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Most the headphone models Blaž named actually were rather low-impedance design which rendered my primary assumption incorrect. It seemed that it was more about a combination of impedance, sensitivity and frequency response than about just impedance itself. The Perfidus allows you to build a reasonably priced system with very satisfying performance. Each of the headphones mentioned do very well. You might also think about a slightly warm source. The description on the maker's website reads bright and quick. I can only concur. This gentleman knows his stuff. He created a nice looking well-built headphone amplifier that should deliver a lot of enjoyment to its owners.
Test methodology. The review was an A/B comparison with both A and B known. Music samples were two minutes long but whole albums were auditioned too. Reference comparators were my Leben CS-300XS and the headphone output of an Arcam FMJ A19 amplifier. Apart from my reference Ancient Audio CD player I also used an Arcam rDAC with Bakoon BPS-02 battery supply and a Restek Epos CD player.
The design of the Perfidus exhibits two weaknesses: the power cord and feet. I couldn't do anything about the former but did what I could about the latter. I placed the amp on Acoustic Revive RIQ-5010 quartz discs with fo.Q G-53FS damping spacers in-between, then placed the lot on the Acoustic Revive TB-38 platform. I decided to place two more quartz discs on top to make me feel better especially since I had a chance to hear the influence of Acoustic Revive accessories during our Warsaw 2012 show when Ken Ishiguro personally set up two systems with active Dynaudio Xeo speakers and Octave electronics. Since then I'm no longer a mere believer but active follower.
Headphone amplifiers are specific kinds of integrated amps especially when reasonable priced. The smallest among them are tiny to remain portable and battery-powered. The bigger ones usually look similar to this one. The Perfidus is a solid-state amp with class A output stage. The elongated casing with narrow front sports a volume knob, headphone socket and a small red LED as dot over the model name's 'i'. The on/off switch is on the back next to the captive power cable. Judging by its looks I'd have preferred replacing the latter with a higher-quality cord. There is also an analogue input on solid RCA sockets. The acrylic front panel with writing on the inner surface is very attractive. The chosen font adds a modern professional touch. The company logo appears twice, once around the headphone socket, then again on the top panel. The logo is a circle with... yes, two little horns. Devilish.
The circuitry sits inside a rigid aluminium clamshell extrusion which bolts together the top and bottom halves, leaving one only to slide in the PCB and add front and back panels - a simple but effective solution seen also on rather costlier gear. The footers hide the vertical bolts. The single board occupies the entire inside but divides into two parts. The power supply with small toroid and four Rubycon smoothing caps occupies the back shielded behind an aluminium divider with voltage regulators bolted to it.
The input signal arrives on long shielded hookup wiring to the front of the board where it lands adjacent to the Alp pot in large Wima caps. The TL072 chip is a DV servo which Blaž Erzetič says compensates for the class A bias increase after thermal stabilization. The first gain stage begins with a Burr Brown OPA627 input chip soldered to a tiny board whose pins plug into the mother board. The next stage is a unity-gain class A push-pull current buffer with BD139+BD140 ST Microelectronics bipolar transistors. All voltage gain thus is exclusive to the first stage. The output transistors mount on either cheek which in this area sports an extra aluminium plate for increased heat dissipation. All passive parts like precision resistors and polypropylene caps seem to be of high quality. There are also Elna electrolytics. The 6.3mm headphone socket isn't gold-plated.
The casing itself is of high quality. From my perspective two elements are problematic – the captive power cords and the long hookup leads passing right by the power transformer.
Specifications according to the manufacturer:
Headphone impedance: 8-600 Ω
Frequency response: 4Hz - 40kHz -1 dB
Power consumption: 15W
Dimensions (W x H x D): 110mm x 64mm x 280mm
Weight: 1.325kg
Sonic character: bright and quick
