Lamp amplification is a fashionable thing, but why is there, semiconductors have occupied our planet completely and irrevocably. They also have their own strengths in the sound paths, and therefore amplifiers exclusively on electrovacuum active elements are found less and less. And they rarely come across in the price category of the order of $ 500. Today we will test one of such radical devices.
Californian Schiit noticeably differs from many developers of sound equipment in the organization of production, sales strategy and, of course, hellish irony and self-irony. Another feature is the lack of design dogmas that many audiophile brands hold tightly to. For example, this is how we have been producing speakers with coaxial emitters (horns, paper diffusers, open cases, etc.) for many years in a row, and we will continue to bend our line, because it is the only right way and, in general, our everything.
Jason Stoddart and Mike Moffat have a much more open and pragmatic approach to business. They made, for example, a delta-sigma DAC Bifrost, but for those who react painfully to a characteristic approximated sound, they released a multi-bit version. Or they invented a hybrid amplifier, and then for rationalists who are not inclined to vacuum heat, they developed a transistor stage, plugged directly into the lamp instead. Well, for radical lamp-lovers looking at such compromises with an ironic grin, the Schiit catalog provides, so to speak, a Valhalla 2 all-vacuum pre-amplifier and “ear” amplifier.
Underworld in heaven
The name, of course, is borrowed from the ancient Scandinavian epic, in which it essentially means paradise. It is another matter that in the representation of the Vikings, the Kingdom of Heaven was so different from Christian concepts that the high priests of northern Europe tried in every possible way to turn Valhalla in the minds of parishioners into a real hell.
Judge for yourself, the warriors who got there after death were doomed to fight again and again cruelly every day, get injured and even die. But towards evening, the dead came to life, the severed limbs grew back into place, and everyone sat down at the table to drink beer and eat fried wild boar. Well, the nights were spent by the cheeky celestials in the arms of beautiful young beauties. In a word, trash, frenzy and no high morality. By the way, for rockers and bluesmen, the situation is quite close and understandable.
At low ohms
Well, in our audiophile reality Valhalla 2 is an all-tube transformerless amplifier. It is interesting primarily because, unlike most of its classmates, it is designed to work with a fairly low-impedance load.
The documentation mentions 50-ohm “ears”, the power at which reaches 180 mW per channel. For comparison, on a 300-ohm load, which is more typical for such circuits, the system outputs 800 mW, and on a 600-ohm load, 450 mW. True, these values are achieved at a high (x7 / 16.9 dB) gain, at which the output impedance is 14 ohms.
For headphones with an impedance of 50 and even 100 ohms, this is a bit too much and may well come back to haunt with a violation of the linearity of the frequency response. Nevertheless, according to the assurances of the developers, the amplifier is able to work effectively even with in-channel “plugs”, as well as low-impedance Grado or AKG. Well, we will definitely check this moment.
Switch on switch off
In addition to the quarter-inch jack on the front panel, the device received an unbalanced adjustable preamplifier output, which means that the Bifrost + Valhalla 2 bundle can act as full-fledged components of an adult setup. And of course work in tandem with active near-field monitors.
In terms of construction and design, Schiit is still true to itself: deliberately rough-cut aluminum does not look flashy, but with dignity, and a solid steel chassis gives the body the necessary rigidity, strength and noise immunity.
The power switches and gain switches are, as always, extremely solid and, as always, are located at the back. If we talk about Valhalla 2, then I, perhaps, join the number of those dissatisfied with this topology. A tube amplifier is not a DAC for you, and it is clearly not the best idea to drive it for days, and even more so for weeks at idle. So you have to constantly stick your palm behind the case and fumble there blindly in search of a small lever. And in order to switch the gain, you will also have to pull your hand over the working lamps, with the risk of breaking the contact or simply getting burned.
With the Bifrost DAC, everything is simpler – with frequent use, you can not turn it off, and on the rear panel, in addition to the line-out tulips, there are only USB and S / PDIF ports (RCA and optics). All three digital ports accept PCM streams up to 24 bit / 192 kHz.
We have already tested an advanced modification of the Bifrost Multibit , but (like all other Schiit DACs) the multibit and delta-sigma versions of the same model are two very different devices in design and sound.
In our case, the circuit is based on the rather popular and respected AK4490 converter manufactured by Asahi Kasei Microdevices. This 32-bit 2-channel DAC is built on the Velvet Sound architecture and is ranked second in the Verita audiophile series. Its distortion level is –112 dB with a dynamic range of 120 dB (in stereo). At the input, the chip supports PCM streams up to 768 kHz inclusive and DSD up to 11.2 MHz (i.e. DSD256). However, the latter value is not relevant for potential owners of Bifrost, since it, like all other Schiit DACs, does not support DSD.
The DAC piping, including the summation and current amplification circuits, are assembled exclusively on discrete elements.
The AK4490 implements five digital filters, differing in slope and phase delays, but it is difficult to say which of them is involved in the work. Running a little ahead, I would venture to suggest that, judging by the sound, this is a Slow Roll-off, which gives a slightly softer sound without ringing on sharp attacks.
An important point: the delta-sigma version of Bifrost can be upgraded to the multi-bit version without any problems. The fact is that their digital-to-analog converter modules are interchangeable and are made on small plug-in cards that can be purchased separately. True, you will additionally need to flash the flash memory on the main board, which is possible only in the service center.
