Retro Instruments Revolver

Retro Instruments Revolver is a dual-channel tube compressor with a fully differential signal path, built on the famous British-modified Altec 436. The project began as an experiment in 2011 and was field tested in selected studios before release. Added to the original compression signature is what tracking, mixing and mastering actually require: a sidechain filter, stereo linking, and continuously variable threshold, attack and release.

A dual threshold that controls ratio and saturation

The Altec 436 gave no access to its ratio or to the point where the amplifier begins to saturate. Here a dual threshold control puts both in reach, with ratio variable between 1.5:1 and 5:1. The practical result is that one unit can gently thicken a stereo bus or push a single track to the edge of tube saturation, without a chain of separate processors. Attack is adjustable from 2 to 40 milliseconds and release from 200 milliseconds to 2 seconds, covering fast drum transients and the long decays of vocals and strings alike.

A sidechain filter that saves the stereo bus

On a mix bus the lowest octave usually takes control of the compressor, so kick and bass drive gain reduction for the whole programme while vocals and the top audibly pump along with them. A switchable highpass filter in the detector path, with a 6 dB rolloff cornered at 90 or 250 Hz, reduces how much the bottom steers the circuit, so compression responds to the whole mix rather than to the rhythm section. Stereo linking meanwhile keeps gain reduction identical in both channels, which is the condition for a stable image. Distortion stays below 0.05% under the threshold and rises to roughly 1% at full-scale compression, so tone changes along with how hard you push.

KEY FEATURES

• Dual-channel tube compressor with a fully differential signal path
• Design based on the British-modified Altec 436
• Dual threshold control governing ratio and amplifier saturation
• Continuously variable input, output, attack, release and threshold
• Switchable highpass sidechain filter at 90 or 250 Hz
• Stereo linking alongside independent controls for both channels
• Transformer balanced inputs and outputs on XLR connectors
• Illuminated VU meters with front-panel zero controls
• Internal tube balancing facility
• 120 or 240 volt operation

TECHNICAL SPECIFICATIONS

• Channels: 2
• Ratio: adjustable between 1.5:1 and 5:1
• Usable input level range: -20 to +20 dBu
• Output level range: -30 to +18 dBu
• Output clip level: +23 dBu at 1% distortion
• Attack time: 2 to 40 milliseconds
• Release time: 200 milliseconds to 2 seconds
• Sidechain filter: 6 dB detector rolloff, switchable 90 or 250 Hz
• Distortion: below 0.05% under threshold, approx. 1% at full-scale compression
• Frequency response: 20-20,000 Hz, +/- 0.5 dB
• Dimensions: 2U, 9.5 inch depth, weight 10 kg
• Power: 120 or 240 VAC, 22 W, IEC inlet