The original Dan Armstrong - Ampeg basses made between 1969 and 1971 had pickups that were held in by a single thumb screw. To swap out the original bass pickups you had to remove the pickguard and loosen three wood screws that connected the pickup lugs to the wiring harness.
Check out the pics of my 1970 Dan Armstrong bass. You can see the chrome thumb screw on the back of the bass. I have a brand new Kent Armstrong pickup installed, but you can see the back of the original pickup and the three terminals in the bottom of the pic. Also notice how the pickup cannot slide into place.
The reissue DA basses had a different design that was very much like the guitar version. These later version pickups used the same thumb screw but could be swapped out quickly without having to remove the pickguard. They use “banana” style connectors rather than the terminals.
The photo below shows a reissue DA bass. You can clearly see the cavity to the left of the pickup that allows players to quickly swap pickups.
Also notice this bass has a selector switch. The very early original basses (such as mine) were not equipped with this switch. Sometime around late 1970 the switches were added. You might ask what the switch did since there is only one pickup. The answer is, there are actually two pickups! Bill Lawrence helped Dan Armstrong design the bass pickups. They came up with the novel idea of placing one pickup on top of another and then encasing both in epoxy. One of the two pickups is designed to have a more treble sound while the other is more bassy. The switch allows the player to mix and match the two sounds. The DA guitars, btw, did not use the same design for their pickups.
As basses go, the Dan Armstrong is very versatile. Apart from being a short scale with 24 frets, the most notable features are a TON of sustain and a super punchy sound. For reasons I’m not sure I can explain, notes on this bass are projected with an extreme amount of authority and clarity.
Replacement pickups for the originals and reissues can be purchased from Dan’s son, Kent (who could easily win awards for being the nicest, most giving person in all of music).
The bridges/saddles on the basses and guitars are the weak point. If you look on my original bass you’ll see I added a split fret onto my bridge to help with intonation. It played well before but is even better now.
Some have pointed out that the DA instruments are heavy. Mine weighs in at 8 pounds 10 ounces. That’s not much more than other basses.
All in all, I love my DA bass. It not only plays well, sounds great, and looks unique, it seems to attract a ton of attention. While the rest of my band mates are enjoying breaks between sets, I usually have two or three people asking me about my bass.