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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MicMicMan
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Post by MicMicMan »

rasta_maleek wrote:all look to be correct, but, why two divisors for the bias supply?
r-customs use one for all the bias.
Probably a routing matter. Anyway, I really don't get why they have an unused opamp and still use divider bias. Using that remaining opamp as a bias buffer you get a perfect solution. This isn't really good design from barber.

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Post by chi_boy »

askwho69 wrote:Sorry for double posting... here's what i saw.. Is it C12 at sub bass is 82n instead of 56n?

It sure looks like it to me. Now that you point it out, that is. Good eye.

But that wouldn't make the treble fizzy, would it? Others have reported success with the schematic. Have you tried 82n?

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Post by rcustoms »

my bomb,my recipe
dt bomb.jpg
dt bomb.jpg (28.16 KiB) Viewed 2900 times
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Post by rcustoms »

I USE THE ORIGINAL SCHEMA AND WORK OK,I THINK THAT THE EQ STAGE WORK BETTER DEPEND OF WHAT AMP AND PICKUPS YOU USE,OF COURSE MODIFIED IS ENTERELLY AT OWN TASTE.
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GodSaveMetal
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Post by GodSaveMetal »

I´m the first guy made the scheme this is based on one that is Dirty Bomb? it is erroneus; the subbass cap that is 56n>>>> in the photo of the real pedal is other value, and the resistors of trebble and the caps of bass are wrong way there have to be inversed:
Image

Here is my contribution of werever guys make this pedal; I have made two, one have the 1N4148 diodes with the 2N7000 mosfet, and the other an 1N34A ge diodes with the 2N7000 it sound best; the five pots are visible for a nice taste to it:
Image

Enjoy!!!

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Nicht Bernd
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Post by Nicht Bernd »

Could you please post the pcb-file?

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lowbrow
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Post by lowbrow »

I've built my second Barber Dirty Bomb clone but this one has some sort of problem. It's got a excessive amount of white noise, or background noise when engaged. The pedal operates fine otherwise and sounds as it should. It does it on power supply or battery. I used the Sabro vero, which utilizes a TL072 and a TL071 rather than one TL074. The noise goes up and down with the volume control, but none of the others effect it. Swapping out op-amps did not effect it either, but it lead to a strange discovery..when I pull op amp 1 (the TL072) it still makes the noise but no guitar signal passes. Pulling op-amp 2 shuts everything off completely. No noise in bypass mode. Can anybody offer some help please? Could it be something as simple as having power and signal wires routed to close, or something along those lines?

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culturejam
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Post by culturejam »

Did you try a small cap (1000pf or less) to ground at the input?

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Post by lowbrow »

No, but it will be one of the things I try when I get home this evening. I also think I will try my audio probe through the circuit to see if I can identify where the noise gets introduced. Thanks!

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Post by lowbrow »

Well, I tried the cap on the input jack and it made no difference. I also tried it on output with same result. I rerouted all the positive power leads to get them away from the signal leads and it made no difference. I have double checked my board to make sure it follows the vero layout and double checked all solder joints (and reflowed many). No joy.

I spent some time tracing with an audio probe and I can hear the noise get introduced right after the first op-amp stage and it essentially gets worse as the signal travels through the circuit and extensive tone stack. My thinking now is that it may be the tantalums? I used some I've not used before (old color striped ones that I suspect are 20+ years old). I picked up three new ones this morning in the more familiar (to me) glossy dipped tan style.

I am still learning a lot, but it seems to me having the ground wires nestled in with the various signal wires shouldn't cause this, correct? I knew the positive leads may, but moving them made no difference. It kind of sounds to me like I'm getting DC leakage into my signal path...

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Post by Liquids »

With no particularly familiarity with this circuit other than looking at the schematic and knowing about the pedal...

