In the late 1990s, a quiet revolution was taking place in the world of high-end digital audio. The compact disc (CD) had firmly established its dominance, but audio purists remained divided. Digital-to-analog converters (DACs) were transitioning from the complex, expensive multibit “ladder” architecture to the cheaper, highly efficient Delta-Sigma design. Right at this technological crossroads, Burr-Brown released the PCM1704. It was the last true 24-bit sign-magnitude R-2R DAC chip ever manufactured. Decades later, the PCM1704 is not just a piece of vintage silicon; it is a legend revered by audiophiles for its unparalleled “analog realism.”
At HeadphonePalace, we have listened to countless source devices, but the unique sonic character of vintage multibit chips remains a gold standard for organic sound reproduction.
The Dawn of Digital Audio and the R-2R Peak
To understand the legend of the PCM1704, we have to look back at the roots of digital conversion. Early CD players used multibit DACs because they were the most straightforward way to convert binary code into sound. An R-2R DAC works by routing electrical current through a ladder network of resistors. The values of these resistors alternate between a base value (R) and double that value (2R). Each bit of the digital signal controls a switch that connects its corresponding resistor to a reference voltage or to ground.
The result is a direct, hardware-based reconstruction of the analog wave. There is no complex mathematical interpolation, no noise shaping, and no reliance on high-frequency switching to “guess” the waveform. However, as CD players became cheaper, manufacturers looked for ways to cut costs. The R-2R design required incredibly precise resistors; even a deviation of 0.001% would cause audible distortion. Laser-trimming resistors on a silicon chip at the factory was slow and expensive. This led to the rise of Delta-Sigma modulation, which could achieve high measurements using cheap, single-bit converters and aggressive digital filtering.
Why Burr-Brown’s PCM1704 Stands Alone
Released in 1998, the Burr-Brown PCM1704 was the absolute pinnacle of multibit engineering. It was a sign-magnitude converter, meaning it split the positive and negative parts of the audio signal into two separate R-2R resistor ladders. This solved the zero-crossing distortion problem that plagued early R-2R chips like the Philips TDA1541. In traditional R-2R ladders, the transition at the zero point required all switches to flip simultaneously, creating a microscopic digital glitch. By using two separate ladders, the PCM1704 achieved perfect linearity even at the quietest levels.
For a deeper dive into how different DAC designs affect your listening setup, explore our detailed audio equipment comparisons.
R-2R Ladder vs. Delta-Sigma: A Tale of Two Concepts
The philosophical difference between R-2R and Delta-Sigma is profound. Delta-Sigma DACs represent audio using a high-speed, low-resolution bitstream (often just 1-bit or 5-bits) running at megahertz speeds. The massive amount of high-frequency noise generated by this process is shifted out of the audible range using noise shaping, and then smoothed out with a low-pass filter. While this looks perfect on static sine-wave tests, critics argue that the temporal “smearing” caused by these heavy digital filters degrades the life and timing of complex music.
In contrast, the PCM1704 accepts up to 24-bit PCM data directly and outputs the corresponding voltage step immediately. It doesn’t rely on mathematical feedback loops or noise shaping. This raw, direct conversion is what audiophiles describe as having an organic, physical, and textured sound. It reproduces the acoustic space of a recording with a realism that modern delta-sigma chips struggle to emulate.
Visualizing the Linearity Difference
The chart below illustrates how the R-2R ladder design maintains perfect linearity at ultra-low signal levels compared to standard Delta-Sigma designs, which tend to drift or suffer from noise modulation as the signal drops below -90dB.
Technical Comparison: Legacy Multibit vs. Modern Silicons
While dynamic range specs have soared with modern silicon, the raw hardware complexity of R-2R chips like the PCM1704 remains highly coveted. The table below outlines how these architectures compare across different eras.
| DAC Chip Model | Architecture Type | Max Resolution | Dynamic Range | Sonic Characteristic | Manufacturing Era |
|---|---|---|---|---|---|
| Burr-Brown PCM1704-K | R-2R Sign-Magnitude | 24-Bit / 96 kHz | 120 dB | Warm, highly organic, fluid, lifelike timbre | Late 1990s – Early 2000s |
| ESS Sabre ES9038PRO | HyperStream Delta-Sigma | 32-Bit / 768 kHz | 140 dB | Clinical, analytical, ultra-resolving, bright | Modern (Active) |
| AKM AK4499EX | Switched Resistor Delta-Sigma | 32-Bit / 768 kHz | 135 dB | Smooth, velvety, wide soundstage, detailed | Modern (Active) |
| Analog Devices AD1865 | R-2R Multibit | 18-Bit / 50 kHz | 110 dB | Midrange-focused, punchy, nostalgic tone | Early 1990s (Vintage) |
The Sonic Signature: What is “Analog Realism”?
When audiophiles refer to the PCM1704’s “analog realism,” they are speaking of a sound signature that mirrors how human ears hear sounds in the physical world. Let’s break down the core pillars of this experience:
- Natural Decay: When a drum skin is struck or a piano string vibrates, the sound decays slowly and organically. The math-heavy filters of Delta-Sigma chips can sometimes truncate this decay prematurely. R-2R DACs preserve the complete, natural tail of each note, rendering the acoustics of the recording space vividly.
- Timbral Texture: The PCM1704 gives instruments physical body. A violin’s wood, the metallic bite of brass, and the rasp of a singer’s voice feel textured rather than artificially smoothed.
- Coherent Imaging: Because there are no phase shift anomalies introduced by steep brickwall reconstruction filters, the stereo image feels stable, wide, and three-dimensional. Instruments occupy precise coordinates in the virtual stage.
To keep up with the latest trends in high-fidelity audio design, make sure to read our ongoing articles in the HeadphonePalace Blog.
The R-2R Renaissance in Modern Headphone Audio
By the mid-2000s, TI (which acquired Burr-Brown in 2000) discontinued the PCM1704 due to the high cost of laser-trimming precision resistors. For a while, it seemed like multibit technology was dead, replaced entirely by highly integrated Delta-Sigma SOCs. However, the rise of high-resolution planar magnetic and electrostatic headphones in the 2010s brought about a change in consumer demands. Modern headphones are so revealing that the glare and analytical harshness of basic Delta-Sigma chips became fatiguing.
This led to a massive resurgence. Brands like Denafrips, Holo Audio, Schiit Audio, and HiFiMAN began developing discrete R-2R ladder networks. Instead of relying on a single chip, they use hundreds of ultra-precision resistors soldered directly onto the PCB, controlled by custom-programmed FPGA chips. While complex and expensive, this resurgence is a testament to the enduring legacy of the sound signature that the PCM1704 defined.
A high-quality discrete R-2R DAC pairs beautifully with top-tier planar magnetic headphones, bringing out a level of resolution and warmth that Delta-Sigma chips struggle to match.
Conclusion: The Unfading Legacy of the PCM1704
The Burr-Brown PCM1704 represents a golden era of audio engineering—a time when physical precision was prioritized over algorithmic convenience. While modern DAC chips beat it on paper with 130dB+ dynamic range and 0.0001% THD, they often fail to capture the emotional essence of a musical performance in the way the PCM1704 does. It remains a legendary monument to the pursuit of pure, unadulterated analog realism in a digital world.
Discuss more about this, FAQ, Announcements and Miscellaneous, over on our community.
