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This is the 15th in a series of reviews dedicated to the concept of 32Ohm Audio as embodied by the store of that name in downtown Portland/Oregon and described here - Ed.

Reviewer: Srajan Ebaen
Financial Interests: click here
Source: Raysonic Audio CD228 [on loan]
Preamp/Integrated: Burson Audio HA-160 [on loan], KingRex HeadQuarters [on loan], NuForce HDP [on review]
Headphones: Sennheiser HD800 w. ALO Audio wiring, AudioTechnica ATH-W5000, Grado PS-1000, AKG K702 with ALO Audio wiring
Cables: ALO Audio Cryo ICs, Crystal Cable Ultra power cords
Powerline conditioning: Furutech RTP-6
Review Component Direct Price: $750

Jan Meier had something new.
"Interested in my new Concerto? It will probably sell for the same price as the StageDAC you recently tested. But this is a pure headphone amplifier, basically something of a Symphony without the DAC section. The amp uses an active balanced ground to give most the benefits of balanced drive without rewiring headphones; built-in analog crossfeed; and a digitally actuated analog volume control with 63 x 0.7dB steps.

"This volume control is very special. It uses an analog potentiometer and an ADC that measures its position. The DAC then controls six relays to change the amplification factor. You will hear it click when the volume is changed.

"Analog potentiometers always have problems with channel imbalances especially at low settings. This is a disadvantage with headphone amplifiers where the load sensitivities and impedances vary steeply to operate across the entire range of level adjustments with ultra-precision demands.

"With loudspeakers the problem is less urgent because their sensitivities and impedances are not spread that wide. Moreover experience has shown that potentiometers do have a very clear sonic signature.

"Using resistors and relay switches simply results in better sound. And as a final advantage, the signal path can be made much shorter. I've checked some optical encoders and they're quite heavy. Also, with the use of an optical encoder the addition of a CPU is almost mandatory. A simple potentiometer + ADC is much cheaper and does the same job."