  We study the LISA sources that arise from isolated binary evolution, and how
these depend on age and metallicity, using model stellar populations from
BPASS. We model these as single-aged populations which are analogous to star
clusters. We calculate the combined GW spectrum of all the binaries within
these model clusters, including all types of compact binaries as well as those
with living stars. These results allow us to evaluate the detectability of star
clusters with LISA. We find at late times the dominant sources are WD-WD
binaries by factors of 50-200, but at times between $10^8$ and $10^9$ years we
find a significant population of NS-WD and BH-WD binaries (2-40 per $10^6$
M$_{\odot}$), which is related to the treatment of mass transfer and common
envelope events in BPASS, wherein mass transfer is relatively likely to be
stable. Metallicity also has an effect on the GW spectrum and on the relative
dominance of different types of binaries. Using the information about known
star clusters will aid the identification of sky locations where one could
expect LISA to find GW sources.
