Schiit Mjolnir 3 Impressions

That's a bummer @ohshitgorillas. With another such report on HF, might be that Schiit caught a bad batch of toggles. Hopefully they get yours sorted asap.

 

I had a similar issue with my gain switch. I sent the amp back in and they re-soldered something to fix it. It took a while, but I got the amp back as good as new. I thought about keeping the amp in low gain to avoid the problem, but in the end, it bugged me enough to send it in. I had quite a few backup amps to tide me over, so that helped.

 

Anyone spend any time with the MJ3 and Susvara and/or Abyss 1266?

 

When I had the loaner. MJ3 drove Susvara very vary well; enough so that I ordered one.

 

Probably good to mention @wbass - I don't listen super loud, and some recordings we're at `3 O-Clock. The weight, speed, fullness, macro and micro were all there (SE and PP), but you might run out of volume if you listen loud.

 

Got a pretty ratty HD 800 balanced XLR cable today ordered used off head-fi -- it's fraying but still works, I suppose.

Anyway the upshot is that I can (I think) hear what others are talking about. Usually I can tell when I first try out a new change in the gear how it lets you "see" a little further into the music, and going balanced on this amp does that. I hear a bit more of the background information in the distance without high gain or even needing to turn up the volume as high, which is pleasing and adds to the realism that I found so nice about this amp.

It only re-enforces an impression I have been getting that the MJ3 is the first amp that makes me reach for the 800s sooner than either of the 6XX series headphones. Which is a strange world indeed.

 

To be lazy, I found Susvara way better than Caldera on MJ3 with A2. Way better. It may have just been my DAC though, but Susvara is absolutely driven - PP though was better to me and I wouldn't use SE with it

 

Well I spent a lot of time writing a manuscript about the Mjolner 3 and then it turned out that it was defective. so I don't know how much of what I heard and wrote was due to the defection and how much carries true. I think that most of my review holds true to a functioning Mjolner 3 based on my impressions of the Jottenheim 2, which I had similar problems with. But I'm not sure the synergy is totally accurate.

Nevvetheless, I'm posting it because I spent a long time on it.





TLDR:

GOOD
Unexpectedly wonderful solid state amp (with the right headphone synergy) that sounds more like a tube amp than many newer tube amps like the Aficionado, Studio B and newer DNA amps while simultaneously having the strengths of SS eg great driver grip, slam, speed, transient attack and no tube rolling or tube expense or tube nervosa. It has a surprisingly delicate, nimble and resolving sound like a tube amp with the same wetness and liquidity to notes while having incredible slam and dynamics and it is not flat like many SS amps, it has great depth.

BAD
However, there are some quirks, weaknesses and annoyances with the sound.
It has a high noise floor so iems are a no go, but it’s quiet enough for even the LCD-X so it’s not a worry or any full size headphones.
It has an overly dynamic sound with too much dynamic contrast, with dynamic swings that are exaggerated which causes fatigue and a feeling of being "battered" by the music, but a lot of people will like this sound.
It also has a slight veil over the entire spectrum that masks subtle details and nuance.
Bass is a bit emphasized so it may not synergize with bass heavy headphones, but the bass quality is excellent.
Synergy with Audeze’s is horrible, look anywhere else for an Audeze amp.
Synergy with the HE6SE is great, but the Mjolner 3 creates an upper midrange emphasis that creates glare on piano. Ruins a great sounding match. I don’t know about other Hifimans as I haven’t heard that Arya, HE1k or Susvara, nor do I own them. But I wonder if the HE1k might sound really good with the Mjolner 3.
The HD650 sounds very mediocre with the amp as well, rendering a real lack of clarity and resolution.


GEAR USED

Tidal/Qobuz -> UPNP -> Pi2AES with 5V mod and Sigma11 LPS -> AES -> Yggdrasil A2/OG -> Mjolner 3 via balanced inputs.

I used all rhythmdevils audio modded headphones and breifly a borrowed HD6XX to help give relevance to this review. My stock Audeze’s and Hifimans are in storage upstairs and I’m not able to get them out just for this review, I’m sorry I know that would be more helpful.

