Pioneer A-8 / F-7 Amplifier/Tuner Review

Pioneer’s line of integrated amplifiers and FM/AM tuners is distinctively styled, the components compatible with each other both visually and electrically. The amplifiers feature Pioneer’s “nonswitching” output circuit, a design that reduces distortion to insignificant (and often unmeasurable) values: Model A-8, in the middle of the amplifier line, is rated to deliver 90 watts per channel to 8-ohm loads from 20 to 20,000 Hz with no more than 0.005 per cent total harmonic distortion.

A-8 Integrated Amplifier

The signal path of the A-8 is direct-coupled from its high-level inputs to the speaker outputs, and the “non-switching” output stage is specifically designed to be free of crossover distortion, giving the distortion-free performance of a class-A amplifier with the higher efficiency of a class-AB design. It is actually a variable-bias system, controlled by the signal level, that adapts the amplifier’s output-stage operating conditions so as to suit the requirements of the signal.

The front panel of the Pioneer A-8 has been visually simplified by locating most of the little-used controls behind a hinged door (the left third of the panel). Protruding slightly through the closed door are the two tone-control knobs. The right third of the panel contains only a large volume-control knob, a muting pushbutton (it reduces the amplifier’s gain by 20 dB), and the headphone jack.

The center third of the panel is largely devoted to a pictographic display that shows the signal path and operating mode of the amplifier at all times. It is dark brown, with white lines to show the signal paths and colored lights that identify the various inputs, outputs, and modes of operation. At the right of the panel is a vertical row of square, flush-mounted buttons that select the program source (phono, tuner, aux, TAPE 1, TAPE 2). A green symbol next to each button lights when it is engaged. Also next to the phono button are lights indicating the mm (moving-magnet) and mc (moving-coil) operating modes. To the left of the selectors is a twin vertical LED power-output display covering a range of 0.01 to 100 watts into 8-ohm loads.

When the top of the left panel section is pulled outward, it hinges down and can be slid under the amplifier to permit full access to the normally concealed operating controls. There is a balance control and a rec out selector that determines the signal source feeding the tape-recording output jacks. In its source position, the tape recorders receive the same program being heard through the amplifier. Other positions (phono, tuner, aux) supply those sources to the recorder outputs regardless of which program is being heard. Two copy settings connect a pair of tape decks for dubbing from either machine to the other (the playback from either can be monitored by pressing the appropriate tape button in the playback-selector group).

The other concealed controls are small buttons, many of which perform their indicated switching functions through relays. In its out position, line straight bypasses the tone-control circuits, as shown by an orange arrow on the display panel. Pressing it in lights the indicators for balance, mode, and tone, showing that those functions are usable.

Three phono buttons select the mm or mc preamplifier gains (lighting the corresponding letters next to the phono-input selector button) as well as the cartridge load terminations. The mc load (R) button changes the MC-input resistance from 100 to 33 ohms, while the mm load (C) button sets the input capacitance at either 200 or 400 picofarads when a moving-magnet cartridge is used.

Other lights show the operation of the amplifier’s protective circuits and when the muting switch is engaged. Thus, when the controls are hidden behind the hinged door, the pictographs on the panel show the complete operating status of the amplifier. The small brown pushbutton power switch, barely visible on the dark-brown strip to the left of the panel, is not illuminated. However, at least some of the lights on the display will be lit whenever the amplifier is on. The two sets of speaker outputs are activated by individual buttons, and the loudness and infrasonic-filter buttons complete the control lineup.

The rear of the Pioneer A-8 contains the various signal-input and -output jacks, two sets of insulated binding posts for the speakers, and three a.c. outlets, one of which is switched. The A-8 amplifier is about 16-1/2 inches wide, 16-3/4 inches deep, and 5-1/4 inches high. It weighs about 30-1/2 pounds. Price: $550.

Laboratory Measurements

The top of the Pioneer A-8 became only moderately warm during the preconditioning period and subsequent testing; elsewhere the exterior of the amplifier remained cool. Pioneer’s claims for extremely low distortion were completely confirmed by our measurements. At 1,000 Hz, with both channels driving 8-ohm loads, the distortion decreased linearly from 0.002 per cent at 1 watt to 0.0005 per cent in the 50- to 90-watt range, and the waveform clipped at just over 100 watts (the IHF clipping headroom was 0.52 dB). Although the A-8 Is apparently not rated for driving loads of less than 6 ohms, we tested it with loads of 4 and 2 ohms. Driving 4 ohms, the A-8 performed much as it did with 8-ohm loads, with the distortion dropping from about 0.003 per cent at 1 watt to 0.001 per cent between 20 and 100 watts, and with clipping occurring at a 148-watt output. The amplifier was even able to drive 2-ohm loads to 130 watts per channel at the clipping point, but the distortion was somewhat higher, between 0.01 and 0.045 per cent over the full power range. This level of distortion can hardly be considered serious except in comparison to the amplifier’s normal performance.

