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JVC K2 D/A Converter Episode 5

The initial decision to modify the JVC RX-8030 was driven entirely by its remarkable musicality—its natural tone is an absolute rarity among home theater surround receivers. After stripping away every unrelated circuit board inside the chassis, all that remained was the front panel control layout, the motherboard processor, the dedicated D/A converter section on the DSP board, and an upgraded 24.576 MHz crystal oscillator. My habit is to audition the sound after every single hardware change; by this stage, the 8030 had already undergone a massive sonic transformation.

 

Originally, my sole objective was to leverage the 8030’s internal JVC K2 processing to evaluate the true potential of XRCDs. However, after spinning several discs, the results fell short of my expectations. The bottleneck, I believe, lies in the modern mastering quality of the XRCD releases themselves. Because most XRCDs were produced in the late 1990s, their source tapes had already undergone heavy digital remastering. Compared to the pure, unadulterated CD releases of the 1980s, the listening experience was significantly compromised.

 

Most 1980s CDs were transferred directly from original analog master tapes—straightforward, honest, and entirely free of artificial processing. Some even carry noticeable tape hiss. But so what? Vinyl playback inherently carries surface noise, and in the digital realm, hearing that original tape hiss can actually be a sign of a healthy, untouched transfer. From the 1990s onward, the proliferation of digital editing allowed record companies to heavily process digital masters with dynamic compression, peak limiting, and digital noise reduction. We were bombarded with "20th Anniversary Editions," "30th Anniversary Special Editions," and "Super 40th Anniversary Deluxe Versions" personally supervised by band members. Realizing the limitation was in the software, I ultimately abandoned the idea of using the K2 processor for XRCD optimization.

 

Deciphering the K2 Architecture

 

The most frustrating aspect of modifying JVC’s proprietary K2 converter is the complete lack of public technical documentation. JVC has never released comprehensive datasheets for the JCV8009 K2 processor or the MN35505 DAC; at most, one can only track down their basic pinout configurations. JVC marketing describes the K2 processor as an algorithm that reconstructs lost high-frequency harmonics and low-level ambient details from the data stream. The matching MN35505 is a 192 kHz/24-bit delta-sigma DAC implementing what they call PEM-DD (Pulse Edge Modulation Discrete/Digital) architecture.

 

Meanwhile, the front panel features a "CC (Compression Compensation) Converter" button, which appears to upsample the incoming signal to to 88.2kHz using 176.4kHz (44.1kHz x 4) sampling frequency. JVC claims this algorithm works wonders for restoring lossy compressed media like MP3s, early streaming, and Bluetooth. Perhaps to me on my dedicated CD playback, however, it offers absolutely no benefits. Engaging it immediately collapses the soundstage, narrowing the stereo image and flattening depth. While it does boost high frequencies, the effect is harsh, digitized, and highly aggressive—resembling a cheap EQ curve. Worst of all, it causes a corresponding loss in low-frequency weight. This button is best left permanently disengaged.

 

An Unexpected Discovery

 

Yet, by a stroke of serendipity, utilizing the 8030’s internal K2 processor for standard Red Book CD playback yielded an unexpected and pleasant surprise. Up to this point in the project, hardware changes were minimal: I had only isolated the stereo DAC section by removing unnecessary circuitry and introducing a dedicated external clock circuit. The improvements at this stage were purely a function of upgraded power delivery and reduced cross-talk/interference from the deleted boards.

 

What I experienced was a gradual but distinct improvement in channel separation, extended frequency responses, and a tonal elegance that reached a remarkably high tier. In certain respects, the tone of the modified 8030 was actually more detailed, more analog, and more non-fatiguing than my long-time reference UltraAnalog D20400A DAC. While a significant performance gap still separates the current 8030 build from the legendary D20400A, its standout tonal signature has prompted me to revisit many CDs I previously dismissed as sonically inferior. Ironically, during this evaluation period, I found myself listening to quite a bit of "elevator music."

 

Make no mistake, the only albums pictured here with subpar sound quality are Out of Africa and Somewhere in Time. The later Dances with Wolves recording is actually quite exceptional.

Similarly, these two Morricone soundtracks—Once Upon a Time in the West and Once Upon a Time in America—are notoriously difficult to play back ideally. Getting digital copies to closely rival original vinyl (LP) pressings remains an uphill battle.

These few titles are definitive "elevator music," though the top disc—a full silver-ring West German pressing of Paul Mauriat—actually boasts impressive sound staging and fidelity.

 

Next Phase: Power Supplies and Op-Amp Upgrades

 

Encouraged by these unexpected results, I decided to push the hardware modifications further. In the latest phase, I implemented four independent power supply units (PSUs) into the 8030 chassis:

• A dedicated +5V rail for the digital circuitry.
• A symmetric +/-12V rail for the analog stages.
• An isolated +12V rail exclusively for the crystal oscillator clock circuit.

Simultaneously, I addressed the analog output stage. I replaced the two remaining factory HA17558 dual op-amps (IC525/524) in the I/V (Current-to-Voltage) conversion circuit with four high-performance OPA134 single op-amps. To achieve this, I fabricated a stacked adapter assembly: a SOP-8 to DIP-8 adapter board coupled to a dual DIP-8 to twin single DIP-8 socket arrangement.

 

Admittedly, this mechanical layout carries structural risks; the top-heavy, elevated design places considerable mechanical stress on the delicate SOP-8 surface-mount solder joints on the factory board. I plan to redesign this entire I/V section down the road. Part of the long-term plan involves building a dedicated dual-mono PSU for this analog stage using four independent +/-15V rails (the current +/-12V setup is merely temporary, which also explains the strategic shift to single op-amps).

 

The JVC RX-8030 chassis following the integration of the four independent linear PSUs.

The custom dual SOP-8 to single DIP-8 adapter socket assembly.

 

With the new power architecture and silicon in place, the components will require at least a week to ten days of continuous burn-in—potentially longer—for the dielectric materials and junctions to settle into their optimal state.

 

To be continued in the next episode.

 

Paul K (05/26)