Barber Electronics - Dirty Bomb [gut shots + schematic]

bonnistyle · Post by **bonnistyle** » 04 Aug 2009, 14:47

Did someone this as a DIY already? Sounds really nice!!

irmcdermott · Post by **irmcdermott** » 03 Sep 2009, 05:40

sorry to bump the thread.

so is the posted schematic good to go? wouldn't mind messing around with this one.

culturejam · Post by **culturejam** » 12 Sep 2009, 22:23

irmcdermott wrote:sorry to bump the thread.

so is the posted schematic good to go? wouldn't mind messing around with this one.

I have not 100% verified it, but I believe it is correct.

I did a derivative project using this schematic, which is the first two gain stages but minus the entire tone stack. And it works fine, so I think the worst mistake might be a wrong cap or resistor value or arrangement in the tone stack. The core of it is correct and verified.

Agreed · Post by **Agreed** » 13 Sep 2009, 04:06

Your description of the behavior of the three-position switch seems very much at odds with my experience with the pedal. It most definitely sounds like it alters the midrange, which would make sense with the Baxandall - basically giving you an overall voicing control with the midrange and then your shelving control from there with the Baxandall. You sure about that?

culturejam · Post by **culturejam** » 13 Sep 2009, 06:10

Agreed wrote:Your description of the behavior of the three-position switch seems very much at odds with my experience with the pedal. It most definitely sounds like it alters the midrange, which would make sense with the Baxandall - basically giving you an overall voicing control with the midrange and then your shelving control from there with the Baxandall. You sure about that?

I guess it was just how I described it to say "cuts bass". I"m sure about my opinion, yeah.

You the same "Agreed" from TGP? If so, you and I just had a fun discussion about replicating power-tube sag in a pedal.

Agreed · Post by **Agreed** » 15 Sep 2009, 13:10

I'm Agreed at a few different musician forums

TGP, HCFX, KVR, Gearslutz, GuitarAmpModeling, SA, uh... here... thestompbox... and probably others, haha. So yeah, we did have a good chat about that. I would be interested to get a more precise bead on which frequencies are affected by the switch, our ears are reporting conflicting evidence!

culturejam · Post by **culturejam** » 15 Sep 2009, 16:36

Agreed wrote:I would be interested to get a more precise bead on which frequencies are affected by the switch, our ears are reporting conflicting evidence!

I haven't plugged mine in for some time. Let me do another listening test and see what I come up with.

Agreed · Post by **Agreed** » 15 Sep 2009, 20:25

Could definitely be the different surroundings, too. I run mine primarily into a THD Univalve going into a 4x12 V30 cabinet. Maybe whatever it's doing doesn't have the same results for different amps.

But then again I also tested it into a Fender Champ 600 and it sounded the same, so...

Let me know what you find!

culturejam · Post by **culturejam** » 15 Sep 2009, 20:37

Agreed wrote:Could definitely be the different surroundings, too. I run mine primarily into a THD Univalve going into a 4x12 V30 cabinet. Maybe whatever it's doing doesn't have the same results for different amps.

Ha! I have a Univalve, too!

But I have a crappy 1x10 cab.

Agreed · Post by **Agreed** » 15 Sep 2009, 23:43

Univalve truly is the shit, eh?

But I bet that 1x10 cab doesn't let it CHUNK much for the higher gain stuff. Still, if it will make my Champ 600 do the dirty thing, I bet it works to a good extent there.

Actually one of the tightest sounding cabs I ever heard was a 4x10 compact cab. I attribute it to the speakers being so much closer together and the resulting phase coupling giving it an undistorted, massive bass.

distortion_gfx1 · Post by **distortion_gfx1** » 01 Oct 2009, 06:43

can't wait on the out come...

culturejam · Post by **culturejam** » 01 Oct 2009, 14:09

distortion_gfx1 wrote:can't wait on the out come...

The outcome of what?

quaternotetriplet · Post by **quaternotetriplet** » 05 Dec 2009, 04:39

sorry to bump this thread. anyone verified this scheme?

culturejam · Post by **culturejam** » 05 Dec 2009, 18:24

quaternotetriplet wrote:sorry to bump this thread. anyone verified this scheme?

