F676 Microphone Preamplifier Operating Manual
Overview: The Fredenstein F676 Microphone Preamplifier is a valve (tube) based preamp with a fully balanced signal path throughout. The design incorporates high quality input and output transformers and features a zero Negative Feedback architecture. The F676 uses a Digital Signal Processor (DSP) to control the operating points of the tubes, guarantying perfect working conditions all the time.
Fig. 2 F676 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. Fredenstein F676 Manual V1.
To turn the F676 on, please push the rotary control. The F676 will power up and go through a tube calibration cycle. During this cycle you will see the anode currents in both halves of the push-pull Class A amplifier. After the currents settled, the unit is fully operational and the user will be forwarded to the main menu. The top of the main menu pages displays the peak output level meter Fredenstein F676 Manual V1.
The Main Menu allows to modify the following parameters: Amplifier Gain: The gain of the F676 can be adjusted in 1 dB steps in the range of 0 db and +76 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 gain “pot”. The change is applied immediately, therefore the engineer can hear the changes right away.
Advanced Audio Sub Menu: Input Impedance: In general the 1000 Ohms setting will work the best with most microphones. Some dynamic and ribbon microphones however require a lower termination to exhibit their optimum frequency response. In this case, please select the 200 Ohms option. Low Frequency Roll-Off: To avoid recording unwanted low frequencies (rumble), a high-pass filter can be inserted.
Output Transformer DC Bias: Another way to influence the sonic characteristics of the F676. A constant DC current can the chosen in the output transformer. Its characteristics are hereby altered, the frequency response becomes narrower and the amp produces more 2nd harmonic distortion. Utilities Sub Menu: Store Configurations: The F676 allows to store 99 complete setups. Please select the storage location by turning the rotary control.
In addition the Utilities Menu displays the output tube currents and the internal temperature. The F676 deploys an ultra low noise magnetic levitation fan inside that has a very long life span. But in case of circuit or fan failures, if the internal temperature reaches 85C (185F) the F676 will automatically shut down. Specifications: Frequency Response: Distortion: Input Noise: Gain Range: Input Impedance: Maximum Output Voltage: Mains Voltage : Power Consumption: 20Hz – 20Khz +- 0.5dB < 0.
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.
