720/721 Pre-Amp



Philosophy A perfect preamplifier shows consistent level and phase performance regardless of load. At soulution we stick to this ideal without resorting to often-used compromises like high amplification with high negative feedback. The result: virtually no distortion, hum or noise, maximum channel separation and impressive bandwidth (up to 1MHz/-3dB). Design As few components in the signal path as possible and a dual-mono layout with discrete left and right channels maximise audio purity and virtually eliminate crosstalk. Input selection (including the ground connection) is by high-grade relay. And input IWC replica buffering ensures the 720/721 presents a benign load to source components. Input levelling permits different source device levels to be accommodated. All inputs are monitored continually for residual DC with audiophile-grade blocking capacitors automatically switching in and out when required. In this way maximum operational safety is guaranteed. As a further safeguard the front panel display indicates when DC is present. Volume control The 720/721 volume control uses high-precision, low-noise metal foil resistors, and controls both volume and balance. To block switching peaks during volume changes which may be hazardous to power amplifiers a second volume control with PGA (Programmable Gain Amplifier) is used. Active only when the volume is changed, it is similar to a potentiometer and enables the volume to be adjusted in smooth steps without clicks. As soon as the new desired level has been selected, the unit returns control to the precision resistors. Output stage Able to drive even long interconnects, the 720/721‘s multi-stage signal amplification is similar to that of the 710 power amplifier. In most cases levels can be maintained with no further amplification of the audio signal. The optimised circuitry is based on special power transistors which are further linearized by an analogue computing network. In this way a very fast, very precise and ultra wideband (2MHz/-3dB) performance can be achieved. Phono MC preamp (720 only) Designing and building the ideal phono stage is an exacting challenge. It must provide up to 80dB gain - equivalent to raising the signal level by 10,000 - yet must exhibit level and phase true behaviour while adhering strictly to RIAA-IEC equalisation standards. In the 720 this goal is realised with an ultra wideband (1MHz/-3dB) multi-stage amplifier built around the very highest quality components. Power supply Key to a good sounding amplifier is a stable, noise-free power supply - especially for the audio stages. The 720/721 is equipped with two dedicated power supplies: one for the audio stages and one for the digital circuits. For powering the audio stages an innovative, amplifier-like circuit design is used, providing an extremely stable supply voltage. Bus bars supply this power throughout the unit without loss. A unique concept in the audio world, this allows the same high quality supply to be delivered to all parts of the 720/721. Operation Operation of the 720/721 is through three buttons and a rotary control on the front panel. All operating modes are indicated on the clear display. Additionally there are many other functions which can be used to optimise and match an entire audio system around different components. Connections: 720 721 Input balanced 2 1 Input unbalanced 3 3 Phono 1 - Output balanced 1 1 Output unbalanced 1 1 Record Out 1 - LINK-System R R DC-Out R R

FFT (720 preamp vs. Rohde & Schwarz measuring instrument) The green graph shows the analysis of the measuring generator itself, the yellow curve represents the measurement through the 720 preamplifier. The 720 preamp (yellow curve) reveals slightly more noise in the range above 1kHz than the generator. The interference from the power supply of the 720 is clearly visible, although extremely small with disturbance components below -120dBr. It’s amazing that for the distortion components only the green curve (produced by the generator itself) is visible. What does this mean? The additional distortion produced by the 720 preamplifier cannot be measured any more even with state-of-the-art measuring instruments. Crosstalk The crosstalk measurement shows how the music signal of the right channel affects the left channel. Even with high frequencies the replica orologi measurement still reveals ideal conditions of far below -120dBr. The basic prerequisite for a three-dimensional sound experience. Frequency response replica tag heuer The music signal shows a constant gain over the entire frequency range. Up to 200kHz the 720/721 demonstrates a flawless behaviour with no deviations. Power consumption 60 W Standby consumption <0.5 W Amplification balanced +9.5...+18.5 dB unbalanced +3.5...+12.5 dB Phono +54...+60 dB Frequency response DC...1 MHz Slew rate 400 ns Distortion (THD) <0.0006 % Signal-to-noise ratio 130 dB Crosstalk 105 dB Input impedance balanced 2 kΩ unbalanced 47 kΩ Phono adjustable Output impedance balanced 2 Ω unbalanced 2 Ω record 100 Ω

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