Radio Design Labs FP-MX3R
Remote Controlled Line Level Mixer


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Radio Design Labs' FP-MX3R is a great choice where a user-accessible mixer must control the volume of multiple sources.  The mixer accepts balanced or unbalanced audio sources through a detachable terminal block.  FP-MX3R outputs are provided in balanced and unbalanced formats.  Two unbalanced outputs are available to feed the mono mixer output to a stereo amplifier input.  Remote control of the mixer allows audio signals to be kept at a single equipment location.  Audio is mixed by VCA circuits that are adjusted by control signals from the remote control.

NOTE: Radio Design Labs' PS-24AS power supply is NOT included but is required in order to power this product.  Please see the "Accessories" tab or click here for more information on the PS-24AS power supply.

Each input is equipped with an INPUT GAIN trimmer to set the proper operating level for each source.  A standard RDL dual-LED VU meter provides visual indication of the output level from the mixer.  Each input is normally adjusted to produce +4 dBu on the VU meter when the corresponding remote control channel is adjusted to maximum.  This assures ample headroom at all normal operating levels.  The mixer output is mono.  The output is available on a single balanced detachable terminal block or on two unbalanced RCA jacks intended to connect directly to the stereo input of a power amplifier.

The AUDIO LED illuminates whenever audio is present at the output of the mixer, defined as greater than 35 dB below +4 dBu.  This threshold triggers the AUDIO DETECT OUTPUTS.  Two open collectors are provided on a detachable terminal block.  One of these terminals switches low when audio is present, and may be used to switch amplifiers or other system components on.  The other terminal is pulled low when audio is not present.  It is intended for muting the digital carrier of power amplifiers equipped for remote muting.  Either of these terminals may be used to trigger a variety of other RDL modules or OEM equipment.  The use of these terminals to shut down unused equipment can produce effective system energy and cost savings.  These control terminals normally remain triggered for 10 minutes after audio is absent.  The delay can be increased to 20 minutes using a ground jumper on the terminal block.

The mixer levels are set by RDL remote controls that connect directly to the FP-MX3R through an RJ45 jack using standard twisted pair cable.  The control ports on the mixer and remote controls are color-coded light blue to distinguish them from other twisted pair jacks.  The mixer provides power to the remote control.  Either a two- or three-channel remote control may be used.  If remote mixing of only two channels is needed, a two channel remote may be used.  INPUT 3 becomes the input channel that is not remotely controlled.  This input may be left active at a level set on the corresponding INPUT GAIN control, typically for a paging or music source, or may be disabled by a switch set during installation.  If the cable connected to the remote control becomes disconnected, the mixer output mutes.


  • 3-Channel Remote-Controlled Audio Mixer
  • VCA Level Control for Each Input
  • Balanced or Unbalanced Inputs
  • Balanced and Unbalanced Outputs
  • Two Mono Unbalanced Outputs to Feed Stereo Amplifier
  • Inputs and Outputs on Detachable Connectors
  • Twisted Pair Interconnection to Remote Control
  • Directly Controlled by RDL Remote Controls with 2 or 3 channels
  • Fixed Level Possible for Input 3 if Two Channel Remote Used
  • Paging Source May Connect to Input 3
  • Front-Panel Gain Trim for Standard Audio Line Levels
  • Dual-LED VU Meter Displays Mixer Output Level
  • Audio Presence Detector Controls Open-Collector Outputs
  • Detector Outputs Intended to Enable Power Amplifiers or System Power
  • Energy Savings Possible Using Detector Outputs
  • Selectable 10 or 20 Minute Detector Release Delay


  • Inputs (3): Balanced or unbalanced line level
  • Input Connections: Detachable Terminal Blocks
  • Input Signal Range: -20 dBV to +8 dBu, adjustable (for +4 dBu output)
  • Outputs (3): 150 O balanced; 1 kO unbalanced (2)
  • Output Connections: Detachable Terminal Block (balanced); RCA Phono Jacks (unbalanced)
  • Output Level: +4 dBu balanced, -10 dBV unbalanced
  • Frequency Response: 20 Hz to 20 kHz (+/- 0.25 dB)
  • THD+N: < 0.05% (20 Hz to 20 kHz); <0.02% (1 kHz)
  • Noise below +4 dBu: < -100 dB (all channels off); <-75 dB (any channel on); <-70 dB (all channels on)
  • Headroom above +4 dBu: > 18 dB
  • CMRR: > 50 dB (50 Hz to 150 Hz)
  • VCA attenuation: >90 dB (each input, remote control volume off)
  • Indicators (3): Dual-LED VU meter (2); Audio present (threshold = 35 dB below +4 dBu output)
  • Power Connections (3): Terminal block; dc power jack (2)
  • Power Requirement: 24 Vdc @ 120 mA plus connected control output loads, if any
  • Overall Dimensions: 1.42" H x 3.25" W x 8.14" L (3.61 x 8.26 x 20.6756 cm)
24 VDC 500mA Switching Power SupplyRadio Design Labs PS-24AS 24 VDC 500mA Switching Power Supply

Radio Design Labs' PS-24AS is a 24 Vdc switching power supply with a North American AC plug.  500 mA, dc plug.Specifications: Input: 100 to 240 VACOutput: 24 Vdc, 500 mA (UL, CSA)Dimensions: 1.65" x 2.75" x 1.45" (4.2 x 7 x 3.7 ...

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