Barber Electronics - Dirty Bomb [gut shots + schematic]  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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culturejam
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Post by culturejam »

Just got this in this weekend. Build quality is superb. And I really like the sound of it. Lots of nice harmonics and some heavy distortion, but it does NOT get into "cookiemonster death metal" territory. And that's fine with me. You could probably do some decent Van Halen covers with this one. It actually reminds a little bit of the BSIAB. Overall, it's well done, which is what I expect from Barber. In my opinion, it is definitely worth the $100 asking price. Too bad about the cheap knobs, however. I really hate those.

After looking the parts values and arrangement, my best initial guess is that it's a derivative of the Marshall Shredmaster. I could be wrong, however. I compared it to the schematic of the BYOC Shredder, and there are enough similarities to satisfy me on first look. Again, this is just a guess and could be erroneous. It uses a JFET quad op amp as the core (JRC 074D). The tonestack is at least moderately modified, and there is a "sub bass" control mounted internally (could be renamed from the original "Contour" control?) . Also there is a three-way switch which cuts bass, but if I were going to build this, I'd leave it out.

I will pull it all apart and do some more pics of the other side of the board tonight or tomorrow. If anyone wants specific angles, let me know.
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guts
guts
tight gut shot, top-side
tight gut shot, top-side

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madbean
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Post by madbean »

Sweet! And look: all the component values are conveniently labeled for you!

The man knows how to put a pedal together.

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KindaFuzzy
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Post by KindaFuzzy »

Makes my pedals look like a pile of puke. Cool stuff.

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Post by DWBH »

What size is that box?
1590BB?

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culturejam
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Post by culturejam »

DWBH wrote:What size is that box?
1590BB?
I think so. It's the same size as several 1590NS boxes I have laying around.

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Post by culturejam »

Rock solid. Barber doesn't play around. I had to desolder the 9v jack connections and then pry the board off the enclosure. It was held in place with some VERY strong double-sided tape. Then of course there was a ton of glue residue left on the board. So after about an hour of gentle scraping with an eyeglass screwdriver and some acetone for lube, I finally got a good look at the bottom traces. See the pics below. Haven't had a chance to analyze yet, but I'll be looking at it over the next couple of days. If anyone else wants to take a crack at a trace, go right ahead. I'm still going to try to trace it as an exercise for myself.

Oh, and the "Sub Bass" on-board pot is A50K.
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double-sided tape
double-sided tape
look all that glue!!
look all that glue!!
bottom board + pot values
bottom board + pot values
Tight shot of bottom side.
Tight shot of bottom side.
another view of the top side.
another view of the top side.

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madbean
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Post by madbean »

dirty_bomb_overlay.jpg
dirty_bomb_overlay2.jpg

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culturejam
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Post by culturejam »

Nice!!

I was going to do that, but you just saved me the time. Thanks.

Now I can put this baby back together and shred!!!! :applause:

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Post by soulsonic »

I'd guess that if it sounds good, then it has nothing in common with the Shredmaster.
Nothing "shred" about the Shredmaster.... should be called the Blandmaster!

What kind of transistors are those?
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culturejam
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Post by culturejam »

soulsonic wrote:I'd guess that if it sounds good, then it has nothing in common with the Shredmaster.
Nothing "shred" about the Shredmaster.... should be called the Blandmaster!
Haha. I'll keep that in mind.
soulsonic wrote:What kind of transistors are those?
2n7000. On first look, from the way the traces look, it seems they are used as simple clippers. I'll start tracing it today.

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Post by culturejam »

I'm about halfway done with the trace. I'll post a draft schem when I'm finished, of course. It'll need some heavy review, as this is my first-ever attempt at tracing.

Interesting notes so far:

* one of the op amps isn't used

* the clipping between the 2nd and 3rd gain stages is mosfet clipping to ground

* most everything up through just after the second op amp's output is very close to a Shredmaster. there are some interesting differences, but to that point it seems clear the Shredmaster was the initial inspiration. Looks like the tonestack is quite a departure however, and obviously the clipping is different.

More to come.

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Post by culturejam »

Getting closer to finishing. I'm at the last op amp stage, and I've found something that I've not seen before. It appears that the both inputs of the 3rd op amp are bridged (pins 9 and 10). They are connected by a 470K resistor that then hits a pair of 10K in a voltage divider setup. Then the output (pin 8 ) goes to the Sub Bass control, which then feeds back some of the signal to pin 9.

I've checked it 10 times now, and that's definitely what's going on. Unless I'm wrong. :lol:

I just wanted some feedback on whether or not that makes sense. I'm not familiar with that kind of setup. And I've been looking at this thing for so long that I'm starting to doubt myself. Maybe I'll just post what I've come up with and let the smarter fellas help me out. :mrgreen:

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Post by bajaman »

I checked the pictures and I see no sign of a connection between pins 9 and 10 - at least not on the bottom side of the PCB :scratch: :scratch: :scratch:
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Post by culturejam »

Okay, here's my first stab at it. I'm sure there are at least a couple goofs, so please point them out so we can get this thing going. Also, my apologies for the ugly, inefficient drawing.

Forgot to mention: I left out the power filter cap (100uf), polarity protection diode (1N4003), and voltage divider resistors (100k).

EDIT: Deleted this older/wrong version of the schematic. Updated version below.

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Post by tube-exorcist »

R11 should be connected to the junction of C12/R10.
(It is a Baxandall-tonecontrol).

Junction of R16/C16 should be connected to plus via a 91 Ohm resistor.
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Post by culturejam »

tube-exorcist wrote:R11 should be connected to the junction of C12/R10.
(It is a Baxandall-tonecontrol).
Cool, thanks.
tube-exorcist wrote:Junction of R16/C16 should be connected to plus via a 91 Ohm resistor.
What do you mean by "plus"?? Also, I don't see a 91R resistor on the board. But there is a 91K resistor (white/brown/orange/gold).

Thanks for taking a look. I appreciate it.

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Post by tube-exorcist »

At the lower right corner is a resistor white, brown, black which is connected on one side to the supply-voltage and on the other side to the junction of R16/C16. R16, R15 and C15 form a bias divider for the third op-amp
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Post by culturejam »

tube-exorcist wrote:At the lower right corner is a resistor white, brown, black which is connected on one side to the supply-voltage and on the other side to the junction of R16/C16. R16, R15 and C15 form a bias divider for the third op-amp
Ah yes, you are correct.

Draft 2 is attached.
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Draft 2
Draft 2
db_draft2.png (11.62 KiB) Viewed 7217 times

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Post by NetStar »

Wow! Quick work, fellas.

I'd really like to try a Dirty Bomb. Great price. I mean, isn't a Metal Zone meant to be $100?

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Post by culturejam »

Well, I know for sure that the schematic is correct up through the MosFET clippers. I built up a derivative project that is the DB minus the tone stack and last op amp stage, and it works fine.

My interpretation of the DB tone stack may not be 100%, but I believe it is at least pretty damn close.

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