Radio World - May 22, 2002
by Skip Pizzi
The variety of telephone interfaces available today is vast, ranging from the simplest analog coupler to the multiline digital hybrid with all the bells and whistles. To be completely prepared for all possibilities, a broadcaster needs to have a stable of many such devices and accessories on hand. That is, until now.
The ComPack from JKAudio, retailing for $545, provides interfacing to just about any type of POTS phone situation one is likely to encounter in the field or studio. It provides all of these capabilities in a simple, robust, no-frills package that engineers will admire for its flexibility and portability, and at a price point that everyone will appreciate for its value.
The device manages the POTS universe with three phone interface methods: an analog hybrid for direct interface to a phone line via RJ-11; a "universal" interface for connecting to the handset port on PBX, ISDN or key systems via RJ-22; and a headset interface to wireless or other telephones via a mini-phone (1/8-inch) TRS plug. (The connector for the latter on the ComPack is a 1/4-inch TRS jack, and the unit is supplied with an adapter cable from 1/4 to 1/8-inch TRS.)
The handset interface has three selectable settings to cover all possible transducer types one might encounter (electret, dynamic and carbon). A full-size DTMF keypad is included, which can be switched off to avoid errant tone bursts during audio feeds, or when the PBX or wireless phone interfaces are used.
On the audio side, the ComPack features a balanced mic/line input on XLR, an unbalanced line input on mono mini-phone, a headphone jack on 1/4-inch TRS and a multipurpose output on XLR (more on this latter).
The mic/line and line inputs each have a separate gain control, with an LED clipping indicator for the mic/line input. As this implies, the device includes 2x1 mixing capability. The headphone output level is adjustable over a wide range.
The XLR output provides a full mix (i.e., phone line plus local audio) as a balanced mic level signal (-25 dBm), or with the flip of a recessed switch, becomes an unbalanced I/O port to most intercom beltpacks, for two-way IFB interfacing to any kind of telephone connection. The latter is a unique feature that may be quite welcome to some users, particularly those who want to extend their studio IFB to a wide variety of remote locations via telephone.
Power is supplied either by an internal 9V battery or an external wall-wart power supply included with the unit. The device is laid out cleverly to allow over-the-shoulder portable use with a supplied, adjustable shoulder strap. In this mode, level controls and the LED input overload indicator face upward for easy viewing and adjustment by the operator while wearing the device.
The ComPack's form factor seems a bit unusual at first, but after some time with the unit, you recognize the efficiency of its design. The device uses both horizontal and vertical space effectively, and it allows comfortable use in both supine (on a tabletop) and upright (over the shoulder) orientations. Its rugged construction should hold up well to the rigors of field work, yet it weighs in at only 1.5 pounds.
The unit's simple and ergonomic layout makes it easy to operate by the typical engineer after only a few minutes' exposure. For the less technically adept, a clear and concise manual is included, which seems to have been written with English as its original language.
Audio and Noise
While the device's audio quality might not match a state-of-the-art studio mixing console, it is more than adequate for the intended application, and beyond reproach for POTS usage.
The AC power supply does not add any audible hum, as occurs in some similar devices, but the handset interface is susceptible to buzz, which is the penalty paid by any such RJ-22 interface. This is due to its insertion in the handset circuit path, which is unbalanced (i.e., no common-mode rejection) and at low level, making it particularly vulnerable to noise pickup.
In practice, this noise is audible only at the remote end; it is largely filtered out of the receive-end signal by the phone line's high-frequency roll-off characteristics. Nevertheless, for this reason the manual correctly advises that the handset interface should only be used if direct phone-line interfacing is impossible.
Indeed, the ComPack's direct phone-line and wireless interfaces work flawlessly. When using the latter with a wireless phone, however, it is important to follow the manual's recommendation to keep the phone unit at least one foot away from the ComPack to avoid audio RF interference pickup from the wireless phone's transmitter. The supplied connecting cable for the wireless phone interface is long enough to easily allow this.
The level controls for inputs and headphone output could be labeled a bit better. Because the unit is designed to be used in both tabletop and portable applications, these rotary attenuators are viewed from a variety of angles. It is therefore difficult to know which way the taper runs (i.e., it's hard to tell which way is up or down in audio level), so some additional min-max labeling or +/- arrows around these pots would be welcome.
A more substantive complaint: If the operator is wearing headphones and listening at a typical level, loud pops are experienced when any of the unit's switches are flipped. Generally this wouldn't happen very often, and rarely when the unit is online, but it is an annoyance, nonetheless.
Overall, the ComPack delivers noteworthy performance and versatility in a single package. It can serve as an occasional problem-solver for broadcast engineers, or as an everyday interface for radio reporters. Its rugged and simple design will make it a welcome tool at any station that covers local news.
It even allows a roving reporter to feed live to air via wireless phone while freely traversing a remote site. Clip the cell-phone to your belt on one side, hang the ComPack on the other shoulder, connect the two devices via a cable around the waist, plug in headphones and a handheld mic - you're doing your own two-way audio remote with interview or sound-gathering capability and you still have one hand free to open doors (or sign autographs). Substitute a headset-mic and both hands remain free for reporter-in-action feeds.
JK Audio has provided another useful phone interfacing device with the ComPack. The unit is a veritable Swiss Army knife for remote POTS feeding, and ensures the broadcaster a win at every venue on the telco tour.
Skip Pizzi is contributing editor of Radio World.
JK Audio ComPack