earth lug to the power supply's 0V if desired although this is not normally needed in most SRE330
builds.
The relay and power muting circuitry on the SREIO board.
The SREIO board is 34mm high and 185mm wide. It is a two layer design. The sockets used are the
industry standard 1/4” TRS (Tip Ring Sleeve) socket, the Switchcraft 114BCPX. Various clones of
this socket are available but arguably Switchcraft still make the best version.
The RPSU is a power supply module designed specifically for the SRE330, although it is likely that
other future Oakley Sound rack projects will use this module too. It gen/-15.3V at up to
around 1A given sufficient heatsinks and a suitable mains transformer. The SRE330 only needs less
than 250mA but even so adequate heatsinking must be used for the two power devices. Since best
performance for any electronic audio device comes from using a metal case it makes sense to use
the case itself as a heatsink. Details on how to do this are given later in this document.
The issue 2 RPSU wired for use with a Yamaha PA-20 external power supply.