Newbie Question: VTA and Rega P25/RB600

you can buy spacers at www.needledoctor.com made for Rega 2mm and 4mm. it's truly a pain to adjust rega arms but that is the only option now for your turntable. in reality you cannot optimize VTA in Rega for the performance you can only optimize it for the cartridge profile i.e. not realy precisely.
you can also experience with different mats and felt mat is not the best for the records in particular. there will be always small particle left from felt when you flip over your record. rubber mats tend to accumulate too much statics.
you can also try to play with no mat.

Origin Live and Expressimo Audio both make variable VTA adjusters for the Rega arms. They are around $40. They are threaded adjusters, and not the easiest to use, but they do work. You can dial it in exactly, with a little patience and a good ear.
Generally, to adjust VTA, you start with the tonearm level while it is playing. Then, you put the arm back on the clip, and perform an adjustment, either up or down. Listen to the result, and determine if you went the right way or not. Make only small adjustments, and play around like this until you get the best sound. Different cartridges like different VTA, and you can only get it right by listening, and adjusting.

As per Mara & Twl. I'll add: patience is rewarding & keep the arm level, if not, SLIGHTLY off (hi or low) until yr cartridge settles. Then go back & re-adjust. Don't worry, it's easy!

I believe the 10x4 dyno is pretty on for the rega, and you may not need to adjust vta for it. You should look into the specs on it as they compare to the rega cartridges. Better yet, contact a rega dealer, or the importer and ask.

enjoy the vinyl!