The HPA-15000 is Allnic Audio’s flagship Output Transformer-less (OTL) and Output Capacitor-less (OCL) stereo headphone amplifier. Unlike the HPA-10000 which is designed to perform best with dynamic type headphones, the HPA-15000 is designed for excellent performance with all headphones, including more inefficient ribbon and planar-magnetic types. Like the HPA-10000, the HPA-15000 utilizes a true balanced Positive-Negative cancellation circuit and has pre-out connections, so it can also serve as a superior Allnic line-stage preamp for most amplifiers. However, the HPA-15000 uses a different tube set and has consequential changes to the circuitry. It also offers a Harmonic Balance Mode option for use with ribbon and planar-magnetic headphones that utilizes an analog filter to produce a more natural sound with those types  of headphones, without reducing any of their unique benefits.

In common circuits, output capacitors or output transformers are required to separate the AC music signal from the DC operating potential. If this is not done, the latter will destroy the power amplifier, the loudspeakers, or both. However, these two coupling devices also introduce their own influences on the transmission of the musical signal, adding their own character (coloration), increasing distortion, and consuming small signals, all as predicted by physical efficiency theory. In addition, they also limit signal dynamics. For these reasons, the elimination of output transformers and capacitors has been considered the best solution for the design of the most accurate amplifiers. Removal of these two coupling devices from the signal path achieves the best results possible:

• No coloration of the musical signal
• Extremely detailed expression, natural harmonics and subtle musical decay
• The lowest possible distortion
• The widest musical dynamics and frequency range
 
In the HPA-15000 OTL/OCL, there is no coupling device between the amplifying tubes and the headphones (or power amplifier when used as a line-stage preamp); that is, the final gain/output tubes are directly connected to the headphone outputs. Thus, the benefits listed above are fully present in the Allnic HPA-15000 OTL/OCL.
 
Like my favorite linestage preamplifier, the Direct-Heated Triode L-8000, the HPA-15,000 OTL/OCL "Signature" reveals previously unappreciated detail in the recording.  If something appears unusual only in certain recordings, the amplifier is articulating these 'newly discovered' details inherent to the recording.
 
The HPA-15000 may be ordered with, at no additional cost, one of the balanced headphone connections a RAAL Direct Drive output dedicated to RAAL ribbon headphones. With this option installed, RAAL headphones can be connected directly to the HPA-15000 without use of the RAAL Direct Drive dongle.
 
The option requires installation of a 0.2 ohm transformer for that output only, so the RAAL output will not be OTL/OCL. However, this output transformer is the best Allnic makes, a silver wire wound, permalloy core transformer like the incredible, silver Step Up Transformers on Allnic’s famous, top-of-the line phono preamplifiers – one of the very best transformers available in the industry and capable of allowing your RAAL headphones to perform at their spectacular best.
 
Please request RAAL Direct Drive when ordering.