Nakamichi SR-4A

 The nakamichi SR-4A redefines the word "receiver". It offers the same convenience and economy but it's designed like separate audiophile components - each individually optimized, each individually powered, each isolated for minimum interference. And what a receiver: STASIS power amplification for uniform impedance, inherent stability and tremendous peak-current capability, a moving-coil/moving-magnet phono preamp with precise equalization, an effective subsonic filter and more. Like continuously variable loudness and tone controls, independent recording and input selectors with two-way dubbing and two video inputs, a 10-preset PLL Quartz-Lock FM/AM tuner with manual and auto-seek tuning, and wireless remote control.

 Multi-stage power supply

The SR-4A's performance is due in part to its unique power supply. Unlike ordinary receivers, the SR-4A's  transfrmer has separate windings, rectifiers and regulators for each major section; power amplifier, preamplifier, tuner and display. Within the audio circuitry, separate regulators are used for the phono preamp and high-level stages, and the video amplifiers are regulated independently of the audio stages to prevent video noise from intruding. Separate grounds are used for audio, tuner, display and power supply so ripple and RF noise will not enter the audio circuitry. The tuner is even buffered from the other inputs to prevent interference. Critical subregulators are discretely configured with a unique topology that cancels noise on the ground line. This unusually exotic power supply permits each section to operate independently of the others - the major advantage of "separate" components.

Stasis Amplification

Audiophiles who hear the SR-4A are amazed at its effortlessly transparent sound. Music has more detail, more impact, more realism - especially when reproduced on "difficult" top-quality speakers. The reason is our "Stasis" power amplifier - the same concept used in the PA-7 and PA-5 Power Amplifiers.

STASIS is a radically different and superior design in which two amplifiers drive the speaker; a high-quality low-power amplifier and a "Current-Mirror Bootstrap" to supply muscle. The low-power amplifier can be designed for virtually perfect performance, "global" feedback isn't needed as in ordinary power amps. Removing the overall  feedback ensures uniform output impedance and inherent stability, and, since the amplifier is stable, there's no need to isolate it from the speaker with a coil as is usually done. This permits the amplifier to control the speaker more preciselly and realize its full potential. The current bootstrap provides tremendous peak-current reserves - up to 25 ampers into low-impedance loads

 An Audiophile Preamp

Special care was lavished on the SR-4A phono preamp. The input circuit is a direct-coupled discrete design using ultra-high-gm FETs in a balanced differential configuration. These drive a differential gain stage with RIAA equalization obtained via a direct-coupled precision feedback network. The preamp accomodates MM and MC cartridges with a choice of gain (24/32 dB) in the MC position. A deleatable subsonic filter is part of the phono preamp. Theanks to a simulated-inductor ("gyrator") design, it has maximum rejection in the "warp" region, minimum loss in bass response and is free of noise pickup.

Only components of thehighest quality are used. Instead of the noisy distortion-prone electronic attenuator now in vogue as a volume control, we use a motor-driven precision potentiometer for local and remote level control. The loudness control is continuously variable to siut any listener's preference and copper-styrene capacitors and metal-film resistors in the signal path ensure minimum noise and distortion.

An Exceptiona Tuner

The SR-4A's Quartz-PLL Synthesized FM Tuner is far from ordinary. Of course,the quartz-locked design ensures accurate tuning and eliminates drift. But typical tuners of this type have high residual noise due to "reference-frequency jitter" the SR-4A tuner uses a reference frequency twice that of ordinary tuners to improve Signal-to-Noise. A dual-gate MOS FET front-end with high-Q twin vari-cap diodes provides selectivity equivalent to a 4-gang capacitor while a special auto-seek circuit that detects both signal and noise level prevents false stops between or near strong stations.

Specifications

Power Amplifier Section

Continuous Average Output Power (IHF-A):  80 watts per channel (8 Ω, both channel driven, 20-20,000 Hz, no greater than 0,1% T.H.D.)

Dynamic Output Power (both channel driven): 

80 watts per channel into 8 Ω

120 watts per channel into 4 Ω

Dynamic Headroom (IHF-A):  1,3 dB

Frequency Response (IHF-A):  5 Hz - 100 kHz +_0,5 dB

Signal-to-Noise Ratio:  better than 106 dB (rated power)

Total Harmonic Distortion (Rated Power, 8 Ω):  less than 0,1% (20 - 20,000 Hz)

Intermodulation Distortion (Rated Power, 8 Ω):  less than 0,1% (60 Hz :7 kHz = 4 : 1)

Preamplifier Section

Input Sensitivity /Impedance (for Rated Output):

Phono MC (gain; 32/24 dB):  60/180 µV/100 Ω

Phonoo MM :  2,5 mV/47 k Ω

CD, Tape, Video:  200 mV/30 k Ω

Maximum Input Level (1 kHz, IHF-A):

Phono MC (Gain; 32/24 dB):  3,5 / 8 mV

Phono MM :  150 mV

Total Harmonic Distortion (20  20,000 Hz, to Rec Out at 1 V):

Phono MC :  less than 0,003%

Phono MM :  less than 0,002%

RIAA Deviation:  30 - 20,000 Hz ±0,5 dB

Signal-to-Noise Ratio (to speaker output, IHF-A):

Phono MC :  better than 73 dB (32 dB gain); better than 72 dB (24 dB Gain)

Phono MM :  better than 89 dB

Tone Control

Bass:  20 Hz ±10 dB

Treble:  20 kHz ±8 dB

Contour (Variable Loudness):  20 Hz +25 dB; 20 kHz +8 dB

Subsonic Filter (Phono Only):  10 Hz, -12 dB/octave

FM Tuner Section

Frequency Range:  87,5 - 108 MHz

IHF Usable Sensitivity [mono]:  11 dBf (1,9 µV)

-50 dB Quieting Sensitivity [mono/stereo]:  14,7 dBf (2,9 µV) / 37,5 dBf (41,2 µV)

Signal-to-Noise Ratio at 65 dBf [mono/stereo]:  better than 79 dB / better than 74 dB

Frequency Response:  20 Hz - 15 kHz ±1 dB

Total Harmonic Distortion [mono/stereo]:  less than 0,07% / less than 0,09%

Capture Ratio:  1,5 dB

Alternate Channel Selectivity:  60 dB (±400 kHz)

Stereo Separation at 1 kHz:  better than 53 dB

Spurious Response Rejection:  better than 90 dB

Image Rejection:  better than 75 dB

IF Rejection:  better than 80 dB

AM Suppression:  better than 60 dB

AM Tuner Section

Frequency Range:  520 - 1710 kHz

Sensitivity:  53 dBµ/m

Signal-to-Noise Ratio (at 90 dBµ/m):  better than 52 dB

Total Harmonic Distortion (at 90 dBµ/m):  less than 0,3%

Selectivity:  better than 20 dB (±10 kHz)

General:

Power Source:  110, 120, 220 or 240 V AC, 50/60 Hz

Power Consumption:  350 watts max

Convenience Outlets:  2 x switched; 1 x unswitched

Dimensions  (W x H x D):  430 x 100 x 370 mm (16-15/16" x 3-15/16" x 14-9/16")

Weight:  9,8 kg (21 lbs 10 oz)