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Digitech Screamin Blues Mod?

Discussion in 'Burnt Fingers DIY Effects' started by Navigator, Sep 17, 2011.

  1. Navigator

    Navigator Tele-Meister

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    Does anyone know of a mod for the Digitech Screamin Blues pedal? I found one for $15.00 and thought I'd gamble on it. The sound is just okay. I'd like to improve it. I did a google search and found inquiries from other people about mods but no mods.
     
  2. rstone770

    rstone770 TDPRI Member

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    What sound are you after? Want grit, more fidelity, transparency, frequency shift, gain, ect? Its nice to have an idea of what your going after before you start taking stuff apart.
     
  3. Navigator

    Navigator Tele-Meister

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    rstone: Thanks for replying. You posed a good question. I searched and didn't find anything so I didn't expect to have choices. Couldn't even find a schematic. All I know is that the tones I got out of it were nothing special and that the pedal only cost me $15.00. So if there is any mod for it, I am willing to gamble the $15.00 to see if the modded pedal sounds better. The entertainment value of taking it apart, doing the mod, putting it back together, and then playing it to see how it changed is worth $15.00 to me. If I had a choice I'd like more of a bluesy grit sound from it. I'd like the pedal to live up to its name: "Screamin Blues".
     
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  5. rstone770

    rstone770 TDPRI Member

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    Yeah. The schematics are very hard to get as digitec doesn't release them. If you can take a huge pic of the top and bottom of the boards I can study them. The first thing id recommend is upgrading all signal caps. This usually makes a huge overall difference in sound especially in 40 dollar pedal. Id see how it sounds after that and go from there.
     
  6. Navigator

    Navigator Tele-Meister

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    Attached are the pics. The first pic is from a book on how to mod pedals and is for the Bad Monkey. It is very similar to the SB but has the SB has six caps and the BM has 5. The C11 cap in the BM pic is to increase bass and to allow the pedal to be used with a bass. The C5 cap (originally a .047 uf to change to .1 uf or .15 uf) change is to make the pedal "more transparent, less mids ..." The electrolytic caps at the top appear to be the same on both pedals. (Are those the signal caps?) The smaller electrolytic caps (three below the right jack, three below the left, and one above the upper left jack appear to be in the same places on the pcb).

    The signal cap change suggestion sounds good. I don't think I want to change the bass. Would the lower of the two caps (the C5 on the BM) just above the right jack have the same function on the SB as on the BM?

    Thanks for your help on this.
     

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  7. rstone770

    rstone770 TDPRI Member

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    Most of this circuit smd less the caps. This being said, unless you are very handy with the iron the cap swap are your only choice. If your only looking to clear up the sound the cap upgrades are your best friends. As for the e caps those are usually used for power filtering but I have seen them in signal path. Take a quick look and see were the caps go and update them as needed.
     
  8. Navigator

    Navigator Tele-Meister

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    Is the signal path, the trace to which the input jack is connected? One of the legs of the input jack is oldered into a trace. there are several green caps that straddle that trace but none are soldered directly into that trace. Are those the signal caps? What would be an upgrade for those caps?
     
  9. rstone770

    rstone770 TDPRI Member

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    I'd find out exactly were the caps go before soldering. However. If the caps are the polyfilm type they are probably in the signal path. Thats a bad assumption but seems to follow suit. It wouldn't hurt to upgrade them anyway as top quility components are not used in 40 dollar pedals. An upgrade would be using an other type of cap with the same value to taste. Polypropylene and mica caps are highly recommended. If you would like to tweak with the smd componets a hot air kit is recommended and pretty cheap.
     
    Last edited: Sep 19, 2011
  10. davmac

    davmac Tele-Afflicted

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    If you head over to http://freestompboxes.org/viewtopic.php?f=1&t=4010 you'll see that someone has kindly drafted a schematic for the Screamin' Blues.

    You need to register to access the pic.

    Once you've got that get hold of a schematic for the Boss BD-2 Blues Driver. I gather there are significant similarities between the two pedals.

    As a start point I'd compare the two schematics and then have a search for BD-2 mods and try and work out which of them might work with the Digitech.
     
  11. Montana_Dawg

    Montana_Dawg Tele-Holic

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    Sorry, but this statement is untrue. There is absolutely nothing wrong with those caps, and changing them out for pricier silver mica or even poly caps is a waste of time and money. The signals in these petals is such a small level, that the type of cap has very little effect. When you get into higher level circuits where frequencies are critical, or power circuits, then the type of cap and it's properties become important.
     
  12. davmac

    davmac Tele-Afflicted

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    Whilst I fundamentally agree with your point, I'd probably be pedantic and say the original statement is most likely true, because he started with the phrase "it wouldn't hurt to upgrade...". It probably won't hurt (other than the OP's wallet). It is unlikely to improve anything either IMO.
     
