Onboard 3-band EQ, potential mod and some more questions

[andruca]

Hi everybody. I've had a couple Yammie BB615s for some weeks and I'm finding what really sucks is that the onboard preamp lacks headroom when boosting EQ past a certain point (more evident when soloing the bridge PU, presumably the hottest?), thus it clips. I've mitigated this by lowering the output from the blend pot using a trimpot, so that it doesn't clip even when boosting. Now, I've been reading that onboard preamps usually can operate with a wide range of power suply voltage. I've been checking electrolitic capacitors and they're all 50V. Looks like there's no op amps here, just some transistors, resistors and ceramic caps too. I've made some pics...

So, (1) does it look like I could get away with feeding this 18V instead of 9V?

The other thing I hate about this preamp is that pots have this grey zone all around the center and only act seriously towards the ends, (2) is there a way I can have a more gradual action? Different pots?

SIDE NOTE. I definitely don't LOVE this preamp so if chances are over 50% it'll work on 18V I'd try. The last thing I don't like about it is that bass control is not low enough. Now, this is a cheap bass so I don't want to spend a fortune. I've already ordered a couple cheapo 3-bands from AliExpress (hideous brands with no feedback, cost 7 & 9€) and an Artec SE3 (with semiparametric mids, 16€) to try on. (3) Any experience/good practices to share about such cheap preamps (on any bass)?

Thanks a bunch for your help.

 

[ddnidd1]

The question is - what voltage will the transistors tolerate.

 

[andruca]

Here's a datasheet for the K30A transistor. It's chinese to me, I'm far from an electronics guy, I completely ignore what any of those voltage figures in the datasheet mean nor know any relation they could have with supply voltage, sorry :-(

 

[BassLife77]

looking at those cheap chinese junk Fullyconned capacitors no wonder it sounds awful. I would replace it. If you buy a $7 preamp off AliExpress more than likely it will be junk. You might get better results with the Artec but it boosts bass at 80Hz. I would make my own so I can control which frequencies to boost

 

[bigtone23]

Honestly, not drastically boosting EQ runs cleaner in most any design. That preamp is not super duper high quality, but I'm sure it's perfectly clean with mild boosts at best.

 

[andruca]

Honestly, not drastically boosting EQ runs cleaner in most any design. That preamp is not super duper high quality, but I'm sure it's perfectly clean with mild boosts at best.

True, but the problem is that setting it is impossible, pots act drastically at the final ~10 degrees of the turn. That was question 2, is there a way I can make it more gradual?

 

[bigtone23]

You can add resistors to modify the taper of pots. They usually go across the center and one outer leg of the pots.

 

[andruca]

You can add resistors to modify the taper of pots. They usually go across the center and one outer leg of the pots.

I see, so that it doesn't go fully open, isn't it? I'll give it a try, have many resistors and trimpots available to try. Thanks!

 

[bigtone23]

It can do that, or just modify the taper so it's more linear/gradual up to it's maximum.