I received my Vali/Modi combo right before the holiday and decided to bring it with me while I was visiting family.
Just to preface: I waited to even look at these because,
When I got to my family's house after enjoying a meal with the fiancee's parents my father and his brother were toying around with a home made synth/controller they have been developing for the past two years. I hopped into the fray with the new schiit toys and I explained the marketing/target demographic of the products.
Together we popped open the cases and my father, the EE, took the time to explain to me the design.
His first comment was, "this is some of the best commercial packaging (referring to the boxes, jacks, boards, soldering) I've seen in a product. Great design."
Modi,
Looking at the modi is really just a matter of looking at the part numbers of the ICs on board. We didn't sit down and source each of the parts, but most DACs/usb audio codec controllers of the quality of the modi are between 10-20 USD each in low quantities. They sacrificed no expense with this device, and what they have is at the forefront of digital to analog. The device is split into three sections.
On the back of the board, what is facing down when you open the case, there is the USB audio codec chip, a memory controller, DAC, and basically all of the thinking parts of the board. On the front of their device there are stamped (2) and (3) markers which designate which part of the boards are responsible for analog (2), and digital (3). Nothing really of note on the back of the board. In all it is a significant markup for the buyer if you were to consider the component cost, but the stamped construction of the case adds a rigid and aesthetically pleasing barrier between the superbly designed board and your cats.
Vali,
Taking apart the Vali for me was really fun. I have a background in tinkering with tube guitar amplifiers. With guitar amps the gain characteristics of the tube stages are where you get signature sounds. Without the acoustic coloring of tubes most guitarists sneer and roll their eyes at the sounds of their instrument. This is mostly because there is nothing grand about the raw sound of an electric guitar... well not most of them. The amp plays as much of a roll in the sound of your music as your pickups and ability to play. As interesting as all of that is- headphone amplifiers are a different story.
In theory the recorded music is your source. In this day we have our digital sources which are loss-less. From our source, which is pure, we need to create an acoustic response from the transducer, speaker, driver... whatever you want to call it.
People have a lot of misconceptions about drivers and the devices used to drive them. I don't want to touch on those misconceptions unless they apply to the Vali, so I will save that ranting for another time. For the most part as a lover of hi-fidelity the objective of an amplifier is to take a source and allow for linear volume gain and distortion-free representation of the source. Every interconnect has an effect on the audio in terms of impedance. If the power of the signal over the interconnect is great enough... the less loss of the high end across the cable. So what does all of this mean?
A great sound will come from a great source, low distortion amplification, interconnects, and a transducer of leading quality. Out of all of the components in this chain the areas which should be of the greatest concern for the listener should be the transducer. That is where the most loss can occur. There is no reason amplification or interconnects should impede the source.
The circuit of the Vali takes an RCA L/R line in and preamplifies the signal with subminiature pentode tube amplifiers. The raytheon tubes which are used in this amplifier are relatively inexpensive, but offer superb characteristics at low voltage. A 16V AC transformer comes with the Vali. This power is doubled and the "doubling" method our engineers at Schiit used creates a plate voltage to the preamp tubes of about 46V. If I may reach pretty far in my memory and understanding this could be because of an AC>DC conversion.
At this point in the path of the signal we have gone from source (DAC), to amplifier... the pre-amp stage. The pre on this device is a fixed voltage. They have made a rather ingenious and clean power supply to prevent irregularities in the plate voltages. The pentode tube is rated for iirc 67V to the plate. By operating the plates at this "sweet spot" voltage they are effectively pre-amplifying the line signal across the tubes to a meaty 46V without any gain and therefore a negligible amount of distortion. The low voltage operation also extends the life of the tube. Huzzah! This tube should last for an amazing amount of time
It was explained to me that the way the Vali's preamp is designed is a
class A amplifier which is great because our little tube is handling the entire signal waveform and there is no possibility for crossover distortion which is a distortion that can occur when the waveform crosses the X axis. On that note we move to what I will refer to as the power section of the amplifier.
The power stage in a guitar amp is where the REAL power is made to drive your transducers. In a 100% tube amp the objective is to filter your audio through your tube gain and hear the characteristic tube sound with all of its micro-harmonics and yadda mojo yadda. I get it with guitars, but with headphone amps I feel like Schiit did the right thing in making this a transistor based (solid state) amplification stage. With the solid state components there is more control over the THD across the available level of amplification. I was told the transistors are in a push-pull configuration with a biasing LED (
class A/B) which make up the power to drive das headphones. The two transistors handle half of the total wav-form which is problematic in terms of distortion. This is much more power efficient than a class A solution and it is VERY important we consider that the power supply of the device would have to be much larger and would require more engineering if this was a class-A amplifier. Without being too critical of their decision I would like to point out that this is a class A/B-- there is significant gains in quality over a class B. Schiit has biased the two transistors in push/pull with an LED. This will simulate a class A amplifier's low distortion characteristics up until the amplification is too large for the bias to regulate the push/pull of the transistor amplification. Most industry engineers have designed the A/B amplifier bias to work up until human hearing could not possibly understand the crossover distortion. This is because the volume of the device has become so great we would not be able to comprehend the effect with our hearing. I'm not saying that everyone is this sensitive/lacking sensitivity, but I want to stress that this solution is elegant and I would assume Schiit provided plenty of headroom with their bias for normal listening.
With that I am pretty certain I've explained what I know about the engineering behind this shiny Shiit stack.
As for my feelings on it... well I've listened to one song on this amp. It is a song I am very familiar with and I use it to demo a number of headphones. It is Imogen Heap - Aha! There is a fantastic mix of hi-fi and lo-fi sounds. With a poor setup or transducers the song feels interrupted at points by the mixing of samples. With the Vali and Modi running a pair of HD650s... I have not heard my 650s sound as clear. The low end of these headphones are not normally as defined as I have heard from this amp/dac combo. With that I will say I am going to keep these headphones because of this stack. After hearing them in this light I am more than satisfied with them and they outperform the HD600 for me.
The reason I was only able to listen to one song was that after I listened to Aha! I passed my HD650s over to my father... he promptly listened to the song, talked about how insane people are if they think they can hear 16 bit vs 24 bit audio, took out my mad dogs (which he loves), mumbled something, said something to my mother to have her distract me, and sat down with the stack to listen to the entire Cat Stevens, year of the cat, master recording which was available on Mog. I was finally able to leave my parents house at 11 PM, my father grinning like an idiot, and hopes of grinning similarly this weekend.
If anyone is without an amplifier right now- I would recommend it. The thing draws more power than most solid state amplifiers, but it is a class A(preamp) to A/B(power amp) solution instead of A/B(preamp) to A/B(power amp) which, by definition, is a more pure signal with lower distortion in the amplifier. They picked the right tube device for this project, and I'm satisfied especially after hearing about how clever Schiit was in developing the little devil.