I should have added....that it depends on the power supply you are using. Most modern power supplies have outputs that are smooth so as not to be a problem running a rotary machine. Personally, I don't see the need for the ferrite if you use a quality power supply. Here in the states you could to find the clamp on ferrite at RadioShack for under $10 or find them online thru electronic suppliers. If you buy online, know that there are different grades of ferrites that filter at different frequencies. You need ones that will filter thru the lower frequency spectrum. Some new rotary machines may use brushless motors and these would be more sensitive to electrical noise than a brush type, but again....use a good power supply.

What is most important is the polarity that you run your machine. As Alie stated before it is a good idea to mark your clip cord connections for polarity. Colored heatshrink works good too. Slip it over the contact wire away from the connection point and then heat....voila!

You would think that after how many years there would be a standard direction on a clip cord.....but still not really. Back when I was doing coil "relay" machines for a company, I suggested using bipolar "non polarized" caps in the machines because they were having caps blow out for some reason....I wonder why??? Because they were hooked up bass-ackwards....DUH!
When working on the wireless footswitch adapter...again years ago....I was amazed to find that MOST of the tattoo supply (big ones too) companies at the time did not know the polarity of their units!... I called each one and asked. So make sure to run you machines with the proper polarity that the machine manufacture recommends.....it will live longer. Use a voltmeter and check.....