Digital-Synthesis FM Stereo Generator

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See replacement model: 272 FM Stereo Processor

The Model 708 is a standalone stereo generator intended for use with an external FM audio processing system. The composite multiplex signal, including the stereo pilot, is generated with digital synthesis techniques to assure optimum stereo separation without need for calibration adjustments.

Additionally, the 708 provides internal combining for one or two SCA or RDS/RBDS subcarriers.


  • Digital synthesis of the stereo pilot and multiplex signals

  • Overmod protection, low-pass filtering and composite clipping

  • Front-panel metering for easy setup

  • Adjustable pre-pilot composite processing

  • Internal combining for RDS/RBDS and SCA subcarriers



Frequency Response

±0.5dB, 20Hz-16kHz

Stereo Separation

60dB (typically 65-70dB), 50Hz-15kHz


Better than 75dB below 100% modulation in baseband and subcarrier;“digital” noise components above 54kHz are –70dB or better.


<0.15% THD in baseband and subcarrier at 95% modulation

Crosstalk (M/S or S/M)

  • “Nonlinear” crosstalk is better than –50dB, 50Hz-15kHz

  • “Linear” crosstalk is better than –45dB with pre-emphasis switched off.

Stereo Pilot

19kHz, ±1Hz; level may be adjusted between 6% and 12%, relative to 100% modulation. <1% THD in pilot signal.

Program Line Inputs  (Left and Right)

Active-balanced, bridging; accept limited program audio levels between –15dBu and +15dBu, corresponding to 100% modulation.

Subcarrier Inputs

Two unbalanced inputs accommodate SCA or RDS/RBDS subcarriers at levels between –20dBu and 0dBu for nominal 5-10% injection.

Primary Low-Pass Filtering

7-pole, phase-corrected, active-elliptic filter with proprietary overshoot compensation (defeatable). –60dB or better at 19kHz and above.


May be jumpered for 75μs or 50μs characteristics; may be defeated by front-panel switch.

Composite Processing

A composite clipper acts on the multiplex signal prior to injection of the stereo pilot and any auxiliary subcarriers. Clipping is adjustable between 0dB and 3dB.

Composite Output

Unbalanced output with 75-ohm source impedance. 100%-modulation level is adjustable between 1V p-p and 8V p-p.

Digital Synthesis Sampling Rate

608kHz (16X subcarrier oversampling)

Power Requirement

105-130VAC or 210-255VAC, 50/60Hz; 10W.

Size and Weight

13/4”H x 19”W x 6”D (1U); 7 lbs.