTAVE AUDIO. We test the Jubilee 300B monoblocks. ⌋

MONG AUDIOPHILE STORIES, the one related to 300B tubes, especially in the so-called SET (single-ended triode) designs, is one of the oldest and most polarizing ones. Supporters of the thesis about the unconditional superiority of power triodes, and in particular this particular model, introduced by Western Electric in 1938, are consistent and unwavering in their conviction.

And there's a lot of truth to that. During my story about audio files, streamed by the Audio Video Summit portal, when asked by an Internet user about my dream amplifier, after a moment of reflection I replied: Kondo OnGaku. So a classic SET, but with 211 tubes, not 300B. My choice was dictated not by the belief in the absolute superiority of this type of design over others, but by many other considerations, such as the history of the amplifier, its appearance, the feeling of having a piece of history and finally - the sound. For me, this is one of those products that you can grow old with.

However, this is not an absolute choice. I didn't have time to tell you then, but it's just that I could live with the top monoblocks from Soulution, or products from FM Acoustics or Spectral. And these are transistor amplifiers. My experience tells me that there is no such thing as "absolute" superiority of one technology over another. Speaking of which, I would like to add that I do not want to force you and bend you to what I am saying, this is not the point. I just want to appeal to you so that you just keep an open mind.

▌ 300B w Jubilee

ONE OF THE MOST SERIOUS DISADVANTAGES of SET type amplifiers is their low output. From 2.5-3.5 W from a 2A3 tube, to 8-9 W from a 300B - it's not much. And even if clever circuitry manages to get 14W (at 3% distortion) from a single 300B tube, like the Western Electric 91E amp, we're still talking about low output combined with high distortion. The tested Jubilee 300B monoblocks largely solve this problem, offering from 15 to 30 W, depending on the selected amplification mode.

Mr. Andreas Hofmann, the boss and chief designer of the Octave, was aware of these issue. That is why he approached the design of his new amplifier from a different angle. Since one 300B tube offers only about 9 W output, in order to increase its power, he reached for a solution known from amplifiers using pentodes or beaming tetrodes, i.e. an output circuit with several parallel-connected tubes - in this particular case with three per channel.

Presented for the first time in May 2019 during the High End Show in Munich, the Jubilee 300B is a combination of the absolutely classic SET circuit with ideas that allowed the use of several 300B tubes in the output. The problem he had to solve was the reproduction of low bass, around 20 Hz, and the difficulties in implementing a parallel circuit for the 300B tubes. As he told the the "Stereophile" magazine at the time, it was his first amplifier of this type, because all the previous ones featured a push-pull design and that he worked on his project for ten years (more → HERE).

The thing is that these are so-called direct heated (cathode in the form of a heated wire) triodes. In almost all other tubes used today, the heating is indirect (isolated heater placed in the cathode tube). In the 300B, the voltage needed to heat the filament is connected to the same point as the cathode voltage. The downside of this solution is higher noise and distortion, most often the so-called "hum", as well as problems with microphoning. To prevent hum, some designers supply the filament with DC voltage, which is considered a mistake by some.

Mr. Hofmann came up with something else that I've seen for the first time:

We have developed a 7 Hz power generator that supplies each of the three 300B tubes with a separate, regulated 7 Hz pure sine wave heating voltage.

• This makes it possible to connect several 300B tubes in parallel.
• Sound-affecting ripple and RF disturbances of the line frequency are completely eliminated.
• Heating and operating voltage are electronically controlled, sound instabilities due the fluctuating mains voltage is a thing of the past.

⸜ Jubilee 300 B, → OCTAVE.de, accessed: 21.03.2023.

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| A few simple words…

ANREAS HOFMANN
owner, constructor

⸜ ANDREAS HOFMANN (on the left) and THOMAS BRIEGER, Octave’s Head of Sales and Marketing • photo: Octave

WOJCIECH PACUŁA Could you explain shortly what was the idea behind this project, what challenges have you faced?

