Efficiencies of nonlinear optical-to-terahertz (THz) conversion below one percent remain a limiting factor for applications of multicycle THz radiation like THz-driven acceleration and inspired the use of multi-line pump spectra. To overcome the difficulty of phase stabilization of multiple narrowband sources required by the multi-line approach, we exploit its temporal analog, i.e., regular pulse trains with THz repetition rate, in which the THz waves generated by rectifying the individual pulses add coherently. The optical setup producing the pulse trains consists of motorized interferometers and enables precise control over the pulse train parameters like pulse spacing and amplitude. It is operated with a laser providing 400 fs pulses and energies of up to 110 mJ, which is the highest yet attempted for a pulse-train-type experiment. Opposed to earlier work, pulse division is done after amplification making the system more flexible in terms of tuning the pulse number. We present initial results of an experimental campaign of multicycle THz generation in custom periodically-poled crystals with large-apertures up to 10x20 mm(2). The available pump energy allows filling these apertures at high fluences, promising increased THz yields. We investigate the dependence of the conversion efficiency on the single pulse duration and aim to find the optimum pulse number for different crystal lengths to determine the efficiency limitations in a regime avoiding laser-induced damage. Since crystal length and pulse number define the bandwidth of the THz pulses, this work demonstrates a path to an optimized THz source tunable to different requirements of applications.