Alembic filter preamp PF-6

Jarno · Post by **Jarno** » 19 May 2023, 14:24

Like the F1x, was browsing and recalled that I actually bought the schematic for the Alembic onboard dual filter preamp (older version of the "series" onboard electronics, I think).
I'll post it here for posterity.
Quite elaborate, these basses have two pickups and a dummy coil, which needs to be carefully adjusted. They also have a second order low pass filter per pickup, with either a switch or a pot for "Q". In the old days, they used a separate outboard power supply, not sure if that is still the case.

The (dual) fet is probably unobtainium by now, as is the weird opamp (Harris HA-911), but that opamp is not great apparently. (well, as can be expected, there has been some progress in the performance of IC's in 45 years

)

: 25013.jpg (108.93 KiB) Viewed 3345 times

bow_and_error · Post by **bow_and_error** » 31 May 2023, 00:22

Interesting use of what looks like RG316 coaxial cable in place of a standard shielded one. I never thought to just terminate both directly to the board. We have a bunch of this at work, so I may have to give it a shot next time I wire up a guitar.

Jarno · Post by **Jarno** » 31 May 2023, 11:11

We have that stuff as well, stripping it is a real PITA, at least the stuff that we have here. Those inline connectors are interesting as well, but knowing Alembic, probably heinously expensive (and I wonder if these are meant for this type of cable and thus lend themselves to proper crimping).
Also, I bought a bass with Alembic pickups, and that has the simpler preamp, will reverse engineer that as well, that does not have the JFET buffers, no dummy coil for noise cancelling, and switchable Q rather than continously variable Q.