Iso-Max PC-2XR User manual

USER GUIDE PRO SERIES AUDIO ISOLATOR MODEL PC-2XR
The PRO series audio ground isolation interfaces are designed for use in the finest professional sound systems.
They use the same Jensen transformers installed in tens of thousands of recording studios, broadcast facilities, and sound
reinforcement venues worldwide. Jensen audio transformers are industry benchmarks for sonic transparency because of
their extremely wide bandwidth, low harmonic distortion, and extremely low phase distortion.
Model PC-2XR is a two channel audio ground isolator designed to convert pro to consumer levels while solving the
following problems, which generally reveal themselves only when pieces of equipment are interconnected in a system:
!Poor noise rejection by the equipments existing balanced input. Most electronic or actively balanced input
circuits have high noise rejection or CMRR only when driven by laboratory equipment. The CMRR of these circuits
is exquisitely dependent on precision matching of impedances in the driving source equipment. The transformers used
in the PC-2XR exhibit very high CMRR when driven by real-world balanced sources, and even unbalanced sources,
effectively eliminating noise due to voltage differences between equipment grounds.
!Noise due to improper shield pin wiring inside the equipment. Sometimes called the pin 1 problem, this
design defect effectively makes the equipments shield connection a signal input. Noisy ground currents, which
normally flow in the cable shield, then inject hum, buzz, and other noises into the signal path. This insidious defect,
which can exist at equipment inputs or outputs, can frustrate attempts to troubleshoot system noise problems because
its symptoms are so confusing. The PC-2XR, via its built-in grounding option switches, can eliminate this problem by
interrupting or re-routing shield current flow.
!Noise due to the equipments susceptibility to RF interference. Most electronic or actively balanced inputs
will exhibit symptoms ranging from subtle audio quality degradation (fuzzy or grainy distortion) to outright
demodulation (heard as voices, music, or other noises in silent channels) when RF fields from broadcast or other
transmitters are present. The transformers used in the PC-2XR inherently attenuate signals above about 100 kHz,
effectively eliminating RF interference. In addition, built-in resistor-capacitor networks help to control standing waves
which can make RF pick-up by cables especially severe.
Model PC-2XR Application Guidelines
Source Impedance Range (output impedance of device driving the input) . . . . . . . . . . . . . . . 0 !to 5 k!
Load Impedance Range (input impedance of device loading the output) . . . . . . . . . . . . . 10 k!to 10 M!
Maximum Recommended Input Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +29 dBu = 22 V RMS at 50 Hz
+26 dBu = 15 V RMS at 30 Hz
+21 dBu = 9 V RMS at 20 Hz
Signal Voltage Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 dB
The PI- series, which is available with various connector options, may be driven by either balanced or
unbalanced outputs and may be used to drive either balanced or unbalanced inputs. When phase (polarity) inversion is
desired in any application, simply reverse connections at the input.
Cables at the PC-2XR outputs should be less than 10 feet long !!
The added capacitance of longer cables can degrade high frequency bandwidth and transient response. Keep the cables
as short as possible, although performance is not improved for lengths under 8 inches. Do not route the output cables to
a patchbay where additional cable lengths will be used to route signals to device inputs. The length limitation applies to
all cable between each PC-2XR output and the device input which it drives.
PROPER INSTALLATION IS ESSENTIAL TO ACHIEVE OPTIMUM AUDIO PERFORMANCE
PLEASE READ THIS GUIDE CAREFULLY !

