MPD Specification

MPD inline attenuator

The MPD inline attenuator can be configured as 12dB, 18dB, or 24dB microphone level pads, a 12dB line matching pad (+4dBu to -10dBV), a 18dB or 24dB line-level pad, a 40dB line to mic level pad, a 620Ω load, a 12dB, 18dB, or 24dB passive mixing network, or a polarity inverter.  Custom values for attenuation and input impedance are available on request.  Polarity inversion may also be added to any balanced attenuator if specifically required for the intended application.

Microphone level pads are intended for use with condenser microphones on loud sources. Microphone level pads have a nominal input impedance of 2kΩ and will thus pass phantom power with minimum voltage drop.  Maximum input level is +20dBV.

Line level pads have input impedance of 7kΩ or higher and are thus not intended for use between microphone and amplifiers, but rather between line level outputs and inputs.  Maximum input level is +30dBV.

If required, the VPD fixed attenuator can tolerate higher levels of +26dBV for microphone input, and +36dBV for line-level input.

The special 620Ω load version reduces effective input impedance of a microphone preamplifier for tonal options with dynamic microphones (620Ω load not recommended for use with condenser microphones or line outputs).  Maximum input level is +12dBV.

The MPD inline attenuator may be ordered in many different cable formats, and is also available in the following barrel adaptor formats:

  • XLR-3-F to XLR-3-M adaptor
  • 1/4″ TRS-F to 1/4″ TRS-F adaptor
  • 1/4″ TS-F to 1/4″ TS-F adaptor
  • 1/4″ TRS-F to XLR-3-M adaptor
  • 1/4″ TS-F to XLR-3-M adaptor balun

Right-angle XLR adaptors can be built with either the male or female connector as the right-angle section.  Right-angle adaptors may also be ordered as a pass-through (no attenuation or polarity inversion).  Cables may also be ordered with right-angle connectors.

MPD inline attenuators are directional balanced or unbalanced (balanced “U”; unbalanced “L” pads), except RCA or TS cables and TS or TRS adaptors, which are symmetrical unbalanced or balanced (unbalanced “T”; balanced “H” pads).

Balanced to unbalanced attenuators, such as dual XLR-F to 3.5mm miniplug or 1/4″ TRS plug (stereo), and XLR-F to 1/4″ TS plug cables, must be wired for one of two options.  XLR-F pin 3 can be floating (not connected), which is the proper unbalanced wiring for active-balanced outputs, or grounded, which is the proper unbalanced wiring for transformer-balanced outputs.  Either wiring may be used with impedance-balanced outputs.

Unbalanced to balanced attenuators will be built as baluns, with the resistor network providing an impedance-balanced output from the attenuator.

MPD attenuator cables may be configured with up to six input connectors, in order to function as a passive mixing network.  Select the 12dB (two-channel only), 18dB (two- or three-channel) or 24dB (two to six channel) MIX options from the attenuator type menu.  Mixing networks are intended to connect from line-level outputs into a microphone- or consumer-level (-10dBV) input.  Three- to six-channel mixing networks must use XLR-3-M, 1/4″ TS or TRS jack output connectors; two-channel networks may use any output connector type.  Two-channel mixing networks may use mic/line narrow (balanced) or coax (unbalanced) cable type; three- to six-channel networks must use lavalier (balanced) or mini coax (unbalanced) cable type.  Each input node has a nominal input impedance of 2.5kΩ; output impedance is less than 500Ω.  Maximum input level is +22dBV.

An MPD with a stereo input connector may be configured as a stereo to mono passive mixing network; please request that function in the order notes.

The MPD attenuators use precision 1% tolerance metal film resistors, so matching between units will typically be within 0.1dB.