1) It's a high gain pedal. Really high gain, with a drastic mid scoop. Any noise is going to be amplified and the fundamental frequencies DE-emphasized to boot, to make matters worse.
2) You are then likely dialing down the volume of the pedal to get it to match your clean volume...then sending it to an amp which is a preamp of it's own, amplifying things (including any noise) all the more.
3) layout, wiring, bypassing, components etc are all critical with such high gain. At least use metal film resistors if you haven't...
4) Are you sure the caps between the 1st and 2nd op amp stages negative input and it's output are fitted? This should be filtering some noise at least. Likewise, if you put another cap in parallel with them, you can tame some of the high end and noise to taste...or, it can be a good experiment to do so as if that has no affect, you'll know more about the cause.
5) be sure you are familiar with anything else in your signal chain that adds noise. If something else adds even a little noise as well, it will be exponentially worse when this pedal is on, and may seem like this pedal is exclusively at fault for all of the noise.

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Post by lowbrow »

Thanks for your input! All excellent points and some of them I have been thinking about. This is the second one of these I have built and I did not have this issue with the first one.

I did indeed use metal film resistors for most of them and carbon film for the rest. Essentially a similar mix to the first one I built which is not noisy. Basically, there are two major differences with this one and the first one I built. I used a different brand of tantalums this time and I used higher quality chip sockets (the machined kind, not the leaf kind). I am really doubting chip sockets do this, so I'm going to try replacing the tantalums next and see if that cures my issue.

If it doesn't, I think I will gut this one and start over with a new board and all new wiring.....

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Post by lowbrow »

Oh and, I get you about how being a hi gain pedal any noise will be amplified, but that's one of the strange things about this...only the volume control has any effect on the noise level. It goes to zero when I turn the volume to zero. But when I manipulate the gain knob, such as turn it down to zero, it has zero effect on the crackle and static. I've also tried different amps, different guitars, different cables and different methods of powering the pedal (wall wart, one spot, battery).

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Post by electriceffects »

Hi. My first post here and i'd like to show my own layout onboard 1590B really small of the Dirty Bomb, the layout runs really well, here the link to download, I hope you enjoy it. :D

http://www.4shared.com/office/yqwkyUy1/ ... histo.html

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Post by bucksears »

Resurrecting this one too - is there a definitive/verified schematic of this pedal?

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Post by J0K3RX »

bucksears wrote:Resurrecting this one too - is there a definitive/verified schematic of this pedal?
Verified... :D
Attachments
DB new.pdf
(27.65 KiB) Downloaded 241 times
Dirty Bomb11.JPG
DB new..JPG

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bucksears
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Post by bucksears »

Thanks!

Two quick questions:
1) On the schematic, the 9V+ goes directly to Pin 4 of the TL074; on the layout, it goes through the 91ohm resistor first. Which one is accurate?

2) What are the LED pads for? I'm assuming they're for the power indicator, but there are two of them.

Thanks again for your time,

Buck

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Post by jymaze »

1) Opamps can be powered by a point before or after the 91 resistor. The point after the resistor is cleaner in term of noise/hum so it is preferable and may even add some sag!. The headroom is more limited though. This 91 resistor can be downsized a little and the 100u cap after it oversized. I would personaly put a 33 ohms resistor and bump the cap to 470u.

2) One LED is for the switching between pedal or bypass, the other one you can do whatever you want with it... Maybe use it to indicate it is in heavy mod, or make it the bright red evil eye of a demon painted on the enclosure...?

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Post by rcustoms »

bucksears wrote:Thanks!

Two quick questions:
1) On the schematic, the 9V+ goes directly to Pin 4 of the TL074; on the layout, it goes through the 91ohm resistor first. Which one is accurate?

2) What are the LED pads for? I'm assuming they're for the power indicator, but there are two of them.

Thanks again for your time,

Buck
a little help,my bomb work ok
https://www.freestompboxes.org/viewtopic ... 40#p146524
i draw the original schema with only tl074 and work .i dont see 91 ohms resistor first. no sense...to me
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bucksears
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Post by bucksears »

That helps - thanks!

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