All Electronic Patch bays have two problems with microphone or other low level sources, these are noise and crosstalk between low level and high level inputs.. For this reason CB have always and still maintain that for optimum performance the Mic Amp should be placed before the Patch bay.
Where this is not possible, the Microphone Boost Card provides a good compromise solution. Providing Eight Channels of 30dB low noise gain at the input to XPatch enables dynamic and ribbon Microphones to be connected directly and by adding a external phantom supply phantom powered microphones. To use with line level sources simply add an in-Line attenuator.
In addition to the 30dB of boost the XPatch has up to 44dB of variable gain available, 22dB on the input and 22dB on the output, giving you a maximum of 74dB gain, you could even use the XPatch as your Mic Amp!
Design Considerations
I would have liked to have used a discrete input stage for better noise but the limited space (55xx35mm for 8 mic boost amps) required some compromises to be made and a dual low noise op amp is used. The Low frequency Distortion and Phase shift also required close attention. (The Line input and Output cards are DC coupled to eliminate any low frequency problems)...
Conclusion
The Mic boost card provides 30dB of gain with an improvement in signal to noise of at least 20dB compared with the standard line input card.
Mic Boost Card Specifications
Gain 30dB.
Equivalent input noise -120dBv
Distortion a 1KHz +4dBu out 0.006%
Maximum input Level -10dBv
Input Impedance 10K ohms
