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Constructing the SRE330
The SRE330 project uses the SRE330 main board, the optional SREIO input/output board and the
RPSU +/-15V power supply module.
The SRE330 main board requires a well regulated and quiet +/-15V to +/-16V supply. The current
taken by the SRE330 varies slightly with modulation depth but the maximum current is around
+225mA and -180mA. Power is admitted onto the main board via a 5-way Molex 0.156” KK or 5-
way 0.156” MTA connector. Pin 1 is +15V, pin 2 and 3 are 0V, pin 4 is -15V and pin 5 is panel
ground. Panel ground is typically connected to 0V at either the power supply or the input/output
sockets. On the SRE330 main board Pin 5 connects only to the pot brackets and switches' metal
supporting tangs.
The SRE330 is a large board at 389mm wide and 153mm deep. It is secured to the front panel by
the pot brackets and to the lower panel of the case with three M3 screws and spacers. The board has
four copper layers, the top and bottom copper layers carry signals, the top middle layer carries
power supplies and some signals, and the bottom middle layer is solely designated to 0V. A four
layer design, although expensive to produce, gives better performance than standard two layer
board designs. It is, however, imperative that when soldering, and especially desoldering, that the
through hole plating used to line all the solder pad holes is not damaged. If you do need to desolder
a part then either use a proper vacuum desoldering tool or cut the component body out first and then
desolder one component leg at a time.
The 16-way ribbon cable used to transfer the balanced audio signals between the SRE330 main board and the
SREIO socket board.
The SREIO board is an input and output socket board designed for this project. It allows the simple
interconnection between the SRE330 main board and the audio sockets via a single 16-way 0.05”
IDC ribbon cable. The SREIO board also features a electromechanical relay to cut the connection
between the main board's output circuitry and the output sockets at power on and power off. This
reduces the likelihood of damaging thumps on the audio output when power is turned on and off.
The anti-thump circuitry is powered from the main power supply module via a three way 0.156”
Molex or MTA connector. Pin 1 is +15V and pin 3 is 0V. Pin 2 can be used to 'ground' the sockets'