'94 Tobias/Bartolini preamp and pickups question

[Combinator]

Hey, TBers-

I just picked up a 94 Tobias classic 6 string, and I really like the bass itself, but am not too fond of the electronics. This was before Tobias/Gibson switched to using the NTMB, so what it has is the XTCT-LZ (low input) preamp, a DTA 1.3 buffer, and an unmarked mid module, fed from the preamp, that may be either of gibson or tobias design. The pickups are both engraved MT6T.

Here's the issue: this bass has like negative treble. Admittedly, the wood combo, purplheart and walnut (walnut neck, pau ferro board) is a darker sounding wood combo to have, but played acoustically, this bass has a lot more high end response than what gets put out it's jack.

I threw an Aguilar OBP-3 pre in there, which I have in another bass and feel very comfortable with, and to my surprise, the problem was not fixed at all. In fact, the output volume was WAY low, and is still pretty low with the stock electronics. I tried many different wiring combinations, incorporating the buffer with the aggy, changing the vol and blend pots from 25k to 250k, etc., but nothing has improved that high response. The other weird thing that it's got going on is an apparent, built in, severe mid cut that totally cuts all the life out of the sound. I have to run it with mids and treble full to even be close to acceptable, then turn the treble ALL the way up on an SWR workingman's 12, and 3/4 all the way on a GK 1001RBII through an Epifani 3x10, and still it's not even as close to the brightness of my warwick streamer stgII with the Aguilar preamp.

So, does anyone know about these MT6T pickups? They seem to be extremely low output, waaay too traditional/dark for my tastes, and a general pain. They are approx. 1.25"x4.375" - does anyone know of a good replacement?

Or better yet, does anyone know of a way to coax more treble and mids out of the existing bart pre, or my OBP-3? Is there a pot value mod I could make, or some resistors I could solder in, or something to make either of these preamps a lot more trebly? I can email the schematics of everything if anyone wants to take a look. The bart treble and bass pots are 500kB, with the mid being 50. The Aguilar's are all 50KB. The bart's mid is a little more complex than normal, as it has a couple resistors soldered from the middle lug to each side lug, and is connected directly with the treble and bass pots. It supposedly cuts at 400hz, but boosts at 250hz plus adds high shelving above 2khz. I want 6khz and above, baby!

What do you think? Pickups? Voodoo? What's going on here?

 

[luknfur]

I think 6K up has minimal impact on bass tone - slappers excepted. To me anything 1K up is treble.

That said I'd wager your frequency issue is much lower than 6K. Bass is really about mids for the most part - roughly 200K - 1K

I think I had that exact pre once (not the bass) but it's been too long ago but I'd also wager the pre isn't the issue - which I think you've already concluded (more or less) as that's substantiated by the Aggie making no difference. To me Bart, Aggie, and EMG pre's all basically sound the same and are not a consideration in tone so much as other factors - size/whatever.

The woods in my experience aren't going to make any significant difference either. You won't know what the acoustic properties of a bass are till it's built regardless of the woods. And the acoustic properties acount for a fairly small proportion of the tone - which is not to imply they may not be significant.

Don't know the pups but my guess is that's you're source (core of the basses tone). In terms of output the earlier Barts were meant to be used with a preamp (and that hasn't changed a whole lot actually). Bart pre's usually have an internal gain control trim pot. Another issue with output is it takes a lot more watts to pump bass that is does mids/trebles - especially anything below about 80Hz.

I recieved a bass with a pair of M34C's that were the darkest pups I've ever heard - basically unusable. Again it's been so long I can't remember the details but I stuck like a modified '54 Les Paul passive v/v/t/t, used two spaced and different cap values and threw in that Bart inner coil/HB/outer coil switching and that resolved the issue. Worked out real well cause the cap values ended up actually being blendable for either or both pups - lots of tone variation for a passive (even for an active). Unfortunately never wrote down the diagram and haven't been able to duplicate it since.

