Schiit Midgard

Schiit Audio Midgard Review

In Norse mythology Midgard is the name for Earth (the realm of the mortals) so in this review let’s see if Schiit Audio new Midgard headphone amp and preamp is earthly treasure for us mortals that can play heavenly audio.

Note: I would like to thank Schiit Audio for providing the Midgard for the purposes of this review.

The Midgard’s shares the same gorgeous design language with the majority of Schiit products. But lurking underneath the midgard relatively straightforward exterior is a possible ground breaking technology. While obviously there are lots of secrets about the ‘Halo Topology’ the tantilising snipbits of information we know about this technology it is normally used with speakers to help reducing distortion and stabilize the frequency response in some specific cases. But the big question is does this technology work with headphones.

So to really understand the Midgard, I decided to do a deep dive on some of the research behind ‘mixed-mode feedback’ technology and then speculate as to how it might work with headphones when implemented with the ‘halo topology’.

But even without the ‘halo topology’ the Midgard represents an amazing headphone amp and preamp especially at it’s price point of $219.

Therefore, I have broken the review into 3 sections:

1. Review of Midgard build, features and sound quality
2. A technical deep dive on Mixed Mode Feedback, the technology behind ‘Halo Topology’
3. Use insights from this research to define and then execute a set of measurements of the Midgard.

So lets start with the more normal review:

Design and Functionality

The Midgard exudes the characteristic Schiit Audio build quality. Its all-metal chassis, adorned with a stamped and painted logo, speaks to its durability and aesthetic appeal. The front panel, hosting a couple of toggle switches and a volume Pot, a 6.3mm Single Ended headphone connection and what looks at first view like a 4-Pin balanced output but in reality this connection is designed to take advantage of the ‘Halo topology’ lots of details about this later in this review.

The back panel is beautifully simple to set up, being a pre-amp we get 2 inputs (RCA and Balaned ) and 2 outputs (RCA and Balanced), in my subjective testing I mainly used a SMSL SU-1 DAC feed by a Wiim Pro Streamer) connected to the RCA input but initially I did try all the connection for the purposes of testing the Midgard using a Topping D10 to feed its balanced inputs. When measuring I have a laptop running REW connected to the RCA inputs.

So obviously depending on the RCA/Balanced toggle on the front you switch the inputs.

I also feed the outputs to a Fosi Audio ZA3 separately testing the balanced and RCA outputs with that Amplifier as it supports both inputs.

Internally, the Midgard uses a fully discrete circuit topology, which means that all of the signal processing is done using individual transistors. This approach is often considered to be more transparent and less prone to coloration than integrated circuits, though obviously some people like discrete op-amps and the sound colorization to taste they can apply.

Sound quality

I will cut to the chase - the Schiit Midgard is a powerful extremely clean and neutral sounding headphone amplifiers. It does an excellent job of bring out the best in the source input whether you use RCA or Balanced Inputs and providing that in crystal clear clarify with great ease to bring out the best in your headphone.

So the key things are that there is no bass or treble roll off or channel mismatches this is the cleanest and best measuring headphone Amplifier that Schiit Audio have produced.

As for power there is ample power for even the most demanding headphones

Power Ratins (Max)

• 16 ohms: 5.5W RMS per channel
• 32 ohms: 4.8W RMS per channel
• 50 ohms: 3.2W RMS per channel
• 300 ohms: 750mW RMS per channel
• 600 ohms: 375mW RMS per channel

On ASR when tested the Midgard actually had higher output of 822mw into 300 Ohms:

The High Gain toggle on the front of the midgard adds 14db. Both the single ended and 4-pin outputs at the same volume (making sighted A/B testing much easier) but obviously the 4-pin may optimise the distortion directly on headphone using the mixed-mode feedback.

