The Versatile RU-MLD4 Audio Distribution Amplifier

The RU-MLD4 is a multipurpose 1 X 4 mono Audio Distribution Amplifier with the flexibility, reliability and quality engineered into every RDL product. The RU-MLD4 input and each of the four outputs are switch selectable between microphone and line-level. A user-adjustable front panel gain trimmer and RDL Dual-led VU meter are provided to simplify set-up. […]

STICK-ON Mic Preamps – Which One do I need?

RDL STM-1, STM-2 and STM-3 Microphone Preamplifiers all seem to look alike and indeed they do have some similarities: GENERAL Identical noise, distortion, frequency response, headroom and common mode rejection specifications. Identical power requirements. 24 vdc @ 25 mA or 12 vdc with a 6 dB reduction in headroom. INPUT Balanced or unbalanced Balanced input accepts […]

Automatic Audio Ducking

In audio, a Ducker is a device used for lowering the level of one audio source based on the presence of another audio source. Often used in paging systems to lower the level of background music during a page, duckers are also used for voiceovers in radio, television and film production. The RDL ST-VP2 Automatic […]

STICK-ON® Compressor/Limiter

When line-level inputs need to be protected against level increases or overloads that cause clipping and distortion, the RDL ST-CL2 Compressor/Limiter is the ideal solution. The ST-CL2 is designed to maintain a constant average output level and provide effective peak control over a wide range of input levels. It can be used to prevent overloading […]

Tidy Up Your Projector / Amplifier Installations

The RDL PM-3T Pole Mount tray provides the perfect solution for the tidy, professional installation of any RU, TX, FP or STICK-ON Power Amplifier and Power Supply that is used in conjunction with a projector.  The design of the PM-3T allows it to be quickly installed above the projector even after the projector is in […]

Switching Controlled by an Audio Signal

RDL ST-ACR Series Audio Controlled Relays are used in any application where an audio signal must be used to create either a relay closure or Open-Collector output to control another piece of equipment or a circuit. Common applications include:   Juke Box overrides Background Music AN-2024 Silence or “Dead Air” Sensor in broadcast environments Automatic […]

The Ultra Flexible SOURCEFLEX™ Distributed Audio System

The RDL SourceFlex system is used extensively in entertainment applications such as Sports Bars, Restaurants and Fitness Centers. With the capability of distributing up to 8 audio programs to any number of SourceFlex listening stations, this highly flexible system is equally at home in: Dental Offices Multi-language Interpretation Systems Multi-station Broadcast Outlets SourceFlex listening stations […]

Compact STICK-ON Audio Distribution

Ever have the need to split an audio signal to 3 separate locations?  How about balance a line-level audio signal and then distribute it?  Maybe your installation requires audio distribution with gain or loss?  Need to distribute an audio line but have no room for a larger conventional distribution amplifier?  Then we may just have […]

High Quality Audio Amplification in the Most Extreme Heat

There are times when it is necessary to install a power amplifier in an uncontrolled environment where ambient temperatures can exceed the normal operating range of traditional electronic equipment. The RDL FP-PA18H 18 W Mono Hi-Temp Audio Amplifier is the ideal solution for these types of environments. It is designed to operate in ambient temperatures […]

Power Supplies

All active RDL modules operate on 24 VDC. Current requirements for each module differ. Using a 24 volt AC power adaptor will likely cause the module to release its MAGIC SMOKE and will certainly void the warranty. Most modules do not ship with a power supply. The reasoning behind this is that in many cases […]

RLC10K Remote Level Control

If you’ve ever used RDL’s ST-VCA3, RU-VCA2 or RU-VCA2D voltage controlled amplifiers, you are without a doubt familiar with the RLC10K remote level control. This premium quality, all-metal remote control is well known for its ease of installation and professional, aesthetic appearance. What might not be so well known is how easily the RCL10K can […]

Low Input Signal?