ANDREAS HOFMANN Octave is building powerful amplifiers since the beginning. Therefore we are able to drive any speaker. We are well known for stable, quiet and reliable models. So it looked like we did not accept single ended amplifiers although they offer a superior performance. Or at least supposed to do. The truth is we saw and accepted the outstanding performance, but there were some serious basic disadvantages:

• we faced not enough power for most of the actual loudspeakers;
• in principal single ended concepts have far too much hum and noise;
• very often music lovers speak about the midrange because of the limited bandwidth. We saw significantly high and low frequency roll-off;
• and finally these amplifiers have a limited damping factor.

We at Octave think this does not fit in our philosophy. We always try to drive most loudspeakers in the world. We don’t like any audible noise. We stand for full bandwidth, deep bass and high resolution in the upper frequency range. And we always try to create user friendly concepts.

We got rid of these limits with our first single ended amp in Octave history: V 16 Single Ended, where we used KT120 in triode mode. We had no hum and noise, the frequency range goes down to 20 Hz and the signal to noise ratio is over -100 dB. So it was possible but with only 8 watts per channel. But music lovers had fear of contact with the pentode KT120 in a single ended amplifier. Such a system must work with a classic triode. And after some research we ended up with the famous 300B.

After this decision the development started and took more or less in total three years before the first prototype was ready. There are – in our eyes - three basic problems with single ended designs we did not want to accept:

• Hum and noise because of the power supply. We solved it with the Octave regulated power supply
• Limited bandwidth and damping factor. We solved this with our special Octave output transformers
• And finally a big issue was the hum and noise because of the heater. We had to start a completely new development for that because we don’t wanted to use a simple DC heating system

The challenge of a conventional system is that the heater is coupled with the 50 Hz mains input. So the mains distortion remains the same at the heater. And new audible harmonic distortions occurred. It was also impossible to use more than one 300B (necessary to increase the power). We also tried DC Voltage but at the end of the day the distortion became higher with a lot more disadvantages.

So we ended up with AC heating. And the main aspect for us was at the end the frequency. We found out that 7 Hz is the best solution.
• Even loading of the tube
• Mains distortions eliminated
• No audible hum noises
• No audible harmonics

The 7 Hz creates the 2nd harmonic at 14 Hz and the third one at 21 Hz. That means the fundamental frequency and the sensitive next two are below the audible threshold. A huge step forward to create a quiet amplifier! So because of this Octave development a 7 Hz true sine wave generator. This makes it possible to use 3 pieces of 300B in parallel. That means higher output power. The regulated power supply means zero noise and extremely high bandwidth. The impedance optimized output transformer gave us a high damping factor and extremely wide frequency response.

There are some more important details. For example, the design follows the function. Due to the tower design we had more headroom to place the power supply, heater transformer and the output transformers in a way that we could minimize the interferences. A significant improvement. That means we developed the first 300 B Single Ended amplifier that delivers true 300 B sound independent of the speaker type!

WP Does the EF800 work in pentode or triode mode?
AH EF 800 works as a driver in pentode mode.

WP There are four large transformers inside, one seems to be a choke. Could you tell us more about them?

AH Yes, Jubilee 300B features four transformers:
• two of them are for power supply,
• one is an output transformer,
• One is the 7 Hz sine wave generator to generate a completely independent filament voltage from the mains for the heater. This is a specialized 7 Hz transformer with three output voltages for each 300 B.

WP Last but not least, what is the output for bias’ „Med” setting? – I am asking because I used this setting for my auditions.
AH Output depends on power tube one uses. In the high position you are able to use so called high power tubes like the 300 B XL Than you can achieve up to 36 watts per channel. In the position medium you achieve up to 28 watts with the 300 B. ●

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▌ Jubilee 300B

THE TESTED AMPLIFIER is a huge device. It is actually a two-box design with two monoblocks weighing 60 kg each, each measuring 660 mm x 240 mm x 400 mm. This is a form previously practiced in such amplifiers as: Jubilee (2003) and Jubilee Mono SE (2015, test → HERE). These devices are more like obelisks placed in the middle of a room than music reproduction products.

