integrated STEREO amplifier with 2 x 50 watt
At popular request from the AudioValve fan community, AudioValve can proudly refer to a successor to the Assistent series, the Assistent 50 – with 2 x 50 watts per channel and remote control. It combines the experience of over 40 years of production and provides the basis for a completely new technical and optical design. Numerous reports around the world repeatedly prove the excellent tonal properties of this sophisticated, refined construction of previous assistant series. You can find the tests of the product in the sub-category. Just like back then, power tubes of the QQE type are used today, this time, however, a total of 8 – four per channel, from which a whopping 2 x 50 watts develop, thereby reflecting transparency and transparency in the clans, as is the case for this series was always proverbial and still is. Each of the tailpipes is controlled by our ABR – therefore does not have to be selected and promises pure musical enjoyment for a long time.
In addition to all the technical innovations, the housing design in particular has many surprises. No controls on the front, 3-D lasered and blue or green illuminating lettering in the transparent front look of the amplifier only indicate in the beginning which innovation push the product is based on and will give you the expected joy for many years. In many years of development work, we have succeeded in developing an electronic circuit that completely eliminates the use of selected tubes in power amplifiers. This so-called ABR circuit is able to correct the flow of any end tubes and to an exactly predetermined value, e.g. To stabilize 40 mA and this until the end of the max. Life expectancy of the end tubes. The usability of the end tube is signaled by a red / green LED´S when the correct working point is found. The drift of the working point due to aging is also corrected and the sound properties of the tube are maintained for a long time. Apart from the volume button, the Assistant 50 has no other operating parts. The entire operation takes place via an appealing remote control made of heavy aluminum and is included in the scope of delivery of the device.
Some interested parties of AudioVale will perhaps still remember the Assistent 10 + 20 series from 1990 – 2000, at the frequent request of the AudioValve fan community, AudioValve can proudly refer to a follow-up product of the Assistent series – the Assistant 50, (and Assistant 30) who has been in sales since 2006. The Assistant 50 combines the experience of more than 40 years of development and production history around the topic of tube amplifiers and provides the basis for a completely new technical and optical concept. It is thanks to you, dear fan community and your loyalty to us, that we at AudioValve have spared no effort and expense to develop a new device on the proven basis that also meets your need for “more performance and above all comfort” .
6moons review Srajan Eben
From our assistant’s spelling, we know ourselves to be on Germanic footing even though Audio Röhre turned to Audio Valve in the marque’s name. The number 50 obviously refers to 8Ω power, placing it between the stablemate 30 and 100 Assistents. The Hessian designer Helmut Becker grew up around his parents’ small electronics business at a time when televisions still did tubes. Post school this very naturally led to formal training as a TV technician. During his military service, this veered into radar with its magnetron, tyratron and klystron big bottles. Helmut capped off his education in telecom tech. Later he worked in the medical sector where he was awarded numerous patents for laboratory innovations in haematology coagulometers which measure blood clotting. Returning to his love of valves led to OTL amps, eventually the formation of Audio Valve in Kassel. This segues neatly back to the 5-input Assistent 50 with tape-out. Clearly it puts on quite a show, somewhere between Art Deco, opulence and Steampunk perhaps. Shazam.
Comparing these photos toggles between blue power-on mode above and red standby mode below. Copious clear acrylic lent itself to stealth lighting and being an open book on guts. For the full glory, unscrew the sun-dial lid to lay eyes on a rarely seen 9-pin* octet of QQE 03/12 double beam tetrodes good for 225MHz, with 7.5W plate dissipation and voltages from 200-300V. Configured for pure class A push/pull, these glow worms are swappable with RS1029 or CV2798. Also unique is the automated grid bias controller. During each power-up, it measures the quiescent current of every output tube, then applies corrections where needed before bypassing the muting relay. Should a tube be out of range to require replacement, the associated red LED will tell you. Easier than pie. The input/driver tubes are pairs of readily sourced double-triode ECC82 and ECC83. A full-function metal remote is included.
