Comrex STAC6 Studio Telephone Access Center

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Comrex STAC6 Studio Telephone Access Center


STAC incorporates a pair of Comrex high-performance digital hybrids with automatic audio level control. The result is the most natural sounding telephone audio, even when conferencing multiple callers. A compact, rack-mounting mainframe houses the hybrids, the multiline controller and all telephone and audio connections.

The attractive, ergonomic control surfaces offer two operational modes, selectable with a flip of a switch:

Studio/Producer Mode provides both pre-air and on-air caller management.
Screener Mode simplifies the task of screening and queuing callers.
Powerful call management can be quickly mastered with minimal training. A single control surface is included for basic operation. For more demanding programming, up to four control surfaces may be used.

Call screening and control are available from any networked computer, using a standard web browser, with the included STAC IP. With STAC IP, your talent can host their shows from anywhere there is an Internet connection or you can economically create more control points from any computer on your local network. No additional computer is needed to serve the STAC IP webpage, as it is served from the mainframe. Your connections are secured by password protection and no dedicated client software needs to be installed. In addition to replicating the call status information on the control surfaces, STAC IP also provides fields for additional information about callers and text chat among those on your show network.

Innovative features include an Auto Attendant that automatically answers incoming callers with your custom message and puts them on hold; dedicated control surface buttons to designate the next caller to be placed on air and to activate an external recorder or delay; and program-on-hold audio.

STAC6 is configured for six lines. Expanding a STAC6 to a STAC12 in the field is quickly accomplished by installing a mainframe extension card and control surface sidecars.

No matter what you’re talking about, you’ll be talking about quality, convenience and value when you put the Comrex STAC on the line.


Key STAC Features

  • Dual, high performance digital hybrids for reliable, natural sounding caller audio, even when conferencing.
  • Configurations for six and phone lines. Easy to expand in field.
  • Flipping a switch on the back of a control surface is all that is required to select Studio/Producer or Screener Mode.
  • A standard web browser can be used on any locally networked or Internet connected computer for call screening and control.
  • Auto Attendant for automatically answering incoming calls with your custom outgoing message. Call is answered after two or six rings, the message is played and, at the end of the message, the line is put on hold. If no message is recorded, lines will automatically be answered and put on hold. Function selected from control surface.
  • Two phone lines can be assigned to VIP mode, removing them from the priority rotation and Auto Attendant. These can be reserved for placing outgoing calls and incoming hot lines.
  • Selectable auto-disconnect of calls terminated by caller.
  • Selectable automatic gain control for consistent levels on-air and send audio down the line to your callers. A separately controllable caller level boost may also be used.
  • Talent maintains control using selectable caller ducking that lowers caller audio level when talent speaks.

STAC Mainframe

No configuration required after initial installation. Set-up controls are behind an easy-access panel and include pots for level adjustments and DIP switches for configuring Auto Attendant, auto-disconnect, automatic audio gain control, VIP and other settings.
Front panel features three bicolor LEDs indicating level status of audio input and hybrid levels.
Telephone line connections provide loop-thru to other systems or telephone sets sensing loop-thru provided for PBX interconnection.
Callers are conferenced within the STAC mainframe requiring only one mix-minus audio input to feed both hybrids.
A separate audio input is used for program-on-hold.
Each hybrid has an individual audio output to send to your audio mixing console or router.
A third audio output sums the two callers with the host audio-great for connection to a recording device.
Ethernet port allows the integrated web server to deliver call screening info and to control all call functions via STAC IP.
Software is field upgradable via compact flash port.

STAC Control Surfaces

One control surface is included with purchase of mainframe. Additional control surfaces, up to four per system, may be added at any time. STAC6 control surfaces can be upgraded to STAC12 in the field.
Clean, logical design allows functions to be mastered quickly. Dedicated buttons, with associated multicolor LEDs, minimize the number of button presses and make it easy to determine status of phone lines and callers.
Any control surface can operate in Studio/Producer or Screener Mode.
Designed to use standard Cat-5 wiring to link the control surfaces to the mainframe. No proprietary cabling or additional power source required for control surface connection.
Common STAC control surface functions available in both Studio/Producer and Screener Modes:
Auto-Attendant activation, deactivation.
Default Priority for next caller to be placed on air is:
Callers on hold who have been screened,
Followed by callers on hold who have not been screened, in order of length of time on hold.
Change Priority function overrides the default priority to select and indicate the next caller to be to be placed on the air.

Busy All function assists in clearing the phones for contests and
other uses. Pressed once, the Busy All button drops all unlocked
lines and will busy them out. On second press, the unlocked
lines are freed up and are now available to receive calls.

Aux button controls logic output to turn on/off external recorder or delay. DIP switch configurable as momentary or latching. The Aux function on each control surface operates independently of the others. In Studio/Producer mode, this button may alternately operate as a Next button, seamlessly putting the next priority line on the air.