Do you love the RDL TX-J2 but sometimes run into situations where your input signal is a little low and could use a bit of gain?  Take a look at our TX-LC2 and prepare to fall in love again!  Like the TX-J2, the TX-LC2 mixes two unbalanced line-level signals into a mono balanced output but […]

Rack Mounting Decora® Remote Controls and Panels

Decora® style remote controls and wall panels are typically mounted in a wall, but given the compact design and wide variety of products available in RDL’s D-Series product offering, RDL customers may wish to mount these products in a rack.  RDL remote controls and D-series panels can be readily rack mounted using the RM-D3 or […]


ANALOG TO DIGITAL / DIGITAL TO ANALOG CONVERSION Broadcasters, mastering studios and system integrators rely on RDL to provide Analog to Digital and Digital to Analog converters with low distortion, low noise and flat frequency response. The HR-ADC1 provides conversion of balanced or unbalanced line-level analog audio to AES/EBU, AES-3ID or Coaxial S/PDIF digital audio […]

Ultra-Compact 40 Watt Stereo Power Amplifiers

Modern flat panel televisions and video displays can provide a wonderful visual experience, but many fall short when it comes to the audio that goes along with the video. On many models the built in loudspeakers are next to each other immediately under the display itself. The proximity of these limits the stereo experience. Furthermore […]


In a perfect world, the audio connections between different pieces of gear would all be alike.  Unfortunately, this is not the case and likely never will be. Balanced and unbalanced audio lines (1) are not inherently compatible and unless they have some help they don’t always play well together. For passive conversion from balanced to […]

Audio Message Repeater for Retail Stores, Hospitals and More

Transportation centers, hospitals, retail outlets, entertainment centers and factories often require that a voice message or series of voice messages be repeated over the public address system at given intervals or upon certain conditions. The RDL FP-MR2 Message Repeater provides up to one minute and forty seconds of music quality digital message storage. Playback of […]

Power Supply Mounting

External power supplies and the associated power cords and low voltage leads can present a problem and even a safety hazard in some, especially compact, A/V installations. For installations requiring the use of multiple power supplies, RDL offers numerous solutions for mounting both wall wart and desktop type power supplies: WH1 and WH2 “Warthog” Power […]

Push-to-Talk Microphone Preamplifier

Some microphones equipped with a push-to-talk function may not mute and unmute as quietly as desired, or some installations (typically paging) may have a microphone which does not have a push-to-talk feature. The RDL STM-2X Switchable Microphone Preamplifier is the perfect solution when quiet on / off switching is required for dynamic or condenser microphones. […]

70V to Unbalanced Line-Level Conversion

Do you ever need to feed the audio from a 70V distributed loud speaker system into a line-level device in a remote location? Do you ever need a few more loudspeakers than your existing 70V amplifier can drive but have no convenient line-level audio to run into a local amplifier? Well RDL has the module for […]

Kill Ground Loop Hum with the EZ-HK1 Stereo Audio Hum Killer

Ground loop hum is often encountered whenever two pieces of unbalanced audio equipment are connected together but are being powered from outlets on different circuits. The difference in ground potential between two pieces of unbalanced audio equipment can be a major cause of noise in audio systems today. The EZ-HK1 eliminates hum due to ground loops […]


Turn on a visual indicator, mute a local sound system or switch loudspeaker loads anytime your paging system is active. The RDL TX-PCR1 Paging Controlled Relay can accomplish these chores and more. Simply connect the input of the TX-PCR1 to any 25 V, 70 V or 100 V (8 Ohm up to 75 Watts) speaker […]


When unbalanced stereo (consumer) lines need to be combined and balanced the RDL TX-J2 Unbalanced Input Transformer is a handy tool to have available. The TX-J2 provides two phono jack inputs that are passively combined and balanced through transformers configured to reject induced hum. A balanced line-level output is provided on a detachable terminal block […]


Are you stuck with a flat panel display that only has speaker level outputs? Do you need to add more speakers and amplifiers to an existing speaker circuit in a remote location? The RDL TX-8A 4 Ohm / 8 Ohm Input Interface will simplify the process of integrating these pieces of equipment with the rest […]

Control One Audio Level From Multiple Locations

Level control from a single remote location is a popular application made simple using two RDL modules. The RDL RLC10K Remote Level Control mounts in the wall; the ST‑VCA2 Voltage Controlled Amplifier mounts in the rack (or wherever the power amplifier is located!). The ST‑VCA2 adjusts the line input level to an audio power amplifier […]

