RC. 436 C

Compressor Amplifier


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REPro built Genuine compressors classic tube

Hand built point to point from the 1968 ALTEC 436C valve vari-mu compressor schematic REPro mod.

2 Unit Rack

Sowter input and output vintage transformers

Metal film resistors 1% 2w

Cap polypropylene film capacitors

Alpha Potentiometer

Vintage VUmeter

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The 436C Compressor Amplifier is a self-powered, level-controlling amplifier with a versatility which makes it a desirable part of most audio installations. In response to a strong input signal, it will reduce gain up to 30 db automatically, rapidly, and quietly, without the introduction of thumps. The 436C utilizes variable threshold/compression ratio and release time controls, permitting maximum flexibility in virtually any type of installation.

The 436C Amplifier is intended for use in automatic level-control applications in recording. The front panel contains all controls and a meter which indicates db of compression and VU. A gain control is provided at the input, and the input and output transformers permit use on balanced lines. The 436C occupies only 2 unit of rack space in the standard rack. The wide range of application and excellent performance of this compressor amplifier will make it a valuable part of any good sound system.



PERFORMANCE SPECIFICATIONS

Frequency Response: ±1.5 db, 30-20,000 cycles

Harmonic Distortion: At 25 db of compression: Less than 1.5%, 35-15,000 cycles;

At 30 db of compression: Less than 2.5%, 25-10,000 cycles;

Noise Level: 74 db (at 50Hz )below rated output (—111 dbm equivalent input noise)

Input Impedance: 10,000 ohms bridging transformer (ungrounded)

Source Impedance: Any up to 10,000 ohms

Load Impedance: 600 ohms

Maximum Compression: 30 db

Attack Time Adjustable : 10ms to 110ms

Release Time Adjustable: .3 to 1.3 seconds

Threshold: 2:1 to 4:1

Compression Ratio: 2:1 to 4:1

Meter : Compression, Vu output

Controls: att input, output level -0 db to -30db , threshold, attack, release, vu meter selection, comp off,

Power Supply: 220Vac 50Hz

Tubes: 6BC8, 6CG7, 6AL5


History


During the 1950s, the American Altec Lansing Corporation produced several compressor models originally intended for telephone, broadcast and public address applications. In fact, the company manufactured a wide range of audio equipment, including a mammoth PA system called ‘Giant Voice’, which incorporated Altec 438 compressors, similar to the 436. The 436 series of compressors were all-valve, vari-mu designs, meaning that the amount of compression taking place depends on the level of the signal that is fed in.

Early Altecs were inexpensive and basic; the original 436A model had fixed parameters and no user controls whatsoever. 1958 saw the release of the 436B, which featured an input gain control, then, a few years later, the 436C included threshold and release-time controls. These modifications came about as a result of Altec’s engineers discovering that the cheap 436s were being modified by studio engineers to make them more suitable for processing pop music in recording studios. Maverick independent producer/engineer Joe Meek, for example, used a pair of Altecs – a model 436A and a model 436B – and modified them to decrease the attack and release times, helping him to achieve the heavy pumping effects that were a trademark of his unique sound.

The Altec 436Bs that EMI bought in 1959 (three years before The Beatles’ first sessions) were heavily modified to include an output attenuator and ‘recovery’ switch, which controlled the compression release-time. A unique feature of EMI’s six-position recovery switch was the Hold setting, which prevented a compressed signal from returning to its original level when in use.