Sony STR 7035 (c. 1975)

Contemporary reviews noted its build and clean signal path, with one observer remarking on the clarity of its preamp stage under real-world conditions. HiFI-Stereo (December 1978, p.112)

At 8.6kg, it is solid-state engineering from Sony's golden era, built to last and tuned to deliver.

Overview

The Sony STR-7035 is an AM/FM stereo receiver that carries refinements from earlier models like the STR-7065. It was priced at ¥67,800 around 1975. It targeted listeners who wanted both tunability and sonic precision. The chassis measures 427mm wide, 149mm tall and 340mm deep, and it weighs 8.6kg. Power draw is rated at 80W from a 100 VAC source. Two unlinked 150W power outlets on the rear let you run external tape decks or accessories without tying them to the main power switch. The design is all silicon: 34 transistors (including FETs), 21 diodes and two ICs form the core of the signal path. Dedicated preamp and power amp sections allow for future bi-amping or separation should the owner choose to upgrade.

The power amplifier section uses a "direct coupling pure complimentary service SEPP circuit" with dual power supplies. The aim is less phase distortion and better transient response. Rated output is 24W + 24W into 8Ω across 40Hz to 20kHz, or 26W + 26W at 1kHz. Those figures reflect conservative IHF testing standards. Dynamic power reaches 65W into 8Ω and 80W into 4Ω under IHF conditions, so it should handle difficult speaker loads better than the continuous rating implies. The damping factor is 25 or more at 1kHz into 8Ω. Harmonic distortion is held to 0.8% or less at full rated output, dropping to 0.1% at 1W. Cross modulation distortion, a rarer spec to see published, is also rated at 0.8% or less at full output.

The FM tuner covers 76 to 90 MHz, a range tailored for Japanese FM broadcasting. It delivers 2.2 μV sensitivity under IHF standards and 1.7 μV at a 30dB signal-to-noise ratio. The 68dB signal-to-noise ratio, 1.5dB capture ratio and 60dB selectivity (IHF) suggest strong rejection of adjacent channels. The 55dB image and 90dB intermediate frequency interference ratios point to a well-shielded front end. Sony used a solid-state filter in the IF section, which reduced drift and improved adjacent-channel separation. That helps in urban areas with strong local stations. The AM section covers 530 to 1605 kHz with a 455kHz intermediate frequency and 30 μV sensitivity with an external antenna. It includes a ferrite bar antenna and an external terminal, with a 56dB image rejection ratio at 1000kHz. Both bands use solid-state filters, which improved stability over traditional LC designs.

Key Features

FET Front-End for FM Reception

A newly developed junction FET is used in the FM front-end. It improves reception by lowering noise and increasing input impedance. Sony used it to enhance weak-signal performance without sacrificing dynamic range, which is valuable in fringe reception areas. FETs at this stage were still relatively advanced in the mid-1970s.

Solid-State IF Filters for FM and AM

Both the FM and AM sections use solid-state filters in their intermediate frequency stages. The original documentation highlights them as a means to improve adjacent-channel separation and reception of weak signals near strong stations. Traditional LC filters can drift with temperature and age, while solid-state filters stay more consistent over time. This likely contributed to the STR-7035's 60dB FM selectivity and 78dB spurious interference rejection.

Frequency Number Line Type Varicon

The tuning mechanism uses a "frequency number line type varicon," a variable capacitor system designed to allow equal-interval dialing. Stations tune in consistent increments instead of nonlinear spacing. That was an improvement over earlier analog dials, and it cut the guesswork in station recall. It also helps tuning accuracy when combined with the receiver's 1.5dB capture ratio, which ensured stable stereo lock-on.

Hybrid Power IC Dual Power Supply System

The power amplifier uses what Sony describes as a "hybrid power IC2 power source direct coupling system," which suggests a blend of discrete and integrated circuitry in the output stage. The hybrid approach may have balanced cost, reliability and performance. The dual power supply design further isolates left and right channels, reducing crosstalk and improving stereo imaging,

NF-Type Tone Control Circuit

The tone control circuit is an NF (negative feedback) type, with ±10 dB adjustment at 100Hz for bass and ±10 dB at 10kHz for treble. This is a conventional topology, with enough range for room compensation and without excessive phase shift. The loudness switch, active at lower volume levels, boosts bass and treble to make up for the ear's reduced sensitivity at low listening levels.

Built-In Microphone Amplifier

A built-in microphone amplifier allows for direct mixing, a feature that might have been aimed at public address or presentation use in homes or small venues. Mic input sensitivity is 2mV with an impedance of 47kΩ, so it is meant for low-level dynamic mics. The 60dB signal-to-noise ratio (B network) suggests it is usable without excessive hiss. Mic inputs were not common on consumer receivers.

Noise and Filter Switches

Besides the loudness control, the STR-7035 has a high filter switch that rolls off frequencies above 5kHz at 6dB/octave. It is useful for cutting tape hiss or AM static. The documentation specifically mentions its role in removing "scratched noise and ヒズノイズ" (hiss noise), which makes it handy with older recordings. A tape monitor function switches between live tuner input and recorded tape output, a standard feature for cassette-based systems of the era.

Flexible Speaker and Input Options

The receiver includes a speaker switch for toggling between two sets of speakers or using them simultaneously, a practical feature for multi-room setups. The preamp section offers phono (2.5mV/47kΩ), aux (250mV/100kΩ), and two tape inputs/outputs, with 80dB S/N on tape inputs—implying very clean tape monitoring. The RIAA phono stage has a frequency response within ±2dB of the standard curve, and the preamp’s wide bandwidth (30Hz–40kHz) ensures minimal coloration of source material.

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