Pioneer KP-500

A car radio that a hi-fi magazine actually measured against home gear — and mostly won.

Overview

The KP-500 is an under-dash FM stereo receiver with a built-in cassette player, and its party trick is that Pioneer published a genuinely complete spec sheet for it — something the competition apparently couldn't be bothered to do. Audio (July 1976, p.29) noted that the KP-500 was the only one of three car units tested that came with a really complete set of published specifications, and the reviewer found them impressive. That matters more than it sounds: when a manufacturer puts usable sensitivity, quieting, selectivity, and capture ratio on paper, it invites the bench test, and the KP-500 largely survived it.

The claimed numbers were usable sensitivity of 12.0 dBf (1 µV at 75 ohms) and 50-dB quieting in mono at 14.3 dBf (1.4 µV at 75 ohms), with selectivity listed at 74 dB and capture ratio at 1.8 dB. Audio (July 1976, p.29) measured IHF usable sensitivity in mono at 0.9 µV (10.5 dBf) — slightly better than the 1.0 µV claimed — and found 50-dB quieting in mono reached at just 1.2 µV (13.0 dBf). Best mono S/N came in at 74 dB. Stereo performance was governed by the stereo switching threshold at 15 µV (34.9 dBf), where S/N was already 52 dB and topped out at 63 dB on strong signals. Mono THD measured 0.58%, rising to 0.85% in stereo at 1 kHz.

Not everything flattered the unit. Stereo THD at low frequencies ran high — 3.0% at 100 Hz — and stereo separation was 35 dB at 1 kHz but fell to 21 dB at 10 kHz. Capture ratio measured just under the 1.8 dB claim, and alternate-channel selectivity came in at 70 dB, which the reviewer called quite excellent for a unit of this type even if a bit short of the published figure. Dial calibration was off by as much as 1.5 MHz at 98 MHz on the review sample, though the magazine noted the sample had been through severe environment and shock testing beforehand and that calibration is easily adjusted. The reviewer's point stands regardless: in a car, you can't spend much time squinting at the dial.

The amplifier section is where the marketing and the measurements part company. Pioneer listed audio power output at 3.8 watts per channel with no qualifying THD or power bandwidth. Audio (July 1976, p.45) measured 2.75 watts per channel at 1.0% THD at 1 kHz with both channels driven into 4-ohm loads, and 3.2 watts per channel at 10% THD — still short of the claim, unless you count a 3.2-ohm load and 10% distortion as "squeaking through." The magazine used the episode to jab at the FTC's power-disclosure loophole, since all three units tested were rated around 3 watts yet showed real differences in power band that would have had to be published for home gear.

What owners actually get to use is more interesting than the wattage. The front panel slopes slightly upward for visibility, with a circularly calibrated FM dial and a clock-type rotating pointer marked every 2 MHz. Tiny bass, treble, and balance controls sit along the upper edge, with larger knobs for volume and tuning. Three small toggles handle interstation muting, a Local/Distant sensitivity switch, and power — and even with the radio switch off, inserting a cassette powers the unit up automatically. A fourth toggle by the cassette door engages the loudness circuit. Below the door are three rectangular transport keys: stop/eject, fast-forward, rewind. There's no play button; normal transport at 1-7/8 ips begins when the cassette is fully seated.

The tone controls are worth calling out because they're separate bass and treble, offering 10 dB of boost or cut at 100 and 10,000 Hz — a real departure from the single treble-cut control most car units of the period settled for. Audio (July 1976, p.29) was plainly pleased to finally find a car unit with separate bass and treble controls that actually work, and found the loudness circuit well calibrated against the master volume.

Cassette performance held up better than the amplifier specs suggested. Wow and flutter measured 0.2% W rms against a claimed 0.3%. Playback response, using a test tape recorded on a Nakamichi 1000, extended from 50 Hz to 8 kHz at the −3 dB points. There's no record function and no Dolby playback — this is a playback-only cassette section — but the reviewer judged the response far better than many AM transmissions and not much worse than some FM broadcasts.

That verdict is the reason this thing still has a following. Audio (July 1976, p.29) concluded that while the KP-500 remained a long way from even a moderately priced home receiver's amplifier section, its FM section was the equal of some home-bound hi-fi components — and in listening tests in the magazine's lab, it beat both the Panasonic CQ-840EU and the Motorola unit hands down, pulling in more stations on a simple indoor dipole. The magazine's reviewer, who a year earlier had mused about installing a converter in the trunk to run a real home receiver, admitted it was time to modify that statement.

The multi-conductor cable at the rear terminates in a socket, a fused positive supply lead with in-line fuseholder, and speaker leads with ground returns. A recessed receptacle on the rear accepts the coaxial antenna connector — 75-ohm unbalanced, as was standard for feeding factory car antennas.

Two different prices turn up in the contemporary record: Audio (July 1976, p.29) gives a suggested retail of $160.00, and a 1978 HiFi-Stereo listing (p.95) shows $275.00, or $300.00 with the AC power pack. The spread likely reflects the unit sold bare versus bundled, and the passage of two model years — collectors should confirm what's included before comparing asking prices.