The design of the Valhalla 2 amplifier is not too confused, and the minimum number of elements, as you know, affects the safety of the signal in the most positive way. By the way, in comparison with the model of the first generation, the output impedance is reduced by 2-8 times, the distortion is also eight times lower, and the maximum output current has doubled.
The stereo path is built on two pairs of 6N1P and 6N6P double triodes. The developers hint at White’s cathode follower circuit with a modified output part, but do not share the fine details. Interestingly, the original Soviet 6N6P produced in 1976 was found in the test device, if this is not a remarked remake, of course. The input 6N1P can be replaced with 6DJ8, 6922, ECC88, ECC85 or 6BZ7 without additional adjustment, but the proprietary semiconductor “tubes” LISST, created by Schiit to give solid-state sound to the Lyr 2 and Mjolnir 2 models, cannot be used here.
Unlike the vast majority of Schiit amplifiers, there is no protective relay in this unit. There is simply no need for it, since thanks to the smooth switching on and off of the lamps, as well as the control of the load current, even for 32-ohm headphones, the transient DC voltage surges do not exceed 100 mV. It is interesting, by the way, that after turning off the amplifier (even from the outlet), the power indicator continues to glow for another thirty minutes, at first causing an acute cognitive dissonance in the music lover.
For testing, I used Sennheiser HD 650 300-ohm headphones, ideally matched with the relatively high-impedance output of the second “Valhalla”, as well as 62-ohm AKG K712 Pro, not provocatively low-impedance, but still quite difficult for a pure tube design.
For the purity of the experiment, I drove the Bifrost DAC a little in a transistor path made up of the NuForce Icon DAC preamplifier and Yamaha HS7 active monitors. The sound turned out to be light and elastic, without the detached chill at the top, which sometimes appeared in the multi-bit version, built on the AD5547CRUZ converter from Analog Device. In terms of microdynamics, the delta-sigma version lags slightly behind the multi-bit version, however, it was noted for excellent articulation on complex vocal parts and embossed, but not a bit exaggerated bass.
Made for each other
In a bundle, Bifrost + Valhalla 2 + Sennheiser HD 650 seem to be specially created for each other (in part, of course, this is exactly the case). The sound is friendly, in the sense of comfortable and not rough, but you should not expect deliberate tube warmth from the kit. In terms of dynamics, resolution, and stage construction (evaluated on a Yamaha HS7), the system is by and large hardly inferior to transistor devices of a comparable price category. But of course, there are certain features of the sound.
The scene is precise in terms of positioning the images, but their sizes are sometimes arbitrary, and the acoustic space does not differ in supernatural width. At the same time, the vocals (both female and male) are simply luxurious. The timbres are dense and rich, the dynamics are excellent. HF does not hurt the ear, but with information content, space and reliability they have order. The bass on the Sennheiser HD 650 sounds rich and velvety – that is, effective, but not for the amateur.
When connecting relatively low-impedance AKG K712 Pro at the base gain, the low ones turned out to be much more lean and restrained, however, in general, the energy on the bass, and the dynamics, and in particular the microdynamics throughout the range, were not too impressive. I flip the gain switch up, and … I get a completely different sound. That is, not just the best in some parameters, but simply different. The edges of the range are clearly raised. The basses become more powerful than the example, the highs come to life, so much so that with a high concentration of percussion and / or brass copper, the instruments sometimes even begin to shout at each other. Well, the vocal part in such a cheerful environment logically recedes slightly into the background.
By the way, Sennheiser HD 650 behave at high gain in something similar, but more intelligent, in the sense that winged highs in their performance sound more harmonious and intelligible.
So, let’s summarize.
The Schiit Valhalla 2 amplifier is an interesting tube device with a progressive interpretation of the “tube-like” sound. With decent detail and dynamics, it does not smear, does not melt and practically does not color the sound. It only introduces a slight smoothness and rounds it up a little, emphasizing the richness of timbre, but not at the expense of the spatiality and naturalness of presentation.
Switching the gain should be considered not only as a way of adapting a heavy load for the apparatus, but also as a kind of tone compensator, shifting accents from the middle to the edges of the range. Moreover, in this case, the tonal balance will greatly depend on the impedance and sensitivity of the headphones.
Developers do not recommend using a particularly heavy load like tight planar “ears” with the second “Valhalla”, and as for classical dynamic structures, in my opinion, it really makes sense to use models with impedance above 50 Ohm with an amplifier. However, pre-listening is mandatory, and at both gain levels, as the results can be very different.
If we compare the Bifrost + Valhalla 2 set with the Bifrost Multibit + Lyr 2 tandem, which is one step higher , then the differences will be, first of all, in microdynamics, resolution at high and spatial characteristics of the scene – after all, whatever one may say, but the multibit DAC and the transistor output the cascade, other things being equal, give a more verified and predictable sound. But on the other hand, even leaving a noticeable difference in price outside the brackets, the heroes of today’s test produce a sound with a very interesting combination of accurate calculation and romance, which is at least worth listening to.
Advantages: compatibility with relatively low-impedance headphones, enviable for all-tube amplification, adjustable preamplifier output, DAC supports high-resolution signal input via S / PDIF, the amplifier allows experiments with tubes and is capable of producing a very interesting sound.
Disadvantages: Bifrost DAC discharges the gadgets connected via USB even when it is off, and the amplifier turns off the power indicator only 40 minutes after it is unplugged. The position of the volume control is practically unreadable.