Sanyo Plus 55

Stereo Reciver with SQL Quartz-Locked Tuning and High Speed DC amplifier

The Sanyo Plus 55 is elegant proof that moderate power and reasonable price in a stereo receiver do not inevitably mean compromise in  performance or features. Every aspect of its design, both internal and external, has been painstakingly worked and reworked to achieve a harmony seldom found even in far more to operate without being oversimplified. The controls are logical and responsive. The front panel gives visual display of a wealth of important information. And the internal circuits are the best that today's technology has to offer. The Sanyo Plus 55 is truly the perfect rceiver for the audio connoisseur with power requirements in the 50-60 watt per channel range.

Tuner Section

Digital Plus Tuning

Unquestionably, the most striking feature on the Plus 55's handsome front panel is its unique dual-mode frequency display. Sanyo engineers knew that digital frequency readout was a necessity for completely accurate, unambiguous tuning. At the same time, they realized that many people do not know the exact frequencies of their favorite stations, and find it easier to remember the approximate dial pointer location for each station. So sanyo Digital Plus tuning includes both a conventional dial scale and a bright fluorscent digital frequency display, which travels with the illuminated pointer along the dial scale as the receiver is tuned. Digital Plus thus combines the convenience of analog tuning with the precision of digital, and is a Sanyo Plus series exclusive.

SQL Quartz-Locked Tuner Circuitry

The Plus 55 incorporates Sanyo's unique Sampling Quartz-Locked tuning system, which provides accuracy impossible to achieve with conventional tuner designs. The special AT-cut quartz crystal locks in stations, with no significant drift due to time or temperature changes.

LED Signal Indicators

Conventional tuning meters are replaced in the Plus 55 by an array of light emiting diodes. Signal strength is indicated by a 5 LED 'bar graph' display, while a separate LED indicates when the SQL system has achieved 'lock' on a given FM frequency (equivalent to a center-channel indicator). Both displays use high gain, DC-coupled voltage comparators for precise indications.

Dual-gate MOSFET RF amplifier

Sanyo solves the problem of FM front-end overload by using a dual-gate MOSFET (metal-oxide-silicon field effect transistor) in the front end circuitry. One of the device's gates recelves the antenna signal, while the second is driven by a DC voltage from the tuner's Automatic Gain Control circuit. Thus the RF gain is automatically reduced in the presence of strong signals, avoiding overload and cross-modulation distortion and keeping other stations from interfering with the one you want.

Advanced IF design

Outstanding performance in the Plus 55 's IF section is achieved by a combination of Sanyo IC's and 3 sophisticated ceramic filters. These solid state resonators provide extremely good rejection of unwanted signals, plus 'linear phase' characteristics in the passband (essential for low distortion in the audio program). A quadrature FM detector and Phase Locked Loop multiplex decoder assure outstanding stereo separation without the need for periodic realignment. The result is clean, clear listening and years of trouble-free reception.

Combined muting/mode switch

When stereo mode is selected, FM muting is automatically engaged to screen out stations which are too weak for enjoyable stereo listening. Muting is defeated in mono mode.

Dolby FM demphasis switch

A rear panel switch changes the tuner's FM deemphasis characteristic from the standard 75 µs to 25 µs for proper decoding of Dolbylized broadcasts with an external Dolby adaptor.

Preamplifier Section

High performance phono preamp

After years of intensive development Sabnyo has perfected an integrated circuit with ideal characteristics for handling low level phono cartridge signals. The Plus 55 phono circuit easily achieves an astonishing 87 dB Signal-to-Noise ratio (re10mV input), frequency response to 150 kHz , and distortion below 0,01% under most conditions. The differential first stage has anexceptionally wide overload margin (150 mV at 1 kHz) to easily handle high output cartridges and the extremely demanding transient peaks found on direct-to-disc and digitally mastered recordings. The differential configuration also isolates the RIAA equalization network from the phono input, to avoid frequency response errors caused by interaction of cartridge impedance with the network. Precision resistors and capacitors are used to hold RIAA equalization eror to a maximum of ±0,2 dB. Records sound the way they should, no matter which cartridge you prefer to use.

Versatile tone controls and filters

Bass and treble controls on the Plus 55 are of the Baxandall feedback type, and combine wide adjustment range with an almost total absence of interaction; even at maximum cut or boost, their effect on th emiddle of the spectrum is less than1/2 dB. You can adjust bass and treble without upsetting the tonal balance of the rest of the music.

The Plus 55 is provided with an 8 kHz high filter useful for removing hiss and scratches from noisy programs, and a 12 dB/octave subsonic filter to remove record warp and arm resonance signals.

These inaudible signals can consume large amounts of amplifier power, creating distortion of audible bass and putting a severe load on woofers. The loudness control provides moderate bass and treble boost at low volume settings to compensate for the ear's reduced sensitivity to these frequencies.

Two tape deck inputs with dubbing

The Plus 55 allows recording and monitoring with two tape decks, as well as dubbing from one to the other at the push of a button.

Power Apm Section

High Speed DC amplifier

Except for the DC blocking input capacitor, the Plus 55 power amplifier is totally direct coupled from first stage to speaker terminals. Frequencies from 5 to 150,000 Hz are reproduced with virtually no phase distortion. Musical signals are reproduced exactlly as recorded, for the ultimate in realism.

