Every contractor troubleshoots noise and hum problems in audio and video systems at one time or another. Although tempting because of its simplicity, using a ground-lifting AC adapter or even cutting the U-ground prong off a plug is not a safe or professional – or legal – solution to ground-related noise problems.
What’s really going on when a cable is “picking up” noise? When two or more AC-powered components are in a system, a significant voltage may exist between their chassis or local grounds. This voltage causes current flow in the shield conductor of RCA cables or any other unbalanced connections between the components, which ultimately adds noise to the signal.
Because lifting the ground interrupts the circuit, it would alleviate the noise problem. But while it solves one problem, it creates a much worse one – if a ground-lifted device develops a short or fails, the interconnection cables will carry lethal voltages through the system and/or start a fire. Even if no one is hurt, the legal liability could bankrupt your business.
Fortunately there is a safe, professional alternative to lifting safety grounds: the ISO-MAX Audio/Video Ground Isolator Kit ($299). Manufactured by Jensen Transformers, the kit is packaged in a compact injection-molded case. It consists of a CI-2RR stereo audio input isolator, a VB-1BB one-channel video isolator, a VR-1FF one-channel CATV (RF) ground isolator, two RCA-to-BNC male adapters, two TA-R1 test adapters and a comprehensive troubleshooting guide written by company president and audio industry educator Bill Whitlock.
This last may be the most valuable component in the kit, since it contains a full discussion, with diagrams, of the theory and practice of troubleshooting signal interfaces to solve noise and hum problems.
The troubleshooting guide sets out a step-by-step procedure for troubleshooting system interfaces, provides typical diagrams showing how to install an isolator to break ground loops in audio and video systems, discusses when to add a ground connection, and concludes with more tips to reduce noise. I wouldn’t want to approach a noise problem without this information.
The components in the kit are essential to performing the diagnostic procedures and ultimately solving the given problem. Included in the standard kit, the TA-R1 adapters are for testing audio RCA connections. A TA-R75 test adapter is available for video RCA connections, and the guide provides a schematic for building adapters with other connector configurations.
The CI-2RR stereo audio input isolator provides isolation at the input of consumer home/audio systems, including computer soundboards and automotive sound systems. It provides audiophile quality, with a frequency response of 0.25 Hz to 55 kHz at -3 dB points. The isolator has RCA connectors and accepts signals up to 7 V at 20 Hz or 11 V at 30 Hz. Input impedance is 50 kohms and insertion loss is 0.7 dB typical.
Overall size is 4.3″ wide, 2.6″ deep and 1.5″ high. Typically, the CI-2RR is installed in the audio signal path from preamp to subwoofer at the receiving end of the cable.
The transformer-based VB-1BB one-channel video isolator is inserted into standard 75-ohm video cabling to eliminate hum bars and can also be used to correct audio hum or buzz in multimedia systems. It has isolated true 75-ohm BNC connectors (or RCA with included adapters). Bandwidth is -3 dB at 10 Hz and 10 MHz; CMRR is 120 dB at 60 Hz, and insertion loss is 0.55 dB typical. The VB-1BB is 3.5″ L x 1.75″ W x 2.1″ H. It can be mounted vertically or horizontally to standard rack rails.
The VR-1FF CATV (RF) isolator can be inserted into standard 75-ohm CATV or VHF/UHF cabling to eliminate audio and video system hum problems. It provides up to 40 dB more isolation than capacitive couplers or ground filters. It features gold-plated female F connectors. Bandwidth is -3 dB at 5 MHz and 900 MHz, with 0.35 dB insertion loss, typical. For example, in a multimedia system with TV and audio, the VR-1FF could be installed as an alternative to using the CI-2RR.
With the ISO-MAX kit, Jensen provides the contractor with a powerful diagnostic tool for a very common problem. All the components are available individually to refill the kit.
Jensen ISO-MAX isolators transparently couple signals with no loss of quality, while eliminating noise by breaking the ground loop. ISO-MAX provides an effective solution that’s simple to implement and – here’s the best part – safe as well.
Contact Jensen Transformers at 818-374-5857; www.jensen-transformers.com.