Pioneer SX-1980

The Pioneer SX-1980 was a radio receiver that Pioneer Corporation introduced in 1978, to be matched with the HPM series of speakers. It is rated at a staggering 270 watts per channel into 8 ohms. However, in the September 1978 issue of Audio Magazine, Leonard Feldman did a spec test on the SX-1980 and concluded that the rating of 270 watts per channel was too conservative. He stated in his report:

Though the new [IHF mandated] "Dynamic Headroom" measurement is specified in dB, it should be mentioned that based upon the short-term signal used to measure the 2.3 dB headroom of this amplifier, it was producing nearly 460 watts of short-term power under these test conditions!

At an official rating of 270 watts per channel into 8 ohms^[1] with a 2.3 dB dynamic headroom, this makes the SX-1980 Pioneer's most powerful receiver, as well as being one of the most powerful receivers ever manufactured in the world, to date. The SX-1980 is 22 inches wide, 19.5 inches deep, and 8.25 inches high; weighing 78 pounds (35 kg).^[1] The case, like the Pioneer HPM-100, has a fine-grain, walnut veneer finish. It has massive heatsinks on the back to dissipate the immense heat the receiver can build up. The receiver had 12 Field Effect Transistors (FETs), 11 Integrated Circuits (ICs), 130 transistors and 84 diodes. Its retail price in 1978 was US$1295.00. According to the CPI inflation calculator, that would equate to about $3,700 in 2015.^[2] The SX-1980 is known for its total harmonic distortion (THD) rating of less than 0.03% at rated power, much less than the 1-10% commonly used today. The build quality is also higher than average. The unit compares favorably in side by side tests with newer large receivers.^[3] With a rated power consumption of 1400 volt-amperes or nearly 1000 watts, it would consume a fair amount of the power a standard 15-amp, 120-volt (North America) circuit can safely deliver.

From the owner's manual:

The adoption of a single-stage differential amplifier with low-noise dual transistors, a current mirror load and a 3-stage Darlington triple SEPP circuit provides a bumper power output of 270 watts + 270 watts (20 Hertz to 20,000 Hertz with no more than 0.03% THD) which is extremely stable. The power amplifier is configured as a DC power amplifier with the capacitors removed from the NFB circuit for a flat gain response. The large-sized toroidal transformers with their superb regulation employ 22,000 µF large-capacity electrolytic capacitors (two per each channel). There are independent dual power supply circuits with separate power transformer windings to provide power for the left and right channels. The FM front end incorporates a two-stage RF circuit that employs a 5-gang tuning capacitor and three dual gate MOS FETs for high gain and low noise. This configuration excels in ridding the sound of undesirable interference. The FM IF amplifier combines five dual-element ceramic filters…for high selectivity (80 dB) and low distortion… The local oscillator includes Pioneer’s very own quartz sampling locked APC (Automatic Phase Control). This output of this extremely precise quartz oscillator is divided into frequencies of 100 kHz and so reception frequencies which are a multiple of 100 kHz are locked at every 100 kHz.

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