J-Iso™ and Pro-Iso™ Using & Applications

The Radial J-Iso is plug and play simple to use. This short section quickly outlines how it is done. For more details, we invite you to download the complete J-Iso manual by clicking on the icon at left.


Both the J-Iso and Pro-Iso share the exact same feature set and functionality. The only difference is the type of transformer that is employed. The J-Iso is loaded with two premium Jensen transformers, the Pro-Iso uses two high performance Radial transformers.

The J•ISO and ProISO do not require any power to operate. Just plug them in and they are ready to use. The J-Iso follows a very simple circuit path with balanced line level inputs, RF noise filters, a dual channel level control and transformers that feed the various output connections. The 100% passive circuit will not add any noise to the signal passing through.

Making connections

Before making any connections, it is good practice to turn all signal levels down. This will help avoid plug in transients that could potentially harm more sensitive equipment such as high frequency tweeters.

Basic connection

Click to view larger.
  1. Connect a stereo balanced +4dB line out from a mixing console to the XLR-female LEFT & RIGHT INPUTS.
  2. Connect one or more of the stereo output jacks to your -10dB device.
  3. Set the OUTPUT LEVEL control full clockwise.
  4. Slowly turn the system level up and listen for noise. If you here hum or buzz depress the ground lift switch to isolate the device.
  5. Rotate the OUTPUT LEVEL control counter-clockwise to reduce the signal level going to your -10dB device if necessary.


Location and cable length

While balanced cables can be run great distances the rule for unbalanced cables is shorter is better. Because of this the J-Iso is always located near your -10dB device. This helps prevent noise and signal loss.

Up to 300 meters
Up to 4 meters

Input panel

J-Iso input panel and ground lift switch.

The XLR connectors follow the AES standard with pin-1 ground, pin-2 (+) and pin-3 (-). The +4dB line level input is standard on most equipment today and will be typical of a mixing console or preamp output. Connect the output from your line-level device here.

Using the ground lift

If you hear hum or buzz, simply depress the ground lift switch on the input panel side. This will disconnect the ground on both XLR pin-1s at the source and isolate the -10dB device connected to the J-Iso.

Output panel

Output panel jacks and recessed level control.

The J-Iso's output panel is fully outfitted with a variety of connectors that are used to deliver an unbalanced -10dB (typical) signal to a consumer level device. This unbalanced line level signal is common to hi-fi systems, CD players, video players and computers.

The ¼" and RCA connectors follow left-right convention. The 3.5mm (1/8") jack is a mini TRS that is commonly found on hand-held devices and on portable computers. It is configured in stereo with tip-left, ring-right and sleeve-ground. Mini TRS cables are becoming more and more popular due to the proliferation of compact digital devices.

Selecting the right output connector is a matter of preference and of course application. Given the choice, we recommend using the ¼" and RCA connectors over the 3.5mm connector as these provide a more 'positive' contact due to the larger size. To aviod noise and signal loss use the shortest possible cables to connect the J-Iso output to your -10dB receiving device.

Setting the output level

As the J-Iso is intended for stereo use, the recessed OUTPUT LEVEL control works simultaneously on both channels. Full output is achieved by rotating the control clockwise. The stereo output is attenuated as the control is rotated counter-clockwise.

Start by setting the J-Iso output level control completely clockwise so that the levels are at full or unity gain. This control is purposely recessed so that it can be set and then forgotten. This precautionary measure ensures that the control will not easily be readjusted by mistake. Use a screwdriver or guitar pick to access the control.

Make sure levels are down on your source device. Hit play and increase the level from the source, then... slowly turn up the other levels. It is good practice to always test at low levels. Increase the source level until you hear distortion and reduce the level by approximately ¼ turn. This will give you some safety margin for added headroom without having to make further adjustments.