Hi John, Irving2008

Thanks for your suggestions. This does all make sense now, and probably explains why the stepper ran smooth at the higher rpm, since the pulses would be closer together and the deceleration of the motor between them would be less, creating less back EMF.

I tried both the 0.1uF capacitor, and the 0.01uF + 0.1uF, and both combinations reduced the kick of the glitch, and also brought the frequency down from >8KHz = no glitches to >6KHz = no glitches. A small improvement, but not solved. I tried a 1000uF 35v capacitor which I had, and this brought the frequency down to about >5.5KHz = no glitch. Roy at DIY CNC said that he had sold alot of these supplies and had no problems, so it could be faulty. He suggested I try a 4500uF - 10000uF 35v capacitor across the power supply in the first instance, so I have ordered a 10000uF 35v unit from ebay. If this does not work, then I'm still open to try a replacement.

Otherwise, I did have a look around the internet for an equivalent linear supply of about 30 - 33v, up to 10A, and didn't find much about. I could probably live with a lower current rating since there are 3 axis of up to 2A each, but some overhead is nice. Alot of people had made their own supply from a transformer, diode rectifier circuit, and capacitor(s), but I don't trust my electronics enough for mains. Where are you buying them from?

Thanks
Barry