* The nine pins, respectively, are to the 1st control grid, cathode, 2nd control grid, 1st heater, 2nd heater, 1st anode, screen grids, 2nd anode and heater centre tap. Input impedance is a bog-standard 47kΩ, THD below 0.3% for 20 watts. Weight is 18kg and dimensions are 42 x 15.5 x 32cm WxHxD. Now you know as much as I did when I accepted the assignment via Elite Audio UK. That’s Mark Cargill’s import house in Scotland. Due to proximity and a shared appreciation of certain brands, I’ve been granted access to their inventory for regular loaner purposes. Having never yet clapped eyes never mind ears on an Audio Valve piece which instead came recommended by Elite, it seemed good form to contact designer Helmut Becker and learn just a bit more about what makes his Assistent 50 tick. Off went an introductory email.
Questions. Presumably this is a 3-stage circuit: input stage, driver stage, output buffer? What is the overall circuit gain? How much negative feedback is applied and where – local, global?With the unusual output tetrodes being twin-tubes in one envelope, you’re really running 16 tubes in the output stage. Any unusual configuration there? What is the effective output impedance? What are the S/N ratio and operational self noise figures? What type of output transformers (C core, double C core, EI, toroidal, other)? Which stage handles phase splitting and is this done by tube or transformer? Where in the circuit is the volume control embedded and what is it (presumably an Alps Blue or equivalent pot)? What is the power supply capacitance? What is the output power into 16Ω, 4Ω and 2 Ω?
Answers. “Our class A amp uses a 12AX7 cascode input with long-tail phase inverter to drive the push/pull power tubes. Phase splitting is thus by tube. See the multisim graph at right [enlarge by clicking on expansion icon – Ed.]. This nets 50dB of front-end voltage gain with max distortion of 0.1%THD. The ratio of the power stage, from grid 1 of the QQE to the output transformer speaker terminal, is nearly 1:1 to have no gain. 20dB NFB is a mix of local and global. By using 4 double tetrodes per channel, the sum total is 16 output tubes with really spectacular auto bias. This unique circuit has proven stable for more than 20 years. It supports our tubes under all static and dynamic conditions. An opamp on each QQE cathode sets the negative grid 1 voltage. This doesn’t require costly matched tubes to save the customer a lot of money. On grid 2 and the power-tube cathodes we use reversible fuses for protection to never need service. The S/N ratio is -86dB. The output transformers are EI cores from Germany’s Pikatron. An internal 4Ω tap allows us to rewire them on demand. 2Ω out equals a damping factor of 4. The pot is an Alps Blue RK with logarithmic curve. Power supply capacitance is just 330/450VAC per channel. We don’t recommend this amp for 16Ω or 2Ω loads.”
Here we see the Siemens QQE 03/12Y output bottles with their biasing opamps; and the 12AX/AU7 input/drivers at right. Bandwidth is 15Hz – 70kHz. Power consumption is 8 watts in ‘remote’ mode (red display); 80 watts in stand-by warm mode (blue display, no red LEDs on mother board); 220 watts in power mode (blue display, red LEDs on mother board on). Here we see the relay-switched inputs and outputs in the left corner; the Alps pot tucked below the suspended red board on the right; and the compact EI-core output transformers strategically rotated for minimal stray radiation between them. Half the power supply can be seen at the lower left.
In use. Like a piece of precision machinery, the Assistent 50 worked as the perfect butler: utterly dependable, without any quirks, annoying habits or ill manners. Bred to please was its MO. It operated dead quiet mechanically and electrically for neither transformer hum nor driver surf or hiss sans signal. The only noise immediately followed the soft-start cycle when a small sound appeared through the speakers only to fade quickly and utterly into oblivion. Remote volume worked flawlessly. Little increments were easily dialed without jumps. Even the light show was surprisingly subdued during the day, coming out to play only at night.
