The six rows of circuit boards in the photograph above are the Quartet's plug-in filter cards.  Each card gives an attenuation of 12dB/octave and up to 4 cards may be cascaded to give a maximum attenuation of 48dB/octave. The filters are linear -phase and are fully discrete class A designs. 

The cards located toward the rear on the unit are the Viola OTA gain modules. Like the filters, these are also fully discrete class A designs. 

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