Twin-Iso™ Using & Applications

The following is a basic rundown on using the Radial Twin-Iso. Complete details may be found by downloading the Twin-Iso user manual.


Following the block diagram from left to right, the Twin-Iso features two discrete transformer isolated signal paths for true 2-channel operation without crosstalk. The Twin-Iso is designed to handle standard +4dB line level signals with 20dB of additional headroom for a total of +24dB signal handling.

With 100% transformer isolation, the Twin-Iso is ideal for demanding applications such as sub-mixing multiple consoles for festivals or connecting distant amp racks on delayed towers where a separate power grid or a generator is supplying electrical power.

To assure absolute phase is maintained, a polarity reverse switch on each channel allows sub-mixing directly to console sub-group inputs, where polarity reverse is often unavailable. This also makes the Twin-Iso ideal for amp racks or distribution amplifiers for side fills, front-of-stage (under cluster) cabinets and balcony reinforcement.

Using the Twin-Iso

The Twin-Iso is plug & play, easy to use and is usually positioned at the send end of the cable. Start by making sure all equipment being connected is turned off and volume levels are at zero. Then, simply insert the Twin-Iso in between the two devices that you wish to isolate using standard XLR cables. Once connected, make sure all pads, polarity and ground lift switches on the Twin-Iso are in the OUT position. Now turn on the two devices and slowly raise the level.

There are two types of switches on the Twin-Iso: A ground lift switch and a polarity reverse. The ground lift switch will lift the electrical ground between the input and output side of the Twin-Iso. Leaving the switch in the OUT position assumes you want the Twin-Iso grounded via both the source and receive devices. Lifting the ground will disconnect the ground path at the Twin-Iso input. If you hear noise, try lifting the ground.

The 180° polarity reverse is designed to perform several functions: It can be used to bring two pieces of gear into ''phase' when interfacing new devices with older equipment that may have been designed before the AES standard was established. You can also use it to flip the polarity going to a remote loudspeaker system as a means of moving a room mode or frequency bump caused by phase addition or cancellation. This can be particularly useful when amplifying acoustic instruments that may have a problematic resonant frequency.

Combining two mixers

Sub-mixing one console to another is often done by sending the line level out from one console into the mic input channel of another. This is not the ideal method of sub mixing as it requires reducing the sensitivity of the mic input channel to handle the high output from the mixer. If at all possible, try using a line level input such as a sub-group in or aux in or see if you can bypass the mic preamp and bridge the two using a Twin-Iso to eliminate noise.

Isolating amp racks

One of the most common problems in night clubs, concert venues and live touring is connecting two distant devices together. More often than not, the electrical power is not well distributed and you may find that when these are connected buzz and hum caused by ground loops will appear. Placing a Twin-Iso at the output of the mixing console will often solve the problem.