More Phantom Power to You

The RDL STD‑150 is a passive audio combiner/divider designed around the standard microphone output impedance of 150 Ohms. If you need to mix two or three microphones at the same level or if you need to split a mic signal to two or three locations, the STD‑150 is a practical yet elegant approach. If the […]

RDL’s Secret Test Arsenal

The PT‑AMG2 Portable Audio Signal Generator and Monitor provides a rugged compact solution for the numerous checks required when installing and setting up a system. The PT‑AMG2 provides a stable tone generator at a reference level of +4 dBu (switch selectable to +6 dBu) on its balanced output and -10 dBu on its unbalanced output. […]

Remote 4×1 Audio Source Selection

The RDL ST-SX4 is the ideal choice when a compact solution for 4×1 unbalanced audio selection is required. The ST-SX4 is a small, simple and cost effective four input audio selector that may be remote conrolled by the RDL RC4-ST Decora® style remote control. The stainless version of this remote control, the RC4-STS, may be […]

Tired of Blowing Your Horns?

Tired of blowing your horns? Need horn loud speaker protection? The RDL ST-HP3 is the device for you. The ST-HP3 is a high quality dual high pass filter offering big horn protection in a small package. The ST-HP3 has one input and dual outputs. The input may be wired either unbalanced or balanced and accepts […]

Multi-point Twisted Pair

RDL Format A twisted pair products make it easy transmit up to three channels of high quality audio from one point to another using twisted pair cabling. Format A products utilize RJ-45 connectors which make field terminations fast and easy. The flexible design of these modules also makes them useful for multi-point applications. Format A […]

LED meter on mixer

The two LED VU meter found in the ST-UMX3 is a good example of how this simple level indicator can be used in equipment setup. The green LED is an indication of average (VU ballistics) audio level. It starts to illuminate when the line level output of the mixer is at -11 dBu. It will […]

Phantom Power

Phantom power specifications are well standardized under IEC 61938 and DIN 45 596. Acceptable voltages and current supply capabilities are well defined. Positive phantom voltage is found on the balanced microphone output terminals (pins 2 and 3 of an XLR connector) with the ground return on the shield. There is no such standard for the […]

ST-TC1 Telco Line Simulator

The ST-TC1 is a device that simulates a telephone company (telco) line for connection to a telephone switching unit (KSU). The ST-TC1 becomes the provider of an inbound line to your switch, so when any of your instruments pick up the line provided by the ST-TC1, a contact closure is provided and bi-directional audio is […]

Connecting Unbalanced Audio To Or From An RDL Product

For most of our products the audio signal input and output wire is connected to the input or output positive (+) terminal. The audio return shield is connected to signal ground. The unused negative (-) input terminal is jumpered to signal ground. The unused negative (-) output terminal has no connection or may be used […]

dB Defined

A decibel (dB) is a ratio unit for expressing signal amplitudes. If the amplitudes are expressed in voltage: dB=20 log (V1/V2). If the amplitudes are expressed in power: dB=10 log (P1/P2). In digital audio systems, decibels are often expressed in dBFS, the voltage value below the value produced by a full scale digital audio signal. […]

Impedance Simplified

Impedance is the resistance of audio circuits to audio signals. Any audio input has an impedance, as does any audio output. Modern input stages are typically high impedance, often 10 kOhms or higher. These inputs accept the input signal without demanding power from the prior equipment output. For accurate amplification, it is generally accepted that […]

Connecting a TX-1A Backwards

The TX-1A is used primarily for galvanic isolation and format conversion between equipment. Conversion from -10 dBV consumer level up to +4 dBu professional level requires voltage gain. The transformer in the TX-1A has a 1:1 ratio and uses an adjustable attenuator circuit at its output to lower the output signal to the level required. […]

The Difference Between Balanced and Unbalanced Audio

Balanced audio carries equal but opposite signals on two conductors. These symmetrical signals are relatively immune from induced hum and noise. Frequently, balanced cables also are shielded. The shield is independent from either of the signal conductors. Unbalanced audio is carried on a single conductor relative to the shield. In unbalanced cables, the shield is […]