  We report on the design and commissioning of a new spectrometer for muon-spin
relaxation/rotation studies installed at the Swiss Muon Source (S$\mu$S) of the
Paul Scherrer Institute (PSI, Switzerland). This new instrument is essentially
a new design and replaces the old general-purpose surface-muon instrument (GPS)
which has been for long the workhorse of the $\mu$SR user facility at PSI. By
making use of muon and positron detectors made of plastic scintillators read
out by silicon photomultipliers (SiPMs), a time resolution of the complete
instrument of about 160 ps (standard deviation) could be achieved. In addition,
the absence of light guides, which are needed in traditionally built $\mu$SR
instrument to deliver the scintillation light to photomultiplier tubes located
outside magnetic fields applied, allowed us to design a compact instrument with
a detector set covering an increased solid angle compared to the old GPS.
