Well remember that doc I linked to back in post #86 - the stepper basics guide from geckodrive? Here's a quote from page 11.
"The drive works best with unregulated power supplies though regulated linear and switching
power supplies may also be used. What matters is the power supply must have a large output
capacitor and an unregulated supply intrinsically has one.
If a linear regulated or a switching supply is to be used, then a large capacitor should be placed
across the output terminals. A 2,000 to 10,000 uF capacitor should do."
However, I note that this has apparantly been dropped from the latest version of this doc
http://www.geckodrive.com/support.aspx?q=10005#Power%20SuppliesMake of that what you will
Ian