  A synthetic fluid dynamo built in the spirit of the Bullard device [E. C.
Bullard, Proc. Camb. Phil. Soc., 51, 744 (1955)] is investigated. It is a
two-step dynamo in which one process stems from the fluid turbulence, while the
other part is an alpha effect achieved by a linear amplification of currents in
external coils [M. Bourgoin et al., New J. Phys., 8, 329 (2006)]. Modifications
in the forcing are introduced in order to change the dynamics of the flow, and
hence the dynamo behavior. Some features, such as on-off intermittency at onset
of dynamo action, are very robust. Large scales fluctuations have a significant
impact on the resulting dynamo, in particular in the observation of magnetic
field reversals.
