We study the LISA sources that arise from isolated binary evolution, and how these depend on age and metallicity, using model stellar populations from . We calculate the combined GW spectrum of all the binaries within these population, including all types of compact binaries as well as those with living stars, and use these results to investigate the detectability of star clusters with LISA. We find at late times the dominant sources are WD-WD binaries, but at times before approx. 10 9 years we find a significant population of NS-WD and BH-WD binaries, which is related to the treatment of mass transfer and common envelope events in , 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. Our results suggest that nearby star clusters might produce GWs detectable by LISA or future missions throughout most of their evolution.