So up for review/comparison is a Modded APPJ pa1502a an stock G1217 Project Ember II and a stock Schiit Valhalla 2 My Ember II has a CNC Chassis 1940 Vintage Sylvania 6sn7 JAN CHS VT231 Bottom Getter Flash Clear Top - $455 as tested if bought New Ember II Assembled - $390 6sn7 Adapter - $26 1940 Vintage Sylvania 6sn7 JAN CHS VT231 Bottom Getter Flash Clear Top - $39 [Though it's the longest established and can be gotten second hand for closer to $350 often with upgraded Tubes or you can opt to assemble it your self and save a little there too] My Modded Set has a set of Russian 6n6c Power Tubes with a 1940s Sylvania 12SN7GT Driver - Cost as tested is $394 Appj pa1502a Base Unit - $199 Pair of 6n6c Power Tubes - $20 Pangea AC 14 Power $30 1940 Vintage Sylvania 12sn7GT JAN CHS VT289 Bottom Getter Flash Clear Top - $10 Audio Note Kasai + Auricap XO Re-cap an installation - $125 The Valhalla 2 is 100% Stock! - $350 As some one whose spent a lot of time tube rolling and modding/tinkering I was really curious to see how a stock amp like the Valhalla 2 compared to my rolled in wonders. Overall I felt my Modded APPJ pa1502a was the most resolving, audibly it had the highest degree of fidelity or exactness in reproducing sound when specifically paired with dynamic headphones. The mods we did were; Replaced existing Output Caps with AuriCap XOs & Audio Note Kaisei's Introduced bypass caps into the Circuit Path All in all it's the result of about 7 months of research and I'm very impressed with the results! At the end of it all I feel if your able to DIY your likely going to get the highest degree of fidelity for your system with the least monetary cost. But there's extensive knowledge and experience required as any mistakes invoke additional cost. I also had to do some digging to figure out who to have install the mods, as I'm not cleanest solderer. So again time and money can quickly add up when putting together a custom piece. I suppose I lucked out! But in a sense I feel it's a bit unfair to compare an amp Modded specifically for my exact system, still I wanted to include it to get some perspective on how a more DIY Focused option compares to available retail products. An I'm happy to say there was in fact a retail amp that followed closely behind my own Modded SET! So much so I kinda wish I'd purchased said amp before venturing into my own little experiment. I did my listening with a ZMF Auteur in Cocobolo with their Silver Michanikos cable as well as with my HD 800 using a Audio Envy Tone Kraft Copper. Each of these I felt was a headphone that had a more natural mid range presentation with even bass response, the HD 800 is brighter up top and very technical with strong staging and the Auteur was a bit more intimate with a more correct timbre and more even tonal response. An I personally enjoy each with a drier sounding tube amp, so the three amps featured all share that slightly drier presentation in comparison to something like a Schiit Vali 1 or a Cavili Liquid Glass with a thicker sounding Tube. An again overall I felt my Modded APPJ pa1502a had the most resolve and audible fidelity how ever on high gain an at over 80% rotation I also noticed it was nosier than the other two amps. Thankfully only about 10% of my music requires me to push the amp to this upper limit, and even then I've got around 3-4 dBs of headroom. But I'll go over 4 aspects of sound quality in comparing the remaining two units; Detail Dynamics Staging Tonality/Timbre/Envelope An as you guys know each of these aspects are often linked together, as tonal imbalances can often lead to perceived changes or in-inaccuracies in regard to staging as well as mask over some detail. Overall I felt these aspects of the Valhalla 2's presentation were better than that of the Ember II; Black background With less audible noise, hum or hiss present during silent or quite passages Clear Micro and Macro Dynamics Gradual changes of individual instruments and musicians were easily identified As were more sudden and intense changes to the intensity of the composition as a whole Vivid Presentation of Transients Tauter Bass With a cleaner more balanced envelope - so no emphasis on attack, decay sustain nor release Overall I felt the Ember II presentation was stronger in these aspects; Staging More precise location of movement of sounds within the audible space Resolved more of the "sound of the room" Such as ambient noise like wall reflections, echo's and things like foot steps More Even Tonal presentation Overall neither forward nor withdrawn throughout the frequency response In comparison I felt the Valhalla 2 did the following different from the Ember II Slightly Forward Mid-Range While tonally not as balanced I did feel the Timbre was more natural With a more even presentation of each part of the envelope Slight forwardness helps define space for more intimate headphones but ultimately skews precision in staging for more open or spacious sounding headphones In comparison I felt the Ember II differed from the Valhalla 2 in these aspects; Some What Polarizing Presentation Slight emphasis on attack and decay over sustain and release on in the mid range an upward With contrasting emphasis in the lows In a sense this some what polarizing presentation is more "tonally" correct but... Slight emphasis on Ambient Noise Part of why I feel it's staging is slightly more accurate An finally I felt the Ember II did noticeably worse in these aspects in comparison; Noisier More audible hum and hiss during quite passages Looser low end presentation Some what skewed timbre Again odd presentation creates a nice tonal balance but skews the overall balance in how the envelope is presented which makes the timbre kinda off An lastly I felt the Valhalla 2 had this single fault; Slight Glare or Hardness A rougher top end texture alongside an unpleasant upper mid glare So it was quite fatiguing with really bright or energetic cans like those from Audio Technica or even the Filter-less Campfire Audio Cascade. Otherwise and overall I felt the Valhalla 2 in stock form was the better amplifier for these more grounded and natural sounding dynamic headphones. Plus it's $100 less offers an audible cleaner output and proves it self more resolving. An while it's slight tonal faults I feel can be remedied with some tube swaps I feel your likely better off just saving that money for a better amp in the future. As again I feel upgrading the tubes on the Valhalla 2 to correct it's tone could get costly and ultimately money spent on new tubes could just be money spent towards a better amp. An yes I also felt the Valhalla 2 did give my little Modded Amp a real run for it's money!!! Thankfully, I have purchased an upgrade to my system so my experiment isn't holding me back at this time, though I wonder how much sooner I might have gotten said upgrade if I'd just gotten the Valhalla 2 in the first place... An I again choose to limit this review to just dynamics as I felt the Hybrid Ember II had a clear advantage driving my Hifiman HE 560 and PreFazor LCD 2. An I've found that typically at this price points Hybrid Units seem to do better with harder to drive Planar Magnetics. Though exceptions may exist and I may explore them in the future. Finally though sound quality aside the Ember II biggest strength is it's versatility. As a single tube swap can make small changes to; Audible Noise/Gain Tonal Balance Timbre or presentation of the envelope You can also change how the circuit operates and these changes bring a slight adjustment to; Audible Noise/ Gain Timbre It's also far more powerful then either amp so it's got much more headroom on tap. To this day I still feel the Ember II is an excellent choice for very power hungry Legacy Planars like the two I own, and I feel the circuit mods help to balance out the sound of these as well. Helping each to be a little more natural, while still be exceptionally "fast" sounding overall. In fact many of the weakness of the Ember II with my dynamics are in fact strengths with my planars as they have a some what contrasted presentation over my HD 800. So for those of you that own large collections of headphones that have very differing sound presentations and amping requirements the Ember II will likely remain an excellent choice given how easily you can adjust it's operation to compliment a variety of gear and sound signatures. Other wise for those of you with single headphones such as the; HD 600 AKG K702 HD 800 ZMF Atticus/Eikon/Auteur An are looking for a nice tube amp the Schiit Valhalla 2 get's an immediate unconditional recommendation from me!