RWAK100-S (Astell & Kern AK100 modified by Red Wine Audio)
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Product information
RWAK100-S
The goal of the RWAK100-S modification is to transform the stock AK100 into the finest sounding digital audio player (DAP) used exclusively to send a line level output signal to your portable headphone amplifier.
We achieve this by:
- Replacing the stock Wolfson WM8740 dac chip with the premium WM8741
- Configuring the WM8741 to run in “hardware mode” – eliminating the digital volume control processing
- Configuring the WM8741 to use its “minimal phase digital filter” option
- Hardwiring the stereo line-out signal to the 3.5mm (1/8”) stereo output jack (formerly the headphone output jack), hence completely bypassing the headphone output stage
- Removing the unused digital volume control wheel
Digital Volume Control and Minimal Phase Digital Filter with the WM8741
The stock AK100 uses a Wolfson WM8740 dac configured in “software mode.” This means that the AK100 software configures the dac and allows for a digital volume control of the unit. We discovered that even with the volume set to MAX (setting 75), the output voltage of the WM8740’s output signal is still attenuated in the digital domain.
The premium WM8741 is not a drop-in replacement for the WM8740 in the AK100. This is because the software control of the WM8740 does not control the WM8741 in the same way. We therefore have to hardwire the WM8741 (pulling up certain pins to logic HIGH, and pulling down certain pins to logic LOW) to configure it to run in “hardware mode.” This means it is NOT controlled by software. The digital volume control is eliminated and does not alter the digital bit stream entering the dac, and we manually configure the WM8741 to use its optional minimal phase digital filter. The result is a more natural, organic sound that is lively, finely-nuanced, open and transparent, and extended – what you should expect from a true reference quality source component!
More impressive than its superior technical specifications (e.g. 8db greater SNR and Dynamic Range) compared to the WM8740, the WM8741 can be configured to use a “minimal phase digital filter” for the data prior to d/a conversion. Unlike most d/a converter chips that use a standard linear phase digital filter, the WM8741’s selectable minimal phase digital filter has no “pre-ringing” of its impulse response. Pre-ringing is an unnatural side effect of using a linear phase digital filter. Real instruments do not ring before they are excited – a guitar doesn’t produce sound before a string is plucked, a piano doesn’t not produce a sound before a key is pressed, and the impulse response of a minimal phase filter does not have prea-ringing and therefore produces a more natural sound.
Line out
The RWAK100-S modification also hardwires the analog line-output stage following the WM8741 directly to the headphone output jack. Therefore, the headphone output stage is completely bypassed and the headphone output jack is converted to a true, 2Vrms line-output.
Hardware volume control removal
Since the digital volume control functionality is completely disabled, we also remove the volume wheel that exits from the left side of the AK100, and we plug the hole so the RWAK100-S is slimmer by 5 mm – and simply looks cleaner.