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The inductance Lsq, transimpedance Z, transfer function VΦ and flux noise SΦ have been experimentally determined, in open loop mode, for a series of simple dc-SQUID amplifiers which varied only in the length of the loop. The SQUID design had no input flux transformer but included a current path for directly injecting flux into the loop. Correlations between these parameters were obtained which compare favorably with theoretical estimates. We confirm that the best device performance (small SΦ) is obtained if Lsq is kept small whilst VΦ is maximized; the latter was achieved in one device by a novel "ion-beam trimming" technique.