Driving 8-ohm loads, the distortion was typically 0.0005 to 0.001 per cent from 40 to 2,500 Hz, reaching 0.002 per cent at 20 Hz and a maximum of roughly 0.005 per cent at 15,000 Hz. When we drove the amplifier with the tone-burst signal of the IHF dynamic-power test, the outputs clipped at about 130 watts with 2-ohm or 8-ohm loads and at 198 watts with 4 ohms. The 8-ohm dynamic-headroom rating, therefore, was 1.56 dB.

The input sensitivity for a reference output of 1 watt was 16 millivolts (mV) for the aux input and 0.23 mV for the phono (MM) input. The respective A-weighted noise levels were —82 and —81 dB, both very good figures. The phono preamplifier overloaded at 260 mV at 1,000 Hz. At 20 Hz the equivalent overload input was even higher (350 mV), but it fell to 92 mV at 20,000 Hz. The phono-input impedance (MM) was 50,000 ohms in parallel with either 200 or 400 picofarads, as rated. No measurements were made in the MC mode.

The IHF overload-recovery time (from a 10-dB overload) was about 20 microseconds. The amplifier was stable with simulated complex reactive speaker loads and had a rise time of 2.5 microseconds. A phase-correcting network in the amplifier output limits its ability to sustain high-power outputs at ultrasonic frequencies, as we discovered during the IHF slew-factor measurement. We estimate that the slew factor is probably greater than 10.

The outstanding high-frequency linearity of the Pioneer A-8 was demonstrated by the IHF intermodulation-distortion measurement using equal-amplitude inputs at 19 and 20 kHz. Their combined peak value was equivalent to that of a 90-watt sine wave. For the first time since we began making this test more than a year ago, we were unable to detect any distortion on our spectrum analyzer (down to the instrument’s residual level at about —96 dB, or 0.0016 per cent).

The tone controls had conventional response characteristics, with a sliding-bass turnover frequency and the high-frequency curves hinged at about 3,000 Hz. The loudness compensation boosted the low frequencies as the volume-control setting was reduced, with no change in the high-frequency response until the control was at least 30 dB below its maximum setting. Even there, the high-frequency boost was very slight. The infrasonic filter began to roll off the response below 100 Hz; it reached — 3 dB at 35 Hz. The RIAA phono equalization was flat within ±0.6 dB from 20 to 20,000 Hz. It interacted very slightly with the inductance of moving-magnet phono cartridges, increasing the output slightly at high frequencies to a maximum of +0.5 dB in the octave from 7,000 to 14,000 Hz and rolling it off slightly above that frequency. With relatively low-inductance cartridges the overall response was still within ±1 dB up to 20,000 Hz, but with some others the output dropped more sharply at the highest frequencies to —2 or — 3 dB at 20,000 Hz.

F-7 FM/AM Tuner

The Pioneer F-7 AM/FM stereo tuner is a companion to the Model A-8 integrated amplifier. Its external styling and width match those of the A-8, although the tuner is only 2-3/8 inches high and 14-5/8 inches deep. The F-7 is a digital-synthesis tuner covering the FM band in steps of 0.1 MHz and the AM band at intervals of 10 kHz (this can be changed to 9 kHz by a switch in the rear of the tuner to match European frequency assignments).

Like the A-8 amplifier, the F-7 tuner has most of its controls behind a hinged door that forms the left third of its front panel. Behind the door are narrow pushbuttons marked tuning (up or down) that step the frequency in the indicated direction when pressed. A smaller tuning mode button has auto and manual settings; in manual, each touch of one of the tuning buttons moves the frequency by one increment, and holding the button in produces a rapid scan that covers the FM band in less than 15 seconds. In the auto mode (which also activates the interstation-noise muting) the tuner scans rapidly and silently until a signal is acquired, at which point it stops and unmutes. This is normally the most convenient way to search the FM (or AM) band for listenable signals.

The Pioneer F-7 has digital memories in which the frequencies of six FM and six AM stations can be stored and recalled instantly at the touch of a button. The buttons are on the right third of the panel, where they are accessible with the door closed. To store a frequency in a memory, a memory button next to the tuning mode button is pressed, followed by one of the station call buttons. The memories are retained when the tuner is shut off as long as it is plugged into a powered a.c. outlet (and for up to three days otherwise).

The hidden controls also include a mode button with auto and mono settings, plus a rec level check which replaces the tuner’s audio output with a (nominal) 330-Hz tone, whose level corresponds to 50 per cent FM modulation, for setting tape-recorder gains in advance of recording off the air.

When the door is closed, the dark-brown center third of the panel contains all the visible operating displays: illuminated identifiers to show which preset memory is in use, a digital frequency display with arrows indicating whether the tuner is on FM or AM, a five-segment horizontal signal-strength indicator, and the word stereo, which lights when a stereo signal is received. The plastic strip containing the station identifiers can be removed and the “FM 1, AM 2,” etc. markings can be replaced with the actual station call letters or frequencies.

