Opti-FET Compressor

Opti-FET Compressor

 


ABOUT THE DESIGN:
The FEA Opti-FET Compressor is designed with both audiophile and studio quality features that many musicians enjoy.
The new audio path has been redesigned with the FEA 3S output amplifier circuit for warm tone and excellent noise rejection that features a “class A” FET output driver. The 3S amplifier utilizes an audiophile grade Texas Instruments™ (formerly Burr-Brown™) SoundPlus™ operational amplifier and a class-A Fairfield™ FET driver for outstanding performance. The operational and FET driver amplifiers are integrated in a unique way to take advantage of the favorable qualities of both types of amplification. This 3S amplifier has selectable modes of operation for a clean or warm tone. The warm tone mode was modeled to match the tone of the original OPTI-FET circuit. The input stage is a high impedance CMOS, hi-fi amplifier buffer with internal RFI protection. The input amplifier has been designed to have minimal signal distortion and noise, with maximum headroom for all input signal levels.
Another feature in the FEA OPTI-FET Compressor is the extensive side-chain control which is not commonly found in most pedal type compressors today. Like many quality studio rack compressors, the OPTI-FET compressor has all of the common controls available to the user to accurately shape his or her tone. Along with the full feature set of side-chain controls, a three band equalizer is available. This EQ only affects the amplitude of frequencies of the signal in the compressor control circuits. This EQ allows the user to modify the threshold setting by frequency band. The OPTI-FET compressor also has a side-chain loop feature, similar to many rack compressors. This allows the user to be more creative with the use of other outboard pedals. Multi-band EQ, or buffered volume pedals are a few that can make this pedal even more versatile when used in the side-chain loop.

FEATURES:

  • Small footprint – 4 1/2 inches by 3 1/2 inches
  • THRESHOLD, RATIO, ATTACK, RELEASE and GAIN controls. The control ranges for the ATTACK and RELEASE have been optimized for use on both bass and guitar.
  • The compressor exhibits soft-knee compression at lower RATIO settings and hard-knee at maximum RATIO settings. The COMP LED indicates when the THRESHOLD has been reached. This LED does not indicate the RELEASE response.
  • The compressor side-chain utilizes precision full-wave rectification of the audio signals in the THRESHOLD circuit for accurate envelope tracking. This also reduces the possibility of “pumping” with very low frequencies.
  • ACTIVATE foot switch places the compressor unit in the signal chain or in Direct Bypass mode. In Direct Bypass mode the signal at the input is directly connected to the output and does not pass through any electronics.
  • EQUALIZER foot switch enables the three band equalizer controls for the side-chain control circuit. The three band EQ only affects the amplitude of frequencies of the signal in the side-chain control circuit to modify threshold sensitivity by frequency band.
  • LOOP SEND/RETURN jacks are for placing external processors or EQ’s in the compressor side-chain control circuit. These jacks are only active when the EQUALIZER foot switch is enabled.
  • Internal DIP switches to select the output amplifier mode of operation. The three modes are clean (SW 1&2 off), warm 1 (SW 1 on) and warm 2 (SW 2 on). The warm 2 mode adds a subtle amount more of the dynamic harmonics of mode 1.
  • Internal DIP switch for a 12KHz filter for an ‘old school’ tone or to reduce the hiss from pedals proceeding the compressor.
  • The audio signal compression is accomplished with only a resistive component (Light Dependent Resistor or Photocell). All resistors in the circuit are low noise metal film type. The audio signal coupling capacitors are tight tolerance, quiet, multi-layer and metallized polyester film type. The transistors utilized in the audio signal path are popular low noise audiophile grade devices.
  • The power supplies onboard voltage charge pump allows the circuitry to operate at 18volts (+9 and –9 volt rails) from a single 9-volt battery or DC power adapter. This allows the audio signal plenty of headroom from active electronic guitars and aggressive playing techniques (i.e. pop and slap).
  • The “switch on” power supply current is less than 1µA (micro amp) on the signal ground at the INPUT jack. This is approximately 45,000 times (-93dB) less than the commonly used method of connecting the battery’s negative terminal to ground via the sleeve of the plug inserted into the INPUT jack. The “switch on” sensing method used in the FEA OPTI-FET Compressor keeps nearly all of the circuit’s generated white noise and transient currents out of the INPUT stage signal ground. Extreme measures have been taken to keep the power and signal paths as clean as possible.