Read up further on this page.

distortion_gfx1 · Post by **distortion_gfx1** » 08 Dec 2009, 02:36

nice

mictester · Post by **mictester** » 08 Dec 2009, 16:53

culturejam wrote: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.

Your interpretation looks pretty much OK.

It's just another version of the Marshall thing, with a remarkably inept electronic "design". Mechanically, I'll give credit where it's due - in this case, it's a well-built hack-job:

The failure to realise that the last op-amp in the package could be used as a buffer to prevent any subsequently connected items affecting the "sub-bass" filter by loading (which is a poor design, anyway), shows that the "designer" hasn't really got a clue. The "sub-bass" is a pretty useless control, anyway.
Also, the failure to realise that the fourth op-amp could be usefully used as an active mid-rail supply (which would confer all sorts of advantages), also shows that the "designer" has just cut and pasted other designs from REAL designers.

culturejam · Post by **culturejam** » 08 Dec 2009, 17:16

mictester wrote:The failure to realise that the last op-amp in the package could be used as a buffer to prevent any subsequently connected items affecting the "sub-bass" filter by loading (which is a poor design, anyway), shows that the "designer" hasn't really got a clue. The "sub-bass" is a pretty useless control, anyway.
Also, the failure to realise that the fourth op-amp could be usefully used as an active mid-rail supply (which would confer all sorts of advantages), also shows that the "designer" has just cut and pasted other designs from REAL designers.

Ouch.

I was puzzled by the dangling 4th op amp as well, but I think the pedal itself sounds really damn good.

Could you explain a bit more about this "active mid-rail supply"?? That's not something I've heard of before, and I'd love to know a bit more directly from someone who understands it. Thanks.

Tube2stomp · Post by **Tube2stomp** » 10 Dec 2009, 15:54

culturejam wrote:
mictester wrote:The failure to realise that the last op-amp in the package could be used as a buffer to prevent any subsequently connected items affecting the "sub-bass" filter by loading (which is a poor design, anyway), shows that the "designer" hasn't really got a clue. The "sub-bass" is a pretty useless control, anyway.
Also, the failure to realise that the fourth op-amp could be usefully used as an active mid-rail supply (which would confer all sorts of advantages), also shows that the "designer" has just cut and pasted other designs from REAL designers.
Ouch.

I was puzzled by the dangling 4th op amp as well, but I think the pedal itself sounds really damn good.

Could you explain a bit more about this "active mid-rail supply"?? That's not something I've heard of before, and I'd love to know a bit more directly from someone who understands it. Thanks.

+1 on the ouch
it's probably her time of the month

Here, now you can also be a real designer:

Thank god for high impedance pickups and tube grid current swamped cathode followers for being EE book "WRONG"

mictester · Post by **mictester** » 11 Dec 2009, 07:06

culturejam wrote: Ouch.

I was puzzled by the dangling 4th op amp as well, but I think the pedal itself sounds really damn good.

Could you explain a bit more about this "active mid-rail supply"?? That's not something I've heard of before, and I'd love to know a bit more directly from someone who understands it. Thanks.

It will sound good, but only as good as the Marshall original it's copying with slightly modified values!

The active mid-rail circuit is commonly used to give a well-decoupled half supply line. It has the advantage of very low noise, too. Furthermore, you also have the option to set any voltage offset you want by altering the relative values of the bias resistors:

: Midrail.jpeg (8.14 KiB) Viewed 2439 times

Liquids · Post by **Liquids** » 11 Dec 2009, 12:11

I'm a big fan of op-amp Vref/bias networks. Good reading from R.G. http://www.geofex.com/circuits/biasnet.htm

The benefit of this is that it will 'flex' with a draining battery, even, and remain at however you divide the voltage. It can be offset for however much above 1/2 V+ you might need/want it to be given rail limitations. Much more stable than the average voltage divider. It is is very useful. If you have a spare op amp channel use it, and if you don't, why not add a dual op amp, and you can throw a good buffer in there somewhere....at the input, after you volume control, etc.

Anyone notice that in some places, TL074s are cheaper than TL072? Or that datasheets (At least one I looked at yesterday) specifies that a TL072 has 4 JFETs (presumably one for each input) and 2 channels, but the TL074 has 6 JFETS in 4 channels?

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