If maximum elimination of ‘ground loop’ buzz is the goal, an input type isolator located at the receive end of an interface cable is always the preferred solution. However, if the signal destination is unknown or may change with setup, an ISO-MAX isolator with an “O” in the model number (PO-2XR, for example) may be useful at the mixer’s balanced output. The isolator output can then drive either balanced or unbalanced equipment inputs with no risk of damage or misbehavior in the mixer, regardless of what kind of output stage it may use. There is generally a reduction in ‘ground loop’ hum but little effect on buzz.
A major benefit of Faraday shielding is high attenuation of RFI (radio frequency interference). ISO-MAX microphone isolators and “splitters” (model MS-2XX, for example) have outstanding rejection of RFI, especially at troublesome AM radio broadcast frequencies.
The laws of physics dictate that a transformer cannot pass DC and, in fact, this guarantees that there is no “offset” voltage at its output. Such offsets are one of the main causes of clicks and pops when audio signals are switched. When inserted at the appropriate point in the signal chain, an ISO-MAX isolator can eliminate such noises.
All transformers inherently behave as low-pass filters. The characteristics of a filter depends on its type or “alignment.” A Bessel filter is optimized for uniform time-domain response. This means all the overtones of a musical instrument stay properly time-aligned, preserving the instrument’s true timbre. In square-wave tests, a Bessel response is free of overshoot or ringing in the waveform. In frequency response plots, a Bessel response produces an unusually gradual high-frequency roll-off. All Jensen transformers are intentionally designed to have Bessel response curve.
There is no “free lunch” in transformer design. In ISO-MAX models with an “I” in the model number (CI-2RR and PI-2XX, for example), the Faraday shields responsible for extremely high noise rejection unavoidably makes their output sensitive to capacitive loading. Since the cable that connects isolator output to equipment input is the main source of capacitance, it must be kept reasonably short. Capacitance up to 200 pF, about 3 feet (1 meter) of standard cable, will preserve the rated high-frequency bandwidth. There is no restriction on length for the cable that connects equipment output to isolator input. Special-purpose isolators (PC-2XR and DB-2PX, for example) are more tolerant of longer cables.
Most ISO-MAX isolators use 1:1 transformers that simply reflect the load connected to their output back to the driving source, so there is no additional “loading” of the source. Because the copper wire used in transformer has resistance, a small signal loss is unavoidable. When used as directed, this “insertion loss” is generally under 1 dB for most isolators. However, some special-purpose isolators (PC-2XR and DB-2PX, for example) intentionally change signal level and impedance.
ISO-MAX isolators with an “O” in the model number (PO-2XR, for example) are most useful when driven by a balanced equipment output and a good choice when driving long cables. The isolator output can then feed either balanced or unbalanced equipment inputs with no risk of damage or misbehavior in the driving equipment, regardless of what kind of output stage it uses. These provide a reduction in low frequency “ground loop” hum but little effect on high frequency buzz.
All ISO-MAX® isolators with an “I” in the model number (CI-2RR and PI-2XX, for example) use transformers with internal Faraday shields. Faraday shields, sometimes called “electrostatic” shields, improve rejection of high frequency buzz by a factor of 100 to 1,000 (40 dB to 60 dB) over transformers without them.