Wednesday, 19 September 2012

Maxon OD880 Overdrive / Soft Distortion

Maxon's now discontinued Overdrive / Soft Distortion pedal.  Brother to the very popular OD820 and in the same series with the same size case.  This layout uses two dual opamps instead of the 3 singles in the original to keep the layout size down.  The equivalent of the LM741 in dual opamp form is probably the LM1458, but it's worth trying this with the other popular dual opamps as well such as the JRC4558, NE5532 and TL072 etc, so you can use your favourite.






13 comments:

  1. Tag it.

    Nice little OD. I subbed 9K1 with 10K and used NE5532s. Sounds good, simple transparent everdrive. Just wish it had a bit more bass and output.

    +m

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    Replies
    1. Miro's back!! :o) Nice one mate. If you want to get a bit more volume try using two 1N4148 pairs in series instead of single diodes, this will mean less of the signal is dumped to ground and so should give some boost. For a bass boost, the 47n and 4K7 to ground from the top IC pin 2 creates a high pass filter which starts rolling off low frequencies starting at 720hZ which seems high. Swapping the 4K7 for a 10K will be 339hZ, 22k will be 153hZ, 47K will be 72hZ. It may even be worth swapping the 4K7 for a 50K pot to give you control over the frequency.

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    2. I think i'm going to swap the 4K7 resistor for 39K or 47K and double up on the diodes. Low E on standard guitar tuning is around 82hZ, so i can't get my head around what the people at Maxon were thinking back in the 70s... 39K with 47nF would be around 86hZ, so that could be perfect with just a tiny cut.

      If those two slight mods do what i think they will do, this one is going to get boxed and soon.

      I recall some build used six 1N4148s for single clipping stage. Just can't remember what it was.. So i might even try six of those :)

      (damn the typos.. :) ^^it's overdrive and not everdrive)

      +m

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    3. IC Big Muff. That's only the frequency where the lows start to get attenuated, it doesn't cut everything from there downwards. But I agree the 4K7 with a 47n seems too high starting frequency for me.

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    4. I'll try those out tomorrow and let you know.
      +m

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    5. Yup. That trrimmer seems like a giid idea. I soldered 39K in, and that kills the clipping stage making it more like ugly saturated light distortion. Then i tried 22K and results were the same. That made me think if there was something else wrong, as i replaced the clipping diodes with 4 1N914s. No there wasn't. 4K7 in it's original place sounded right.

      So one option could be to find out what resistor value keeps the clipping in tact, but still let more lows pass. Other would be to up the cap. But don't know if that kills the clipping too...
      +m

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    6. In conclusion, i really like the open, softly distorted sound, but the thinness could be the reason for discontinuation of the product. It saddens me a lot to play with the circuit - and when i switch to bypass. Bypass, or my amplifier's clean, has much more dick in the bottom, which is not necesserily the best thing.

      Don't really know if it is worth it to mod the attenuated frequencies back to life, as it seems to kill the clipping.

      Sad thing really. Sounds really good, but in my humble opinion, there is a fundamental flaw in the original design.
      +m

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    7. Thanks for letting us know Miro. I've removed the trimmer version, there's not much point in it if it changes the clipping character too much. It's perculiar though. That's definitely the high pass filter before the clipping, and the last opamp channel is a low pass filter to cut highs before the output. Increasing caps really isn't going to do anything because the HP filter will suck it all back out again anyway. Hmmmm. Maybe for the first opamp channel we would be better making it a (slight) booster instead of a unity buffer, to boost the signal before the HP filter and clipping.

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  2. Great overdrive. Miro has a point with the loss of bass but this is actually part of the charm with me. In a band setting this means you and the bass player are not walking in the same frequencies and this helps the guitar to cut through at higher volumes. I jammed a 1p6t rotary switch in for different diodes. May be on the board for good. Thanks!

    ReplyDelete
  3. Great overdrive. Miro has a point with the loss of bass but this is actually part of the charm with me. In a band setting this means you and the bass player are not walking in the same frequencies and this helps the guitar to cut through at higher volumes. I jammed a 1p6t rotary switch in for different diodes. May be on the board for good. Thanks!

    ReplyDelete
  4. While I am sharing pics.

    http://i1273.photobucket.com/albums/y413/glenncohen/_DSC0065.jpg
    http://i1273.photobucket.com/albums/y413/glenncohen/_DSC0066.jpg

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    Replies
    1. Excellent, thanks for all the pics Glenn

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  5. Just put two circuits together and tested them. I personally think that this is what TS9 should have sounded in the first place :) Nothing too special, but really nice, good sounding OD. Not as harsh as Klon. Compresses nicely with gain down. For you mild to medium OD freaks - this one's for you.
    Quite tight for 1590, but i think i may try to squeeze one in...
    +m

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