RDL ST-UMX3 3x1 Universal Audio Mixer 3 Mic or Line In x 1 Mic or Li

MSRP: $238.80
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The ST-UMX3 is a three-channel audio mixer for combining mic-level or line-level signals to a single output. A MIC/LINE switch is provided for each input. A separate MIC/ LINE switch selects the output level. Each input features a separate preamplifier circuit, which isolates it from the other inputs. An audio taper single turn gain adjustment is provided for each of the three input preamps. Signals from the three preamps are actively summed and fed to the output amplifier which includes an RDL® dual-LED VU meter.

Each input level is set while observing the LED output level meter. The dual-LED output meter follows standard VU ballistics. The intensity of the green LED progresses from minimum at -11 dBu to full intensity at +4 dBu.

The flexibility of switching each input and the output between MIC or LINE allows installers to address a wide variety of mixing solutions with only one product type.


  • Audio Mixing with Up To Three Inputs
  • Switch-Selectable Mic or Line Inputs
  • Switch-Selectable Mic or Line Output
  • Add Additional Microphone or Line Level Inputs to an Existing Mixer
  • Combine Signals of Different Level, Impedance, or Balanced /Unbalanced Configuration


Inputs (3):
Mic: 600 Ω; Line: 50 kΩ, balanced

Maximum Input Signal:
Mic: -18 dBu; Line: +25 dBu

Gain (each input):
Mic: Adjustable from OFF to 60 dB
Line: Adjustable from OFF to 21 dB

150 Ω balanced; 75 Ω unbalanced

Output Signal:
Mic: 50 dB below line level
Line: +4 dBu nominal

< 0.006%

Mic (@ 50 dB gain): < 0.04%
Line: < 0.008%

Freq. Response:
Mic: 50 Hz to 100 kHz (± 1 dB)
Line: 10 Hz to 100 kHz (± 0.05 dB)

Noise (each input):
Mic: < -70 dB (50 dB gain)
Line: < -82 dB (unity gain)

18 dB

Mic: > 60 dB
Line: > 50 dB, (50 to 120 Hz)

Ambient Operating Environment:
0° C to 55° C

Power Requirement:

Package Type:
Cardboard Box

Package Dimensions:
2 x 2 x 4 in.

Shipping Weight:
0.175 lbs.

WEEE weight:
0.12 lbs.

Tariff code:


RDL Three-Year Limited Warranty Installation of these products by the Purchaser shall constitute Purchaser’s acknowledgement and acceptance of the terms and conditions for sale and of this warranty, and shall constitute the Purchaser’s determination of the suitability of this product for the Purchaser’s intended application. Radio Design Labs, Inc., also referred to as RDL®, warrants to the Purchaser that products manufactured by RDL are free from defects in material and workmanship. This warranty applies to the period of three years from the date of shipment, except for component parts or products purchased from other sources and supplied by RDL. Such component parts or products bear only the warranty of the manufacturer thereof in effect at the time of shipment to the Purchaser. RDL will, without charge, and after written notice has been received and acknowledged by RDL, repair an RDL product if proved to be defective according to the usage of the trade, when such equipment is received by RDL at the location it designates with shipment costs prepaid by the Purchaser. RDL shall not be liable for any expense whether for repairs, replacements, material, service, or otherwise, incurred by the Purchaser or modifications made by the Purchaser to the product. No equipment shall be deemed defective if it shall fail to operate in a normal or proper manner due to exposure to excessive moisture in the atmosphere, excessive temperature extremes, improper environmental cleanliness, or any other environment not consistent with the principles of good engineering practice. In no event shall RDL have any liability for consequential damage or expense directly or indirectly arising from the use of the products, or any inability to use it either separately or in combination with other equipment or materials, or from any other cause, whether used in accordance with instructions or not. This warranty is void if equipment is altered in any way by other than RDL. RDL products are NOT intended for use in life support appliances, devices, or systems. Use of RDL products in such applications is done solely at the liability of the reseller/installer and/or end user. RDL reserves the right to change design parameters and specifications at any time without notice. The performance measurements reflect the products at the time of printing. This warranty is in lieu of all others, either expressed or implied. No representative is authorized to assume for RDL any other liability in connection with RDL products.