Sunday, 9 November 2014

DOD Overdrive Preamp 250



26 comments:

  1. Miro, am I crazy or didn't you do a layout for this already? Not complaining, btw, cause I've wanted to build this for awhile, and thought it's in my "to build" folder.

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    1. I think the other one was the re-issue version, at a glance it looks like only a few value changes although the gain pot looks reversed on this one

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    2. The reissue uses 4558. This, the old version has LM741 in it.

      How does it look reversed? Clockwise grounds the 47n.
      +m

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    3. This used to have version noted on it, but that got "no, you're wrong" comments in the first minute, so i removed the version notes. The video should give you an idea.
      +m

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    4. well at least i'm not crazy. i'm glad to know that the other one is the reissue, cause i wanted to build the original. awesome job as always man, thanks.

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    5. I meant reversed compared to your post on the re-issue

      "mirosol20 July 2013 10:43

      Dude! I just built two of these and it's definitely ground to gain 3 :) So i'm swapping the wires back"

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    6. In essence those both do the same thing. The inverting input gets closer to ground when the pots turns clockwise.
      +m

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  2. I am very sorry Mirosol. I posted that reply. I deleted it quickly after i did some more checking and found out i was wrong. I love your work and really appreciate you sharing your knowledge with us! Thank you! I didn't want to be a smartass, i was just confused about the versions. I will definately build this layout!

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  3. Thanks mirosol for re-posting this one!

    I saw it the other day but when I got home to download it the post was gone. Thought I had imagined it :0)

    Love this pedal! (Although I may be a bit biased as this was the very 1st pedal I bought way back in 1980. Lent it to a co-worker in the late 80s, he left and I never got it back!)

    Another perfect layout, but for those of you who like to avoid double links like me the board and layout can be easily modified. In a nutshell, I flipped Rows 9 & 10, juggled around a few components and moved 1 of the links and 2 of the cuts.

    Here are some pics: (verified by me last night)

    https://lh3.googleusercontent.com/-YhIYikOuq-c/VGOwzL49KNI/AAAAAAAAAX4/X7EBWAethbE/w521-h553-no/DOD250-no-dbl-link.png

    https://lh4.googleusercontent.com/-g0WEC6Z9D7g/VGOwzb88LHI/AAAAAAAAAYA/0jbv5QYp8L4/w981-h552-no/DOD%2B250%2Bboard.jpg

    Now that I have my pedal back, wish I could get my hair back too.

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  4. Built and fired up first time!

    Never realized how "classic" this pedal is. I socketed most of the circuit so I can play with values. My first mod was putting BAT42s as diodes instead of 4148s. I like them much better. Very smooth. Going to try BS170s next as clippers.

    Thank you very much for all your veros. They are greatly appreciated and anticipated.

    Peace!

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  5. I built this last night and it sounds awesome except that it's super noisy when the gain is up all the way. I did sub a 100pf ceramic cap for the 120pf. Could this be causing it?

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  6. To answer my own question yes.
    Also, this sounds killer with red leds for diodes.

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  7. Can't get this work. Tl071 or lm308 are good subs for the ic?

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    1. This comment has been removed by the author.

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    2. No. LM308 won't work. It needs compensation between pins 1&8, which isn't present on OD250, or in LM741 or UA741 for that matter. It should work with TL071 or other basic single opamps.
      +m

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  8. Ok i dont know why but now is fixed. Tl071 works

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  9. Hi
    This is the first pedal i ever build so sorry if my question is stupid. I have assembled the vero board and now i wire the offboard components but i dont know where to connect the first lug of the gain pot. Any help will be appreciated.
    Thank you and well done for the work you have put into this site

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    Replies
    1. Just leave it unconnected ;)

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    2. Thanks for the immediate response Warrior.
      I finished but something isn't working. My guitar signal travels unaltered through the circuit no matter the position of the switch. Do you have any general idea what might be the problem?
      Thanks again

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  10. Looking at this layout, it appears that IC pin 6 goes into a 10k resistor, which goes into a 4.7uF cap. Other schems I've seen swap it so that the cap comes before the resistor.

    Am I going crazy?

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  11. Hello, this one is my first and when is the gain pot at its maximum, it makes lot of crapy noise. Coulde anyone help me, please?

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    Replies
    1. Does it sound correct when the gain pot isn't maxed?

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  12. Hi, I've only built a few pedals and still consider myself new at this. I have tried to build this one and seem to have similar problems to others. Instead of nice distortion, there is a crackling like noise when the gain is turned up high enough that the IC begins to clip. Even with the clipping diodes removed, it still makes this noise when the gain is turned up.

    I tested all the parts before the build and everything was within reason. Most of the parts are socketed and I've checked the caps again, they all check out. Also, I've tried about 10 different LM741CN opamps as well at 4 different TL071 and they all make the same noise. I've changed the cap on the feedback loop between pin 2 to 6 from 10pf, 20pf, 47pf, 100pf, and 120pf, all have the same noise.

    Here are my voltages:

    1: 0
    2: 4.24
    3: 3.03
    4: 0
    5: 0
    6: 4.54
    7 9.01
    8 0

    I've made an audio probe and the signal is clear up until it comes out of the IC at pin 6.

    Images:

    http://1drv.ms/1JoRYYO
    http://1drv.ms/1JoS3Md
    http://1drv.ms/1A6U1ic
    http://1drv.ms/1A6U7Xj
    http://1drv.ms/1JoSmGP
    http://1drv.ms/1JoSrKp
    http://1drv.ms/1JoSuWS
    http://1drv.ms/1JoSCpa

    Any help would be appreciated.

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  13. Another one I got built and tested over the weekend, used an LM741 and there's plenty of gain on tap, though I'll probably try a few alternatives at some point just to see which I like the best. At minimum gain it never gets completely clean, more a gritty edge of breakup sound even on a clean amp but into a slightly driven amp there is plenty of scope for playing dynamics and the guitars volume control to clean things up a bit if the mood takes you. Pretty good classic rock style overdrive and will probably get boxed at some point :o)

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  14. I just finished one with 3mm red LED clipping diodes and the lm741

    sounds fantastic for a preamp!

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