Bartolini NTMB reverse engineered (schematics inside)

[Bernardduur]

HA, me too.....

dual concentric pots were hard to find, and way to expensive. So I was forced to use individual pots.... I've now narrowed it down to 5 pots (found a blend pot very cheap).

(and I like to have total control)

One last question: are the values of the inductors that high? (150 milli Henry?). I have a lot of problems getting them here......

[markusw]

One last question: are the values of the inductors that high? (150 milli Henry?). I have a lot of problems getting them here......

I did'nt measure them but they were labelled 154J, so they should be 150 mH. I also could'nt get 150mH coils. Therefore, I replace them with three 100 mH.

Markus

[Bernardduur]

Ah OK, I did the same.

I could not get hold of the IC so I swapped it with a OPA2134 IC I had laying around (few samples). Now waiting for the last part and I am ready to turn it on (and off of course).

[markusw]

I was thinking too to check how it sounds with Burr Brown opamp. Unfortunately, they seem to draw much more current from the battery than the MC33178. Anyway, it will be interesting to hear if they sound different.

Now waiting for the last part and I am ready to turn it on (and off of course).

Right now, I'm etching the PCBs for my modded version. Basically, it has two input buffers that get blended by a fake log/antilog pot. Since I intend to put it into my Carvin bass that has a large, shielded cavity and I wanted to reduce the number of cables I'm using PCB mounted pots.

Markus

[Bernardduur]

Nice... PCB..... No, I am using a breadboard; only things I have right here. The IC will come somewhere next week (free samples!!) and my new control plate will come soon I hope.

We'll see!

[markusw]

Nice... PCB....

I like to use them because once the layout is done on the PC, things usually work. Especially since the only equipment I use for making foto PCBs is a writing desk lamp, some transparencies and a inkjet/laser printer....and a little trial and error  :wink:

Markus

[Bernardduur]

Have fun. Let me know how it works out!

[MR COFFEE]

Thanks for passing this along Marcus!!!!!!!!!!

[Gabriel Simoes]

Hello...
I was looking for the MC33178 ic ... and I found at TI that the TLE2142 is a direct replacement for that motorola ic.
But I know almost nothing about that TLE family. Could we use them as replacement for tls and stuff like tl072 ?
Thanks for your help
Gabriel

[MR COFFEE]

Gabriel,
The TLE2142 op amp has a bipolar input stage which is fairly quiet for a bipolar op amp 10nv/hz, and has a low 1/f corner of only 10 hz.

As long as your source impedances are low, you can use it lots of places and get good performance.

It's not a good sub for a TL072 in circuits with higher source impedances because even though the '072 has higher voltage noise, it has much lower current noise which makes it a nice low noise op amp at higher source impedances (>8k or so).

FWIW

[Gabriel Simoes]

Thanks MR COFFEE

I know not much about ICs and stuff. I was trying to know what a bipolar input stage is, or what a jfer or fet input stage is, but I can't find any info about it.

So, I have a bass with 2 asb5 from seymour duncan basslines, wich are active pickups, but I don't know if their output is high or low impedance ....
and this schematic is for passive pickups with hi impedance , but it says MC33.... (forgot the name of the IC) ... and the TLE2142 is a direct replacement in the TI list.

I would appreciate if you could help me with this too.
Thanks for you attention and patience.
Gabriel

[markusw]

I dont´t know whether the input stages are important for this circuit. One feature that makes the MC33178 attractive is the low supply current that is roughly 1/10 of a NE5532 or OPA2134. Therefore, your battery should last much longer.

Please correct me if I am wrong.

Markus

[Bernardduur]

I added a stereo plug on the output and added a 9v supply line in the first pedal my signal runs through, so no battery is needed. I used a XLR cable (three lines) and stereo plugs.

[markusw]

I added a stereo plug on the output and added a 9v supply line in the first pedal my signal runs through, so no battery is needed. I used a XLR cable (three lines) and stereo plugs.

