727 Preamplifier

Description

Input stage
The innovative input stage of the727 preamplifier enables exceptional common mode rejection without compromising the input stage by introducing noise. This is achieved with parallelized instrumentation amplifiers designed for wide bandwidth (20MHz), lowest noise (noise density < -160dBV/√Hz) and optimal common mode rejection (CMMR >105dB). This ensures that even the faintest musical signals can be properly received by the 727 preamplifier.

Volume control
Relay-switched high precision metal foil resistors form an 80 step (1 dB) volume control. Each channel has its own volume control resistor network. The volume control also allows balance adjustment. To avoid unpleasant clicking noises or harmful voltage peaks during volume adjustments, the 727 preamplifier is provided with a second volume control path which is active only during volume adjustments. This secondary, IC based volume control alters the volume without any click or pops. Once the new volume is set, the 727 will revert to the sonically superior path with its high-precision metal foil resistors.

Phono-preamplifier(optional)
Small and fine output signals, especially from MC cartridges, are received by an instrumentation amplifier optimised for lowest noise and highest common mode rejection. With its adjustable gain (+40 dB to +80 dB @ 1kHz) and termination impedance (20Ω to 1kΩ, 47kΩ, 0pF to 70pF) the phono input can be adapted very precisely to your pickup system. The use of very fast amplifier stages (-3dB @ 2MHz) ensures highly accurate reproduction of the RIAA equalization curve (frequency and phase response).

Output stage
The Class-A output stage has been optimised for speed, precision and high peak currents. Thanks to its low output resistance the output stage can drive even long cables without difficulty. With a frequency bandwidth of 20 MHz (-3 dB) and the accompanying minimal phase shift in the audio band, all details of the music are reproduced true to life. The result is a three-dimensional spatial sound experience full of musicality and natural timbres. The sheer power of the output stage guarantees that the rich detail of the music reaches your power amplifier.

Distributed Local Power Supply:
The basis for the dual mono power supply of the 727 preamplifier is a switched mode power supply (SMPS) which converts mains voltage into an intermediate DC voltage. Highly efficient DC-DC converters and extremely low-noise and fast linear regulators generate the supply voltages needed to operate the 727 preamplifier. Local linear regulators are placed next to each current sink (OpAmp, transistor, etc.). This ensures lowest noise levels on the analog supplies and shortest signal paths. Large filter capacitors, as typically used for linear power supplies with transformers and rectifiers, are no longer required.