Bottom line - wire the bridge pup straight to the jack and see what tones you can get running off amp controls. A decent amp pre will exceed anything you'd get from a typical onboard pre and if you can't get a useable tone from the brighter bridge then it's not gong to happen from a neck pup. You could also just throw a cap in between the Bart ground and jack if you wanted to dink with the pups a little to make sure they're to be jetisoned. I wouldn't give up on them after my experience with the M34's.

For replacement you'll just have to measure the pups and go to maker sites and see what matches. Bart doesn't really make freak shape pups (unless they're "whatever repalcements) so you should be good. I also wouldn't rule out a different Bart by any means cause they all sound different.

 

[Combinator]

Thanks hoss, I appreciate it. I think it's the pickups, too. I'm going to sell an Ibanez SR1006efm to help fund the purchase of this bass, but before I do, I think I might try its barts in the Tobias first. I think they're MK1s, which aren't thought of too highly, but they did sound really nice in the Ibanez.

One question - around what cap value should I experiment with for your suggestion, and did you mean between the PU and ground, or preamp and ground? What is this doing, in electrical terms? Thanks!

 

[luknfur]

A lot of guys like the MK1's.

Standard caps roughly a .050mfd (.047 more precisely I think), the smaller value the brighter and it takes about .010 for me to really tell a difference so probably start with a standard, then about .03, .02 will tell you. I'd wire it straight to the jack first as the caps may not be needed. Cap would go between the pup ground lead and the jack ground. Forget the pre cause you want it out of the circuit to check the pup for exactly what the pup puts out.

 

[Lewis Young]

Hey, TBers-
Hello kind sir.
I just need to know which wire is the Hotwire from the pickups on my Toby Pro 6 string???
I just picked up a 94 Tobias classic 6 string, and I really like the bass itself, but am not too fond of the electronics. This was before Tobias/Gibson switched to using the NTMB, so what it has is the XTCT-LZ (low input) preamp, a DTA 1.3 buffer, and an unmarked mid module, fed from the preamp, that may be either of gibson or tobias design. The pickups are both engraved MT6T.

Here's the issue: this bass has like negative treble. Admittedly, the wood combo, purplheart and walnut (walnut neck, pau ferro board) is a darker sounding wood combo to have, but played acoustically, this bass has a lot more high end response than what gets put out it's jack.

I threw an Aguilar OBP-3 pre in there, which I have in another bass and feel very comfortable with, and to my surprise, the problem was not fixed at all. In fact, the output volume was WAY low, and is still pretty low with the stock electronics. I tried many different wiring combinations, incorporating the buffer with the aggy, changing the vol and blend pots from 25k to 250k, etc., but nothing has improved that high response. The other weird thing that it's got going on is an apparent, built in, severe mid cut that totally cuts all the life out of the sound. I have to run it with mids and treble full to even be close to acceptable, then turn the treble ALL the way up on an SWR workingman's 12, and 3/4 all the way on a GK 1001RBII through an Epifani 3x10, and still it's not even as close to the brightness of my warwick streamer stgII with the Aguilar preamp.

So, does anyone know about these MT6T pickups? They seem to be extremely low output, waaay too traditional/dark for my tastes, and a general pain. They are approx. 1.25"x4.375" - does anyone know of a good replacement?

Or better yet, does anyone know of a way to coax more treble and mids out of the existing bart pre, or my OBP-3? Is there a pot value mod I could make, or some resistors I could solder in, or something to make either of these preamps a lot more trebly? I can email the schematics of everything if anyone wants to take a look. The bart treble and bass pots are 500kB, with the mid being 50. The Aguilar's are all 50KB. The bart's mid is a little more complex than normal, as it has a couple resistors soldered from the middle lug to each side lug, and is connected directly with the treble and bass pots. It supposedly cuts at 400hz, but boosts at 250hz plus adds high shelving above 2khz. I want 6khz and above, baby!

What do you think? Pickups? Voodoo? What's going on here?

 

[Lewis Young]

I need to know which wire is the wire to connect to the new preamp??

 

[Lewis Young]

Coming from the stock pickups!!!