Sony STR 7035 (c. 1975)

Contemporary reviews noted its robust 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 rests in the rack like a promise kept—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 developed during a pivotal moment in the company’s audio evolution, incorporating refinements drawn from earlier models like the STR-7065. Priced at ¥67,800 around 1975, it represented a serious investment in high-fidelity performance for its time, targeting listeners who demanded both tunability and sonic precision. At 427mm wide, 149mm tall, and 340mm deep, the chassis is compact by modern standards but substantial in weight—8.6kg of dense engineering packed into . Power draw is rated at 80W from a 100 VAC source, with two unlinked 150W power outlets on the rear for driving external tape decks or accessories without tying them to the main power switch. The receiver’s all-silicon transistor design underscores Sony’s full transition into solid-state dominance, with 34 transistors (including FETs), 21 diodes, and two ICs forming the core of its signal path. This isn’t just a receiver—it’s a system built for integration, with dedicated preamp and power amp sections that allow for future bi-amping or separation should the owner choose to upgrade.

Its power amplifier section employs a "direct coupling pure complimentary service SEPP circuit" with dual power supplies, a configuration aimed at minimizing phase distortion and improving transient response. Rated output is 24W + 24W into 8Ω across 40Hz to 20kHz, or 26W + 26W at 1kHz—figures that reflect conservative IHF testing standards. Dynamic power, a more revealing metric of real-world headroom, reaches 65W into 8Ω and 80W into 4Ω under IHF conditions, suggesting it can handle difficult speaker loads with more authority than the continuous rating implies. The damping factor of 25 or more at 1kHz into 8Ω further supports this, indicating solid control over bass drivers. Harmonic distortion is held to 0.8% or less at full rated output, dropping to 0.1% at 1W—typical of well-engineered receivers from this period, where low distortion was a badge of honor. Cross modulation distortion, a rarer spec to see published, is also rated at 0.8% or less at full output, pointing to a clean power supply and robust stage isolation.

The FM tuner is where the STR-7035 reveals its pedigree. Covering 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, making it responsive even to weak signals. The 68dB signal-to-noise ratio, 1.5dB capture ratio, and 60dB selectivity (IHF) suggest strong rejection of adjacent channels, while the 55dB image and 90dB intermediate frequency interference ratios confirm a well-shielded front end. Notably, Sony employed a solid-state filter in the IF section, a design choice that reduced drift and improved adjacent-channel separation—particularly useful in urban environments with strong local stations. The AM section is equally competent, covering 530 to 1605 kHz with a 455kHz intermediate frequency, and offering 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, indicating decent AM performance for nighttime DXing. Both bands benefit from solid-state filters, a forward-thinking touch that 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, a design decision aimed at improving reception capability by lowering noise and increasing input impedance. This was a strategic move by Sony to enhance weak-signal performance without sacrificing dynamic range, particularly valuable in fringe reception areas. The use of FETs at this stage was still relatively advanced in the mid-1970s, and their inclusion here signals Sony’s commitment to cutting-edge RF design.

Solid-State IF Filters for FM and AM

Both the FM and AM sections employ solid-state filters in their intermediate frequency stages, a feature highlighted in the original documentation as a means to improve adjacent-channel separation and reception of weak signals near strong stations. Unlike traditional LC filters, which can drift with temperature and age, solid-state filters offer greater consistency and reliability over time. This design choice likely contributed to the STR-7035’s 60dB FM selectivity and 78dB spurious interference rejection, making it less prone to overload in electrically noisy environments.

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—meaning users could tune stations in consistent, predictable increments rather than dealing with nonlinear spacing. This was a usability improvement over earlier analog dials, reducing the guesswork involved in station recall and improving tuning accuracy, especially 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," suggesting a blend of discrete and integrated circuitry in the output stage. This hybrid approach may have been used to balance cost, reliability, and performance—leveraging the precision of ICs while retaining the robustness of discrete transistors. 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 employs an NF (negative feedback) type design, offering ±10 dB adjustment at 100Hz for bass and ±10 dB at 10kHz for treble. This is a conventional but effective topology, providing enough range for room compensation without introducing excessive phase shift. The inclusion of a loudness switch, active at lower volume levels, applies a psychoacoustic boost to bass and treble, compensating for the ear’s reduced sensitivity at low listening levels—a thoughtful touch for late-night listening.

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. With a mic input sensitivity of 2mV and impedance of 47kΩ, it’s designed for low-level dynamic mics, and the 60dB signal-to-noise ratio (B network) suggests it’s usable without excessive hiss. While not a common feature on consumer receivers, its inclusion hints at Sony’s broader vision for the STR-7035 as a multi-purpose audio hub.

Noise and Filter Switches

In addition to the loudness control, the STR-7035 includes a high filter switch that rolls off frequencies above 5kHz at 6dB/octave, useful for eliminating tape hiss or AM static. The documentation specifically mentions its role in removing "scratched noise and ヒズノイズ" (hiss noise), confirming its utility with older recordings. A tape monitor function allows users to switch between live tuner input and recorded tape output, a standard but essential 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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