I'm considering building up a passive bass with a MM pickup and, sparked by someone necro-ing a Wal thread on here I went and revisted: https://www.herrickpickups.com/products/split-8-coil-mm-humbucker/ I was looking to get an idea of the tone but didn't find too much except for these 2: Which are pretty tantalising - just wondered if anyone had some direct experience they could share!