Description

Requisite Audio OS1 Preamplifier MK II

MICROPHONE PREAMPLIFIER

The OS1 was developed around the 6SN7 vacuum tube. The 6SN7 was developed in 1939 and, over the years, has become my personal favorite and often considered king of the general-purpose audio triodes. High headroom and broad frequency response are the hallmarks of the OS1. The OS1 can drive a 600-ohm load at a +40dB output and has an internal frequency response of 10Hz to 600,000Hz. This is a very special microphone preamplifier, designed especially for the most demanding audio professional.

TECHNICAL DETAILS

FRONT

  • Variable Microphone Impedance – Six Positions
  • Hi-Pass Filter – Four Positions
  • Mic/DI Gain – Infinitely Variable
  • Meter Range – Three Positions
  • DI Input
  • 20dB Pad
  • Phantom Power
  • Polarity Reverse
  • Extra Large VU Meter

REAR

  • Power Supply Inlet (choice of Tube or Solid-State Supply)
  • Transformer Balanced XLR Output (pin 2 HI)
  • Tube Channel (6SN7 – shock mounted – 3 each)
  • Transformer Balanced XLR Input (pin 2 HI)

INTERNAL

  • Solid-Core Copper/Silver Wire with Teflon Dielectric
  • Handwired, Point-To-Point Throughout (only Meter/Phantom on PCB)
  • Custom Input and Output Transformers
  • Audio Circuit Shock Mounted
  • Overbuilt – using highly rated, quality components

SPECIAL FEATURES

VARIABLE MICROPHONE IMPEDANCE

Microphone input impedance is selectable using a six-position rotary switch. Available Impedances are: 50, 200, 300, 600, 1200 and 2400-ohms.

VARIABLE HIGH-PASS FILTER

Low frequency response can be contoured with the variable High-Pass Filter. Positions available are: Flat, 35Hz, 70Hz and 120Hz, each with a slope of 12dB per octave. Frequencies are selected via four-position rotary switch.

VARIABLE VU METER RANGE

For monitoring the OS1’s prodigious output capabilities, Meter Range is selectable using a three-position rotary switch with +4dB, +10dB and +20dB ranges. Each position has it own calibration trimmer which can be adjusted to any level desired. As an example: the +20dB position can be calibrated to 0dB = +28dBFS. With the OS1, you still have 12dB of headroom beyond that!

SELECT A POWER SUPPLY

RTS-4A VACUUM TUBE

The RTS-4A is built on classic, no compromise design and techniques. It is tube regulated, tube rectified and capable of powering any Requisite Audio vacuum tube audio processor in current production. It is expandable from one to four channels. Filtering is accomplished using custom made poly/oil capacitors and a heavy duty audio frequency choke.

RECTIFIERS

Standard with the RTS-4A is the GZ34 (5AR4) tube rectifier. DC filtering is via custom AF Choke input & custom made oil & polyprophylene capacitors.

VOLTAGES

Power Supplied: B+, Heater, Meter Driver, Lamps. Power Required: The RTS-4A can operate on 115V or 230V mains.

  1. Single channel RTS-1A
  2. Dual Channel RTS-2A
  3. Three Channel RTS-3A
  4. Four Channel RTS-4A
OPS-2D SOLID STATE The OPS-2D is a single or dual-channel solid-state power supply designed to power all current production Requisite Audio vacuum tube audio processors: L2M MkIII, PAL Plus MkIII, OS1, SM 162 Summing Mixer and the SMX 1748 Summing Mixer Expander. The OPS-2D can be configured for single or dual-channel operation.

RECTIFIERS

Standard with the OPS-2D are ultra-fast, soft-recovery diodes with balancing resistors and polypropylene bypass caps. DC filtering is via Nichicon audio capacitors with polypropylene bypass caps. Power Supply coupling is via AF Chokes.

VOLTAGES

Power Supplied: B+, Heater, Meter Driver, Lamps. Power Required: The OPS-2D can operate on 115V or 230V mains.

    1. Single channel
    2. Dual Channel