I was thinking too to try this approach. So the first pedal could also simply be a power supply box with either 9V or maybe even 18V and just a stereo input plug and a mono output plug. I suppose it just has to be a good regulated ps without any ripple. Othrwise there would be hum.
Hmm, may be I will upgrade to this version once my NTMB clone is working.

BTW, Bernadduur how's yours working?

Cheers,

Markus

[Bernardduur]

Right now it is working like a charm. I need to experiment a bit with it because I get too fast too much gain and overdrive the amp a bit (also because I do not have a good bass amp (will change soon)). I made the trimpot accessible on the control plate (screwdriver) so I could change that when I play through different amp (I organise jamsessions and therefor play a lot through different amps). Here are some pics:

pic 1
pic 2
pic 3
pic 4
pic 5
pic 6
pic 7
pic 8
pic 9
pic 10
pic 11
pic 12

[markusw]

Right now it is working like a charm. I need to experiment a bit with it because I get too fast too much gain and overdrive the amp a bit (also because I do not have a good bass amp (will change soon)). I made the trimpot accessible on the control plate (screwdriver) so I could change that when I play through different amp

Great to hear that it works. Nice pics! Congrats!!   So obviously my tracing work produced something useful. One Q: with the switches do you change only midrange caps or also other tone control caps? Do you prefer any other setting over the stock version?
One comment regarding the trimpot. IIRC it was set to about 50% on my original unit which gives you about 2-fold gain at all tone-controls flat.

I already got some pots that fit into my bass but I'm still waiting for some other parts (the austrian mail is terribly slow ). Since I now know that it's working I am even more keen to rebuild mine (I had a few bugs in my layout).

Markus

[Bernardduur]

I found a schematic on the Bartolini site for a midrange switch with 3 stages that shifts between 3 different mid settings. It is really useful. Other switches are active / passive and series / parallel for the two pickups.

[Gabriel Simoes]

Hey Bernardduur,
Did you use the original schematic or the modded one ?
As i told markusw before, next week I will try to build only the eq stag and maybe skip the gain one .. so I guess I won't face this gain problem ... and if I need it, maybe I can do what you did, use the gain stage, since I have a volume/blend stack pot, and room for an othe one, who would be gain ...
I'd like to know 2 things ... could I mix the 2 pickups signal and use a single opamp ?
I cant find tantalum caps, would the sound get too different if I use eletrolitic ones ?

[Bernardduur]

Hmm, I have no modded ones. I just use the schematic as on the first page here and added some "extra" features by searching the Bartolini site where they offered some (three position switch, etc.).

You could mix the 2 pickups signals; when I am correctly every time you use 2 or more pickups you mix some pickup signal. A stacked pot would be decent, but I could not find any dual concentric pots (or they costed me an arm and a leg) so this was the only way possible.

Second, the unit would sound different with using elco's instead of tantalum caps because the elco's have a bigger leakage and would affect the sound; I would not know how much and how it would sound. I just got the tantalum for very cheap so I used them.

[markusw]

As i told markusw before, next week I will try to build only the eq stag and maybe skip the gain one .. so I guess I won't face this gain problem ...

I was just browing through the other thread. Actually I'm quite sure that it really does not matter whether your pus are active or passive. If you build the orginal version with the gain stage included  (which is just a few caps and resistors more, and the second half of the opamp is used too) you can simply turn the trim pot down until youre unity gain.  Or even easier, ommit the trim pot as well as the three resistors in the feedback loop of IC1 and connect "neg in" with "out". You then can connect your active pus to the input of the original schematics via your blend pot. If you keep the trimpot you're a bit more flexible if you once decide to use passive pus.

I just believe that blending the two pus with a single linear pot will give you a different blending feel than with a MN taper or a log/antilog and probably you won't be able to have 100% pu1 or 100% pu2 signal. But I really may be wrong with this.

Regarding the tantals, maybe you can get the via mail order. In Europe Conrad, RS comp,...... carry them.

Markus