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...
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...
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 for...
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 l...
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 rol...
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...
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 autom...
Contact info: fredenstein professional audio by orion communication 7f-1, no. 582, ruei guang rd. Neihu district taipei 114 taiwan phone : + 886-2-2657-2618 email : info@fredenstein.Com web : www.Fredenstein.Com.
