Universal Preamplifier with Mic Pre, Line Input Amp and DI-Input for Instruments
A mono microphone, line and keyboard pre-amplifier, with outstanding sonic qualities and features.
The microphone input is always transformer balanced and floating. Depending on the version, the line input and the output is either transformer balanced and floating or electronically balanced. The DI-Input is always electronically balanced. The entire audio chain employs symmetric circuitry, and the headroom level from input to output is +30dBu.
The balanced and floating input of the mic pre is equipped with oversized torodial transformers. The common mode rejection ratio of the microphone input is better than > 76dB @ 15kHz. A stepper switch with calibrated positions provides coarse gain adjustment. Below 22dB the switch changes the pad, so that in every setting an optimal gain is maintained. Another control with a range from 0dB to +10dB is used for the fine gain adjustment. The maximum gain of the unit is 80dB. A passive subsonic filter with the edge frequencies 20, 40 and 80 hertz can be activated directly in the input. The LC filter uses the primary winding of the input transformer and prevents the amplifier from subsonic disturbances and foot fall sound that can cause intermodulation effects. Two knobs adjust input impedance for the microphone load. Resistive load can be applied with the values 200 ohms, 300 ohms or 600 ohms. For the capacitive load, the values 0.33, 0.68 and 1.5nF can be selected.
The electronically balanced instrument input has a very high input impedance that does not alter the sound of a pick up. The UNBAL and GND LIFT switches are used for un-balanced and high-Z signals. UNBAL switches the usually balanced input between to unbalanced mode.
The GND LIFT switches floats the connection between the ground of the V776 and the sleeve of the TRS jack. The balanced input uses the ground of the connected device. This circuit is meaningful when keyboards or amplifiers are connected which are already grounded. The gain has a range between 0dB and 36 dB and is infinitely variable. The electronically balanced input has an input resistance of > 200kOhm. Special filter circuits take care of an effective oppression of rF disturbances without influencing frequency and phase response. The Instrument input circuit of the amplifier is optimized on the lowest noise for medium to high impedance sources. The selection of the instrument input takes place by the switch INSTR IN.
The line input is implemented either electronically balanced and floating or transformer balanced. The transformer balanced version is equipped with an oversized torodial transformer. The gain range is ± 20 dB. The switch LINE selects this input.
The high-pass filter has a steepness of 24dB/octave and a range of <20Hz to 300Hz. The low-pass filter has a range of >20kHz to 2kHz and a steepness of 12dB/octave.
A peak meter indicates the output level. The Ø switch rotates the input phase.
The V776 is a standard V700 module and fits into standard mounting frames.