The power switch is a button on the dark-brown strip that separates the display panel from the hinged door. To the right of the display panel, in the position corresponding to the amplifier’s input selectors, are the two square buttons that select AM or FM reception. On the rear of the tuner there are antenna binding posts for AM and 300-ohm FM antennas and a coaxial jack for a 75-ohm FM antenna. There is also a hinged ferrite-rod AM antenna. In addition to the 9/10-kHz AM selector switch, there are L and R audio outputs and an AM Stereo-output jack. The latter is intended to be used with an external stereo adapter once a stereo AM broadcasting system has been authorized in this country. The Pioneer F-7 weighs about 10 pounds. Price: $325.

Laboratory Measurements

The IHF usable sensitivity (FM) of the Pioneer F-7 tuner was 11.8 dBf (2.1 microvolts, or μV) in mono. The stereo sensitivity was set by the switching threshold of 21 dBf (6 μV). The 50-dB quieting sensitivity was 14.3 dBf (2.8 μV) in mono and 37.8 dBf (40 μV) in stereo. The signal-indicator lights came on at input levels from 24 to 55 dBf (8.5 to 300 (Continued on page 42) mV). Thus the first light corresponds to a marginally useful signal, and a reasonably strong signal will cause all the lights to be illuminated.

The distortion at a 65-dBf (1,000-μV) input was 0.1 per cent in mono and 0.09 per cent in stereo. The respective noise levels were very low, reading —78 and —71.5 dB. The intermodulation distortion was measured by modulating the signal generator with 14- and 15-kHz tones of equal amplitude to a peak deviation of 75 kHz. Spectrum analysis of the tuner output (with a 65-dBf input level) showed third-order products at 13 and 16 kHz at —51 dB (referred to the primary modulating tone levels) in mono and —53 dB in stereo. The second-order difference-tone IM product at 1.000 Hz was 65 dB below 100 per cent modulation in both modes.

The tuner's frequency response was ruler-flat, within ±0.4 dB from 30 to 15,000 Hz. The multiplex filters reduced the 19-kHz pilot carrier in the audio outputs to — 61 dB (the 38 kHz to —67 dB) yet had no effect on the tuner’s audio response at 15.000 Hz. The stereo channel separation was relatively uniform over the audio frequency range, increasing from 32 dB at 30 Hz to 40 dB at 15,000 Hz and averaging between 35 and 38 dB over most of the range.

The FM capture ratio was about 1.5 dB at a 45-dBf (100-μV) input, and the AM rejection was 60 dB. Both figures improved somewhat at a 65-dBf signal level. The image rejection was a fair 56 dB, and alternate-channel selectivity was also fair at about 52 dB (adjacent-channel selectivity was 6 dB, a typical figure for FM tuners).

The muting threshold was at 23.8 dBf (8 μV). The tuner’s hum level was —65 dB. The rec level check output signal was at a —4.5-dB level relative to a fully modulated FM signal, equivalent to 60 per cent modulation. The only measurement made on the AM tuner section was of its frequency response, which was down 6 dB at 35 and 2,600 Hz.

Comments

The Pioneer A-8 proves that the front panel of a flexible integrated amplifier need not look like the flight engineer’s station in a 747 jet. Without any sacrifice of flexibility or control functions, it can be designed to look “at home” in almost any listening room and not like a fugitive from an electronics testing laboratory.

If one concedes that most of the controls found on today’s integrated amplifiers do serve a useful function and deserve to be retained, it is equally true that most of them are used but rarely, and some may never be used by an individual user. There have been numerous efforts to hide little-used controls behind doors or fit them with small and unobtrusive knobs or buttons. Pioneer has done both, and with considerable success.

The pictographic panel display is genuinely useful (and would have been equally desirable even if all the controls had been exposed to view). Literally at a glance, and from a considerable distance, one can determine the complete operating status of the amplifier. It is both a functional and an attractive feature.

There is not too much to be said about the electrical performance of the A-8 amplifier. It is not only distortionless by any reasonable criterion one could apply, but even by what we consider to be downright unreasonable criteria. We specifically refer to the total absence of detectable IM distortion, even at the highest audio frequencies, which sets the A-8 apart from any other amplifier we have tested. Not only is the amplifier “distortionless,” but it is hundreds of times better than that by any subjective criterion. The Pioneer A-8 is an outstanding product in performance and appearance, and one we would be pleased to have in a home music system.

The Pioneer F-7 tuner is one of the simplest to use (and, to our eyes, one of the most functionally designed) units we have had the pleasure of testing. One could hardly ask for a less cluttered panel, with no exposed controls other than a nearly invisible power switch, equally unobtrusive band-se-lector buttons, and six small station-selector buttons. In spite of its seemingly spartan control lineup, the tuner’s information display contains everything that anyone will need to know—frequency, signal strength, and even the call letters of the station if they have been inserted into the station display windows.

The operation of the tuner was flawless, with the completely silent station selection that is characteristic of digital-synthesis tuners. Our performance measurements generally ranged from good to excellent, the most impressive being the noise levels, which were well below those of most FM tuners we have tested to date. The Pioneer F-7 provides good evidence that it is still possible to combine fresh styling, compact dimensions, and a moderate price with fine performance.

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