Fully Balanced Discrete Volume Control
The volume control is realized with a 16-bit balanced resistor ladder, which uses low-resistance, high-linearity solid-state switches and discrete precision resistors. Control signals for the switches are optically coupled for low noise and maximum signal integrity. The bandwidth and transient response of the preamplifier circuitry are virtually unaffected by the volume setting. As a result high frequencies sound especially smooth and extended, and music seems to emerge from “jet black” silence. The analog and digital signal paths are not interconnected. Where neces- sary, digital control signals are optically coupled to analog circuits.
The Evolution Two has two buffered tape outputs: one linked to the main signal- selection bus, and another with its own independent signal-selection bus. This allows the option of listening to one source while recording another, or the option of connecting two tape decks having different input signals. Both tape outputs have single-ended and voltage outputs. Either the fourth single-ended input or the third balanced input can be user-configured as a tape monitor input, allowing the opportunity to use home or professional recording equipment.
Separate Power Supply
Housed in a separate chassis, the power supply makes use of extensive electrical and magnetic shielding to keep radiated interference out of critical preamplifier cir- cuits. Internal line conditioning circuitry filters RF noise on the AC power, and compensates for asymmetric power waveforms and DC on the mains.
Power for the analog stages comes from a large 170 VA toroidal transformer. This transformer drives four 8-amp bridge rectifiers and 39,600 microfarads of filter capacitance. Each monaural preamplifier has as much power supply capability as many stereo power amplifiers.
The main regulators for the analog stages are scaled-down versions of those used to power the output stages of the Evolution One amplifier. Operating in current mode, with fully complementary gain stages and output drivers, wide bandwidth, low output impedance, and high current capability, the main regulators easily exceed the requirements of the analog stages. The driver and output stages in the main analog regulators use five pairs of 150 Volt, 8 Amp, 40 megahertz power transistors.
A dedicated 90 VA toroidal transformer with three independent secondary wind- ings powers the preamplifier's digital control circuitry. The regulators for the con-
