Thursday, 19 November 2020

Dinosaural OPA-101 Overdriven Pre Amp

 Just traced by Aion Fx as their Ixuea project. This layout is slightly modified compared to the original pedal. First, stock units had a fixed low pass filter before the volume control. The resistor in the filter is now replaced by an external tone control. Secomd, it is wired for true bypass with the input buffer hardwired.



 

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19 comments:

  1. MDC4 December 2020 at 03:59

    Just gave this one a shot and no sound. Has anyone been able to verify the layout?

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  2. Eike20 January 2021 at 19:45

    It kinda works but still hard to verify cause there are no actual clips of a working pedal.
    The sound is getting really fuzzy at higher gains.
    Can anyone confirm?

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  3. Eike20 January 2021 at 19:50

    there is an article from a dude who bought the pedal and it kinda matches my experiences

    https://www.mylespaul.com/threads/dinosaural-opa-101.248478/

    i just did not expect a fuzztone after all :D

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    1. fuzzhead20 January 2021 at 20:58

      After reading that guys review I suddenly got very interested in this.:-)
      So it does Boost OD and Fuzz? And does it sound good? Comparable to anything else out there?

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    2. Eike21 January 2021 at 19:46

      The sound sorta goes broadcast territory if u ask me. I ditched the first one some time ago and build a second one this morning. The circuit is pretty noisy. I subbed the 5457 for a J201. I'll try to fix that tomorrow. A 470pF cap (D1/E1) might help. Got a lot of sqeel when the Gain is maxed. I also dont like the tone control that much. U can just get rid of it by omitting the 22nF and the 470R. All I can say right now is that this little beast has quite a lot of potential. It does boost, OD, Distortion and even Fuzz depending on ur PUs.

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    3. fuzzhead21 January 2021 at 21:20

      Thanks for the build report. I'll tag it as verified.:-)

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  4. Eike21 January 2021 at 06:48

    tons of beautiful low end

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  5. MDC18 February 2021 at 01:16

    Glad to hear this one is verified! I'll give it another go.

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    1. MDC18 February 2021 at 13:50

      Dug my previous build out of a box and found a simple/obvious/dumb mistake. Pedal fires up fine; can't find a demo to see if it's close to the original but it's definitely functional.

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    2. fuzzhead18 February 2021 at 20:27

      Great! Glad you got it working. Yes no demos online...so how do you like it? It's like a fuzzy overdrive, right?

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  6. atomicwombat30 March 2021 at 04:37

    Can you use an electrolytic cap for the 2.2uf? If so , would it be negative lead to ground?

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    1. fuzzhead30 March 2021 at 18:23

      Yes, negative lead to ground. I think it will work fine with an electro cap.

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    2. atomicwombat1 April 2021 at 23:02

      Built this one, the only substitution was a tantalum cap for the 2.2uf and I used a 2n5457. It fired right up and sounds awesome! The only issue I had was the gain control working backwards. I swapped the leads and tied 2 and 3 together on the pot and it’s working good now. Compared to Eikes build, Mine is nice and quiet, with minimal squeal at full gain. Maybe it was the j201? I found the tone control useful. This circuit has a great feel, and sounds good at just about every setting I’ve tried so far. I’ll be boxing this one up tonight

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  7. Convergent Sound13 April 2021 at 23:54

    I like this one, it sounds kind of unique. Anyone have any clue where I might start if I wanted to reduce a little of the bass content on this one? The input cap (33nf) maybe?

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    1. fuzzhead15 April 2021 at 19:06

      Not sure if reducing the input cap helps since there is a even smaller cap (10nF) between the input buffer and the input of the first op amp. Usually I would tweak the eq responce by tweaking the RC filter connecting to the left side of the op amp. In this case it is the 2,2k and 2,2uF cap. But since this is a quite unique circuit it may also affect other parts of the circuit as well like the BJT transistors...

      Here is a useful calculator for tinkering with RC filters:
      http://www.muzique.com/schem/filter.htm

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    2. Convergent Sound17 April 2021 at 19:12

      I ended up pulling the 2.2uf at the lower left and replaced it with a DPDT on/off/on toggle with 220nf in the center, and 470nf and 150nf on the other side. This gave a decent bass cut in the center, mild cut on one end of the switch, and nearly stock bass content on the other. I didn't notice any other audible difference in the circuit other than the change in the bass content. I'd recommend the mod if you are a fan of the stock circuit.

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    3. fuzzhead17 April 2021 at 19:16

      Sounds like a really useful mod. Will try it when I tackle this one.

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    4. Convergent Sound17 April 2021 at 20:00

      *Correction: 1.5uF on one side, not 150nf.

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  8. NDF Paintings28 August 2021 at 20:41

    I built this. It works great. Only thing, as atomicwombat mentions, is the drive works in the same direction as the other controls if you tie lugs 2and 3 together instead of 1 and 2

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