List of headphones used:

• RD-S12 (custom modded S12 ortho iem)
• RD-HE6se (custom modded HE6SseV1)
• RD-X (custom modded LCD-X)
• RD-5 (custom modded LCD-5)
• HD6XX (briefly, I borrowed it last minute and I only had a single ended stock cable, which doesn’t give the Mjolner 3 everything it’s capable of, esp with the HD6XX which would probably benefit from being balanced most out of all of these headphones)

How I used the amp:

I used no feedback and pure class A. I honestly couldn’t tell much difference with push pull even with power hungry headphones, but I just seemed to like class A mode better and didn't do enough investigating to explain why because I don’t care enough. I was never in the mood to sit there flipping the switch back and forth and scrutinizing.

Before you squack about an ortho iem being a bad test for this amp or any desktop amp, it is actually a great test. I find my RD-S12 to sound like a full size TOTL ortho but with smaller soundstage but equal sense of space. But. more importantly, IME they are very revealing of an amp’s tonality and technical abilities and don’t need a lot of power so synergy isn’t usually an issue the way an 650 can sound bad out of a great amp just because of the way the amp is designed rather than how the amp sounds, or the HD800 which needs specific things out of amps that don’t translate to other headphones. My RD-S12 doesn’t have these requirements or synergy issues with a few exceptions - it didnt sound good at all with the Cavalli Liquid Crimson but this is the only time I’ve run into a synergy issue. So you can ignore my review if you like, but I really trust my RD-S12 as a test headphone for amps. And i also used my RD-HE6SE and RD-5 and the HD6XX which is a very different headphone and load, etc. I think ultimately you will find that my conclusions about the sound of the amp are accurate for my preferences at least.

Introduction:
This review feels pretty unorganized to me, but I guess that’s just where my mind is at the moment. Sorry for not being able to put this review together better. I did spend quite a bit of energy trying to.

I really like the Mjolner 3 and I came into it thinking I would be underwhelmed or actively dislike it due to what close friends who’s taste I always agree with told me about it, with specific ideas of what i would dislike. I also have never liked a high end Schiit amp. But as has often happened to me in audio, my expectations were different from my experience.

This is the first Schiit amp i have ever liked except for the Magni 3+ (for it’s good tone despite being SS though lacking technicalities) and the Magni Piety (for the same reasons). I have not heard the Ragnarok.

Mjolner 3 vs the new DROP TA-84 amp with my RD-S12

The new Drop TA-84 OTL el84 amp has wonderful synergy with my RD-S12 and it does some things better than the Mjolner 3. But the TA-84 using NOS tubes, in comparison to the Mjolner 3 with my RD-S12 is more open sounding, more transparent sounding due to not having this extra dynamic contrast. But it has less satisfying tonal density, wetness and less sweet timbre. And is of course, less dynaimc. But over long listening, I prefer the TA-84 with my RD-S12. I haven’t even plugged the HE6 into the TA-84 though because of my experience with the prototype distorting with orthos. These days, sometimes I just don’t test things that feel like a waste of time and energy and I’m more interested in what I think than being super comprehensive for the sake of a review.

Mjolner 3 vs Stratus with my RD-S12

Over long listening sessions both have things that bother me. The Stratus’s tone is too dry even with a huge attempt to add wetness and liquidity via certain tubes, but the Mjolner 3 has too much dynamic contrast or too bombastic dynamic swings. So i don’t know which I prefer, i don’t think either one is ideal. But for short listening sessions before fatigue from the pummel affect, I find myself preferring the Mjolner 3. It has more of everything good, while adding some solid state technical chops. The Stratus is also good, but it’s still a bit dry even with the wettest 2a3 tubes on the market. And this is WITH a slight hiss on the Mjolner 3 ruining any kind of black background which the Stratus has.

Mjonlner 3 vs Stratus V3 with RD-HE6se

Both my RD-S12 and my RD-HE6se sound better with the Mjolner 3 in many ways and my RD-S12 has a hiss like a tape hiss sound because the noise floor on the Mjolner 3 is too high for them which ruins any kind of black background that gives the Stratus the advantage. With my RD-S12 the 2 amps are closer, but with my RD-HE6se it is no contest, the Mjolner 3 is wetter, with more tonal density but never too much, it has more space between notes, better separation, more depth, sweeter treble that has better tone, more realism throughout the spectrum and is significantly more resolving. And at the same time, the Mjolner 3 has those qualities of solid state amps that tube amps aren’t as good at like speed, sharper transients, bass impact, and driver grip. The Mjolner 3 REALLY grips the drivers of both of these headphones.

Mjolner 3 with my RD-HE6se

For the most part (see below for the weaknesses of the amp) my RD-HE6se sounded the best I have ever heard it including speaker amps out of the Mjolner 3.

