Bartolini NTMB reverse engineered (schematics inside)

Bernardduur · June 11, 2005, 03:13:27 PM

The blend is very different than with a MN pot; for best blending use two pots or a MN pot.

Gabriel Simoes · June 15, 2005, 01:18:44 PM

Hey ... here in my city (Salvador , in Brazil) ... it's impossible to find a polarizes 820n cap .... some people laugthed at me today .... and the inductors too ... kind of impossible ...
Would you guys recomend any other mid section from an other pre amp

Thanks ...
Gabriel
ps: if I can not find em ... could I just skip that mid section and use treble and bass ?

Gabriel Simoes · June 15, 2005, 08:57:17 PM

Come on guys ... I have all the other parts but if I can't build this without the stuff for the mid control I will send them back ... =)
give a hand here

markusw · June 16, 2005, 02:10:11 AM

Sorry for the delay. I`ve used two MKS film caps in parallel : 0.33ÂµF and 68nF which gives approx. 398nF.

The two 820 nF caps in series give 410 nF, so it's close enough. I doubt one will hear the difference especially since the tolerance is between 10 and 20%. If you want to be more exact, measure some caps and use the ones that give you 410n.

Good luck,

Markus

PS: BTW I also replaced the two 22Âµ tantals with the 2700 resistor between them as well as the 10Âµ output cap with a 10Âµ Wima MKS.

Bernardduur · June 16, 2005, 02:18:06 AM

Ah, I had some laying around so I had no trouble in finding those hard to find caps. Luckily you can "cheat" a bit by putting things in series or parallel as I should have advised.

Gabriel Simoes · June 16, 2005, 08:13:28 AM

The biggest problem here is to find the inductors .... almost impossible

...
I will try to build this thing without the mid section .... and see what happens ....
thanks for everything
Gabriel

Bernardduur · June 16, 2005, 10:35:13 AM

Use three 100 mH inductors or 6 50 mH or so. I had some problems but it took some looking around here.....

Second, the mid section in my unit is very important; with this setting I can easily overload my amp or get a nice rock-bassy sound. I don't know, I use that knob the most (bass and treble are most set in one position).

markusw · June 16, 2005, 01:29:58 PM

I also had to use 3 100mH coils. I don't think it makes a difference.

BTW, Gabriel you've got PM.

Bernardduur, two Q: IIRC you've used the OPA2134. Did you use the 25.5k R in the voltage divider or did you use two 30k? What Vref do you get?

Markus

Bernardduur · June 16, 2005, 02:35:04 PM

25.6k (made it with some other resistors). I don't know the Vref I got.... I once measured it and found it was quite low but all works fine so I don't mind. Will measure it later this day.

markusw · June 16, 2005, 02:55:52 PM

QuoteI once measured it and found it was quite low but all works fine so I don't mind.

Although I built a modified version with two separated input buffers and therefore used two opamps I had similar results:

25.5k

a: with two NE5532, V+=8.48V Vref=3.22V
b: with two MC33178 V+=8.55V Vref=4.08V

2x 30k

a: 2x NE5532 V+ 8.48V Vref=3,51V
b: 2x MC33178 V+ 8.60 V Vref=4,47

Would be interesting to see what you get with a MC33178.

Please correct me if I'm wrong, but all this makes me believe that the 25.5k is not for lowering Vref, but probably to adjust it to V+/2. :?: :?: :?:

Any explanations because I really don't understand this?

Markus

Bernardduur · June 16, 2005, 03:44:53 PM

I measured it and these are the outcome:

- 8.96 volt as V+;
- 4.07 volt as Vref.

Enjoy these measurements.

And I don't know why it is used; I don't mind also because it functions

BTW, did you use 2 IC's??? Was a dual IC not usuable?

markusw · June 17, 2005, 01:46:01 AM

QuoteI measured it and these are the outcome:

- 8.96 volt as V+;
- 4.07 volt as Vref.

Enjoy these measurements.

And I don't know why it is used; I don't mind also because it functions

Thanks for your measurments. I really enjoyed them :wink:
Of course, the most important thing is that it works, but it does'nt hurt to know whats going on, does it?

QuoteBTW, did you use 2 IC's??? Was a dual IC not usuable?

Modfever. On the Bartolini hp I saw that they also have variants with two separated buffers.....therefore I needed another IC. Frankly, I don't know whether the two-buffer version changed the sound. I just know that it works, and that like with my original unit it's pretty easy to find a sound I like.

Markus

Bernardduur · June 17, 2005, 04:16:14 AM

Ah, OK. I understand. Could the measurement also different because of the fact I use a 9V obtained from a PSU, not a battery?

puretube · June 17, 2005, 05:45:29 AM

http://diystompboxes.com/sboxforum/viewtopic.php?t=33107

markusw · June 17, 2005, 07:34:49 AM

Quotehttp://diystompboxes.com/sboxforum/viewtopic.php?t=33107

I know :oops:

Sorry, but I did'nt understand it. Although I basically can imagine what you meant I'm unable to say whether this might be the case for this circuit or not.

When you look at the schemo is it possible to check whether the positive half of the phantom gnd draws more current than the negative half? I'd be more than happy for an explanation for dummies (if it's not too complicated). Thanks a lot in advance.

QuoteCould the measurement also different because of the fact I use a 9V obtained from a PSU, not a battery?

No idea :?:

BTW here is my modded schemo:

Markus

Bernardduur · June 17, 2005, 07:59:33 AM

Nice one. Two individual gain parts for both pickups and then mix the sound of it. I like it. Wish I had more space in my control cavity.

No, I am happy with the unit I have right now

markusw · June 17, 2005, 08:29:51 AM

Quote from: BernardduurNice one. Two individual gain parts for both pickups and then mix the sound of it. I like it. Wish I had more space in my control cavity.

No, I am happy with the unit I have right now

Actually I don't think it makes a huge difference with the two buffers, especially since the pickups I'm using are the same type. As I said..modding fever. Anyway, I happy too with it. IMHO the most important part is the tone control. According to my Spice simulations the EQ bands are rather broad. This might explain why it's so easy for me to get the tone I like. Please correct me if this is rubbish.

From the pics you've posted however I think there should be enough space in the cavity of your bass to allow the addition of a second opamp and the few other parts, just in case you get the modding fever :wink:

BTW, as soon as my digicam has new batteries I will post pics of my version, but basically it looks the same as on the pic in this thread http://diystompboxes.com/sboxforum/viewtopic.php?t=33729&start=0&postdays=0&postorder=asc&highlight=ntmb

Markus

puretube · June 17, 2005, 08:37:37 AM

like I mentioned in the other thread weeks ago,
I think there is an unequal current draw on both "halfs",
and that`s probably the reason for the unequal divider:
so in the end, Vbias will finally be half Vsupply.

markusw · June 17, 2005, 09:01:21 AM

Quote from: puretubelike I mentioned in the other thread weeks ago,
I think there is an unequal current draw on both "halfs",
and that`s probably the reason for the unequal divider:
so in the end, Vbias will finally be half Vsupply.

Thanks a lot!! Is it obvious (at least for someone with more knowledge than me) from the schemo, that there is an unequal current draw? Sorry for the dumb questions. :oops:

Markus

Bernardduur · June 17, 2005, 09:12:26 AM

Nice pic. You used the same inductors as I did.

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Bartolini NTMB reverse engineered (schematics inside)