Mark Levinson No 523 Preamplifier, Phonostage And Headphone Amplifier
UNIT WAS A STORE DEMO, GREAT CONDITION!
In its literature, Mark Levinson declares their No 523 preamplifier "the definitive preamplifier for the analog music lover". This is because in addition to its six line-level inputs the No 523 also includes a phono preamplifier. Plus, the No 523 also includes a headphone amplifier with a 1/4" jack on its front panel. If one insists on also having a digital-to-analog-converter inside their preamplifier one can opt to purchase the preamplifier one step higher in Mark Levinson's preamp line, the No 526, which also has inputs for a DAC which supports PCM files up to 32-bit/192kHz and DSD files up to SD 5.6MHz (double DSD).
Per Mark Levinson's website and in their literature, the No 523 has a "proprietary Pure Path discrete, direct-coupled, fully balanced, dual-monaural signal path". The Pure Path amplifier circuit, it continues, uses a circuit element they call a cascode. This was originally used for bettering the bandwidth of tube circuits in radios, but they use these cascodes not only to improve bandwidth but to also enhance linearity. A cascode uses two transistors to work in tandem to act as a single transistor, rejecting the disadvantages of each and only using its sonic benefits. They call this arrangement a folded cascode. The No 523's gain stage uses pairs of JFET (which by the way, is an acronym for junction field-effect transistors) that Levinson chose because of their low noise and high gain. Although this often has an unwanted side-effect of distortion, the remedy for this is that BJTs (bipolar junction transistors) are used in the circuit.