Bartolini NTMB reverse engineered (schematics inside)

[markusw]

You used the same inductors as I did.

Yup, I noticed Could'nt find any 150mH.

Markus

[DavidS]

Mouser has 150mH inductors available.

Does anyone feel like sharing their PCB layouts for this?

[markusw]

I just did a layout for my modded version. See pic in http://diystompboxes.com/sboxforum/viewtopic.php?t=33729&highlight=ntmb It was done for my Carvin bass.
As you can see it has several micro dip switches I justed added because there is plenty of space in the cavity (and of course for checking the influence of different cap sizes mainly in the tone control section). Also, the distance between the pots is tailored for my Carvin.

In summary, I doubt that it will be of any use for you. Bernardduur did the original version on vero. Maybe ask him for a layout. He also did not use any PCB mounted pots.  Therefore, it's a lot more flexible than my layout. What bass do you want to put it in?

If you nevertheless want my layout just drop me a pm.

Markus

[DavidS]

Well, I WAS looking for a more generalized layout... My bass is most likely not one you've ever seen, or heard of, for that matter.

I guess I was just being lazy, anyway. It's not a terribly complex circuit, I should be able to make my own layout without too much trouble.

[Bernardduur]

What bass are you playing then? Now I am curious.

[DavidS]

Sorry, didn't mean to be enigmatic :)

It's an Alfredo Bugari Stonehenge. I Added an EMG-40P active to it, sounds great.

[ejbasses]

Can i use NE55323s in this circuit?

[Bernardduur]

Wow, I never heard about that bass.

And yes, you could use a NE5523 but I would not know how it would sound as my OPA IC must sound different than the stock IC's.

[markusw]

Can i use NE55323s in this circuit?

When I first fired up my modded NTMB I put in 2 NE5532, to avoid killing my MC33178 just in case some was wrong. I had several NE5532s laying around and just two MC33178. Also the MC33178 are more expensive here in Austria. It worked the same with the NE5532s. Soundwise it should be at least equal to the MC33178.

Two comments regarding the NE5532:
1) it will draw much more current from the battery than the MC33178 (roughly 8-10 times). So your battery will be empty much faster, unless you go with a "phantom power" cable like Bernardduur did.

2) Vref most likely will be lower if you use a NE5532. So you might want to put in a 50k trim pot instead of the 25.6k resistor in the voltage divider. This would allow you to trim Vref to V/2 (depending on the opamp you're using).

Good luck,

Markus

[lovekraft0]

You own a Stonehenge??!? As in Castelfidardo? That's truly an axe to be reckoned with!!  

[DavidS]

Wow, someone else has heard of it :)

I picked it up at a music shop in town for $350 US. Got lucky.

[ejbasses]

Markus,

What would happen if my Vref is a little bit lower? When you used NE5532 did you change anything in the biasing? Current consumption wouldnt be much of a problem to me because i plan in using it as a stompbox.

[markusw]

Markus,

What would happen if my Vref is a little bit lower? When you used NE5532 did you change anything in the biasing? Current consumption wouldnt be much of a problem to me because i plan in using it as a stompbox.

You simply have a little less headroom. Most likely you won't hear any difference unless you set the gain trimpot rather high and your pickups have high output (e.g. active pus). The Vref trimpot would it make just a bit easier to test different opamps while having Vref set to V/2 (which usually means most headroom). If you put it in a stompbox the NE5532 for sure is fine.

Markus

[DavidS]

In the schematic, I see that C5 and C6 are polarized, but they're really tiny, and according to the note, they should be ceramic. Was the polarization just an error?

Also, the "off" resistance of the push/pull... Don't see anything like that in Bartolini's wiring diagrams. Also, the value of the gain trimpot is 5k in the Bart docs. Is this just an older revision of the preamp?

[markusw]

Sorry I was not clear enough. C5 and C6 are tantals too (they are nearly µF  ). I replaced them with two film caps in parallel (0.33µ + 0.068µ). Honestly, I don't know whether my unit is older than the diagram on the Bart hp (I bought it in 2001), I just know that the trimpot in my unit was 10k (as indicated in the schemo), and there were two 47k resistors soldered to the push/pull switch (I suppose to prevent popping).

[DavidS]

Ok, I read C5 and C6 as 820p instead of 820n... Don't know why :)

Anyways, I'm working on my own PCB layout of this thing (hence all the "brilliant" questions) and I've run into a few more questions:

Is the signal routing terribly crucial? That is, should I take pains to keep the input and output lines physically distant? I know it's not a distortion unit, but there IS some gain in this, so I thought I'd ask.

What about using an MC33078 for the opamp (seems the best equivalent that Mouser has)? I haven't checked the datasheet about the whole asymmetric v-ref thingie yet, but if it's different, I could just compensate by making the v-ref v/2 (or whatever is called for), right?

What about substituting silver-mica caps for the ceramics? Judging by the capacitor comparison table in "The Art of Electronics", this would be a good thing, right?

Lastly, has anyone else done a single-board layout they'd like to share? :)

I'm also toying with the idea of making a surface-mount board. We'll see how far I get :)

[markusw]

I don't think that the signal routing is terribly crucial because the gain is not that high. However, if you can manage to keep input and output physically separated it wont hurt.

Regarding the MC33078, it has about the same power consumption as a NE5532 or OPA2134. So there wouln'nt be any benefit in this respect. IMHO the MC33178 was primarily used in the original Bart unit because of it's low power consumption (your battery simply lasts 8-10 times longer compared to a NE5532 or OPA2134). If I'd put it in a stompbox I'd go with a OPA2134 or NE5532 (btw I'm really curious if you can hear any difference once your build is done) and adjust Vref with a 50k trimm pot.

Silver-mica for sure is fine, I've used Wima FKP and MKS films.

[Bernardduur]

Question: What do I gain or loose when I put the preamp in a pedal sized box instead of my bass; right now I have purchased a second bass (different setup / tuning / etc.) but to build the unit again as I can share them by adding the preamp to a box. Ant thoughts on this?

[puretube]

this would be worth a new thread: active guitar/bass... (pros & cons)*

you loose the ability to drive long cables to your rig,
and you loose some high frequency content;
you could load your pickups with some "tonesucking"...

you gain the easier battery replacement/powersupply;
and you gain the advantage of more universatility
to plug your axe wherever you want it...

(there may be different/additional opinions, though)

[EDIT]: * NEW THREAD HERE:  

[Bernardduur]

Ah, thanks for the linking. I thought it would be a bit too much attention getting from my place (I am humble)....