WEM Mk4 Copicat - low volume output

[Murphyv310]

I know some have polished up heads with the likes of Solvol Autosol or even rubbing compound, wet & dry would need to be done carefully so the head face remained perfectly parallel. But don't forget that any further reduction of material off the face of the heads widens the head gap thus reducing the frequency response.
Can you confirm or otherwise that the straight through output is normal or low? If you haven't done this test then that changes things.