Subjective listening

Subjectively over the past few weeks I have been swapping between both interfaces and numerous times I have went “eureka” I can hear the difference ‘Halo’ makes only to switch back over to the single ended interface and listen again and think “maybe / maybe not” as it sounds very similar. So while I was convinced numerous times the power of ‘sighted bias’ is incredible strong so I will say I preferred using XLR interface but I am not 100% convinced if I was to do a full blind test that I could tell the difference, though as you will read later in the review this might be because of the selection of headphones I have in my collection.

I was initially using the midgard with my planars (mainly Hifiman Edition XS and HE400-se) but also the new FiiO FT5 but as you will see in the research section I did add some AKG dynamic driver headphones, even a balanced ‘modded’ version of the AKG K702 and I also listened with some IEM’s (Truthear Zero and KiwiEars Orchestra lite) in all cases the Midgard sound completely transparent bringing out the best in these headphones and IEM’s.

Here are some brief subjective opinions:

Bass

The Midgard’s bass response is detailed and precise with no roll off in the sub-bass regions, the midgards pushes even my most depending planar’s sound fantastic even when I pushed the bass using EQ to really test that the midgard was driving the bass response appropriately.

Midrange

The amplifier shines in the midrange, rendering vocals and instruments with exceptional clarity and dynamics. The natural timbre and resolution of this range are particularly noteworthy, offering an engaging and realistic listening experience. The lack of colorisation really helps the midrange with the midgard.

Treble

In the treble region, the Midgard demonstrates a fine balance of detail and smoothness. Metallic sounds are rendered with an authentic crash and reverberation, showcasing the amp’s ability to reproduce high frequencies without artificial brightness.

Soundstage

The soundstage presented by the Midgard is impressively holographic, with excellent channel matching the midgard provided well-defined depth and layering. Its ability to precisely position sound sources within this space contributes to an immersive auditory experience.

What is the ‘Halo Topopoly’ - Some research

Halo Topology is an unique mixed-mode feedback technology specifically applied to headphones, I believe Schiit are the first company to use this in a headphone amplifier and to introduce this technology at this price point rather than in some $800 headphone amp shows Schiit commitment to getting exciting new technology into as many customers as possible.

Executive Summary:

From reading about this technology, I believe this technology has tremendous potential to provide lower distortion in specific headphones. Specifically low impedance headphones with large swings in impedance, specifically this is because when used to optimise the response of speakers (as you will see below) it in relation to allowing an amplifier to respond appropriately when a specific speaker has large variations in impedance.

`So first lets delve into Mixed Mode Feedback:

Mixed mode feedback in speaker amplifiers

Mixed mode feedback in the context of speaker distortion refers to a technique used in audio engineering and speaker design to manage and reduce distortion. To understand this concept, it’s important to first grasp the basics of speaker distortion and feedback mechanisms.

Speaker Distortion

Types of Distortion:

• Thermal Distortion: Caused by changes in the speaker’s temperature, affecting its performance.
• Mechanical Distortion: Due to physical limitations or mechanical failures in the speaker components.
• Inter-modulation Distortion: Occurs when multiple frequencies interact, producing sum and difference frequencies not present in the original signal.
• Doppler Distortion: Results from the movement of the speaker cone, affecting the frequency and phase of the output.

Causes of Distortion:

• Exceeding the linear operating range of the speaker.
• Imperfections in speaker design or manufacturing.
• Inadequate power handling or poor thermal management.

Feedback Mechanisms

Voltage Feedback In a traditional VF amplifier, the feedback loop measures the output voltage and compares it to the input voltage. The amplifier then adjusts its gain to minimize the difference between these two voltages. This approach is known for its stability and ability to handle high input impedance’s.

Current Feedback CF amplifiers, on the other hand, measure the current flowing through the output stage and compare it to the input current. The amplifier then adjusts its gain to minimize the difference between these two currents. This approach is known for its high power output and efficiency, making it suitable for driving demanding headphones.

Mixed-Mode Feedback MMF amplifiers combine elements of both VF and CF to achieve a balance of performance characteristics. The feedback loop typically incorporates a combination of voltage and current sensors, allowing the amplifier to optimize both gain and power delivery. This approach can potentially improve the amplifier’s ability to control driver resonance and reduce distortion.