Jack provided for headset connection to provide alternative to handset.
Screener Mode functions:
The top row of buttons performs off-air call answering, including placing calls on hold or releasing them. Callers selected from these controls communicate via the control surface handset. Bicolor green/yellow LEDs indicate whether the line was answered at this control surface or another.
The middle row of buttons is used to signal screening status to studio/producer control consoles, place callers on hold and to change priority. A screener cannot place callers on air. Bicolor red/blue LEDs indicate which lines are on hold, which lines are on screened hold, and priority status.
The bottom row of buttons drops lines that have been selected using the top row of buttons.
Studio/Producer Mode functions:
The top row of buttons performs off-air call answering, including placing calls on hold or releasing them. Callers selected from these controls communicate via the control surface handset. Bicolor green/yellow LEDs indicate hold and priority status.
The middle row of buttons places callers on air, with or without screening. Lines will drop when another caller is selected. Alternately, by pressing the corresponding line button a second time, the line may be locked for conferencing and requires pressing the drop button to disconnect. Bicolor red/blue LEDs indicate which lines are on air, to which hybrid the lines are assigned, and whether the line is locked on air.
The bottom row of buttons drops lines that have been selected from either the top or middle row.


Duplicates control surface functions on any network-connected computer using standard web browsers.
Password protected access to talent, producers and screeners on existing local networks and Internet connections.
Software is served from STAC mainframe, so no dedicated server is required.
Call timers are displayed for each line, showing length of time on hold and length of time on air.

CONNECT to a Working STAC (Password: comrex)

This link is to an actual working STAC system at our facility in Massachusetts, USA. The demo works best via Internet Explorer 6 or higher or Mozilla Firefox 1.0 or higher. The username can be anything you like but the password is comrex (lowercase) We recommend running the demo in full-screen mode (F11 toggles full-screen mode on most browsers).

STAC Sharing Lines with Production/News Studio

The Comrex STAC (Studio Telephone Access Center) is a powerful tool to manage on-air phone calls in the broadcast environment. In some installations, it would be advantageous to be able to manage calls using the STAC system, but share phone lines with a news or production studio for separate handling. This is possible using an extra STAC control surface dedicated to the alternate studio and an extra, stand-alone hybrid. For details on this set up, please look at Tech Note – Creating a Production/News Extension to the Comrex STAC System.

Technical Specification

Technical Specification

STAC Configuration

STAC6 Complete System includes mainframe for six phone lines and one six-line STAC control surface

Additional items:

Extra control surfaces are available with either 12 or six lines
STAC6 to STAC12 mainframe upgrade includes field-installable plug-in circuit board
Sidecar Upgrade increases the number of lines managed by a control surface from six to 12 STAC Mainfram
STAC Mainframe
Rear panel connections

Send input:XLR female: 0 dBu nominal, adjustable, balanced, bridging, 20 k impedance
Caller 1 and 2 outputs: XLR male: 0 dBu nominal, adjustable, balanced, 50 impedance
Telco lines:Two x RJ-45 connectors per six phone lines: POTS (plain old telephone service) line, analog extension from a PBX or dry line (no DC offset voltage)
Auto-disconnect: Disconnects on loop drop or loop reversal. User selectable.
Key service compatibility: Any key system providing true tip and ring compatibility to telephone instruments
Tip/ring switching-Solid state relay
Loop-through to PBX Two x RJ45 per six phone lines
Hybrid expansion port RJ-45
Control surface Four x RJ-45
Network connection 10Base-T Ethernet
Hybrid Performance
Telephone transmit
Nominal send input: 0dBu referenced to -15 dBu onto the telephone line
Frequency response: 250 Hz to 3.5 kHz, 1 dB
Signal-to-noise ratio: >56 dB
Distortion: <0.2%
Telephone receive
Nominal telephone line level: -15 dBu referenced to caller output of 0 dBu
Frequency response: 250 Hz to 3.5 kHz, 1 dB
Signal-to-noise ratio: >56 dB
Distortion: <0.2%
Send-to-caller separation:
55dB nominal
Tail time: 32 milliseconds
Caller-to-send separation:
50 dB nominal
Tail time: 32 milliseconds
Power and physical
Internal supply:
Auto Adjusting 100/240 VAC 50/60 Hz
Dimensions: 19″ W x 11.5″ D x 3.5″ H (48.26cm x 29.21cm x 8.89 cm)
Weight: 12.5 lb (5.75 kg)
STAC Control Surface
Rear panel dip switch adjustments

Selection of control surface mode: Screener or Studio/Producer
Aux mode selection: Momentary or toggling
Aux/Next button mode assignment
Handset level boost
Headset mode selection
Rear panel connections

Headset jacks:Two stereo mini-jacks
Aux control output:DB-9: Selectable as momentary or latching signal
Powered by STAC Mainframe


Control Surface for STAC6
10″ W x 7″ D x 3.25″ H (25.4 cm x 17.78 cm x 8.25 cm)
Weight: 2.2 lbs/ 1 kg
Control Surface for STAC12
Size: 16.5″ W x 7″ D x 3.25″ H (41.91 cm x 17.78 cm x 8.25 cm)
Weight: 3 lbs (1.4 kg)

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