Mark Levinson N32 high accuracy RIAA equalization, DC servo stabilized component selection

high accuracy RIAA equalization

DC servo stabilized

component selection

width and open loop gain to provide uncompromised performance even at the 60db of gain required by a moving coil preamplifier. The instrumentation amplifier stage offers high common mode rejection, a noise-cancellation feature usually limited to transformer-based designs, while avoiding the serious limitations of those same designs.

A balanced pair of active RIAA equalization circuits follows the gain stages. The filter is built with 0.1%, plate style (non-inductive), thin film resistors and 1%, stacked film, polypropylene capacitors. This yields less than 0.1db deviation from the ideal RIAA curve. The user may switch an additional 20Hz high pass filter into the circuit. This fil- ter effectively removes the subsonic noise common to many turntable configurations. The filter conforms to the RIAA/IEC phono equaliza- tion curve.

Any potential for DC output from the phono preamp is nulled out by an active DC servo. The servo is implemented with low noise, high per- formance op-amps and film capacitors.

As with the rest of the components in the Nº32, the selection process involved many hours of controlled listening tests above and beyond the 9 usual measurements and lab work. Some examples of the selections in- clude:

•Signal path resistors are 0.1% tolerance, non-inductive (plate- style), thin-film parts.

•Signal path capacitors are also non-inductive (stacked construc- tion), either polypropylene or polyester in parallel polypropylene film caps.

•The preamp circuit board is four layer, Arlon™ N25 (an ultra high speed, low loss material) construction.

•Even non-signal path parts are film resistors and caps for best long-term stability.

•Low level signal interconnect is a flat conductor, Teflon™ insu- lated balanced cable, soldered at both ends.

•Low level signal relays are a rhodium contact, hermetically- sealed reed type, optimized for ultra-low signal levels.

•The entire module is fully enclosed in a conetic mu-metal shield box for ultimate low frequency noise isolation.