The circular back vents aren’t for a fan but simply a passive air exchanger. Whilst armchair engineers will have pondered the guts of the previous page to wonder about the power supply—it appears to be unusually small—veteran readers might remember the late Eduardo de Lima of Audiopax. This uniquely gifted valve amp designer from Brazil was convinced that each circuit had the ideal power supply. Anything beyond it wasn’t just excessive and empty kowtowing to bragging rights. It was actually counterproductive sonically. This flew in the face of common wisdom where unending improvements are promised for bigger and bigger PSU; and where overkill is never on the map. Suffice it to say that Audiopax amps begged to differ from award to award; and that on bandwidth both bassment and attic, the Audio Valve really left nothing to the imagination. That its season was quite different from the 1MHz direct-coupled Linnenberg Audio Allegro monos flanking it in these photos was no surprise. If an all-valve amp sounded like solid state, why bother?
By popular request of the AudioValve Fan Community, AudioValve proudly presents a succession model within the Assistent series, the Assistent 50. Here the experience of 10 years production is combined and provides the basics for a completely new technological and optical design. We have to thank you, dear fan community, it is owed to your loyalty to the product that we at AudioValve did not avoid expenses nor troubles to develop a new unit based on the trusted basics, which allows for your demand for “more performance and comfort”.
Several reports around the globe document time and time again the excellent sound performance of the sophisticated construction of previous Assistant series. Just like before, today power tubes type QQE are employed, but now 8 tubes – four per channel, developing full 2 x 50 Watts, reflecting a sound transparency that was and still is proverbial for this series.
True to the slogan: “Once Assistent – always Assistent.”
Besides all the technological innovations, especially the casing design offers several surprises. No controls on the front panel, 3D-lasered and lit writing in the amplifier’s transparent front look hardly show, what wave of innovation forms the basis of the product and will give you the expected joy for many years to come. With these features AudioValve without doubt is again trend-setting.
Juxtaposing Albedo Audio’s Aptica and Amira speakers below created a neat parallel scenario in how what distinguished the ceramic-driver model from that with the cellulose tweeter and Curv mid/woofer closely tracked what separated the Assistent 50 from the Allegro twins. The ceramic Accuton drivers had more sparkle, speed, separation and incisiveness. The mate’s were softer, moister and warmer as though their suspension was dialled for a bit more comfort than top acceleration and cornering stability. Even though the delta of difference between amps was larger on quantity, it very much mirrored the speakers’ offset on personality type. Like the ceramic membranes, the high-speed transistors were quicker, sharper and leaner. Like the silk dome and fused polypropylene cone, the tube amp was mellower, denser, warmer and more saturated. What else is new the experienced tube hounds grumble?
The relative distribution of these attributes. Clearly the Assistent 50 was no legacy-voiced 300B SET of limited bandwidth, with a very euphonic midrange, soft woolly bass and lazy reflexes. Purely on sight, the QQE 03/12 could suggest EL84/6BQ5 kinship. After all, those pentode minis are sized very similarly. Sonically however—and speaking in generalities rather than to unusual exceptions of implementation—they didn’t remind me of any EL84 amp of my acquaintance. Those can get slightly piquant in the presence region. Whilst often very open and feisty but also a bit fiery, I’ve not heard them get as gloriously porcine in the bass as the Audio Valve managed on the big electric bass of Patrick Chartol’s Istanbul album which in our library stands in brilliantly for Mercan Dede. Whilst the Audio Valve had the type saturation one gets from direct-heated power triodes, unlike them it wasn’t allied to bandwidth issues. This was ‘yes’ for tone density and colour temperatures, ‘no’ to sluggishness and darkness. This butler had warmth and fluidity but no darkness.
It also wasn’t an ethereal ultra-airy lit-up performer like a certain 45 SET in my past had been. It was nearly as dense but not as hulking as big 6550 monos had been. Perhaps the closest I’d heard were amps based on the 6V6. The Assistent 50 wasn’t as fast as the transistor monos but had very unexpected kick on the 98dB Zu Druid V. Digging out bass-heavy and percussive fare with plenty of polyrhythmic drums and beat makers came like a hardwired reflex. It’s not what über gemütliche pipe’n’slippers prejudices would anticipate for a valve amp. Where our German did behave unapologetically tube was with its relaxed attitude. The transistors felt more high-strung and tensioned. The QQE bottles were bodacious yet settled and never on edge. They replaced nervy adrenaline with strong colour ‘pop’. This supported great solidity that wasn’t about extreme ambient recovery. Instead, it focused on in-room hereness. Not to the extent of a wall of sound, its portrayal nonetheless veered in that massed direction. Sorting out the precise positions of five vocalists on a Vicente Amigo disc came off rather less specific than the lateral Exicon Mosfets managed. Conversely, these virtual bodies on stage were more flesh’n’blood gutsy than teleported in from a faraway recording venue replete with overtone halos and reflective trails. When time came to commit to the final review speaker, I settled on the Zu Druid V in a deliberate scenario of like meets like. This was a very compelling combo.
