Mic pre and line input amp are totally separate amplifiers, each with its own gain control. The mic pre input is transformer balanced and floating. The oversized input transformer, brand Haufe, Germany, in combination with a dual balanced input circuitry offer a pristine but warm sound performance, a maximum gain of 70 dB and + 30 dBu headroom at the output. The ultra low noise input stage has a noise figure of less than 1.3 dB @ 70 dB gain that remains below 2 dB down to less than 40 dB gain, which is actually more important than the noise performance with very high gain settings. In most cases a gain setting of 40 dB or less necessary. The input pad of 25 dB makes possible to use the microphone input with high level signals. The P48 switch activates the phantom power supply.
The ToolKit Mic Pre as well as line input and filters are used with almost all input modules of adt-audio's large format consoles.
Very well balanced RF filtering maintains a power bandwidth of more than 100 kHz with a very flat phase response. The frequency response is better than +/- 0.2 dB between 30 Hz and 20 kHz with all gain settings. The very important low frequency phase shift is less than 10° with gains up to 70 dB even though a soft subsonic filter protects the entire signal chain from intermodulation by subsonic interference.
The internal RF filters suppress high frequency intereference above 100 kHz in a well-balanced way that maintains the phase response of the high audio frequencies and the transient performance but rejects RF signals that can cause intermodulation and distortion effectively. The common mode rejection ratio of the microphone input is better than 70 dB @ 15 kHz and better than 90 dB below 1 kHz.
The oversized microphone input transformer keeps low frequency distortion caused by saturation of the transformer's core extremely low.
The line input is totally separated from the microphone input. The input is electronically balanced and can handle levels of up to +30 dBu. The gain control range is +/- 20 dB. The center detent is precisley trimmed to 0 dB.
The phase reverse switch operates on both the microphone and the line input.
High-pass and Low-pass Filters
The filter section is fed from the input amplifier and inserted by the FILT switch. The high-pass filter has a sweep range from less than 20 Hz to 600 Hz and a steepness of 24 dB/oct. The sweep range of the low pass filter is from > 20 kHz to 1.5 kHz. The steepness of the low-pass filter is 12 dB/oct. The frequencies are calibrated to the -3 dB point. Both filters are 'maximum flat', active RC filters that are well balanced for best possible phase response.