Hum and buzz (50Hz/60Hz and it's harmonics) occur in unbalanced systems when currents flow in
the cable shield connections between different pieces of equipment. Hum and buzz occur in balanced
systems when the ground voltage differences between different pieces of equipment are so large that
the Common Mode Rejection of the input stage of the receiving device is insufficient to reduce
the noise signal to in-audible levels.
The cable shield currents and ground voltage differences are caused by several mechanisms.
The most common source is the capacitance between the A.C. power transformer primary and
secondary windings. Since the secondary winding which provides the power to the device must
at some point connect to the circuit ground, a portion of the A.C. line voltage will ALWAYS
be capacitively coupled directly to this same circuit ground. This capacitivly coupled power
line signal will usually contain significant harmonics out to 1MHz or more. These signals will
cause currents to flow in the cable shields of unbalanced systems, adding this noise directly
to the audio signal. These signals will cause large voltage differences between pieces of
equipment in balanced systems, over-whelming the capability of equipment input stages to
The second most common source of hum and buzz is the voltage difference between two safety
grounds separated by a large distance or the voltage difference between a safety ground and an
"Earth" ground (such as a grounded satellite dish or cable TV source). This source of hum and
buzz is more of a problem in unbalanced systems, since the low impedance nature of these sources
can cause very large currents to flow from one device to another through the cable shields.
Hum and buzz can also be magnetically induced or capacitively induced directly into signal
cables when A.C. power cables are run right next to them. This tends not to be a problem in
any but the most unusual situations where common sense cable routing is not possible for some
Transformers eliminate hum and buzz in unbalanced systems by preventing the flow of ground
currents in the cable shields, and in balanced systems by greatly increasing the Common Mode
Rejection capabilities of equipment input circuits.
For a more detailed explanation of these topics, see AN-004 in our Applications section.
Jensen transformers improve signal quality by removing hum, buzz and interference signals
of other types (such as radio frequency interference) from the audio signal. The Bessel low
pass filtering effect also removes ultrasonic distortion products generated by previous
amplification stages from the audio signal. These ultrasonic distortion products create
additional intermodulation distortion products when amplified by succeeding stages. These
signals are folded back into the audible frequency range, generating an audio modulated,
non-harmonically related noise floor. This type of noise is characterized by listeners as a
"veil" in front of the music. The term "Spectral Contamination" was coined for this effect
by Deane Jensen and Gary Sokolich in their 1988 AES Paper titled "SPECTRAL CONTAMINATION
MEASUREMENT". Copies of this paper are available from the Audio Engineering Society and from
Jensen Transformers, Inc.
Computer controlled winding for extremely consistent unit-to-unit performance
Others use crude manually controlled winding equipment resulting in large unit-to-unit
variations in bandwidth and phase characteristics.
Soldered Faraday shield and case connections for guaranteed long-term reliability
Others simply tape bare wires to the copper foil shields and "pinch" the ground wire
between case and lid. Over time, these connections can open or become intermittent,
seriously degrading noise rejection. Worse yet, through oxidation, the shield
connection can become a copper oxide rectifier turning the transformer into a
radio receiver !
Custom nickel/molybdenum/iron alloy core materials for vanishingly low distortion
Others use cheaper, unselected materials resulting in substantially higher harmonic
distortions at low signal levels.
Superior performance through computer aided modeling and design tools
Jensen uses some of the most sophisticated laboratory instrumentation and
circuit simulation software available to monitor quality and refine transformer
designs. We were among the first to recognize that extended low frequency response
and Bessel function rolloff of high frequency response is necessary to produce
true waveform fidelity. We actively promote the use of "Deviation from Linear
Phase" as a measure of time domain performance.
Applications engineering support from real audio experts
The Jensen staff includes three full-time analog circuit design and audio system
engineers. Drawing on years of professional experience, they will give you free
advice, whether it's choosing the right transformer for your application, finding a
system problem, building a piece of new gear, or upgrading some old gear. Jensen
was founded by and is owned and operated by engineers, not marketeers. Solving your
problems is our business.
20 year transformer warranty
All Jensen transformers are 100% tested and built to last.
We have the warranty to back it up.
