I play bass just for fun. Recently, I have been considering an external preamps such as a Sadowsky SBP2 or an Aguilar AG for my passive Fender Jazz. The reviews say it give 'better' tone. But my bass combo has a 5 band EQ section. Assuming, i am not looking for a second sound whilst playing (soloing or overdrive), would I really need a pedal EQ to shape the tone? Any clear benefits of using a pedal preamp? Thanks!
It totally depends upon how your bass and amp sound together. 5-band EQ's can be great, or they can pinpoint all the wrong frequencies. First question is "are you happy with the sound you get from your amp without a preamp pedal". If so, then don't buy a pedal.
If you're not happy, have you exhausted all the capabilities of tone shaping in your amp. Are you familiar with how each of those 5 EQ's affect your sound. If not, you need to dedicate some more time to understand your amp and familiarize yourself with what each EQ option does. I have a few different amps, all but one are Eden or DNA amps (all were designed by David Nordschow aka: David Eden). The other one is an under-powered GK amp that I kept to use with guitar.
My big Eden amp is a WT500 that was upgraded from 500-watts rms bridged to 800-watts. It has the power supply from a WT800 in it so I refer to it as my WT500/800. It was the actual amp that David used to design all the Eden cabs from 1999 until he left to found DNA in 2009. It has a bass shelving EQ for everything from 30Hz down, and then three semi-parametric controls that, between them, let you control three octaves of Frequencies, from 30Hz up to 12KHz. Finally it has a Treble Shelving control for everything from about 2KHz up.
I spent a LOT of time figuring out what each of those controls did to my sound and the screwy thing is that I figured out that the only adjustment I need from setting all the EQ options flat, is to boost my low-mids at either 250Hz if my amp has the semi-parametric control to dial it in, or 500Hz if that's the only low-mid frequency the amp provides. I also have an Eden WTDI (Eden DI pedal with built-in WT preamp) and its mid-choices are either 500Hz or 2KHz. So I toggle it to 500Hz.
I also figured out while making small adjustments at a time (2-clicks makes a noticeable difference in the sound) that with my Bass, turning that low-mid boost up to 1:30 was what I needed to sound good in the mix. A little boost in the low mids anywhere between 250Hz and 500Hz gives you nice presence and definition in a mix. I also found that if I turned the boost up too much at either of those low-mid frequencies that my sound would honk at me - sounded bad! So then I slowly turned it back down until the honk went away and that's where I run it now.
Moral of the story is you need to spend time with your amp's EQ to figure out what its tone shaping possibilities are and do they let you get "your" sound. Now, if it doesn't let you get your sound, then you may want to get a DI with built-in preamp. Pretty much every major manufacturer makes one and if you like a sound from a particular brand, get that one. I carry a WTDI with me in my gig bag just in case I have to use a backline or need to run direct to the sound board. With its Eden WT preamp I just set it the same as I EQ my Eden amps; plug it into the effects return of a backline amp; and Voila' it sounds like my Eden gear. That's because I just bypassed the backline amp's preamp and hooked my preamp directly up to its power section by plugging it into the effects-in/return. That way I get the sound I want without wasting time trying to dial in the backline amp to something I deem acceptable. At one gig, a promised amp was not there, so I just ran into the FOH. My bass came out the mains and I heard myself just fine in my monitor.
I can also hook that directly into a snake for the soundboard and get my sound. In the case of a sound tech, I always tell him I have it set flat except for a boost to 1:30 at 500Hz. That way if he needs to make changes he knows where I'm starting from. Just an FYI if you get an Eden WTDI; if you have a passive Jazz Bass; and if you want the best sound for a pro-studio recording; toggle the mids to the 500Hz position and add a little boost in those low-mids. When I did that, they took my raw signal exactly as I sent it and just adjusted the level to match the mix. They were amazed how good it sounded coming into them and had to come inspect what I was using after the 3-hour session.
So those preamp pedals can come in handy. But as far as running them always, don't do that unless you can't get your amp to sound good enough using its native EQ section/graphic Equalizer. Then a DI stompbox with preamp can be a god-send