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The AGATA triple cluster (ATC) detector consists of three asymmetric, 36-fold segmented, hexagonal shaped, encapsulated tapered high-purity germanium (HPGe) detectors. The cluster detector comprises 111 high resolution spectroscopy channels which are operated in one common cryostat. All 111 energy signal channels are equipped with a preamplifier stage based on a cold FET technology in order to provide best energy resolution of core and segment signals. The three average energy resolution values of the segments at low γ - ray energies of 60 and 122 keV were measured to be in the range of 965–1040 eV. For γ - ray energies of 1332.5 keV the average energy resolution of the 36 segments is between 2.10 and 2.19 keV for the three detectors. Crosstalk properties of the highly packed analog preamplifier circuitry and detector assembly were investigated. The crosstalk level between different detectors was found to be negligible on a level below 10−5. A low crosstalk level of 10−3 was found for the segment signals within the same HPGe detector caused by the interplay of the core coupling capacitor and the capacitances of the 36 segments. The measured values compare well with expected calculated contributions.