Exclusive Sanyo Hybrid IC power stage

Sanyo's pioneering work in high power integrated circuit design now makes it  possible to put the entire power output stage of one channel of the Plus 55 in a single compact hybrid IC. Using a fully complementary, Darlingto-connected circuit configuration, the power stage achieves ultra-low distortion, outstanding waveform symmetry, plus a fast 60 V/µs slew rate to prevent transient distortion. Close mounting of the hybrid components on a copper plated aluminum substarate assures ideal thermal tracking of all components, for better bias stability and greater reliability  than an equivalent discrete circuit.

LED power indicators

These attractive 5-LED 'bar graph' displays give instantaneous indication of right and left channel output level. The LED's response time is far faster than any mechanical meter, and special 'peak-stretching' circuits make sure that even extremely short transisnts are visible to the eye. Amplifier output and possible overload canbe monitored precisely and easily. A range switch increases the sensitivity of the indicators by 10 times, for useful readings at low listening levels.

Speaker A/B switching

Allows connection and operating two pairs of speakers separately or simultaneously. Ecxcellent performance with 4 Ω loads permits running most popular speakers in parallel without loss of power or sound quality.

4-way output protection

A protective relay locked between teh amplifier output and the speaker terminals operates to disconnect the load under any of the following conditions.

When the unit is first turned on ( after a 5 second delay for the circuits to stabilize the speakers are reconnected)

When the heat sink temperature becomes too high for safe operation ( due to inadequate ventilation or sustained overload)

When special protection circuits sense the presence of a DC voltage at the outputs (which can quickly damage speakers)

In addition, current monitoring circuits operate to instantly shut down th epower stage if, for any reason, the output current should reach an unsafe level.

Specifications:

Amplifier Section

Continuous Power Output (minimum sine wave RMS per channel at 8 Ω, 20 - 20,000 Hz no more than 0,04% T.H.D.):  55 watts into 8 Ω; 60 watts into 4 Ω

Maximum Total Harmonic Distortion (from 250 mW to rated power into 8 Ω, 20 - 20,000 Hz, Aux input):  0,04%

Intermodulation Distortion (rated power, Aux input, 60 Hz : 7 kHz= 4 : 1):  0,04%

Input Sensitivity/Impedance:

Phono :  2,5 mv/47 k Ω

Aux, Tape 1 and 2 :  150 mV/47 k phm

Frequency response:

Phono (RIAA standard curve):  ±0,2 dB

Aux, Tape :  ±0,5 dB (20 - 20,000 Hz);  ±1 dB (10 - 40,000 Hz)

Signal-to-Noise Ratio (IHF-A weighted)

Phono (at 10 mv):  87 dB

Phono (at 2m5 mV) :  75 dB

Aux,  Tape :  95 dB

Damping factor:  40 (1 kHz, 8 Ω)

Residual Hum and Noise at Speaker Outputs:  0,6 mV

Transient Response (Slew Rate):  60 volts  per microsecond

Phono Maximum Input Capacity (1 kHz):  150 mv RMS

Tone Controls

Bass :  ±10 dB at 100 Hz

Treble :  ±10 dB at 10 kHz

Loudness Control (Vol. -30 dB)

100 Hz  / 10 kHz :  +8 dB /+3 dB

Filters

Subsonic (30 Hz) :  -12 dB/oct

High (8 kHz) :  -6 dB/oct

Output Voltage

Tape Rec 1 and 2 :  150 mV

 FM Tuner Section

Frequency Range:  88- 108 MHz

Usable Sensitivity [mono]:  10,8 dBf (1,9 µV)

50 dB Quieting Sensitivity

Mono :  13,7 dBf (2,7 µV)

Stereo :  37 dBf (39 µV)

Maximum Signal-to-Noise ratio

Mono :  75 dB

Stereo :  70 dB

Total Harmonic Distortion [Mono]:

At 100 Hz :  0,2%

At 1 kHz :  0,2%

At 6 kHz :  0,35%

Total Harmonic Distortion [Stereo]:

At 100 Hz :  0,35%

At 1 kHz :  0,3%

At 6 kHz :  0,4%

Frequency Response:  20 Hz - 15,000 Hz, +1 -2 dB

Alternate Channel Selectivity (at ±400 kHz):  75 dB

Capture Ratio:  1,2 dB

AM Suppression Ratio:  55 dB

Stereo Separation [1 kHz / 10 kHz] :  45 dB / 35 dB

Spurious Response Rejection (98 MHz):  80 dB

Image Rejection ratio:  70 dB

IF Rejection Ratio (98 MHz):  90 dB

Muting Threshold:  5 µV

AM Tuner Section

Frequency Range:  525 - 1620 kHz

Usable Sensitivity (Ferrite External Antenna):  300 µV/m - 30 µV

Signal-to-Noise Ratio (at 5 mV/m):  45 dB

Selectivity:  35 dB

Image Rejection ratio (1000 kHz):  50 dB

IF Rejection Ratio (1000 kHz):  45 dB

General Section

Power requirements:  AC 120V, 60 Hz / Ac 220 - 240 V 50/60 Hz

Power Consumption:  200 W

AC Outlets [switched/unswitched]:  1 x 100 W max./ 1 x 100 W max.

Dimensions (W x H x D):  18-7/8" x 5-1/4" x 11-1/2"