In summary, mixed mode feedback in speaker systems is an advanced technique for managing distortion. It requires a delicate balance and deep technical knowledge in audio engineering to be effectively implemented. The goal is to enhance the speaker’s performance by minimizing distortion without compromising on sound quality or introducing new problems.

Post-Filter Feedback in Speaker Amplifiers

I thought I would put small section here about PFFB as that is a hot topic with Class-D amplifiers and allowing Speaker Amplifiers managing impedance variations in speakers. Specifically it is a Voltage Feedback mechanism which when implemented will reduce distortion and avoid variations in frequency response.

For example the otherwise excellent Fosi Audio V3 does not support PFFB feedback so when paired a speaker with large variations in impedance it causes the V3 to sound either bright or dull as far as the treble when paired with different speakers:

While a similar TPA3255 based Amplifier (3e Audio TPA3255) that does implement PFFB both reduces distortion and is not dependent on the speaker impedance:

And comparing the distortion the V3 does well (note the comparison is the 48 Volt):

While the 3e Audio does much better:

This is what interested me the most when I heard about the Midgard and to do this innovation in a $219 Amplifier (instead of a $800) is pretty special.

That said most headphones do not have massive swings in Impedance the way some speakers do as we shall see later in the measurement section.

Mixed mode feedback with Headphones

In headphones, mixed mode feedback plays a slightly different role compared to loudspeakers, primarily due to the differences in design, application, and user experience. However, the fundamental principles remain similar: it’s about managing distortion and improving audio quality. And specifically this affects headphones which are more like traditional speakers (hence why its more relevant for dynamic headphones than planar or electrostatic). Let’s delve into how mixed mode feedback applies to headphones:

Distortion in Headphones

• Inter-modulation and Harmonic Distortion: More critical in headphones because they can significantly affect the perceived audio quality in the intimate listening environment that headphones provide.

Factors Affecting Distortion in Headphones:

• Driver quality and design.
• Enclosure design (closed-back, open-back, in-ear, etc.).
• Power handling and impedance characteristics.

Mixed Mode Feedback in Headphones

Implementation Challenges:

• The close proximity to the ear means that any distortion or artifacts introduced by feedback mechanisms are more easily perceived.
• The small size and delicate nature of headphone drivers require a very careful application of feedback techniques.

Benefits:

• When implemented correctly, mixed mode feedback can help in fine-tuning the headphone response, reducing certain types of distortion, and improving overall sound quality. This is the key benefit of Halo Topology
• Can be particularly beneficial in high-end headphones where fidelity and accuracy are paramount.

Research Conclusion

As you can see from the benefits above mixed mode feedback is around lowering the distortion of traditional speakers, and with Halo Topology it is now uniquely applied to headphones, this technology should provide the same benefit to similar architected headphones, i.e. when applied to dynamic driver headphones as some unique headphone drivers have that same variable impedance as some speakers.

Therefore, I will use a word that is seldom used in an online review the word ‘Assurance’, the assurance that if you have or possible in the future will purchase a headphone that might benefit from lower distortion then with the midgard (and only the midgard) you have that added assurance.

But the purpose of this deep dive was to understand what I should specifically try and measure with the halo topology and it became obvious as I research this that I need to look at difference in distortion with specific headphones by measuring the headphone response (not the amplifier output).

Some Measurements

Measurement process

Given the objective is to now measure a delta in distortion between the single ended and the ‘Halo’ 4-pin interfaces from the headphone itself I used my Minidsp Ears, obviously this is a much simpler measurement tool than BK-5128 or a Gras Coupler, but given I was looking for a statistical difference I decided a methodological and repeatable process could be used with the Minidsp.

