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Twin-Servo™ Using & Applications

The following is a short 'how to approach the 500 series module Twin-Servo'. For more information, we invite you to download the manual. (PDF download)

Making Connections

Before making connections, ensure your audio system is turned off and volume levels turned down. Hot swapping or inserting the module into a 500 series power rack when power is on is not recommended as it can harm some equipment and shorten the lifespan of the card edge connectors. Gently slide the Twin-Servo module into place ensuring you align the card edge with the 15-pin receptacle. If you have a newer Radial Workhorse, the nylon guides make this easy. The Twin-Servo comes with a pair of handy ThumbSet™ thumb screws. These should be hand-tightened to secure the module in place before use.

Your power rack will likely be equipped with XLR inputs and outputs for each strip. Connect your microphone to either the female XLR input on the rear panel or the handy front panel Combo connector. These are wired in parallel and only one should be used at any one time. Connect the output using the male XLR on the power rack to your recording system. Ensure the volume levels on your recording system are turned off and set the volume control on the Twin-Servo fully counter-clockwise to 7:00 o'clock. You are now ready to turn on your power rack and recording system. Note that there is no power switch on the Twin-Servo. As soon as your power rack is turned on, the Twin-Servo will spring to life.

If you are using a condenser microphone, activate the phantom power by depressing the front panel 48V switch. All other switches should be in the out position. Slowly increase the volume on your recording system and then turn up the volume on the Twin-Servo. It is always best to test at low volumes as this will reduce the opportunity of damaging more sensitive components such as tweeters should a connection be improperly seated. You should now hear the audio and see activity on the 10 bar LED meter.

The Control Panel

The 10 Segment LED

The Twin-Servo is equipped with a 10 segment LED meter that gives you instant visual feedback of the incoming input signal. Although the Twin-Servo is unlikely to ever distort, keeping the signal within normal working range will ensure optimal signal to noise. Turn up the level control by testing for maximum volume. When in the red, turn down for headroom and you are set to go.

180º Polarity Reverse

Another handy feature on the Twin-Servo is the polarity reverse switch. This can be used to better phase-align two sources such as two microphones that may be spaced differently in a room or when combining a microphone with a direct box. You can also increase the width of the stereo field when the two mics are out of phase. It is also great for matching up older audio gear that may not follow the AES standard with pin-2 hot.

High-Pass Filter (HPF)

One of the truly unique advantages with the Twin-Servo is the amazing frequency response. Most preamps are unable to effectively reproduce frequencies below 20Hz. The Twin-Servo actually measures down to 5Hz! With so much bass, you will hear low end like never before. The downside is that with so much bass to work with, it may be excessive, particularly when recording several acoustic instruments together. The solution: reduce the resonance and excessive bass by engaging the high-pass filter. This is one of the most practical features on the Twin-Servo. When engaged, it gently rolls off bottom end below 80Hz and can help clean up the mix.

-15dB Pad

A pad is primarily used to reduce the preamp's input sensitivity so that when confronted with an extra high level output signal, it will not overload the input stage of the mic preamp and cause distortion. As the Twin-Servo has so much headroom, it will be unlikely that you will ever need to use this feature. But it's there just in case.

48V Phantom

This switch activates standard 48V phantom power to remotely feed your condenser mic, active direct box or McBoost mic booster. When on, 48 volts DC is sent from the Twin-Servo using the pin-1 (ground) and pin-2 (hot) wires to power the connected device. Simply engage if needed. Be careful to turn off your audio system before activating! This will avoid a big 'bang' in your audio system due to the power-turn-on transient.

Ground Lift

There is a hidden ground lift switch (mini slider) that lets you lift the ground on the front and rear XLR inputs. As the Twin-Servo is equipped with an input transformer, you will likely never need to lift the ground. This should be set in the upward position. However, a unique situation could arise where you may incur noise. To lift the ground, you have to pull the module from your power rack and then move the slider downwards towards the 15-pin card edge connector. The ground lift switch does not affect the ¼" guitar input portion of the Combo jack or the output side of the Twin-Servo. Note that when the ground is lifted, the Twin-Servo will no longer pass 48V phantom power to your microphone.

HI-Z Input and Omniport™

The Twin-Servo has two instrument input options. The immediately obvious one is on the front panel - as part of the Neutrik combo connector. Note that this is a standard hi-Z ¼" instrument input and using a ¼" TRS connector is not recommended. The second is via the Omniport™ for those that are equipped with a Radial 500 series power rack. Both are connected in parallel but as soon as you engage the front panel jack, it will automatically switch the rear panel ¼" input off.


Although preventative safety measures have been designed into Radial 500 series products we strictly advice against hot-swapping modules or plugging and unplugging them when the Workhorse or other 500 series rack are powered on. Hot swapping can cause connection sparks at the card-edge connector that could send damaging transients to other equipment. This also greatly reduces the life span of the contacts. Damage due to hot swapping is not covered under warranty. There are no user serviceable parts inside.