Each of the monoblocks offers output ranging from 15 to 30 W, with exceptional current efficiency, depending on the selected bias current of the output tubes. The bias current is set with a switch located on the top of the device, right next to the switch and voltmeter used to set and monitor the parameters of the output tubes. Bias is set in three steps: "low", "medium" and "high", corresponding to the currents, respectively (25, 50 and 70 mA). This is the second single-ended design in the history of the Octave, i.e. with a class A circuit in unbalanced mode, but the first one featuring triodes (SET = Single-Ended Triode); all others were push-pull devices.

The input gain is provided by an ECC82 double triode and the output tubes are controlled by the low noise EF800 pentode. The first one was developed for audio applications, but the EF800 is a tube used in RF and IF systems, where a wide frequency response and minimal noise are required. These tubes are hidden in a housing inside the chassis, thanks to which they are properly shielded. The output tubes are visible from the outside if the metal covers are removed. These are three 300B triodes working in parallel. All tubes were purchased from the Slovak company JJ Electronics.

Signal can be delivered to the Jubilee 300B either via the XLR or RCA inputs. One chooses between them with the switch located right next to them; the third position is "Mute". Let's remember, however, that the Octave is an unbalanced amplifier, so the signal behind the XLR input is de-symmetrized. So, if the connecting cables are not long, it may be better to use RCA ones.

The amplifiers feature an extremely robust chassis. This is one of the most important features of this product. The mechanical structure of the device is based on an internal truss with individual modules screwed on to it. At the very bottom there are two huge, resin-dampened and shielded power transformers. Above there is an equally large choke and an output transformer. When we reviewed the Mono SE model, Mr. Hofmann said:

All transformers are manufactured in-house and each of them, like the output transformer, is optimized and adapted to each model. We have two Meteor winders, this type is extremely precise and, due to the programmed process, very uniform in winding quality. In the photos, this machine looks tiny, but it weighs 150 kg. Damping resin is poured into power transformers housings in a vacuum, output transformers undergo a similar process.

On the same level there are rectifying circuits and filtering capacitors, and in the back, bolted to a huge heat sink, voltage stabilizing circuits and a 7 Hz generator for the filament voltage. These are top quality components, but they are industrial components. You won’t find any of the audiophile-praised components in there, maybe apart from the Mundorf components. The latter provided also speaker terminals - separate ones for 4 and 8 Ω taps. You may notice the extremely clean and orderly assembly, also when it comes to cable routing.

The structure is stiffened by external, thick and heavy steel plates, closing the chassis on the sides. At the front, there is a thick aluminum panel, in the middle of which a wooden marquetry is glued. This strap is available in one of three colors and the aluminum can be silver or black. The whole thing stands on a pedestal which optically relieves these giants.

▌ SOUND

⸜ HOW WE LISTENED The Octave Jubilee 300B amplifier was compared to my reference amplifier, the Soulution 710 transistor power amplifier, and drove the Harbeth M40.1 loudspeakers. The manufacturer suggests that the "high" output should be used for loudspeakers with efficiency from 82 dB, and the "low" option for those above 106 dB. The efficiency of the Harbeths, according to the manufacturer, is 84 dB/1 W/1 m, but in my case the "medium" position was enough to adequately fill in the room with sound and properly control the speakers. Remember that the higher the gain, the higher the noise of the amplifier - the "low" and "high" positions differ by as much as 10 dB!

The initial gain was delivered by the Ayon Audio Spheris III tube preamplifier, but the manufacturer offers its own Jubilee preamplifier, one should start listening sessions from. The set looks and sounds great. The signal between the preamplifier and the power amplifier(s) was sent in both cases by the Acrolink 8N-A2080III EVO interconnect. The amplifiers were powered using Acoustic Revive Absolute Power cables.

The signal to the loudspeakers in my system is sent using the Siltech Triple Crown speaker cable. However, it is very stiff, so for some time in such cases I have been using another, equally wonderful cable - Da Vinci's Crystal Cable Art Series (test → HERE | PL |). The signal source was the Ayon Audio CD-35 HF Edition SACD player.

