Pioneer SX-1250

The Pioneer SX-1250 remains one of the most coveted receivers ever made. Released in 1976 with a $900 price tag, it represented everything Pioneer had learned about crafting high-end audio equipment. This wasn’t just their flagship model – it was a statement piece that showed what was possible during the golden age of stereo.

The design alone tells you this is something special. From its brushed aluminum face to the warm amber glow of its display, every detail was carefully considered. The faceted control knobs feel perfectly weighted in your hand, while the walnut cabinet adds a touch of warmth to all that precision engineering. Decades later, the SX-1250 still turns heads.

The late 1970s marked the peak of the receiver wars, when companies like Pioneer, Marantz, and Sansui were locked in an arms race to build the most impressive equipment possible. The SX-1250 was Pioneer’s answer to this challenge – a receiver that combined raw power with exceptional build quality. While other manufacturers were pushing boundaries too, Pioneer went all out, creating a unit that wasn’t just about specs and power ratings. Every component was chosen with a single goal: to deliver the kind of sound quality that would stop listeners in their tracks. This wasn’t just another high-end receiver; it was Pioneer showing the world what they could really do when they pulled out all the stops.

Key Features

Power Output:

The Pioneer SX-1250 is equipped with a direct-coupled DC amplifier that delivers 160 watts per channel into 8 ohms, with a total harmonic distortion (THD) of less than 0.1% at full power. This high power output ensures clean, distortion-free audio, even at high volume levels. The amplifier’s direct-coupled design eliminates capacitors from the signal path, enhancing bass response and providing a more accurate, dynamic sound.

The SX-1250’s dual-mono power supply architecture, featuring a large 22 pound toroidal transformer and separate power circuits for each channel, improves channel separation and stability, further reducing cross-talk and ensuring high performance. Additionally, the large 22,000 µF filter capacitors provide ample energy storage, allowing for superior transient response and maintaining clarity even during dynamic shifts in the audio.

The build quality of the SX-1250 is exceptional, with a robust chassis designed for long-term durability. The unit’s stability is enhanced by its use of high-quality components, such as transistors, capacitors, and wiring, ensuring that the receiver remains reliable over time.

FM/AM Tuner:

The FM tuner in the Pioneer SX-1250 is known for its high sensitivity and selectivity, allowing it to pull in distant or weak signals with clarity. Technically, it features a dual-gate MOSFET in the RF front end, which improves its ability to capture weak signals while minimizing interference. The tuner includes a 5-gang variable capacitor for accurate tuning and enhanced performance.

The phase-locked loop (PLL) MPX decoder contributes to superior stereo separation, ensuring the sound remains rich and well-defined, even when dealing with multipath distortion in urban areas. These technical features combine to provide excellent signal-to-noise ratio (70dB on FM) and low distortion, resulting in crisp, clean sound reproduction from FM broadcasts.

Phono Circuit:

The SX-1250 preamplifier circuit boasts an exceptional feature: an unusually high phono overload level of 500 mV. This means that no matter how powerful the magnetic cartridge, the preamp will not become overdriven, resulting in a strained or harsh sound. This is a common flaw in many vintage receivers. The SX-1250’s RIAA equalization is remarkably accurate, with a deviation of only ±0.2 dB.

Multiple Input and Output Options:

The SX-1250 offers flexibility with multiple inputs and outputs, allowing users to connect various audio sources, such as tape decks, auxiliary devices, and additional amplifiers or preamplifiers. This makes it adaptable to different setups and allows for easy system expansion.

Adjustable Tone Control:

The tone controls on the Pioneer SX-1250 provide precise control over the treble, midrange, and bass frequencies, allowing users to fine-tune the sound to their preferences. The receiver features separate tone adjustments for bass (20Hz), midrange (1kHz), and treble (20kHz), each with its own dedicated knob. These controls offer ±10 dB adjustment, which gives significant flexibility in shaping the sound signature, whether boosting the low-end for more bass or enhancing the clarity of higher frequencies.

This level of control ensures that users can achieve a tailored listening experience, making the SX-1250 suitable for various musical genres and personal sound preferences.

Dual Meters and Display:

The front panel features dual VU meters for signal strength and tuning. These meters not only add a visual appeal but also provide practical information, allowing users to monitor the receiver’s performance in real-time.

Large Cooling Fins:

To effectively manage heat dissipation, Pioneer employed massive heat sinks with large cooling fins strategically placed around the exterior of the SX-1250. This design allows heat to be efficiently dissipated away from the internal components, rather than accumulating inside the unit, ensuring optimal performance and longevity.

Protection Circuit:

When the SX-1250 is powered on, its robust power supply can surge to an inrush current of up to 200 amperes. To safeguard against this intense power spike, the SX-1250 features a unique combination of a power relay and an advanced protection circuit. This innovative design provides a layer of defense for the receiver’s transistors and your speakers, shielding them from potential damage caused by the initial power surge.

