Here is my personal experience with a twice(2x) used AmpsandSound pre-production (pre ZMF) model Pendant headphone/pre-amp unit. The original user was also the builder, Justin Weber (of Amps&sound fame), as verified via e-mail directly and by the second owner who purchased the amplifier direct from mr. Weber.
Short story: This is an extremely respectable and powerful tube headphone amplifier and in my set-up also a very solid performing pre-amplifier.
TL:DR; The unit uses 1x EZ81/6CA4, 2x EL84/6B05, and 1x 12AX7/12AT7/12AU7 tubes. All of the tube styles are still available in same or equivalents across the internet from a variety of sellers and can be had for what are currently considered reasonable prices in the tube world today.
https://www.zmfheadphones.com/pendant
My first surprise was that this amplifier drives BOTH Planar magnetic and dynamic or moving coil driver type headphones well. For whatever reason I was not sold on the hype until I actually plugged in some planars and experienced the SQ for myself.
My second very pleasant surprise was that this amp pushed Hifiman He6se headphones respectably well, good enough to enjoy. That was impressive considering how many “powerful” amplifiers I tried that failed/did soso at this task.
Most of the high end tube amps I have personally experienced top off in MSRP at $8K, my experience is limited so I will be brief and cautious in what I say.
Source was Qobuz stream-> via Innuos Zenith MK3 server-> Exogal Comet+ DAC -> Pendant. I tried the unit on every HP I own just to get a feel for things.
My longest and favorite session was about 3hrs continuous with Senn HD6XX from Massdrop. My least favorite listening session was barely 15 mins long with Phillips SHP9500s. (see my profile for HP list)
Music used was a few blues tracks, some EDM, classic rock, movie soundtracks and a few female vocal tracks just to keep me interested and familiar with the song quality.
This particular amplifier is a real pleasure to listen to, I will assume that the current versions of the ZMF Pendant are very similar. The music sounds very lively and musical, at no point did the amplifier limit the individual headphones, it really maximized what level every single unit was able to perform to. I say this because the sound is very clean, and there is enough power to allow what you plug in to play at it’s full potential. I am sure there are exceptions but I sampled a moderately popular cross section of headphones minus TOTL units in excess of a $2k price point and beyond. (see my profile for list)
In direct comparison just to make sure I was actually hearing something “better” I plugged in a Monoprice Cavelli designed $125 Liquid Spark SS into the same exact signal chain. I am willing to unequivocally state that I preferred the sound of the Pendant on almost each and every headphone over the Monoprice Liquid Spark. There is a difference in clarity, soundstage, depth, air, and in general just a much more musical and lively presentation in almost each and every headphone. You have to listen for it and A/B a few times with the same song over but it is absolutely a much nicer overall presentation to my ears with the Ampsandsound unit.
Short and to the point, If I HAD to choose 1 single amplifier to keep out of my small collection, this unit would make the cut due to its versatility. It performed well with a wide variety of Headphones and as a pre-amplifier with my other amps and speakers. The tube compliment is currently available for a fairly reasonable price, and it’s a sensible combo of tubes whose purpose individually makes sense to me and i find it fairly straightforward to roll.
The BAD: My unit is sensitive to RF interference. I need to keep both my cell phones on the opposite side of my desk 4ft+ away to keep RF noises out of my ears. I can tell when I am about to get a text, call, email etc. a second or 2 before my phone rings.
Other than that I have NOTHING (EDIT: see posts below reference volume and power output) at all negative to say about this amp. For about $2k it’s worth every penny and will certainly outperform, at least in my eyes, anything at the $100 +/- mark… 
I say this tongue in cheek, everyone talks about how much “better” everything gets the more $$$ you throw at it, sure it does, “better” is relative, 25%, 10%, 5% better? I don’t know, I’m older and not particularly picky, I just happen to like nice things, this amp is certainly capable and performs at its price point in my opinion.