⸜ Recordings used for the test | a selection

⸜ JOHN SCOFIELD, Swallow Tales ECM Record/Universal Music Classic & Jazz UCCE-1183, CD (2020).
⸜ MICHAEL JACKSON, Thriller, Epic/Mobile Fidelity Sound Lab UDSACD 2251, seria „Original Master Recording, Ultradisc II”, SACD/CD (1982/2022).
⸜ ABBA, Gold - Complete Edition, Polar/Universal Music K.K. (Japan) UICY-91318/9, 2 x SHM-CD (2008).
⸜ SUZANNE VEGA, Nine Objects of Desire, A&M Records 540 583 2, CD (1996).
⸜ KRAFTWERK, 3-D. The Catalogue, KlingKlang | Parlophone 95873424, 8 x CD (2017).

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ONE OF THE FEATURES WE LOVE SET amplifiers for is the energy transfer - an incredible one, let's add. It is so that designs of this type, thanks to their simplicity and short gain path, do not reduce the dynamics, especially of small signals. As a result, we get a presentation that largely resembles what we hear at live performances, standing in front of the drums, guitar amp or vocalist. All other amplifiers modify this aspect of playing, calming down the sound. Even the best ones.

This is why JOHN SCOFIELD from Swallow Tales seemed incredibly real. His guitar, recorded with a microphone placed by his guitar amp and directly through the line, was three-dimensional, had a clear body and incredible "power". The tonal balance was perfect and I was sure the mics were positioned fairly close to the instruments. The frequency response seemed to have no limits, neither from the bottom nor from the top. Not just that "there was a lot of bass and a lot of treble", because it's a cliché, we are in a completely different mental space. The point is that the scale of sounds was large, the space was extensive, and the midrange was open. And this can be achieved only due to a wide and even frequency response.

Density - density is another term that should be engraved on the chassis of these monoblocks. It was selective density, not "syrupy" one. Because although with the Scofield the sound was presented close to me, the instruments had a large volume, and the leader's guitar almost "jumped" out of the speakers, when playing MICHAEL JACKSON's Thriller album, remastered by Mobile Fidelity Sound Lab and released on SACD, the sound was completely different. The vocals were placed far in the mix, and the bass, although strong and clear, sounded somewhere in the area where the mixer "set" the vocalist. And only, entering in the middle of the fourth minute, in the left channel, David Williams' guitar came out in my direction.

This comparison showed the excellent differentiation that the Octave amplifier offers. Although the ECM disc seemed almost warm, the Quincy Jones-produced masterpiece of popular music had a much higher tonal balance and was not so "tangible". What was common for both discs was the energy. Multi-track recordings, long sessions and heavy production can kill even the most dynamic recording. Thriller also succumbed to this inevitable process. However, with the Jubilee 300B I got a very nice, emotionally engaging presentation. And not only with the greatest hits from this album, but also with tracks that I listen to less often, for example P.Y.T (Pretty Young Thing).

Curious about how the amplifier would treat material with an even more pop structure, I reached for a selection of ABBA's greatest hits, released in Japan on SHM-CDs. The Visitors, the title track from the album released in 1981, sounded as I remembered it from the best playback experiences in my system. So it was quite light, without a low bass base and with a little filled-in midrange, but with a very well-preserved structure of the whole. Let me remind you that it was the first commercially produced Compact Disc in the world (although it was the second one released). Pressed at the Philips/Polygram factory in Langenhagwy, Netherlands, it was released on August 17th. 1982.

This recording is really nice, because there is no exaggerated playing, like on some of the previous ABBA albums, and it also has a nicely set stereo stage. And now - the Octave amplifier showed how its sound differs both from previously listened to albums and from other tracks on the Gold compilation. More Abba Hits. Recorded on a digital 32-track 3M tape recorder, it should have been too bright and sharp, and it wasn’t. Brighter and sharper are, as I said, the recordings on disc number 1, dating back to the analog times.

Interestingly, the Jubilee 300B easily drew my attention to something I know from LPs recorded with this type of tape recorders: they have a slightly reduced resolution, but excellent timbre. Although the producer Lennart Östlund, responsible for the ABBA album, did not like the digital recording, the result is really very good. For the record, let's add that the first three tracks of this album were recorded on a 24-track analog tape recorder and only after the purchase of a 3M tape recorder by the Polar studio, they were transferred to a new, digital machine.

