Understanding the Twin Iso

Over the past decade, the move away from transformer coupled inputs on consoles, crossovers and active speakers to more affordable op-amps has yielded greater ‘bang for the buck’ at the expense of greater susceptibility to noise caused by stray voltages in real-world environments. Outside of the laboratory, ‘perfectly balanced’ signals are severely compromised due to imperfections in wiring, less than perfect power distribution and differing ground reference voltages from equipment. The result is generally hum, buzz and noise caused by so-called ground loops.

A transformer provides a magnetic bridge that allows a source and destination to be interfaced while virtually eliminating that nasty 60-cycle hum that can be the scourge of the sound engineer. No other
company produces higher quality transformers than Jensen. Renowned for their warm Bessel curve, high signal handling capacity and extended frequency response, Jensen transformers are the pro-choice when interfacing equipment where optimum sound quality is desired.







You can mount up to eight Twin-Iso's into a Radial J-Rak for 16 channels of isolation.

Following the block diagram from left to right, the Twin-Iso features two discrete signal paths with two Jensen transformers for true 2-channel operations without crosstalk. The Twin-Iso is designed to handle standard +4dB line level signals with 16dB of additional headroom for a total of +20dB 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 gas-powered 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.

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 pad, polarity and ground lift switches on the Twin-Iso are in the OUT position. Now turn on the two devices.

Sub-mixing one console to another is done through channel strips, sub-groups or auxiliary inputs. In each case, the output of the 1st mixer will be line-level. This dictates that you should be coming into the 2nd mixer at line-level, therefore bypassing the mic preamp. Due to the fact that there are never enough input channels, most engineers prefer to sub-mix through the auxiliary path if available. The downside is that the aux inputs generally have fewer features than the mic input strips such as a polarity reverse. The good news here is that the Twin Iso is equipped with a 180º polarity reverse that makes up for this deficiency.

A simple way to check polarity is by splitting a low frequency steady source such as a constant bass tone from a synthesizer or organ to both consoles. Start by listening to the main console and then increase the level of the second console. If the bass signal increases, then the polarity is likely matched. If the signal ‘thins out’, then the two mixers may have their polarities reversed. Simply depress the 180º polarity reverse switch on the Twin-Iso to fix.