Magnetic Film Recording System

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The Inovonics 390 is an audio electronics package specifically intended for motion picture sound recording on sprocketed magnetic film. It was engineered to meet the needs of top-quality original installations, and to retrofit existing recording systems for a substantial improvement in performance.

The Inovonics 990 is a companion Power Supply used with the 390 system. It can power a maximum of 8 channel modules in a single system, and in addition to regular DC voltages, also contains the bias pilot oscillator and LINEUP mode circuitry.


  • Modular design with complete Erase, Bias, Record, Reproduce and "Recordist Monitor" functions

  • Automatic Bias, Level and EQ Swithcing

  • OLX™ (Oxide Linearity eXtension) predicts, cancels and eliminates THD and IM distortions.

  • HFX™ (High Frequency eXtension) program-adaptive biasing

  • Two sets of non-interactive IN/OUT timing adjustments

  • LINEUP mode with front panel "trim" adjustments for Bias, Record Level and Record EQ.



Overall Frequency Response

  • 35mm/ ± 1.5dB, 25Hz - 20kHz
  • 16mm/ ± 2dB, 20Hz - 12kHz

Signal-to-Noise Ratio

  • in dB, referred to a “peak” flux level of 370nW/m, or 6dB above Operation Level
  • 35mm/ OVERALL(u’wtd -67/A-wtd -75)
  • 35mm/ STANDBY(u’wtd -74/A-wtd -82)
  • 16mm/ OVERALL(u’wtd -63/A-wtd -70)
  • 16mm/ STANDBY(u’wtd -70/A-wtd -77)


  • Oxide-induced distortion will reach aproximately 1% THD at a fluid level of 290W/m, or approximately 4dB above Operating Level. (This depends on an oxide formulation.)
  • Distortion in the electronics is >0.1% at any level up to signal clipping. The electronics internal clipping points are at least 20dB above typical operating levels.


35u-sec for 35mm tests, 70u-sec for 16mm, and a “flat” low frequency characteristic per the SMPTE Specification. Equalization presets are automatically switched with jumpers in plug-in head assemblies.

Line Input

Transformerless, electronically-balanced/bridging; appears at the back panel “XLR” female connector. Differential input impedance >10k-ohms; accepts nominal program line levels between -5dBu and +15dBu, +4dBu nominal. (0dBu = 0.775V r.m.s.). Common Mode Rejection >40dB.

Line and Recordist Monitor Outputs

Transformerless, electronically-balanced; appear at 600-Ohm source impedance; clipping level +24dBm into 600-Ohm load.

Erase Frequency



<75dB erasure of 500Hz signal recorded at or below oxide saturation.

Bias Frequency


IN/OUT Timing

Separate, non-interactive adjustments for 35mm and 16mm film speeds. IN and OUT timing delays are each independently variable between 40 and 500ms.

Head Requirements

  • Erase: 2mH, ±10%, with >90% magnetic efficiency at 125kHz; dual-gap construction.
  • Record: 5mH, ±20%, with >80% magnetic efficiency at 250kHz; recommended gap spacer, 200u-inches.
  • Reproduce: (Recordist Monitor) 5mH, ±20%; recommendedgap spacer 200u-inches.

Power Requirements

The Model 390 Channel Modules each require a preregulated bipolar supply of ±118vdc at 350ma, and a 500kHz Erase/Bias “pilot” signal of 15 volts p-p. The Inovonics Model 990 Power Supply, which satisfies these requirements for a system of 8 channels or less, operates fro 115/230-volt AC mains, 50/60Hz, and draws about 120 Watts fully-loaded

Line Output

Balanced, transformer-isolated, with provision for balanced, transformerless operation if desired. May be adjusted for nominal line levels between +4 and +10dBm. Clipping level, +28dBm into 600-ohm load; +30dBmV into bridging inputs.

Size and Weight

  • 390 Channel Modules: 7 x 4.3 x 8”: 4lbs.
  • 990 Power Supply: 3.5 x 19 x 10” (2U); 17 lbs.
  • 999 Rack Frame: 7 x 19 x 8” (4U); 3lbs.