Hi everyone. Not sure if this topic has been covered elsewhere, and if it has please feel free to point me in the right direction.
I’m about to purchase a Charvel San Dimas PM 4.
I’m immediately going to upgrade the preamp.
I’m thinking of going with the Aguilar OPB-3 SKPP.
Any guidance and/or suggestions on different onboard preamps and why would be greatly appreciated. 
Great bass, one of my favorites. I pulled the preamp out in my first one, it was broken. But I got that one used. Anyway, check with @Wombat-metal, they’ve upgraded the preamp in theirs. I think… Darkglass Tone Capsule, if memory serves?
Thanks! What did you go with?
hey @Pablo - I think a lot of things.
I think the Darkglass Tone Capsule is a good preamp if you’re looking for that Darkglass tone. It’s an excellent preamp
I think Aquilar is an excellent company, I am putting an Aguilar pickup in one of my basses. I don’t have any experience with their preamps and can only speak well of their reputation as a company. I just have no direct experience with their amps and have done no research so offer no opinion on amps by them.
I think Audere makes some good preamps which offer good bang for the buck. I have one in my Jazz bass and it sounds great.
The darkglass doesn’t allow you to adjust treble, just bass, high mid and low mid which has great effect on the sound. The Model P and Model J pickups in your bass have strong mid presence, and the DG helps shape that. I think it’s a good match for the pickups
The Audere is more conventional. and a 4 band preamp is pretty cool. Looking at their sight. for a 5 hole configuration you would have vol, bal, hi mid, lo mid, and stacked treb/bass for $153
TLDR:
I think the Charvel stock preamp is meh. I think an Audere will give you good tone, I think a tone capsule will have more character, I think either are good and would buy both again if I were in the market. For the Charvel I might lean towards the tone capsule because I like leaning into the strengths, and those DiMarziospickups are strong mids and good rockers. If you want a more traditional sound would go Audere or Aguilar
Are you keeping the original pickups @Pablo?
Are you running 9v or 18? I put that exact model on my Fender Deluxe before and it’s not bad. The PP mid sweep is kinda overrated, lol. I had it paired up with the 4 pj HC. Tried both 9v and 18 power plant. It’s usually not what you think. 18V is not twice as loud.
I’d be keeping the original pickups. I like how they sound.
I was thinking 18V just because my previous bass was 18 as well, and, for the extra bit of headroom, but 9 would be fine too. It’s not a big deal.
If it’s got a DiMarzio Model P (like it sounds like it is), IMO you can’t get better anyway - it’s my favorite P pickup 
It’s a Model P/Model J combo for stock pickups
Can’t do much better than that
In my first San Dimas, the pre-amp was bad. It would randomly static out, where the signal would decrease in volume and become just a static buzz for a couple of seconds, then it would pop back to normal. I pulled that pre-amp and converted the bass to passive, with volume/volume/tone controls.
I’m leaving my second San Dimas alone. I’m happy with it, although it could use some extra shielding (my house is an… amusement park for EMF). I’ll probably just spring for a noise gate and be done with it. Different discussion for a different day, though. With regards to the pre-amp in my second San Dimas, I’ll probably leave it as is, although I am dreadfully curious about the Aguilar and the Darkglass.
I have a DG preamp in a bass and I really like it. Like @Wombat-metal said, there is no treble knob, but I find I leave that at zero on all my other active basses. The Aguilar has a good rep too, I dont think you could go wrong with either.