RWAK120
The RWAK120 is a modified version of the Astell & Kern AK120 digital audio player (DAP)
We achieve this by:
Bypassing the 3.3 ohm resistors in the headphone output stage, which results in a < 1-ohm output impedance that can drive IEMs and headphones whose impedance is as low as 8-ohms
Hardwiring the headphone output stage FETs directly to the pins of the headphone output jack to provide the shortest, cleanest signal path. This also bypasses the tiny circuit board traces and the header that connects the main board to the smaller headphone jack board.
The result is a very portable (smaller and lighter than an iPod) DAP that now has a clean, low-impedance headphone output stage. The RWAK120 can drive IEMs with ease, as well as most full-sized headphones to more-than-adequate volume levels. The RWAK120 unravels layers and layers of detail and nuances from your music, and is free of any audible background noise.
RWAK120 Q & A
Q: Do you warranty your modification work?
A: Yes, we warranty the RWAK120 modification for as long as you own it (applies only for the original owner). Note - This excludes any issues unrelated to the modification, such as the battery, LCD, etc., but we still try to offer prompt repair service for such non-warranty items.
Q: Besides what is listed above, does the RWAK120 modification alter features/functionality of the AK120 in any way?
A: No
RWAK120-S
The goal of the RWAK120-S modification is to transform the stock AK120 into the ultimate digital audio player (DAP) used exclusively to send a line level output signal to your portable headphone amplifier.
We achieve this by:
Replacing the two stock Wolfson WM8740 dac chips with the premium WM8741 chips
Configuring the WM8741s to run in “hardware mode” – eliminating the digital volume control processing
Configuring the WM8741s to use their “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 and installing a higher quality 3.5mm (1/8") stereo line-out jack that is hard-wired to the line-out signal.
Installing 1000uF super-low ESR capacitor across the battery rail for increased dynamics and noise filtering
Digital Volume Control and Minimal Phase Digital Filter with the WM8741
The stock AK120 uses two Wolfson WM8740 dacs configured in “software mode.” This means that the AK120 software configures the dac sand 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 signal is still attenuated in the digital domain.
The premium WM8741 is not a drop-in replacement for the WM8740 in the AK120. 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 chips (pulling up certain pins to logic HIGH, and pulling down certain pins to logic LOW) to configure them to run in “hardware mode.” This means they are 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 chip to use their 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 RWAK120-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 install a new, higher quality 3.5mm (1/8") stereo jack in its place.
RWAK120-S Q & A
Q: Can you preserve the headphone output stage with the RWAK120-S mod?
A: Unfortunately, no. Without a custom firmware update that is designed for the WM8741 and allows it to both run in software mode AND use its minimal phase digital filter, this is not possible. We therefore make the best of the situation by dedicating the RWAK120-S modification to those who exclusively use it as a source component to feed an external headphone amplifier (required) with the best possible, true-line out signal.
Q: Since the RWAK120-S uses the WM8741 chips, which supports DSD, can we play native DSD files when Astell & Kern come out with DSD support?
A: Unfortunately, no. The AK120 firmware is designed for the WM8740, and this dac does not have DSD support. So even though the AK120 to allows for DSD playback, it still convert DSD files to PCM. The only way to achieve native DSD support is if custom firmware is written for this unit to utilize this feature of the WM8741 chips that we install.
Q: How much better does the RWAK120-S sound compared to the RWAK120 used as source feeding a portable headphone amplifier?
A: Remarkably better! The main reasons for this are:
The WM8741s are better sounding dacs, especially when using their minimal phase digital filter to eliminate pre-ringing
The digital volume control is completely eliminated – so no attenuation of the digital signal occurs
The output is a true-line out signal taken from the analog output stage that follows the WM8741 chips and is hard-wired to the 1/8” (3.5mm) stereo output jack - so the headphone output stage is completely bypassed as well.
In other words, the RWAK120-S is configured like a dedicated source component such as a high-end external dac unit, where there is no digital volume control or headphone output stage.
Q: Besides requiring a headphone amplifier to drive headphones and removing the digital volume control, does the RWAK120-S modification alter features/functionality of the AK120 in any other way?
A: Due to the higher current draw of the WM8741 dac chips compared to the stock WM8740 chips, the max. play time of the RWAK120-S is expected to be up to 20% shorter.
Q: Does the RWAK120-S modification alter the optical digital output feature?
A: No – the optical digital output is not altered and still works the same.
Q: What headphone amplifier do you recommend with the RWAK120-S?
A: There are many excellent portable headphone amplifiers that should all work very well with the RWAK120-S, assuming they have a line-input and input impedance of 5k ohm or greater. The RWAK120-S, headphone amplifier used, AND headphones used all work together to deliver a particular sound signature. We can only describe the sound signature of the RWAK120-S. From there, you will need to determine the amplifier and headphones that best suite your taste.
Q: What cable is recommended between the RWAK120-S and my headphone amplifier?
A: Assuming your headphone amplifier uses a 1/8” (3.5mm) stereo input jack, there are numerous “mini-to-mini” cables out there to choose from at various price points.
Q: Can I use the RWAK120-S to feed a home audio stereo preamplifier or integrated amplifier?
A: Absolutely – we have tested the RWAK120-S modification to achieve remarkable high-resolution playback performance in home audio systems as well as portable audio systems, so go for it! Note - you’ll probably require a 1/8” stereo mini to RCA cable for this application.
Q: What about using the RWAK120-S in the car?
A: As long as your car has an AUX input jack AND can handle a 2Vrms line-out signal, it should work without any trouble in your automotive stereo.
Q: Do you warranty your modification work?
A: Yes, we warranty both our RWAK120 and RWAK120-S modifications for as long as you own them (applies only for the original owner). Note - This excludes any issues unrelated to the modification, such as the battery, LCD, etc., but we still try to offer prompt repair service for such non-warranty items.
RWAK120-B
The RWAK120-B modification is identical to the RWAK120-S, however we install a 3.5mm TRRS jack (4-pin) where the unused volume control was located, and hard-wire this jack directly to the balanced analog output sections of the WM8741 dac chips. This provides a true balanced output signal to feed the balanced input of external headphone amplifiers that offer this feature (e.g. ALO RX3, RSA SR71B).
The headphone output jack is still converted to a single-ended line out, just like the RWAK120-S modification. So you obtain the modded SE ane BAL outputs with the RWAK120-B modification, making it the most versatile AK120 modification!
RWAK120-S Q & A
See above RWAK120-S Q & A section, and well as below:
Q: What is the pin-out of the 3.5mm TRRS jack?
A: L+ is the TIP, L- is RING 1 (closest to the tip), R+ is RING 2 (closest to the sleeve), and R- is the SLEEVE
Q: Does RWA offer a 3.5mm TRRS to Kobiconn line-out dock, and what is the cost?
A: Yes. We only offer one kind. It is a right angle, 3.5mm male TRRS to male Kobiconn line-out dock. TRRS is gold-plated. The cable is very flexible. Both pugs and the cable are black. We can make it any lenghth you specify up to 10 inches (25mm). The cost is $100 and you must paypal us to purchase with your RWAK120-B player or mofication.
Q: Do any other cable manufacturers offer the same type of cable?
A: We recommend you contact them and ask if they offer or will be offering this cable.