The German amplifier shows these characteristics of recordings exceptionally well. It delivers an extremely dynamic, energetic sound and, in addition, differentiates these two elements to an above-average degree. It also perfectly shows even subtle differences in color. I already mentioned the comparison of ABBA's analog and digital recordings, but it struck me again when playing Nine Objects of Desire, SUZANNE VEGA's fifth album. It has a dark, dense sound, almost devoid of treble.

I was delighted with how nice it sounded with Octave! Completely different than the albums of Jackson and the Swedes, more in the spirit of Scofield. And it would make sense, as it's a jazz album. The guitar of Tchad Blake, a musician and producer, known - for example - from the recording of the album Binaural by Pearl Jam, sounded great on it. And the bass - it was great. Which brings us to something that will be the most important thing in this test for many listeners.

The Octave amplifier extends bass very low, I have already mentioned that. What's more, the descent is so unforced that it allows large phantom images to be built and creates a dense, extremely wide sound stage. The latter is not a collection of sounds thrown in front of us like - say - stars in a black sky. It's more of a woven image where all the instruments are interconnected, where they only exist as part of a whole.

What about that bass? – you may ask. That's what I'm talking about. Bass is part of the performance not only as the sound of the bass guitar, double bass or kick drum. This is, of course, the absolute basis, but many amplifiers can do it. In turn, what I was talking about a moment ago - not many of them can. And this is something that made me recall the sound of Kondo's OnGaku, because it is an extremely similar presentation. Although I set the Octave's bias switch to the "Med" position, i.e. in the middle, not using the full power of the system, I never lacked either "power", or just the authority of the bass.

The latter has a soft character and the hard attack is not emphasized. Except that it's not slowed down, because the attack of the instruments is really perfect. The beat of the drums snare, the cymbals, the attack of the bass guitar are all clear and energetic. But also the nature of this attack is soft, very "physiological". I've never run out of pure power either. The pulse starting KRAFTWERK’S Radioactivity, and then a very low voice declaring "radioactivity" had the density, volume and power known to me from the best and most powerful amplifiers I had at home.

It helped that I sit near the speakers, that is, that the room (including its surroundings) is no more than 35 m2. However, I know the behavior of other devices in the same conditions and I know what I am talking about. Only the already mentioned Kondo amplifiers, the FM ACOUSTICS 711 MK II and my Soulution 710 could generate a sound of this class.

▌ Summary

I REMEMBER WELL HOW MUCH I liked the Octave Jubilee Mono SE monoblocks. But even they couldn't project the incredibly expansive and "live" sonic panorama in front of me so smoothly, seamlessly, which the Jubilee 300B did so easily, so effortlessly. Yes, in large rooms, with large, medium efficiency loudspeakers you will have to look for more power in other amplifiers. However, if your listening conditions are similar to mine, these twenty-odd watts, obtained in the "Med" bias position, should be absolutely sufficient.

Then you will get the sound that fans of 300B tubes dream of, but with a larger scale, better controlled and - as a result - even better. While power corrupts and absolute power corrupts absolutely, with the Jubilee 300B, that principle seems suspended. The best devices featuring single 300B tubes that I know offer a slightly stronger sound attack and differentiate details better. But none of the ones I know can put everything together so beautifully. This is a remarkable design! ˻ GOLD FINGERPRINT ˺. ●

▌ Technical specifications (according to the manufacturer)

Tubes: 3 x 300B, ECC82, EF800 (per channel)
S/N: from > -100 to > -110 dB (bias: „high” - „low”)
Frequency range: 20 Hz - 50 kHz (±0.5 dB)
Output: from 15 to 30 W (bias: „low” - „high”)
Gain:
• gain „low” 19.5 dB/4 Ω; 22.5 dB/8 Ω
• gain „high” 30 dB/4 Ω; 33 dB/8 Ω
Damping factor: 4.5
Power consumption: 400 W (@ full power)
Dimensions (W x H x D): 240 x 660 x 400 mm
Weight: 60 kg/pc