McIntosh SCR3 (1970)
The McIntosh SCR3 is an all-solid-state audio compressor/limiter introduced in 1970 at an original price of $249.00. It's a single-rack-unit-high component, sometimes described as a "recording accessory" — intended to sit between a tape deck and an amplifier to improve recording quality, though it could also serve PA applications.
What makes the SCR3 unusual among consumer compressors is its flexibility. It will compress, peak limit, or downward expand either one or two channels simultaneously, selectable via a three-position mode switch on the front panel. All modes can be bypassed with a pushbutton in the center of the panel. It can also function as a microphone preamplifier with variable output. Despite that range of functions, operation is deliberately simple: a single large knob adjusts compression amount, with timing and release automatic. A peak-reading meter with McIntosh's signature illuminated glass panel monitors the amount of compression being applied.
The front panel is brushed aluminum with a black inset area. Input jacks are high-impedance (100k ohm) and outputs are low-impedance (600 ohm), using phono-type connectors on the back panel.
Known specifications are limited but respectable for the era: frequency response of 20 to 20,000 Hz ±0.5 dB, THD of 0.05% or less, a dynamic range of 88 dB, compressor/expander action up to 20 dB, and gain adjustable from 0 to 25 dB. A full specification table has not survived in the available documentation; several figures are noted only as "and a few other specifications we don't have."
Surviving documentation on the SCR3 is thin — no owner reviews, listening impressions, or comparative assessments have turned up in period literature. Beyond the specification sheet reproduced by an owner on AudioKarma and a current eBay listing for a serviced example, almost nothing else is recorded about this model. The SCR3 appears in Audio Classics Ltd.'s buy-sell-trade listings in Audio, June 1995, p.101.
- Type: Solid-state compressor/limiter (also usable as mic preamp)
- Introduced: 1970
- Original price: $249.00
- Modes: Compress, Limit, Expand (plus bypass)
- Input: High impedance, 100k ohm
- Output: Low impedance, 600 ohm
- Frequency response: 20–20,000 Hz ±0.5 dB
- THD: 0.05% or less
- Dynamic range: 88 dB
- Gain: 0 to 25 dB
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