HOWEVER, and this was a deal breaker for the Mjolner 3 and my RD-HE6SE, it gave my RD-HE6SE hot upper mids. i couldn’t find the hot spot with my test tracks in any hot electric guitar tracks, but very well recorded piano on multiple different albums and recordings had a glare to it that was very uncomfortable and which isn’t coming from the headphones and was not there with the Stratus or any other amp I have tested the headphone on. I don’t know why this match has this glare, it’s not there with my RD-S12. It’s a mystery, but maybe the Mjolner 3 doesn’t have enough power for the HE6? Given that it is not there with the Status I don’t think this is the reason and i don’t know. I tried all the modes and gain and nothing changed it at all.

I found no significant difference with the HE6 with push pull vs class A, or low or high gain. They both had the same basic strengths and weaknesses. But I think if I investigated further i would say I prefer the amp in low gain in pure class A mode. That was my gut reaction, which is usually right.

The Mjolner 3 really excels at bass reproduction, it’s very well separated from the rest of the spectrum, has wonderful control and grip and drive. It’s very satisfying until it becomes a bit too much… see below

Mjolner 3 with Audezes

With my RD-X

The amp does better with the RD-X than the RD-HE6se. My RD-X sounds more resolving and open with the Stratus, while having more weight and punchier dynamics with the Mjolner 3. You can hear the Mjolner 3 sounding more liquid and wetter with more tonal density, but here it’s more a matter of taste which you’re going to prefer -aside form the better resolution and air and spaciousness of the Stratus - I’m taking tone only. But the Mjolner 3 seems to pair pretty well. Mind you, this is my RD-X which does not have the scoop in the upper mids that stock Audeze’s have (the larger driver Audeze’s pre MM/LCD-5) and sounds lighter, more neutral and less weighty and dense and warm. So i think my RD-X is likely a better pairing with the Mjolner 3 than a stock large driver Audeze would, might just be too much warmth and density and thickness and get murky. I don’t have a stock Audeze I’m able to get just to test here, sorry.

With my RD-5

The same pattern follows here, however the denser, bassier, punchier Mjolner does good things or the RD-5 tonally. But the Stratus still wins with so much more resolution and air and space. The Mjolner 3 sounds dull in comparison.

Audeze’s with Mjolner 3 vs LauX

The Laux walks all over the Mjolner 3 in every way, air, spaciousness, detail, tone. The Mjolner comes off as dull and muddy in comparison and makes the LauX sound like it is just singing. The Mjolner 3 seems to mute transients, which are much faster and sharper (but not sharp in general) on the LAuX. Vocals are much more natural and clear on the LauX, the upper frequencies are much more fleshed out and have much more air and sound more delicate. The Mjolner 3 has more bass but no appreciable increase in quality of bass.

The Drop TA-84 otl el84 amp described below with my RD-S12 distorts audibly with the LCD-5 (probably because it's OTL). I don’t hear any distortion with the RD-X though and I prefer this amp with the RD-X over the Mjolner 3. which is really surprising. It’s got better tone, more air, a bigger sense of soundstage, it sounds lighter on it’s feet and moves the drivers faster. The LauX is much better than the TA-84 though.

Stratus vs Laux with Audeze’s (briefly because someone will ask).

I don’t think I have the right tubes in my Stratus for Audeze’s i think they would do better with a more linear 2a3 tube so i don’t think this is fair, but with the Full Music 2a3/Q tubes, the LauX is again the clear winner. This shouldn’t be the case though based on my previous impressions and many other impressions so you should just ignore this. I’ve heard my friend Josh’s Stratus and it sounds fantastic with Audeze’s with the Linlai Global Elites/Cossor’s and easily beats the LauX. I just know someone will ask so Im including this paragraph. TLDR: the Stratus is better with Audeze’s than the LauX, you just need more linear tubes, not necessarily expensive tubes, just not tubes that are intentionally wet and liquid, which is what works better for my RD-S12 and the Stratus. i can’t listen to full size headphones for more than a few minutes due to a chronic illness which has worsned in the last year (my head overheats and I get sick) so I haven’t been listening to my Stratus or Stellaris with Audeze’s at all, or tube-tuning it for them.