This type of application is the most common one that we encounter. Our
JT-11P-1 line input transformer is ideal for interfacing balanced lines to unbalanced
inputs such as power amplifiers or unbalanced mixer console inputs. This transformer is
also available in our ready to use ISO-MAX® Model
If it is necessary to reduce the signal level in addition to converting from balanced
to unbalanced, Jensen offers the
JT-10KB-D 4 to 1 step-down line input transformer which works very well in
"Pro" to "Consumer" level conversion applications. This transformer is also available
in our ISO-MAX® Model PC-2XR product.
Jensen makes a wide variety of line output transformers for manufacturers who wish to
design system interconnect compatabilty into their products or for users trying to "fix"
equipment with poorly designed interfaces.
JT-11-EMCF are our highest quality
"studio grade" line output transformers with +27dBu, +22dBu and +18dBu level handling
capability respectively. Frequency response is guaranteed to be within +/-0.1 dB from
20Hz to 20kHz and -3dB response typically extends from below 0.3Hz to many MegaHertz.
Distortion for these models is less than 0.007% at low frequencies and is unmeasurable
The JT-11-ELCF and
JT-11-FLCF are our more modestly priced "sound
re-inforcement" grade line output transformers, offering +24dBu and +21dBu level
handling respectively. Frequency response is guaranteed to be within +/-0.1 dB from
20Hz to 20kHz and -3dB response typically extends from below 0.3Hz to many MegaHertz.
Distortion for these models is a very low 0.04% or less at low frequencies and 0.001%
or less at 1kHz.
We have 2 of our output transformers available in our ISO-MAX® line of
products, the DM2-2XX for 1 to 1 applications and
our SL4-2XX for 1 to 2 and 2 to 1 applications. We recommend
the DM2-2XX model unless a step-up or step-down is absolutely required, as it has
better high frequency response and presents less of a capacitive load to output driver stages.
We also have Printed Circuit Mount versions of these transformers available, as well as
many other models for special applications.
Please keep in mind that whenever possible, an input transformer should be used at
the destination end of an interconnect cable instead of an output transformer at the
driving end of the cable. Input transformers offer much better Common Mode and Radio
Frequency Rejection than is possible with output transformers.
Jensen manufactures the ISO-MAX®
Model VB-1BB Baseband Video Isolator,
which provides 10Hz to 10MHz bandwidth and 120dB of 60Hz Common Mode rejection.
This product incorporates true 75 Ohm BNC connectors for low VSWR.
Model VB-1RR Baseband Video Isolator is an IHF/RCA
connector version of our VB-1BB Video Isolator with 10Hz to 15MHZ Bandwidth.
Model VS-1SS S-VHS Video Ground Isolator
provides independant transformer isolation of both Video and Chroma signals to
allow isolation of DVD Player and Satellite Dish Receiver S-VHS outputs.
Model VRD-1FF CATV Ground Isolator, provides the high 60Hz isolation required to
eliminate "ground loops" in Home Theater systems. The 1300MHz bandwidth
of the VRD-1FF maintains the high signal quality required for Digital
Cable TV and Cable Modem signals.
The Jensen JT-10KB-D
4 to 1 step-down line input transformer works very well in "Pro"(+4dBu) to "Consumer"
(-10dBV) level conversion applications. This transformer provides excellent isolation
for unbalanced consumer inputs, while also providing the required signal level
conversion. This transformer is also available in our ISO-MAX®
Model PC-2XR product.
The Jensen JT-DB-E is specifically designed
for interfacing unbalanced high impedance outputs such as guitars to low impedance
balanced microphone inputs. This allows long cables to be connected to these devices
without excessive high frequency bandwidth loss. Dual Faraday shields provide the
Ultimate in isolation for hum free inter-connection of musical instrument devices.
This transformer is also available in our ISO-MAX®
Model DB-2PX product.
The Jensen JT-115K-E, JT-110K-HPC, and JT-13K7-A are all
excellent choices for Tube microphone preamp applications. The step-up ratios
of 1 to 10, 1 to 8, and 1 to 5 respectively provide excellent performance when
interfaced to the relatively noisy inputs of vacuum tubes. The
JT-110K-HPC with their higher step-up
ratios are ideal for no feedback preamp designs intended to add "tube warmth" to
the microphone input signal. The
JT-13K7-A offers the best low frequency
response and lowest distortion of the 3 models and is the best choice for designers
trying to achieve high accuracy and transparency in their preamp design.