Audio Video News

Charlie Hansen, founder and chief engineer/product designer of Ayre Acoustics, and John Hamm, CEO of Pono, provided the following technical information about the PonoPlayer’s design. They originally prepared this content as project updates for Pono’s Kickstarter supporters, and they’ve revised it here for S&V.

Our singular aim during the development of the PonoPlayer was to build a device with one purpose: the playback of music at the highest possible level of performance. This design called for a small, handheld, battery-powered device capable of storing high-resolution digital files and converting them to analog music that can be played back through high-quality headphones or a high-fidelity sound system. This product wouldn’t function as a phone, Wi-Fi router, Bluetooth transceiver, portable gaming platform, or GPS widget. Any additional features at this point would only detract from the resolution of music in its fullest dimension.

Ayre Acoustics designed the circuitry in the PonoPlayer that follows the main processor, basically the audio signal path through the digital-to-analog converter (DAC) and the output amplification stages for the headphone and line outputs. For the DAC, they chose the recently released version of ESS’s top-of-the-line ES9018. It’s a high-resolution, two-channel, 32-bit device that comes in a very small package (5 mm square) and is extremely customizable, able to tackle the rigors of sensitive, low-level signal-path design.

The filter generally favored by Ayre to prepare the signal before it hits the DAC is what’s called a minimum-phase digital filter (to eliminate pre-ringing) with a slow rolloff, which further minimizes overall ringing. This is critical—ringing can be thought of as an oscillation in the digital signal, and it can cause all sorts of errors if misconstrued as part of the actual signal and converted to analog to be heaped in with the music. For the PonoPlayer’s DAC, Hansen went a step further and used a “moving average filter” for both the double and quad sampling rates because it has no pre-ringing, no post-ringing, no overshoot, and no undershoot. These could create inaccuracies in the actual rendering of the analog signal from the digital input and sacrifice fidelity. Put another way, every step has been taken to eliminate traditional digital artifacts.

The DAC chip’s output comes in the form of current, so Ayre designed a proprietary, fully discrete, fully balanced, zero-feedback current-to-voltage stage. This then goes to a fully discrete, zero-feedback buffer stage to drive both the headphone output and the line-stage output. The output impedance is roughly 5 ohms, allowing the PonoPlayer to drive any headphone on the market with minimal frequency response errors. This approach minimizes interactions between the headphone amplifier and the headphone while maintaining good battery life and avoiding any sonic problems that might be created by the use of negative feedback.