I don’t think the Mjolner 3 is the best pairing for my rhythmdevils audio Audeze’s or very very likely stock Audeze’s. And I don’t think it’s just a sound signature mismatch, because of what i hear from my RD-S12 and RD-HE6se which I would guess would sound good with Audeze’s, I think it is something about the amp’s topology and design that doesn’t do well with Audeze drivers. I am guessing the Piety would likely be a better match for Audeze’s but I don’t have one hooked up right now to test that. The Mjolner 3 does not have these characteristics with the HE6se or RD-S12, so I would recommend Audeze fans to steer clear. Even my RD-5 and especially the LCD-5 which I feel could use more heft and more weight to the sound, still sound better out of the LauX even though the Mjolner 3 has this denser, weightier tone which you would think would be a good thing. But it doesn’t translate.

This is a surprise to me based on how the Mjolner sounds with my RD-S12 and HE6se, I would expect to hear that same resolution, and kind of magical liquid leading edges to notes while still being impactful, and i would have expected it to move the drivers faster because it has that grunt to it, but the LauX shines over the Mjolner 3 in ever way with Audeze’s. Honestly, the Mjolner 3 is just boring with Audeze’s. Buy an LauX even at the highest retail price instead, or get the Drop TA-84 (described below) if you have an LauX, or I’m guessing even a Piety would do Audezes more justice. Or possibly the Pietus Maximus but I have not heard one.

Mjolner 3 with the HD6XX (single ended )

I find the HD6XX to sound very muffled and garbled, like the sound waves are getting all mixed together before they get to my ears, though I don’t hear any time domain or resonance issues. Or there is cardboard over the drivers. So I’m no authority on the best amps for them. However, I can tell better/worse even with headphones I don’t like especially when they aren’t committing sins of commission but rather sins of omission so I’m looking for them to just sound their best with these amps, rather than the amps hide peaks or funky FR or boost the bass or tame the treble, etc.

With the HD6XX: Stratus > Drop TA-84 >> Mjolner 3

Of the 3 amps listed above, the Mjolner 3 was by far the worst in terms of clarity, definition, texture and resolution. The TA-84 sounds much more clear and resolving (with NOS tubes) and the Stratus takes this up a noticeable notch. But the TA-84 is honestly closer to the Stratus than the Mjolner 3. The Mjolner 3 is the most dynamic of the 3, following it’s pattern of strong dynamic swings, but it doesn’t matter to me given how much more clear the other amps are. the HD6XX’s muddy qualities are the worst with the Mjolner 3. The veil" in the Mjolner 3 that I describe later seems to be stronger than with any other headphone.

I don’t know how to go into more detail because I don’t like the headphones on any of these amps. I’m sure people will blame not being balanced for this outcome, but I’m doubtful. Still, it’s a possibility the Mjolner 3 would sound better with the balanced outputs and a balanced cable with the HD6XX.

WEAKNESSES OF THE MJOLNER 3

with my RD-S12 and HE6se and not Audeze’s because I don’t think its really beneficial to evaluate an amp with headphones it doesn’t synergize well with.

The thing I don’t like about it is this overly dynamic sound, like it has too much dynamic contrast. This affect is WAY worse on the Jottenhiem 2, which I couldn’t stand because of this, it was like being pummeled through the ears with music. The Mjonlner 3 has much less of this, but it’s still there and still fatiguing for me. Dynamic swings in all music are exaggerated so that notes hit too hard when they should not. At the same time, I would say the Mjolner 3 has a lot of finnese, so it does this in a pretty elegant way. The amp is very refined IMO. But i still feel like i’m being pummeled especially after listening for some time.

There is also something about the sound of the Mjolner 3 that is as if there’s a veneer covering up something not so great, like the amp actually isn’t able to create the sound it is creating with the parts used, so it employs a filter to cover up the actual sound of the amp and give it it’s final character. Another way of describing it is that it is as if the sound is being created by a filter like one of those "low bitrate MP3 enhancer" affects on stereos from the 2000’s. (Or at least I had a stereo with one of these buttons). It’s hard for me to describe beyond that, but I imagine it is being tuned to have this very dynamic sound and one of the parts used gives it this, and I’m hearing it on top of all the other components. Something like that. I am curious if a cap or small part swap would make it a much better amp for me. The Jottenhiem 2 for reference is much worse in this way for me, the "sound enhancer/veneer" affect is much worse and I can’t tolerate it.