I decided that I would follow this process:

1. Use Left Ear in all measurements
2. Only measure when the headphone was properly positioned with reasonable good seal (throwing away any outlying measurements that looked like in-accurate placement of the headphone)
3. Once properly position - measure the distortion 3 times using REW
4. Swap from SE to the 4-pin and repeat from 2. above
5. Repeat this process 10 times (5 times per SE and 5 per 4-pin)

The average of the 3 seated measurements is taken at each frequency during the sweep and then the 5 SE and 5 4-pin measurements, this was to avoid as much as possible differences due to the headphone moving around while the cable was swapped.

One problem. I had was the selection of headphones was to identify a suitable set of headphones to measure. From the research above (and from reading online forums) I would ideally measure a headphone with large swings in impedance but also support a balanced cable. Even though the Midgard is not a balanced headphone Amplifier, for the Halo Topology to work the extra wire in a 4-wire balanced cable is used by the mixed-mode feedback to adjust the output, so a headphone (or IEM) that supports balanced connections is required.

Also, Dynamic Driver headphones and not Planars are the ideal headphone to measure a differance, as Planar have a very even impedance so not ideal for this test but after looking at my small collection of headphones, the only ideally suited headphone in my collection was an old AKG K702 ( being a dynamic driver) which was modified a few years ago to supported balanced cables, but in the interests of this experience I also decided to measure against one planar (the Hifiman HD200-SE and one IEM the FX-15 as I had both balanced and SE cables for that IEM ).

But even the K702 only has a minor variation in impedance:

For example, diyaudioheaven measured the frequency response differences (i.e. tonal differences) when this headphone was presented with different impedance amplifiers

Again this upper treble region has slight variations depending on the impedance.

Note: One headphone that might have the right criteria is the Sennheiser HD650:

Amir from ASR, during his review on ASR actually subjectively mentioned that he thought they sounded better on the 4-pin than the SE which would make sense based on the research above.

So with this process in place I believe the laborious task of capturing: 3 (measurements per sitting) x 5 (sittings per interface ) * 2 (interfaces) * 3 ( headphones / IEMs) so a total of 90 measurements of the distortion difference. So lets see the results:

1. Headphone 1 - the Hifiman HE200-SE

• Distortion Via Halo:
• Distortion via SE:

So no significant difference was measured but a few times there was less distortion via the ‘Halo Topology’ though this wasn’t consistent could have been a measurement anomaly.

2. IEM - FX-15:

• Distortion Via Halo:
• Distortion via SE:

So no significant difference was measured.

3. Headphone 2 AKG K702:

• Distortion Via Halo:
• Distortion via SE:

So no significant difference was measured.

Note: I have a few links here, here and here for raw measurements used above.

Measurement summary

Sadly I could not proof the technology with my limited measurements and
my limited set of headphones.

While these measurements did not show any significant differences between the Single End and the 4-Pin ‘Halo’ interface the process of researching and then measuring the Midgard with my headphones gave me a both a sense for what Schiit Audio have implemented with the Midgard and the audio ‘problem’ that they were trying to solve.

This has given me an even more impressive feeling about the Midgard and I now believe the Midgard is the perfect headphone amplifier for someone who is growing their collection.

What could be better

There are a few things I think Schiit could improve on:

1. Include both a ‘Halo’ 4-PIN and a Balanced output as well as the Single Ended interface
2. Switch off the RCA / Balanced output on the back when a headphone is connected

Rating

I gave this a 5-star rating as it’s rare to get a premium audiophile product that has outstanding measurements and unique technology at this reasonable price.

Summary

The Schiit Audio Midgard stands as a testament to engineering ingenuity and affordability. This $219 headphone amplifier and pre-amp, proudly American-made, encapsulates a blend of robust metal construction, discrete circuitry, with the standout feature the intriguing addition of ‘halo topology’.

While I could not measure a notable difference, from the research I made I believe that the ‘halo topology’ adds a level of assurance to your listening pleasure, that is unique within headphone amplifiers. This alone should be a reason to purchase the midgard but even without the ‘halo topology’ the Midgard is a top product which measures exceptionally well and most importantly make your headphone sound like they belong in the realms of the gods.