F660 Limiting Amplifier Operating Manual
Overview: The Fredenstein F660 Limiting Amplifier is a valve (tube) based compressor and limiter with the same very short signal path as the famous Fairchild 660/670. it uses the exact type of tubes, the 6386 LGP, as the Fairchild. Fortunately, new production tubes are available today, since original tubes are hardly available anymore.
Fig. 2 F660 Rear Panel Operations: After turning on the MAINS SWITCH on the rear panel, the unit performs a self test and after successful completion you will see the following screen: At this point the unit is in stand-by mode and the audio circuitry and the tubes are still powered-off, the unit is in bypass mode, but the output meter is connected to the main output. This allows the user to measure the level even in bypass mode. To turn the F660 on, please push the rotary control.
After the currents settled, the unit is fully operational and the user will be forwarded to the main menu. The Main Menu allows to modify the following parameters: Compressor Gain: The gain of the compressor without gain reduction can be adjusted in 0.5dB steps in the range of -11db and +11 dB. To adjust the gain move the cursor with the rotary control to the gain field and then press the rotary control. The cursor will move from the left to the right and the rotary control becomes the level “pot”.
satisfied with the gain, push the rotary control again and the cursor will move back to the gain field and can be moved down to select different items. This procedure applies to all parameter adjustments Compression AC Threshold: The compression AC threshold determines at which level the compressor activates. Please note it is displayed in dBu not in the standard U.S. studio level of +4 dBu. This allows to easier match the maximum input of A/D converters almost always specified in dBu.
Link: This enables the multi-channel link capability. Please note that is feature has to be turned on on all participating units. Sub-Menus: There are three sub menus available to adjust the following parameters: Meter: Utilities: Output Meter adjustments Safe/Recall Parameters, Calibration etc. Meter Sub Menu: After selecting the meter menu on the main menu page the screen below will be displayed.
Meter Mode: The meter is capable to display peak and RMS values. The two modes are peak only as a bar graph or peak and ppm displayed simultaneously. In this case the PPM result is displayed as a bar and the peak result is displayed as a dot. Utilities Sub Menu: Store Configurations: The F660 allows to store 99 complete setups. Please select the storage location by turning the rotary control. If the location was previously used, it is indicated, but you can overwrite it.
Gain Calibration: Due to the fact that no negative feedback is used in the audio circuitry, the actual gain is dependent of the state of tubes, therefore the 0dB gain level can be adjusted. Apply a 1kHz test tone at 0db level at the main input and adjust the AC calibration for 0dB gain on the output. The range is -3dB to +3dB in 0.5dB steps.
Contact Info: Fredenstein Professional Audio by Orion Communication 7F-1, No. 582, Ruei Guang Rd. Neihu District Taipei 114 Taiwan Phone : Email : Web : + 886-2-2657-2618 info@fredenstein.com www.fredenstein.