The Mjolner 3 is a bit bass emphasized, and that should be taken into consideration for synergy and preferences. For example, I don’t know if the Atrium and the Mjolner 3 would be a good match, but I’ve never heard the Atrium. I’ve just read about it’s well known bass reproduction. This is just a random example and guess. However, this slight emphasis works really well because of the quality of the bass. It is super well controlled and has tons of texture, is never loose, and really grips the drivers. So for many people I think this will be a good thing due to hearing this great bass response more prominently and thus these good qualities in the bass response being easier to hear.

One more subtle Weakness

I also often felt like there was a sort of fog over the entire spectrum, or some kind of misty substance . It’s hard to describe this one, but I just often had the feeling that there was something between me and the amp, which went away switching to other amps. And both of the other amps i directly compared it to have Cinamag 600 transformers in the signal, but the. Mjolner 3 did not, so it had a more pure connection to the Yggdrasil. Continuing, it was like a slight cloudy or gray cast on top of the sound of the amp. This is not to say that the amp sounds cloudy or gray or murky or anything like that, it really is like a layer on top of everything else. And it is very subtle. Think a beautiful landscape that has some very light mist hovering over it obscuring the land underneath.

As stated above, the Mjolner 3 does not work well with Audeze’s which is a weakness as on paper and based on how it sounds with other headphones you would think it would, at least with the LCD-5 which is too thin and on paper seems like a wonderful pairing.

Recommendations

• From memory, if you like the Jottenheim 2 and want an upgrade in all departments plus a more tube like presentation, you should jump at the Mjolner 3. The Jottenheim 2 is more warm than liquid/wet like the Mjolner 3 so you need to want that tube wetness/liquidity/slight bloom to make the jump.

• I personally could not own this as my only amp, due to the fatiguing pummeling overly dynamic contrast. But if you like this sound, which I think a lot of people will, and you want a solid state amp that sounds like a tube amp, the Mjolner 3 is a great choice.

• If you want an extra secondary/ third/fourth/whatever amp to use sometimes for fun, this could be a great choice especially since you don’t need to buy tubes for it or worry about that.

• If you are new to headphones, I think this would be a great choice because I think most newcomers would like its dynamic contrast and everything else about the sound as well. It reminds me of students first learning to print black and white in a darkroom. It is very common for new students to pump the contrast to get a very dramatic effect that they are very happy with. But in time with more experience you learn to appreciate more subtleties in images and you want more tones, more detail in shadows and highlights, you want an image that you can explore for a long time and which gives you more to think about and work through than simple, stark, black and white shapes. Similarly, I think newcomers to headphones or audio will like this high dynamic contrast because it catches your attention fast and holds it and I don’t think this crowd would find it fatiguing especially coming from something like Beats or other popular headphones. NOTE: I am not saying that if you like the Mjolner 3 you are a noob. So don’t freak out on me please.

Final Words of so much Wisdom

Technically speaking with preferences put aside, the Mjolner 3 is really a TOTL amp IMO. It’s resolution, sense of space, imaging, image placement, depth, soundstage, sense of realism are all TOTL level and you’d have a hard time finding better in ANY amp. I love the treble presentation of the Mjolner 3, it is very sweet yet maintains near perfect timbre for cymbals etc. Maybe just adding a bit of sweetness from what you’d consider accurate but in a very pleasing way. The bass reproduction is also one of the best out there of any amp I think, unless you find it fatiguing. It is a bit bass emphasized but the bass has such good control I don’t mind it until hour 2 or so. The Mjolner 3 also has a few potential drawbacks that you an read about above in the "weaknesses" section.

I am starting to get the feeling that my preferences align more with Mike Mofatt than Jason at Schiit (no offense Jason, everyone likes something different, your amps sell very well, are very popular and I have tons of respect for you) because I love my Yggdrasil and can’t find a DAC I prefer but don’t really like Schiit amps. i have not heard the Ragnarok.

 

Great in depth write up!! I hope eventually you get a chance to listen to a MJ3 that is working 100%. I only tried the old Sony EX1000 and 7hZ Timeless, and both didn't exhibit any noise on low gain, non push pull, no feedback.

@purr1n other than the borked XLR output, what exactly was amiss with the loaner unit?

 

My MJ3 (the first batch) also has low level background hum with sensitive low resistance headphones (Grado, Sony R10, both single ended). It is unnoticeable with HD650. I am unsure whether this is normal or not. Overall, this is not something that bothers me enough to contact Schiit to inquire about.

