Bartolini NTMB reverse engineered (schematics inside)

[markusw]

Finally I've depotted my faulty NTMB onboard bass preamp. All parts were identified by their labelling and/or measuring with my DMM. Could some one please have a look whether the schemo makes sense. Interestingly Vref is NOT exactly V/2, whats the use of this?

I also did a simulation in LTSpice and all pots do what they are supposed to do. I will post images of the simulation later on.

Thanks for your help in advance.

Markus

[lethargytartare]

Fantastic!  How big of a circuit board did the thing take up?

[markusw]

Glad to hear that someone has a use for it!

Actually it uses two small PCBs. See also http://diystompboxes.com/sboxforum/viewtopic.php?t=30484&highlight= for a pic of the unit before depotting it.

One PCB measures 41x23mm, it carries the opamp, virtual gnd circuit, input, output and the bass control parts. Treble and mid control parts are on the second PCB that is 23x29mm.

Both PCBs were shielded by a brass foil, at least it looked like brass. The layout was rather dense with some jumper wires crossing several components, though not really tidy. But who cares, it was a nice sounding unit before it got faulty.

I am right now doing the layout for my clone. Since my Carvin has a large and nicely copper shielded cavity I do not stick to the Bartolini layout. Furthermore, I want to use PCB mounted pots, so I'm restricted anyway.

Good luck,

Markus

[Nikolay]

Great marcus ) !!!
Thanks  

[Ben N]

Nice job.  I had the same question about an asymmetric voltage divider in the power supply re: my Soundtank FZ5 Sixties Fuzz.  Still curious about the answer.  Edit:  Ah, just saw the other thread--never mind.

BTW, does that Bartolini require special (lo-Z?) pups?

Ben

[Nikolay]

Ben, bartolini are like other pickups, az  you see for volume there is used 250k pot. You can use bartolini pickups without this NTMB, and you can use ntmb with any other single pickup.

[Ben N]

Nikolay,

Am I missing something?  You may be right about the pickups, but the vol pot I see in the schematic is 25k and comes after active circuitry, so it does not interface with the pickups at all.  Or do you mean that 250k is the recommended pot value for using the pickups passively?

Ben

[Nikolay]

Or do you mean that 250k is the recommended pot value for using the pickups passively?

Ben

Yes

[Perco]

What do those B2Grey, B2Viol, B2Orange and others refer to ? Are they wires from the Bartolini active pickup ? If yes, how to adapt the schematic with a pickup wich has only 2 wires ?

[markusw]

What do those B2Grey, B2Viol, B2Orange and others refer to ? Are they wires from the Bartolini active pickup ? If yes, how to adapt the schematic with a pickup wich has only 2 wires ?

They just connect the two PCBs/blocks of the NTMB. If you look at the NTMB wiring diagram, you can find them too. I just added it for internal reference.

Regarding the blend pot: its a double MN tapered pot (250k). I suppose it could also be used for just mixing two passive pickups without the subsequent NTMB. For the exact wiring of the blend pot please refer to the NTMB wiring diagram (can be downloaded from the Bartolini hp). Two active pickups probably might overload the NTMB (depending on the setting of the trimpot).

Regards,

Markus

[markusw]

I just updated the schematics. Now the blend pot is included too.

Good luck with your clones  :wink:

Markus

[Bernardduur]

Thanks man.

[Bernardduur]

Hi. I almost finished building the clone. I just wanted to know where the grey wire should go (as it has a start, but no ending). As you said it connected the two PCB to each other, but a loose wire?

Second, is it possible in this NTMB to add a second 9V battery to get more headroom (don't know what model I just cloned).

Thanks!

[markusw]

I just wanted to know where the grey wire should go (as it has a start, but no ending). As you said it connected the two PCB to each other, but a loose wire?

Sorry, I did'nt describe it properly. There are three wires (grey, orange and violet) that connect the mid and treble control PCB with the main PCB (basically the caps and resistors as well as the coils for the mid and treble control are connected via these three wires to the second opamp on the main PCB)  I just added the labels for internal reference. So all connections are shown in the schematics. Maybe it's better if I delete the labels.

It's the 9V version. However, if the caps (esp. the tants) you're using are rated a high enough volatage, I suppose you can connect two batteries to it. The opamps should'nt have any problems with 18V.

Good luck with your clone. BTW, where did you get the MN taper blend pot?

Markus

[Bernardduur]

OK, thanks! Will go on. The guitar store on the corner here supplied them, but I had too much pots already going so I decided to get total control and added two individual volume pots (small ones, stock). Now I have 6 knobs on my jazz bass...... and a switch

[markusw]

Now I have 6 knobs on my jazz bass...... and a switch

:shock:

What controls do you have?? Two volumes, bass, mid, treb, ....:?:

Markus

[Bernardduur]

6 knobs:
- volume neck
- volume bridge
- bass
- treble
- mid
- end volume

and a 3 way switch to add 3 bands of mid control

the end volume knob is a push / pull pot switching passive / active.

[markusw]

the end volume knob is a push / pull pot switching passive / active.

how do you switch the NTMB active/passive?

[Bernardduur]

OK, it is not that great; it is a bypass switch so I let the signal from my pickups or through my clone NTMB or directly to the output (I have no treble / bass control than).

There is a wiring guide on the Bartollini website.

[markusw]

I did'nt want to drill a 6th hole for a mid select switch. Also I could'nt find a concentric dual pot for a continous mid sweep like some of the EMGs have. Therefore, I added a 6-fold micro switch to my layout to switch several mid caps. I my original NTMB there was a 100nF mid cap. By pulling the pot it was switched out of the circuit. However, I never used this setting since it took away to much bass IMHO.

I'm keen to see/hear your clone.

Markus