PRE 3 complementary-differential preamplifier
PRE 3 is a complementary-differential preamplifier with JFET input stage and MOSFET output stage. It is a minimalist approach to a high quality, good sounding preamplifier.
PRE 3 follows positive experience obtained with Dispre 2-JFET preamplifier. It uses tightly matched input JFET quadruplet and power MOSFETs in the output stage.
The output is single-ended. The purpose of XLR is to offer possibility of 3-wire connection to eventual true balanced input of power amplifier; the 3-wire connection reduces interference voltages across signal ground wire by subtraction.
Simplified circuit diagram
There are 2 options of the JFET devices for the input stage. 2SK389/2SJ109 dual JFETs, that are very difficult to buy. The 2nd option is to use single JFET parts, well matched within 3% of Idss. The PCB is prepared for these single devices. For the output stage, Hitachi 2SK413/2SJ118 are used.
PCBs are not available now.
Pavel Macura 1/2011