Saturday, 15 June 2013

DOD Overdrive Preamp 250 Reissue

Got an early 90s unit recently, the chinese reissue with JRC4558 chip. I'm still really surprised how good it sounds. So i do think this is very neglected and underrated pedal. I've added polarity protection diode and pulldown resistor for the input. The chip is stated as KA4558 in the italian reissue schematic i found (and some random gutshots from the web confirm that), but you could try any dual opamp in there. Now you can build your own with true bypass, indicator LED and standard power jack!



51 comments:

  1. Hey dude, seems like you're on a roll today! This one's good to be tagged, am I right in thinking it's pretty much the same as the original but with a dual op-amp in place of the 741? It certainly sounds pretty similar to the Distortion + variants I've built.

    Oh, the gain pot works backwards at the moment so 3 and 1&2 need flipping.

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  2. And I totally agree with you when you say this is an underrated pedal. It sounds excellent, I need to try it out at a louder volume tomorrow morning when I'm not going to wake up half the street. I think with the gain rolled back and the volume cranked this could make quite a nice booster.

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    1. Thanks. Swapped the labels and tagged it.

      My favourite setting is definitely gain at the middle and volume maxed.

      And yes. It's pretty much the 1:1 with the old schem, exepct for the dual opamp instead of single. Don't know why they changed that, but JRC4558 does work miracles in there.
      +m

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

      Sounds just amazing. Exactly like the original i have. There's not that much difference to Dist+, but this is still 100 times better than any revision of the plus. Wonder if i should draw up a dual version that would use the other half of the opamp for second same circuit...
      +m

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  3. Would it be hard to use the original single op amp in this layout?

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    Replies
    1. Yes. It would be next to impossible.

      On the other hand:
      http://tagboardeffects.blogspot.fi/2010/07/dod-250.html

      +m

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  4. mirosol, thanks for the link and the candid response. :) Which one of these circuits sound better?

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    1. I've built the single opamp one with rev log pot at the gain and linear at the level. That was quite some time ago. For some reason it didn't impress me back then. Haven't built this one as i have the original with JRC4558, but it sounds so sweet that i just had to draw the layout for this reissue. Both are with fairly low parts count, so you could build both and let us know which one sounds better to you. I'm thinking about building the reissue myself to compare it with the DOD unit. Let's just see when i find the time to do it...
      +m

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    2. Sorry quick question, just double checking this layout is drawn for a dual-op amp so I can just drop in a TL072 I have on hand? I know the pedal only uses one channel.

      :)

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    3. That should work just fine.
      +m

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  5. Well, I'll start with the dual op amp version and let you know how it goes. I'll whip up the single one if I get bored one day. :)

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  6. Sorry guys, I'm a newbie to this. I managed to build this up on a breadboard a while ago. Now I've finally got down the commuting it to veroboard I'm struggling with a couple of things. The links underneath the ic, how do you go about making these connections? There's not enough room under the chip so do you make the connection on the other side of the board?

    Cheers

    Chris

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    Replies
    1. Umm. Yes there is room. What do you use for links?
      +m

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  7. Oh ummm maybe I've got the wrong idea here. Fir these small links I've just been using some jumpers I had. What should I be using?

    Cheers

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    Replies
    1. Just use cut off leads from resistors or caps and you can get them under the IC no problem. You don't need to use insulated wire on the top of the board.

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  8. Excellent, I'll try this then. I have already soldered the IC in place so with have to desolder this and add the links. Is it okay just to remove the chip, add the links then re solder the IC in place again? I read somewhere there is a risk of overheating the pins on the IC if your solder it in/out too much. Is this something that happens a lot ( hence IC sockets ) or just if your not too handy with a soldering iron? Thanks for you help.

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    Replies
    1. Do it quickly and preferably with some de-soldering braid to soak it up quickly. They can take a bit of heat, but you still run the risk of damaging it, which is one of the reasons I always socket ICs.

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  9. Thanks for your help. Ive completed the build, at least I thought I had. I'm not getting any output at all. The only sound I get is when I touch pins 2 or 3 of the level pot, almost like I'm grounding it. Even then all I get is buzz, no guitar signal.
    I could really do with some help/ tips with this (fault finding etc). Is this the right place to post for help or should I be looking to post elsewhere? Thanks again for your help.

    ReplyDelete
    Replies
    1. To give a clue what could be wrong you'll need to measure the voltages between all the IC pins and ground. Measure them and post the results here, remembering the pin numbering is:

      1---8
      2---7
      3---6
      4---5

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    2. This comment has been removed by the author.

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    3. Ok I have the correct chip in there now, a 4558 ( that is right isn't it?) however I'm not getting anything. Voltages at the IC pins are as follows:

      1- 0.45v
      2- 0.58v
      3- 0.16v
      4- 0.00v
      5- 0.01v
      6- 0.00v
      7- 0.00v
      8- 0.00v

      Not sure how but I think I may have blown something here along the way. The IC isn't getting any power and I don't understand the vero board routing enough to figure out where the problem may be. Any help would be greatly appreciated!! Thanks

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    4. Those voltages are not ok. You should have supply voltage at pin 7 and about a half of that on pins 2, 3 and 6.
      +m

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    5. yeah, I figured this wasn't right. Why would that be? Are there any other points at which I should check the voltage that would help to figure this out? There is definitely 9v/slightly less and ground , going to the correct places on the board. Cheers

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    6. Sorry, my mistake on the pins above, those need to be supply voltage on pin 8 and about a half of that on pins 1, 2 and 3.

