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Revolution Recording Equipment R.47 MkII
The Classic British Vacuum-Tube Microphone Amplifier

The Revolution Recording Equipment Microphone Amplifier Type: R.47 is a single channel microphone and line valve amplifier based on a true classic. The Class A circuitry utilizes a pentode to triode configuration that provides up to 46dB of effective gain between an incoming signal and the balanced line level output.

While derived from a vintage design, many refinements have been employed which take advantage of contemporary electronic technology.  The signal-to-noise ratio is extremely good, and the equivalent hum and noise can be taken as equal to or better than –130 dBu referred to the input when the amplifier is set for maximum gain. The unit is capable of an output level of +23 dBu on overload peaks before severe audible distortion becomes apparent.

The vacuum-tube circuitry adds warmth and colour to the bass and the low-mid range of the frequency spectrum, resulting in a distinct richness to vocals, drums and bass. The frequency response is relatively flat through the upper end of the audio spectrum, with a wonderfully ethereal and open high end not typically associated with valve designs. The amplifier circuitry has a very fast response that captures every delicate dynamic nuance of vocals and instrument transients. What truly distinguishes the R.47 is the way signals acquire a clarity and presence that floats them to the front of the mix, this characteristic is consistent through a wide range of sources, from inexpensive dynamic microphones to classic valve types.

John Hinson, acclaimed for his achievements with Universal Audio, is the engineer behind the Revolution equipment design and development. For this very special endeavor, John embraced two important principles in his design philosophy: simplicity and uncompromising standards. The signal path requires only the essentials, especially for the active amplification circuitry. The audio signal path uses only the highest quality commercial components, and custom transformers that meet rigorous standards. The painted steel chassis and engraved front panel complement the sturdy selectors and switches, and the solid construction is built to service studios for decades to come.

Partial List Of Users

  • Abbey Road Studios
  • Brian Kehew (Recording The Beatles)
  • East West Studios (Formerly Cello)
  • Billy Corgan (Smashing Pumpkins)
  • Marc Streitenfeld (Film Composer)
  • Steve Kempster (Film Score Engineer/Mixer)

Features

  • Hand assembled using only the finest components (Hovland, Caddock, Mills)
  • Selected New Old Stock (NOS) vacuum tubes
  • Custom made gold plated switches (ELMA)
  • Massive, custom-wound input and output transformers
  • Fully regulated, over-designed H.T. & L.T. power supplies
  • Switched gain and attenuator controls for repeatability
  • Cardas and Kimber chassis wiring
  • No silk-screen! - front panels are engraved and painted
  • Thick, welded steel chassis for extreme durability
Specifications
  • Source Impedance: 200ohms
  • Input Loading Impedance: 2K ohms (attenuator off)
  • Maximum Input Level @ 20 Hz: +7dBu (attenuator & pad off)
  • Minimum Gain: -4dB
  • Maximum Gain: +46dB
  • Frequency Response: +/- 0.25dB 20Hz to 20kHz (high end -3dB point @ 48 kHz)
  • Signal to Noise Ratio: 80dB
  • Equivalent Input Noise: -130dB
  • Internal Output Impedance: 50 ohms
  • Suggested Minimum Load: 450 ohms
  • Maximum Output Level: +23 dBu
  • Power Requirements: 120 or 240 VAC, 50/60 Hz
  • Dimensions: 19" W, 3.5" H, 7" D
  • Weight: 19lbs

 

Details

  • Standard Single Channel R.47 MSRP: $3000.00 USD
  • Custom Matched R.47 Units: Please Inquire
  • The R.47 Microphone Amplifier is available only by special order at this time
  • Delivery Time: Please Inquire



R.47 SIGNAL DIAGRAM

MIC. INPUT Balanced Microphone Input. Pin 2 [+] with switchable Phantom Power. 200 ohm Impedance.
MIC. ATTEN. Eleven Position Input Attenuator Network (Pad) with a range from -20dB to 0dB in 2dB increments. The Microphone Attenuator is a Pad network that will change the impedance of the input load. Subsequently, the increased impedance will change the character of the microphone response changing the colour of the signal.
–10dB PAD On/Off Switch for fixed 10 dB input pad.
BASS LIFT A unique passive filter circuit to compensate for a loss in low frequencies when using microphones with a figure-of-eight pick-up pattern.
AMPLIFIER The amplifier consists of two valve stages, resistance-capacitance coupled with two loops of negative feedback. In the block diagram, the input and output transformers are nested in the amplifier section.
GAIN CONTROLS Four Position Rotary Selector to control amplifier gain (frequency compensated) fixed at 34dB, 40dB, and 46dB. The optimal setting for the Gain control is 40dB. Not only does this conform to the original specifications, but it has the best colour for general purposes from vocal to instrument recording. 
POLARITY The Polarity reverse switch reverses the output phase from Pin 2 [+] to Pin 3 [+]
OUTPUT Floating Balanced Line Level output. Pin 2 [+]


R.47 CONTROLS

1. MIC. ATTEN. (dB) Eleven Position Input Attenuator Network (Pad) with a range from -20dB to 0dB in 2dB increments.
2. –10dB PAD On/Off Switch for fixed 10 dB input pad.
3. GAIN Four Position Rotary Selector to control amplifier gain (frequency compensated) fixed at 34dB, 40dB, and 46dB. 
4. POLARITY On/Off Switch for polarity (phase) reversal of the output signal.
5. +48V On/Off Switch for supplying phantom power (48V) to non-valve condenser microphones.
6. BASS LIFT On/Off Switch for a unique passive filter circuit to compensate for a loss in low frequencies when using microphones with a figure of 8 pick-up pattern.
7. GAIN TRIM Locked fine gain adjustment control for balancing gains of matched pairs of R.47 amplifiers.  The range of adjustment depends on the setting of the main gain control (# 3 above) but is approx. +/- 1 dB.
8. STUDIO REGISTRATION Custom units require component and tube matching. These are issued with the Studio Name and Serial Number engraved on the front panel.
9. POWER On/Off switch for main AC power.