The PP500 phono preamplifier, built around the JRC4580 op-amp, originally uses 3.3 kΩ resistors and 4.7 µF capacitors in the feedback network. While this design is stable, it can result in a lower output level when used with medium-output MM cartridges such as the Audio-Technica AT3600L, and the stock power section is highly susceptible to interference.
To optimize both the gain and power filtration, a comprehensive modification was applied. In the feedback network, after iterative testing with different values (1 kΩ, 2 kΩ, and 2.5 kΩ), a 4.7 kΩ resistor in parallel was selected as the perfect sweet spot—balancing high clarity with the necessary volume output. This was combined with an upgraded 10 µF capacitor to optimize the low-frequency response and ensure proper RIAA correction.
Significant improvements were also made to the power supply stage to eliminate noise. The stock 1000 µF filtering capacitor was replaced with a much larger 2200 µF unit, bypassed with a 68 nF filter capacitor to suppress high-frequency ripple. Additionally, a 68 nF shunt capacitor was added across the M7 rectifier diode to absorb switching transients. Finally, the noisy stock switching power supply (SMPS) was replaced with a traditional 9V Ktec transformer-based linear power supply, completely removing unwanted high-frequency oscillations.
After this modification, the PP500 sounds much louder, cleaner, and remarkably quiet. The frustrating background hiss and switching noise from the original power supply are completely gone. The midrange is richer and more organic, highs remain clear without fatigue, and the bass is significantly deeper and more pronounced, providing a much fuller, dynamic, and engaging listening experience.
This approach targets the core weaknesses of the stock unit, making it an incredibly effective and rewarding upgrade for the PP500.
- 2× Resistors 4.7 kΩ
- 2× Capacitors 10 µF
- 1× Capacitor 2200 µF
- 2× Capacitors 68 nF
- 1× 9V transformer-based (linear) power supply (e.g., Ktec)
