Allnic Audio RD-7500 OTL/OCL DAC
Allnic Audio RD-7500 OTL/OCL DAC
Design Goal: Minimization of Distortion (Straight Wire with Gain)
The “Straight Wire with Gain”—the North Star of audio design—is the goal of delivering an input signal with zero modulation or processing, increasing only its magnitude with absolute precision.
Unlike general amplifiers that amplify power, a DAC is a device that converts delicate digital signals into analog and transmits them to the next stage. Therefore, “precision” and “signal purity” are the highest priorities. To achieve this, the RD-7500 eliminates all interference that obstructs the signal flow throughout the entire digital and analog process.
- Digital Part: The World’s Most Precise DAC Chip (ESS ES9039PRO)
Precise analog transmission begins with perfect digital reconstruction. The RD-7500 is equipped with the ES9039PRO, the flagship chip from ESS Technology, widely regarded as the finest DAC chip in existence.
- HyperStream IV Architecture: Utilizing 4th-generation technology, it undergoes a conversion process far more sophisticated than previous generations.
- Ultra-High Resolution Data Processing: Based on a 32-bit, 8-channel architecture, it achieves overwhelming Dynamic Range (DNR) and extreme Total Harmonic Distortion (THD+N). It perfectly restores even the micro-details hidden within digital sources.
- Methodology 1: Non-Feedback (Zero Negative Feedback)
While Negative Feedback (NFB) is an engineering “correction tool” used to adjust measured figures, Non-Feedback is an “artistic frontal assault” that maximizes the inherent purity of the components.
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Category |
Negative Feedback (NFB) |
Non-Feedback (Allnic) |
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Design Philosophy |
Compares output to input to correct errors |
Amplifies the input signal exactly as it is |
|
Distortion (THD) |
Lowers distortion figures artificially |
Resolved through the component’s own linearity |
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Response Speed |
Micro-delays occur due to loop latency |
Instantaneous response without delay (Transient) |
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Phase Characteristics |
Possible phase distortion in high frequencies |
Extremely stable phase across all bandwidths |
|
Output Impedance |
Forcibly lowered through feedback |
Determined solely by the component’s low internal resistance |
|
Sonic Character |
Precise but can be somewhat flat |
Vividness, vast openness, and natural harmonics |
|
Design Difficulty |
Relatively easy due to corrective circuitry |
Extremely difficult; the circuit itself must be perfect |
The Essential Difference: If feedback is a method of “fixing a mistake after it happens,” Allnic’s Non-Feedback is a method of “ensuring no mistake happens from the very beginning.” This design is made possible by the overwhelming linearity of the 5687 vacuum tube.
- Methodology 2: OTL/OCL (Output Transformer-Less / Output Capacitor-Less)
Through its OTL/OCL design, the RD-7500 completely removes the physical signal barriers of output transformers and coupling capacitors. This realizes true broadband transmission—from DC to ultra-high frequencies far exceeding the audible range—without phase distortion or information loss.
- Removal of Transformer (L): By fundamentally blocking leakage inductance and distributed capacitance that degrade high-frequency resolution, it secures a crystal-clear high end.
- Removal of Capacitor (C): By breaking down the reactance (XC) barrier that blocks low frequencies, it eliminates low-end phase shift. The result is an extremely elastic and fast bass response.
- Methodology 3: Single-Stage 5687 Vacuum Tube Amplification
In a DAC, signal purity is more important than excessive amplification. For this reason, the RD-7500 insists on a Single-Stage 5687 amplification circuit.
- Realization of the Shortest Path: Unlike IC/TR circuits or multi-stage amplification circuits that pass through dozens of components, the RD-7500 prevents signal contamination at the source through a single stage of amplification.
- The Power of Direct Drive: The 5687 tube features very low internal resistance and high transconductance. This allows it to secure sufficient gain and low output impedance simultaneously with just one stage, driving the connected amplifier with powerful authority.
- Conclusion: An Unprecedented Design Solving Technical Challenges Simultaneously
The RD-7500 is an uncompromising reference for audiophiles worldwide.
Combining the world’s best chip, the ES9039PRO, with Allnic’s proprietary Single-Stage, Non-Feedback, and OTL/OCL technologies into a single circuit is a high-level engineering achievement—designed to reach the pinnacle of digital precision and analog purity at the same time.
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Category |
Item |
Details |
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Digital Inputs |
Input Terminals |
One (1) USB, One (1) Optical, One (1) AES/EBU, One (1) Coaxial |
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Bluetooth |
Bluetooth 5.1 (aptX, aptX-LL, aptX-HD, aptX Adaptive) |
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Digital Performance |
DAC Chip |
One (1) ES9039PRO (32-bit HyperStream IV Architecture) |
|
Sample Rates |
PCM: 44.1kHz – 384kHz / DSD: DSD64 – DSD512 |
|
|
DoP / S/PDIF |
DoP: up to DoP512 / S/PDIF: up to 192kHz |
|
|
Output Performance |
DNR: +132dB / THD+N: −122dB / Output: Balanced 2Vrms |
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Supported OS |
USB Input |
Windows (7, 8, 10/11), Mac (OSX 10.6+), Linux (UAC2 compliant) |
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Analog Specifications |
Circuit Type |
Full OTL/OCL (Output Transformer-Less / Output Capacitor-Less) |
|
Vacuum Tubes |
5687 x 2 |
|
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Gain / Impedance |
Gain: +5dB / Output Impedance: 500Ω |
|
|
S/N Ratio |
-110dB |
|
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Physical & Control |
Front Panel |
Buttons & LEDs (USB, Optical, AES/EBU, COAX, BT, Ext. Clock) |
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Dimensions (W×D×H) |
35.5cm x 44.5cm x 14.0cm (14 x 17.5 x 5.5 inches) |