  13. rstone770

    rstone770 TDPRI Member

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    Please note signal levels have very little to do with the reactance of the cap. And though its true 1uf electrolytic cap is equivelent to a 1uf ceramic, they will sound different due to the chimestry and mechanical construction of the cap which inherently give different caps different properties. This is why electrolytic caps in the signal chain seem to sound more wooly and ceramics tend to sound shrill and sharp. You are currect that vast difference are seen at higher frequencies, they still are verymuch percieced at lowher frequencies to an extent. That being said there are 1000s of effects mod articles that are based of changing cap types and 1000s of people notice a complete difference in sound.

    Currently I do not have an account with DIY stompbox, can you please forward the schematic to my emails?
     
  14. davmac

    davmac Tele-Afflicted

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    Nope still not true. There's a good detailed article debunking capacitor hype over at http://www.aqdi.com/tonecap.htm

    And just because 1000s of people think it sounds better doesn't mean its right. That's how Bieber can still sell music. ;)
     
  15. rstone770

    rstone770 TDPRI Member

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    Hahaha. That is true! I have a signal generator and a signal sampler setup that ill have going to trully test this scientificly. A good scientific paper is really lacking for caps and tone. Ill have one posted meanwhile, I beleieve the op should read about cap choices and experemnt and draw a good conclusion for himself. Because although we both are not fans of beiber, millions are.
     
  16. 11 Gauge

    11 Gauge Poster Extraordinaire

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    Not only that, just for giggles, let's say that there is an audible percentage of "distortion" or whatever you want to call it with capacitors. That is still a fallacy, because "a dielectric doesn't have a sound."

    ...That said, the magnitude of distortion/noise/signal intermodulation/etc. from the actual amplifying components is such a large tsunami compared to even a monster pile of "crap ESR" caps that any "sound" that one dielectric might have (in 9VDC effects, at frequencies from ~20Hz to ~20KHz) would be completely inaudible.

    IOW, you'd essentially have to purposefully design something to exploit the "noisy nature" of certain dialectrics to be able to accurately point the finger at caps, specifically.

    Someone mentioned testing or measuring to prove this out, one way or the other. I suggest something easier - just keep building the same basic circuit, over a period of years. Build about 200 or more of them, and use different types of caps. Mix and match, or do some sort of groupings, like Picasso's blue period or something.

    ...After awhile, you will most likely find yourself simply reaching for whatever component value you need instead of questioning the dialectric composition.

    If anything, the only reason that I will pause before selecting one cap over another is due to physical dimensions, or if I can grab one that isn't polarized just so I don't put it in backwards, I'll do that. I typically just buy the multilayer monolithic ceramic caps for my personal builds, because they are super cheap in bulk, and they fit in EVERYTHING. And - you've got sizes from 1pF up to about 2uF in very similar physical dimensions.

    ...The little multilayer things are possibly only the more "ghetto of a cap" than the "greenies" that everyone rolls their eyes at (but are in some of the most sought after pedals ever made).
     
  17. Manolete

    Manolete Friend of Leo's

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    Sorry to bump an old thread...

    Is there a dead-cert mod for increasing the bass response of a Screamin' Blues pedal? I quite fancy picking one up for bass use.
     
  18. cousinpaul

    cousinpaul Friend of Leo's

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    The Screamin' Blues is a Boss BD-2 clone. C20 and C21 are your tone control caps (same as C100 and C101 on the BD-2). Increasing one or both of these caps is part of every well known BD-2 mod that I'm aware of. Try anything from .033uf to .1uf for C20. Allums used .047uf on his H2O mod while Keeley used a .033uf, adding a .068uf when the Phat switch was engaged for a whopping total of .1uf! The Boss OD-3 values of .033uf for C20 and .022 for C21 will also work very well. Any of these changes will give you a stronger tone control and help to cure the fizzies.
     
  19. Anchoret

    Anchoret Friend of Leo's

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    I think you'll find it's essentially a DOD FX102 Mystic Blues Overdrive that's been SMT converted.
     
  20. Manolete

    Manolete Friend of Leo's

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    Sorry to bump again.

    I modded my SB, and now it is a bass monster. The first pedal I've modded whereby I lose absolutely no bass end. It does a good SVT-type grit now (but what do I know?)>

    I will need to mod it to have a bit more mids though... at the moment the scoop is pronounced, which takes all the 'fun' out of a P-bass or similar. When I open it up next I will put the mods I made in this thread for future reference.

    My other ongoing mod project is to turn a Digitech Grunge pedal into a bass monster. I found the pedal works nicely with the input cap changed out for something tiny... maybe a 0.0033uF or something. I found a little circuit jump on the pedal that makes it really fuzzy. The stock Grunge doesn't have a lot going for it, so I will keep modding away. :twisted:
     
  21. Lunchie

    Lunchie Poster Extraordinaire

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    Bingo

    Its one thing to change the values, its another to upgrade just because a cap is more expensive or made out of a different material. When i built my EM-Drive I breadboarded it with Ceramic and PIO caps and there was not a bit of difference. $8 a pair vs. .018 cents a pair. When it comes to the boutique guys and their $200 pedals, you will find a lot more high end components, imo, only because if you open it up and find 30 cents worth of components in a $200 pedal, your not going to be very happy.

    ahh shucks I just got zombied....
     
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