I wonder what is the best - or the most expensive - OTL tube headphone amp currently existing in the market. OTL tube amps tend to be less expensive than their transformer-coupled counterparts because they don't have a output transformer as their name implies. Yet they are usually optimized for high-impedance headphones, especially Sennheiser HD600/650/800.
The best sounding OTL headphone amp I've heard with the HD800 is Allnic HPA5000, hands down.
http://onsongaudio.com/hpa5000/
Allnic amps are not well-known in Head-Fi, but I got to listen to it here in Korea and mother of God... I honestly didn't think I would find an OTL amp that could beat my maxed out ZDSE in its performance to drive the HD800. It was even better than the Bakoon HPA-21 in my opinion, another headphone amp made in Korea which is the best solid-state amp I've heard with the HD800. Unforunately, the HPA5000 is very expensive, priced at around $5K as its name suggests (one could buy a top-of-the-line electrostatic headphone amp or fully balanced amp with that kind of money!). The owner of Allnic claims that the HPA5000 is not only OTL but also OCL (output capacitor-less) in the strictest sense, I have no idea what that means but he says that is why the HPA5000 sounds so good. I only listened to it with the stock tubes but it was nevertheless the best sounding OTL amp, period. The downside of this amp is that it didn't sound that good with low-impedance headphones, including my LCD-3.
The second best OTL headphone amp I've heard was my ZDSE, which I'm sure everyone's familiar with.
I'm not sure about the HPA5000, but is anyone aware of an OTL amp that beats the ZDSE in sonic performance? I know several renowned OTL amps such as Schiit Valhalla, Bottlehead Crack w/ Speedball, Decware CSP2+, RSA Raptor, WBA Virtus-01, EarMax, EternalArts, and so on, but I haven't heard anyone claiming that any of these are superior to the ZDSE (I've heard the other way around). While I found an OTL amp that beats the ZDSE (albeit at more than double price), has anyone else?
Also,
IS THERE SUCH A THING AS A "BALANCED" OTL HEADPHONE AMP? It seems that every tube balanced headphone amp I've seen on the market is transformer-coupled. I am not an engineer, but does the inherent design of an OTL toplogy make it impossible to be built balanced? Why haven't I heard of any balanced OTL amp? Does anyone else know?