General Information About Noises
Hum, buzz, and other noises in audio systems are nearly always caused by so-called "ground loops." A ground loop creates
a voltage difference between the ground references (chassis) at each piece of equipment. This voltage can couple into the
signal path, especially in unbalanced signal interconnections. Since this voltage is ultimately coupled from the power line,
its usually heard as 50 or 60 Hz hum if the equipment has grounded (3-prong) AC plugs. For equipment with
ungrounded (2-prong) AC plugs, its usually heard as a harmonic-rich buzz because the coupling mechanism favors high
frequencies. ground isolators can eliminate hum and buzz as well as the intermittent pops and ticks
frequently caused by on/off operation of switches and relays or appliances which contain them.
isolators cannot eliminate hiss, which sounds like a waterfall or an FM radio tuned between stations. A
predictable amount of hiss (random or white noise) is unavoidable in any electronic system. Excess hiss sometimes is
the result of improper system gain settings. For example, if the output level control on a CD player were set too low, the
downstream preamp would have to operate at very high gain to compensate. Such high gain operation will generally
produce more noise at the system output.
Buzz which occurs only when an AM receiver is the signal source, and is worse when the receiver is tuned to weaker
stations, is probably caused by radio frequency interference or RFI. Power line operated devices such as fluorescent lights,
electric motors, computers, and TV receivers produce high frequency interference can be conducted through or radiated
by the power line and picked up by the antenna of AM receivers. These problems can often be eliminated by installing
power line interference filters as close as possible to the offending source. A portable battery-operated AM radio tuned to
a very weak station can be useful in locating the source.
Location, Location, Location
ground isolators use transformers to magnetically couple the signal while breaking the electrical paths between
input and output connections. Once these connections are broken, the ground loop current, and the resulting noise, is
eliminated. Ground isolators are not filters which attempt to remove noise from the signal after the fact  they eliminate
the cause of the noise coupling. For this reason, an ground isolator MUST be inserted into the signal
path where the noise coupling actually occurs.
As a general rule, noise coupling most frequently occurs at interconnections using the longest cables. Problems are most
severe, even with short cables, when the cable connects two pieces of equipment which both have grounded (3-prong)
power connections or there is another ground connection (CATV, DSS, grounded rack, etc.) somewhere in the system.
NEVER defeat the safety grounding provided by a 3-prong power plug, whether with a 3 to 2 ground
adapter or by removing the plugs grounding pin. This practice is not only illegal, it can result in shock trauma or
electrocution of persons touching equipment anywhere in an interconnected system. Detailed technical papers on the
subject of system grounding and its effects on signal interfaces are available from Jensen Transformers.
The following method (as opposed to trial and error) will save time, labor, and frustration when selecting
an effective location for the isolator. Existing system switches and gain controls can provide very
important clues about just where noise is entering the signal path. If interrupting the signal path stops the noise,
the noise must be entering the signal path at a point upstream of the interruption.
For example, if the noise is present only when a specific signal source is selected, the noise entry point is likely upstream,
i.e. somewhere between that source and the device which contains the selector. Likewise, if the noise is present with any
input selected, the noise entry point is likely downstream, i.e. somewhere between the device which contains the selector
and the speaker (or other monitoring point). Generally, working backward (from the speaker toward the signal source)
through the system is the fastest way to determine which parts of the system are noise-free.
Obviously, the signal path can also be interrupted by selectively disconnecting signal cables between pieces of equipment.
Important note: if a "ground loop" does exist between two pieces of equipment, it will not be broken until all cables
which directly connect them are disconnected.
If the above tests are inconclusive, there may be a defect with one or more pieces of equipment. An insidious design defect
called the pin 1 problem is very common. Since it effectively turns the equipments input and/or output shield
connections into audio inputs, it can be revealed through a simple test: with the signal path interrupted (see note in
previous paragraph), temporarily connect only the shield contact (pin 1 for XLRs) of the cable to the shield contact of the
suspected input or output using a jumper wire. If this connection causes hum or buzz, you have a pin 1 problem. See
the Setting the Grounding Option Switches for proper settings to overcome this problem.

Setting the Grounding Option Switches
The settings of the 8 DIP switches on the bottom of the unit determine
if and how input and output shields are connected to the case,
denoted at the terminal strip, and to each other. Switches 1 through
4 apply to Channel 1 and switches 5 through 8 apply to Channel 2.
Normally, the shield of any balanced audio cable should always be
solidly grounded at the send (source) end. At the receive (load) end,
there are disadvantages to both solidly grounding the shield and leaving
it disconnected (floating). An RF damping network, which effectively
disconnects the shield at audio frequencies but grounds it at RF
frequencies, usually offers the best overall performance.
This configuration is achieved by the as shipped settings as shown in
the drawings. These settings, switches 2 and 6 off (open) and all others
on (closed), will give the best results in most systems.
If a pin 1" problem exists at the output
of the signal source equipment, it can
usually be eliminated by opening S1
and/or S5.
About Floating Equipment
Equipment which has a 2-prong power cord and has no other ground
connections through other signal cables may float at a relatively high
voltage (approaching line voltage, but harmless because of the limited
leakage current) above the ground voltage reference for the remainder
of the system. If the output of the PC-2XR drives such equipment, hum
may still be a problem because of the high common-mode voltage.
In these cases, it will be necessary to connect a
wire (gauge unimportant) between the case,
denoted at the terminal strip, and the
chassis of the piece of equipment which the
output drives and close S2 and S6. This
reduces the voltage between the floating
equipment and the driving equipment without
passing the small AC line current through the
shield of the output RCA cable, which would
produce hum. If the PC-2XR is connected via
rack mounting to the equipment being driven,
this is unnecessary.
If You Need Help
If you experience difficulty or have technical questions, our staff engineers are available from 9 AM to 5 PM Pacific time,
Monday through Thursday, by calling [phone]. You may also reach us by FAX 24 hours a day, 7 days a week
at [phone] or e-mail us at [e-mail].
Several Jensen application notes discuss the technical aspects of grounding and interfacing in audio and video systems.
They are available free on request. This information, as well as data on our full line of products for audio and video, may
be obtained from our website at www.jensen-transformers.com.
is a registered trademark of Jensen Transformers, Inc. © 1998, Jensen Transformers, Inc.

ISO-MAX®PRODUCT WARRANTY
For a period of 1 YEAR after purchase, Jensen Transformers, Inc. will, free of charge, repair or replace
any part of an ISO-MAX® product that fails due to defective materials or workmanship.
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replace any Jensen OEM transformer or any Jensen transformer contained in an ISO-MAX® product
that fails due to defective materials or workmanship.
Both limited warranties are subject to the following limitations:
1) Defects that are, in the sole judgement of Jensen, the result of accident, misuse, abuse, neglect,
mishandling, misapplication, faulty installation, unauthorized repair, modification, or acts of God will
not be covered by this warranty.
2) In the absence of proof of date of purchase, the date of manufacture (as determined from lot
numbers of internal parts and the records of Jensen Transformers, Inc.) shall be used in its place.
3) There are no express warranties except as listed above.
4) JENSEN TRANSFORMERS, INC. SHALL NOT BE LIABLE FOR INCIDENTAL OR
CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OF THIS PRODUCT OR ARISING
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