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 reject them.

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 reason.

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.

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 CI-1RR, CI-2RR and PI-2XX products.
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.
The JT-11-BMCF, JT-11-DMCF and 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 at 1kHz.
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.