 

Interesting. I assumed it was normal because on the Schiit website for the Mjolner 3 they say it’s not quiet enough for iems.

 

I'd be very surprised if Jason didn't design the analog output for all Yggdrasil's; which should IMO have a non-trivial impact on tonality, macro / micro, etc.

 

Yeah that thought has occurred to me, but I just have yet to hear a Schist amp I like except for the Magni 3+ but it really lacks technical chops, I just think it has good tone for SS. And I really like the Gungnir A1 and Yggdrasil A2. Better than any other DAC on the market I've heard.

 

Interesting, I have no hum whatsoever with my Grado RS2x. Chain Pi2AES —>Yggdrasil GS —first run MJ3 XLR. All of the above is plugged into Belkin power conditioners. The Yggdrasil into the smaller PF30 and the MJ3 into the bigger PF60

 

I agree with numerous points @rhythmdevils made above. However I do not find the MJ3 overly dynamic or too high contrast analogous to soap opera effect on video monitors when engaged. Then again, I am using Holo Spring 2/3 DACs with HD800-JAR and the system synergy works well for me.

Noise Discussion

During warmup (30 to 60 minutes) occasionally there are barely audible static sounds similar to those heard on my tube amps during warmup, also occasionally. Could be L ch, R ch, both ch or not at all. Lately it has been not at all.

A few select measurements
All measurements made as follows:
Amp adjusted for 0 dB gain
Balanced Input
Single Ended Output (TRS)
Load 32R
Hi Gain mode
Feedback Off

Residual noise is higher in Push-Pull mode than Single Ended.

Push-Pull Mode

IEMs listeners might pick up on the -77 dBu 120 Hz hum in Push-Pull mode in quiet listening environments.

Single Ended Mode

Not likely to hear less than -90 dBu 60 Hz hum in SE mode.

Distortion suite at 1 KHz 0 dBu

Push-Pull Mode


Single Ended Mode

Definitely Class A operation descending 2nd and 3rd harmoncs. Higher harmonics are clearly much lower. Excellent!

For my money (and it is My Money) this is an extraordinary SS amp that behaves substantially similar to the best DHT SET and Pentode strapped for Triode opereration SET amps. This amp has been in high use in my listening lab since its arrival.

 

What about low gain mode?

 

Two things to be noted.
1. Residual noise is dominated by AC mains noise which is primarily 60 Hz for SE mode and 120 Hz for PP mode.
2. Low gain mode attenuates only. It is not possible to reach A = 0 dB.

All measurements made as follows:
Amp adjusted for 0 dB gain in Hi gain mode or minimum attenuation in Low gain mode
Balanced Input
Single Ended Output (TRS)
Load 32R
Gain mode as noted
Feedback Off

Depending on other settings in Low gain mode maximum output for 0dBu input was between -1 and -2.5 dBu as will be seen in the following measurements.

Push-Pull Hi gain


Push-Pull Low gain


SE mode Hi gain


SE mode Low gain


Animation comparing Push-Pull Hi to Low gain


Animation comparing SE mode Hi to Low gain


60 Hz AC mains hum is reduced in Low gain for either Push-Pull or SE mode.
As residual noise is dominated by AC mains noise, Low gain correspondingly reduces residual noise.

 

I wanted to put the above figures in perspective.

The S12's sensitivity is 122dB per 2.83 Volt, according to my ears (volume matching pink noise against speakers at 80dB, then measuring the resulting voltage).
2.83Vrms is 11.25dBU, so we're still talking about 111dB at 0dBU. so 34dB of 120Hz hum. Which should be some 15dB above threshold.
I wonder if the noise itself (without hum) is audible. Schiit specifies around -97dBU, which might be audible.

Note that the S12 IEM has a roughly 10dB lower voltage sensitivity than the UERM and many other IEMs. It is quite inefficient.

 

@Serious you need to remember the ISO Contours of Equal Loudness for the Human Auditory System (HAS) in predicting audibility for the AC mains noise for a given transducer.



Listening to sounds at 34 dB SPL would be approximated by the 30 phon line shown below:

At 120 Hz the HAS needs approximately 54 dB SPL for to achieve same loudness as 30 dB SPL at 1 KHz. So the 120 Hz AC mains hum will be perceived by the HAS as 24 dB lower than the IEM sensitivity or approximately 10 dB SPL in your example. This is why I stated the 120 Hz hum might be audible, but it would require a really quiet ambient environment.