Shopped photos tell all? Like the next shot, the Assistent 50 + Druid V combo played it rich, chunky and, in old 35mm terms, fully developed. Rather than lily white, the speaker skins are really a fat bone/ivory hue. In fact, that aspect would stand in nicely for the Assistent’s treble: fully visible but weighty. In this paler rendition—overbleached for emphasis but pointing at the transistor gestalt—the foliage of the indoor trees is far better separated. So are the album covers on the iMac. The seam on the red leather seat and the separate whizzer cones in the widebanders aren’t even addressed by the upper color balance and white value. On raw transparency, we might argue that the second image wins. By the same token, there’s no argument that the upper one is far more dramatic. By contrast, the second’s colors are washed out. The tones inside the carpet’s window reflections have disappeared altogether whereas in the first photo, they remain clearly visible. The point/s should be clear. What the Audio Valve integrated brought to the party was the same aesthetic as the first photograph. Your personal ideal might be somewhere in the middle. In our digs, substituting the Druid with the Accuton-driver Aptica accomplished that. With that ascertained, I was simply on a different kick.
To close out this visual exercise, the deeper black values of the first shot parallel the tubes’ fleshy and extended bass which made for a very anchored ‘foundational’ presentation. This might seem counterintuitive for such petite output glass but was a fact all the same. Readers who maintain a constant sonic tally based on what they already read now easily predict dynamic behaviour. And just so, the Assistent 50 was more focused on the macro end than the quasi subcutaneous little tremours of the micro scale. This smaller microdynamic resolution thus slightly delayed coming on song. To really ‘show up’ meant room not whisper levels. Here the higher S/N ratio of the transistor amps had the advantage. Likewise for superior phase linearity that didn’t contend with coupling capacitors and output transformers. These elements flow into the traditional understanding of resolution. According to the pixel-count definition, the Mosfets had more. If your expectations for the sonic recreation of a recorded event rate believable tonal saturation and image density just as highly, they become other aspects of resolution; equally important elements that also want to be resolved. Now the twin tetrodes had the lead. This juggling act of dissimilar virtues flew much higher than the earlier speaker comparisons. Those were different in the same ways but far less so. Viewed from here, Audio Valve’s use of tubes was far from faint. These tube qualities were potent and unmistakable even if aspects like image density and solidity were shared with our class A Pass Labs XA30.8.
One of the original features of the Audio Valve products is to be found in the utilisation of the valves in such a way that they operate as closely as possible to their ideal reference values each according to its type. One recalls, for instance, the output pentode-triode PCL 805 and most particularly the small beam tetrode with a common cathode QQE 3/12. This valve with a noval (nine pin) base was manufactured formerly by Valvo, Philips and Telefunken etc. (the latter was used in our test amplifier) It has a per plate power dissipation of 7,5 W and may be used with plate voltages ranging from 200 to 300 V. It is ideal in class A and AB amplifiers. This valve, according to Helmut Becker, is ideally adapted to be integrated in a circuit which includes another very innovative concept, an automatically operating grid bias control, refered to as “ABR” and used to great advantage in the integrated amplifier Assistent – 50.
The amplifying circuit uses 12 valves, but the push-pull output stages are coupled to the ABR circuit for each power tube. This exclusive AudioValve feature, allows a comparison of the reference voltage value with that engendered by the quiescent current and which appears at the terminals of a small value resistance in the return cathode circuit. A small operation amplifier monitors, as comparator, the divergence and deliverers the compensation voltage to the grid of the valve. Each valve, young or old, reaching reference values or not is thus compensated in its Grid bias to operate at a value which corresponds to its optimal quiescent currant. A red LED diode, at the foot of each value lights up preventing the use of inadequate or defect valves. For each channel the input stage and driver stage are served by an almost known noval valve, the double triode ECC 82.