      Something is preventing the pin 8 getting the supply voltage. See if you can figure that out first.
      +m

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  10. This comment has been removed by the author.

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  11. How critical is the 25p cap? the closest I have is 47p - almost double will it work?

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    Replies
    1. That'll work fine. That cap is there to tame possible oscillations. 47p is small enough not to cut your high end.
      +m

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    2. thanks mirosol, I did use the 47p and it works fine. My pots are the-other-way, but that could be just me being sleepy. Nice sounding OD. I get some jump in the noise level at max gain, I guess that is to be expected.

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    3. http://youtu.be/fbVfKB8qvUY here is a quick test of the build, it's unboxed and the volt meter on my test rig PSU I a bit noisy so ignore that small noise.

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  12. Hi mirosol...
    I built two of this pedal...
    the first one works but the gain just changes between 3 o'clock and 6 o'clock and before 3 o'clock just the treble of sound decreases and the bass increases...it doesn't sound well...
    the voltages of IC pins is:

    1- 4.11v
    2- 3.98v
    3- 3.79v
    4- 0.0v
    5- 7.54v
    6- 0.0v
    7- 7.55v
    8- 8.05v

    the second one I've build doesn't work at all...

    ReplyDelete
    Replies
    1. You must have some error on both your builds. The voltages are not too bad though. How about the voltages on the other circuit?

      I've built at least 4 of these circuits myself without an issue..
      +m

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    2. Hi mirosol...
      this is the voltages of the other parts of circuit...
      plz check link below:

      https://www.sendspace.com/file/syl30p

      the voltages of pins of IC from second circuit that I built is same as first one...

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    3. Image shows that you're having 0V at pin 8 of the opamp. That's where you need to have the supply voltage via the 100R resistor.
      +m

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    4. I checked the 100R resistor and resolder that and now the voltages via 100R and 22K changed to 8.05V but still the problem exists!!!

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    5. Have you tried probing it to see where the signal dies?
      +m

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    6. no I didn't...how I can do that?
      but what would cause that the gain works just between 3 o'clock and 6 o'clock?!!
      I also replace the gain potentiometer with a new one but still the same...
      sorry for my bad english...

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    7. http://www.diystompboxes.com/pedals/debug.html

      Are you using rev log pot for the gain?
      +m

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    8. in my country I can find just LINEAR pot...so I used linear for the gain...

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    9. Then your gain knob is working as it should. The circuit needs reverse logarithmic for gain control to have the entire sweep usable.
      +m

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    10. is there a way building this circuit with linear pot?
      I thought that the linear pot can be use instead of the logarithmic :(

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    11. Yes you can. And it will have all the same settings on its sweep. Just in different locations of the turn. http://www.geofex.com/Article_Folders/potsecrets/potscret.htm
      There are ways to tweak the tapers as written on that article - but in this case it won't work as there'll be only two of the lugs in effective use. For all OD250 versions and its derivatives, it's always reverse log that gives the sensible control.

      You could try 200K linear pot instead, but that will lose a lot of the lower settings. Or you could try ordering pots from Tayda. They ship worldwide.
      http://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/anti-log-reverse/500k-ohm-c500k-500kc-anti-log-taper-potentiometer.html
      +m

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    12. tnx mirosol...
      I'm searching some stores that maybe I could find the rev log pots...
      tnx for helps :)

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  13. I made this circuit and only the Volume pot worked. The Gain pot (500k rev log) did not express any kind of sound or variation on the sound :(
    I thought the error could be the Gain 1 and 2 to the 4K7 resistor and Gain 3 to ground but the first question of this topic said that was in the right place. Now I do not know what to do.

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  14. If you compare the schematic with this layout, it can be seen some differences in the Pot connections.

    http://img4.hostingpics.net/pics/514256DOD250BG.jpg

    For example,

    In the scheme of this website, the Gain pot 1 and 2 goes to Ground. The Gain pot 3 goes to the 4k7 resistor.

    Anybody did have this kind of problem ?


    thank you

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    Replies
    1. It seems that schematic is wrong. The gain pot is the wrong way around I think.

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    2. Hello Charles,

      Thank you for answer me.

      What schematic are you talking about ??The Tagboardeffects layout or from this site: http://img4.hostingpics.net/pics/514256DOD250BG.jpg

      Did you already construct it ?

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    3. yes i have had the same problem, the gain pot doesn't change anything. i tried flipping to see if maybe that other schematic was right, but then i got no sound.

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  15. I made the circuit again with new components and new board... I had the same problem... Only the level knob works...

    ReplyDelete
    Replies
    1. With the exception of the input cap...100n here and 10n in your linked schematic...the layout is exactly per schematic. It may be worth taking some hi res photos of your board front, back and off board wiring and upload to a photo sharing site. Fresh pair of eyes couldn't hurt.

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    2. Hello,

      I will upload some photos.

      Thank you

      Delete
  16. The photos are here:

    http://migre.me/pQh5S

    http://migre.me/pQh2v

    http://migre.me/pQh3k

    http://migre.me/pQh43

    http://migre.me/pQh4E

    http://migre.me/pQh5i

    ReplyDelete