The proposed power amplifier is an "Inverting GainClone". The history of this denomination is born from an amplifier planned and produced from Japanese house SAKURA SYSTEMS, with name "Gaincard". The author, Junji Kimura, planning the amplifier has made use of a minimal formulation (minimal number of components in order to obtain the desired high quality) with the ascertainment that exists power operational amplifiers with better characteristics than many amplifiers realized with discrete components. Because of the simplicity of its schematics, the Gaincard has been taken as model from many diyers that have proposed a series of variant of the original plan on several Internet sites that are generally called "Gainclone". Nearly all of these variant stem from the schematics on National datasheet of the used devices (LM3875, LM3886 o LM4780).
Not considering small adjustments in the disposition or the choice of the values of the little discrete components, main variant consist in INVERTING GAINCLONE, that is the use of the inverting configuration of the power operational amplifier used (National LM3875 or LM3886).
The schematic on the previous figure is an extract of the National LM4780 datasheet (a double LM3886 in the same one package) and contains errors in the values of Ri and Rf. The correct values are 10Kohm and 200Kohm respectively otherwise the input impedance (Rin// Ri) would turn out too much low.
This configuration has the advantage to allow to realize an amplifier with lower values of distortion (and consequently higher sound quality) as evidenced from diyers in the net and from National in the datasheet. The only negative collateral effect is that the input impedancs becomes equal to Rin//Ri. This comes resolved with the use of values of Ri and Rf 10 times greater then in the not inverting configuration, carrying to an easy interfacciabile amplifier with whichever source from the escape to level of line (type CD). In the case that between the source and the amplifier comes used an preamplifier, like the PRE, from the low stiffness of escape it is possible to use values lower than Ri and Rf with consequent lowering of the level of noise (however low).
Z-AMP 1 Schematic
Z-AMP 1 PCB Layout
Z-AMP 1 View 1
Z-AMP 1 View 2
Z-AMP 1 View 3
Z-AMP 1 View 4