Dynaco PAS-2 Preamplifier

The Dynaco PAS-2, introduced in 1960, stands as one of the most iconic tube preamplifiers in the history of high-fidelity audio. Designed as a companion to Dynaco's popular power amplifiers like the ST-70, the PAS-2 offered exceptional sound quality, modular construction, and affordability—especially in its widely sold kit form. Its enduring popularity among audiophiles and DIY enthusiasts speaks to its influence in making high-end tube audio accessible to a broader audience.

Specifications

Feature	Specification
Year of Production	1960–1969
Type	Tube Preamplifier (line-level output only, no built-in power amplification)
Tubes Used	2 × 12AX7, 1 × 12AU7
Input Impedance	47k ohms
Output Impedance	Low impedance (optimized for Dynaco power amplifiers)
Phono Input	Yes, with RIAA equalization
Line Inputs	4 high-level inputs (Tuner, Tape, Auxiliary, Turntable)
Tone Controls	Bass and Treble controls with defeat switch
FM Tuner Support	Optional FM tuner module compatible (via internal connection)
Power Supply	Internal linear transformer; no external power amp integration
Dimensions	19" (W) × 5.5" (H) × 9.5" (D)
Weight	~10 lbs

Historical Context

The Dynaco PAS-2 emerged during a golden era of tube audio, when high-fidelity systems were transitioning from luxury items to attainable components for serious music lovers. Manufactured by David Hafler and Herb Keroes under the Dynaco brand, the PAS-2 was designed to pair seamlessly with the legendary Dynaco ST-70 tube power amplifier. Its modular design allowed for easy servicing and upgrades, and its availability as a kit—priced affordably at under $100—made it a favorite among hobbyists.

Over 100,000 units were sold, many in kit form, cementing the PAS-2’s reputation for value, reliability, and sonic excellence. It played a pivotal role in democratizing high-end audio, offering performance that rivaled far more expensive preamps of the time. The PAS-2 was succeeded by the PAS-3 and later the PAS-4, but many enthusiasts still regard the PAS-2 as the most musical and balanced of the series.

Sound Signature

The PAS-2 delivers a warm, smooth, and richly textured sound characteristic of well-designed tube circuitry. Its detailed midrange brings vocals and acoustic instruments to life, while the overall presentation remains highly musical and engaging. The phono stage, designed for moving magnet cartridges, provides accurate RIAA equalization and low noise when maintained properly.

While some modern listeners may notice a slight roll-off in the extreme highs compared to solid-state designs, this characteristic contributes to the PAS-2’s non-fatiguing, analog warmth. When paired with high-quality sources and amplifiers, it continues to impress with its three-dimensionality and dynamic expression.

Maintenance and Restoration Tips

Due to its age, most PAS-2 units require careful inspection and servicing to perform safely and optimally. Here are key considerations:

Capacitor Replacement: Replace all electrolytic and coupling capacitors. Old capacitors can leak, degrade performance, or pose safety risks.
Resistor Check: Test carbon-composition resistors, which often drift in value over time. Replace as needed for accurate circuit operation.
Tube Replacement: Use tested, low-noise 12AX7 and 12AU7 tubes. Microphonic or noisy tubes are common and should be replaced.
Cleaning Controls: Use contact cleaner on potentiometers, switches, and jacks to eliminate crackling and channel imbalances.
Grounding and Hum: Some PAS-2 units exhibit hum due to original grounding schemes. A careful review of the grounding layout—sometimes modified to a star ground—can resolve this.
Power Transformer: While generally robust, verify the transformer’s integrity, especially if the unit has been unused for years.

Safety Note: Always have a qualified technician inspect and service vintage tube gear before use. High voltages are present inside the chassis.

Collectibility and Market Value

The Dynaco PAS-2 ranks 8/10 in collectibility due to its historical significance, modularity, and enduring sonic reputation. Units in original, unmodified condition with documentation and packaging command higher prices. Restored models with quality parts and proper calibration are also highly sought after.

As of recent market trends, the PAS-2 typically sells for $200 to $500, depending on condition, originality, and provenance. Fully restored examples with low-noise performance and correct components may exceed $500 in premium markets.

Conclusion

The Dynaco PAS-2 remains a landmark in audio history—a preamplifier that brought high-fidelity tube sound within reach of everyday enthusiasts. Its combination of elegant design, modular construction, and lush sonic character ensures its place in vintage audio collections and high-performance tube systems alike. Whether experienced as a restored classic or a carefully rebuilt project, the PAS-2 continues to deliver a listening experience that is both timeless and deeply rewarding.