The classical chassis has been set into a caisson (a case-like frame). The valves sit in their sockets mounted on a double side printed circuit board. Little columns support the glass cover preventing dangerous hand contact burns or electric shocks could ensue conforming to the CE requirements. The cooling is achieved through the rearsides and topglas. The minimal controls mounted at the front consist of and a volume control the two channels and input selector being coupled in their operation by a remote control. At the back are the cinch input sockets, two pairs of output terminals and a mains switch and connector.
To close out this visual exercise, the deeper black values of the first shot parallel the tubes’ fleshy and extended bass which made for a very anchored ‘foundational’ presentation. This might seem counterintuitive for such petite output glass but was a fact all the same.
Readers who maintain a constant sonic tally based on what they already read now easily predict dynamic behaviour. And just so, the Assistent 50 was more focused on the macro end than the quasi subcutaneous little tremours of the micro scale. This smaller microdynamic resolution thus slightly delayed coming on song. To really ‘show up’ meant room not whisper levels. Here the higher S/N ratio of the transistor amps had the advantage. Likewise for superior phase linearity that didn’t contend with coupling capacitors and output transformers. These elements flow into the traditional understanding of resolution. According to the pixel-count definition, the Mosfets had more. If your expectations for the sonic recreation of a recorded event rate believable tonal saturation and image density just as highly, they become other aspects of resolution; equally important elements that also want to be resolved. Now the twin tetrodes had the lead. This juggling act of dissimilar virtues flew much higher than the earlier speaker comparisons. Those were different in the same ways but far less so. Viewed from here, Audio Valve’s use of tubes was far from faint. These tube qualities were potent and unmistakable even if aspects like image density and solidity were shared with our class A Pass Labs XA30.8.
A decisive circuit advance must be Helmut Becker’s precision bias system. With practically eight power tubes per side, tight matching between them is vital for half-wave equality. This had to be key to the amp’s excellent focus. Images locked tightly without drift, wavering or ballooning. Whilst they weren’t backlit with emphasized venue data where the transistors had the edge, they were just as steady and specific. They simply felt bigger because their colour temperature was punched up. Coupled to Zu’s expressive widebander which excels at the same qualities, this combination really spun the colour wheel. Big dense sound with rich tone, ready dynamics and powerful bass… it’s not what 50 watts from pinky-finger tubes might promise but it’s exactly what these delivered. It made even lean, sharp, pale or nervy recordings agreeable. Add utterly fuss-free operation and 20-year circuit maturity. Despite its slightly loud looks, the Audio Valve Assistent 50 struck me as really an ultra-conservative recommendation like blue-chip stock. That’s short hand for utterly without risk. And a sure thing in hifi is a very fine thing indeed. With this my first-ever Audio Valve assignment, I felt I’d rather made a discovery… 6moons – Srajan Eben
Push-Pull 2 * 50W Sound, Stereo Tube Integrated Amplifier
Pure Class – A operation – high precision full automatic bias adjustment
NOS – SIEMENS germany military high grade power tubes 8 pcs. QQE 03-12
input tubes: 2*12AU7, 2*12AX7
main voltage: 110 V – 240VAC
Frequency: 20Hz-50KHz +/-3 dB
Signal/Noise Ratio: 90dB
ALPS volume control motor pot
Distortion: typical 0,25 %
Input Jack: 5 pairs cinch, switchable
REC – out ( or PRE – OUT )
burn in time: 50-100 hours
Input Consumption: 170W
Size Dimenson:220 mm wide x 360 deeph x 230 mm high
Best of all: Germany’s best address for output transformers – Pikatron – in collaboration with Audio Valve develop the ultimate higend output transformer designed for the Assistent 30 and gives the amp a superior sonic and hightech measurement characteristics.