Technical Specifications

The SX-1250 is not only known for its power but also for its precise engineering. Some of the critical technical specifications include:

• Power Output: 160 watts per channel into 8 ohms (minimum RMS)
• Frequency Response: 5Hz to 100kHz (+0dB, -1dB)
• Total Harmonic Distortion (THD): Less than 0.1% at rated power
• Damping Factor: 30 (8 ohms)
• Signal-to-Noise Ratio: Phono Input: 80 dB; Auxiliary Input: 90 dB
• Power supply: AC 120V, 60Hz.
• Speaker load impedance: 4Ω (minimum)
• Dimensions: 21.89 x 7.32 x 18.31 (556mm x 186mm x 465mm)
• Weight: 64 lbs (29.1 kg)

Here is a more complete list of specifications:

Comparisons

Here is a comparison of the Pioneer SX-1250 to other competitors such as Marantz, Kenwood and Sansui:

The Technics SA-5760 was another premiere competitor to the Pioneer SX-1250 at the time. Here’s how it compares:

Design and Build Quality

The build quality of the SX-1250 is impressive. The use of durable, long-lasting materials ensures that the SX-1250 can withstand years of use without significant wear or degradation. Its internal layout is designed for easy access to components, making repairs and maintenance straightforward. Pioneer also incorporated a dual-mono power supply design, which further improves the performance by providing each channel with its own dedicated power supply, reducing crosstalk and enhancing sound separation.

Performance

The SX-1250’s performance is one of its standout qualities. Its high wattage output makes it ideal for driving demanding speakers, producing a full and rich sound across the entire frequency range. The receiver’s low distortion ensures that even at higher volumes, the sound remains clean and undistorted.

For vinyl enthusiasts, the phono preamp provides a clean and accurate reproduction of records, with enough sensitivity to pick up even the most subtle details in the music. The SX-1250’s ability to handle various sources with such fidelity has made it a favorite among audiophiles, both during its production run and in the decades since.

Rear Panel

The rear panel of the Pioneer SX-1250 is comprehensively equipped with a range of input and output connectors. Two sets of phono inputs are provided, along with tape output jacks and dual tape input jacks. A versatile adaptor in/out combination jack allows for the connection of add-on devices such as noise reduction systems, expanders, and graphic equalizers, effectively creating a third “circuit interruption point” in the signal chain. Ground terminals are conveniently located below the phono inputs.

The SX-1250 also features a DIN socket that mirrors the functions of the Tape 2 input and output jacks. Spring-loaded speaker terminals enable the connection of up to three pairs of stereo speaker systems, with the ability to select two sets for simultaneous listening. Jumpers on the rear panel connect the preamp outputs and power amp inputs, allowing for easy separation and separate use of these receiver sections.

Additional features include screw terminals for 75 ohm, 300 ohm, and AM external antennas, as well as an FM-detector output jack for potential use with four-channel FM adaptors. A slide switch enables the adjustment of FM de-emphasis between 75 microseconds and 25 microseconds, facilitating proper Dolby FM listening when used with a separate Dolby decoder. Switched and unswitched a.c. receptacles are located beneath the speaker terminals. There is also an adjustable AM ferrite bar antenna near the antenna terminals.

Pioneer SX-5590

Pioneer marketed the SX-1250 as the SX-5590 in Europe. The only difference was that the faceplate and cabinet were black.

Pioneer launched the SX-1050 ($700) and SX-950 ($500) concurrently with the SX-1250, offering a range of options with varying power outputs. The SX-1050 boasts 120 watts per channel, while the SX-950 delivers 85 watts per channel. The SX-1050 is nearly indistinguishable from the SX-1250 without removing the cover.

Reviews

“It’s a beautiful thing… the SX-1250 rules.”

“One of the best sounding receivers I have ever heard, unmatched in power and clarity.”

“Its superb audio performance and aesthetic appeal have kept it in high demand.”

“The SX-1250 produces a clean, full-bodied sound across the entire frequency range.”

“I wouldn’t trade it for anything.”

“The SX-1250 is just better built.”

Conclusion

Since its release in 1976, the Pioneer SX-1250 has achieved legendary status in vintage audio equipment, favored by serious music lovers in the 1970s for its power, build quality, and flexibility. Today, it commands premium prices on the secondhand market due to its exceptional performance and quality.

As an icon of high-fidelity audio, the SX-1250 combines powerful performance, versatile features, and robust construction, making it a highly desired piece of audio history. Its nostalgic value and exceptional sound reproduction continue to drive demand. For those seeking a high-powered vintage receiver that delivers quality and reliability, the SX-1250 remains an outstanding choice.