Friday, 7 September 2012

RVIII Distortion

Request.  Not heard of this before but it's apparently a fuzz pedal made by Claudio Dias for his brother Sérgio Dias from Brazilian rock band Os Mutantes.  Anyway here's a vid of one and it sounds pretty good to me:






33 comments:

  1. The MUTANTES FUZZ! Kick ass. Thanks, man! Saw a schematic for this once back a few years ago.

    Now do the fuzz inside Mark Farner's guitar and I'll die a happy man!

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  2. Should the first 10u cap on the left go to the base of Q1? Or are BC109c pinouts slightly different?

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  3. Here is another vid of a commercial version of the circuit. And he's playing an Os Mutantes song at the beginning for the demo.

    http://youtu.be/AECvJA-Nd9Y

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  4. I built this on my own layout before and modded it heavily.

    1. Was quite sick of trying to get the bias of the two transistors right so I put in a Starve/Bias/Stability pot to reduce the power supply from the 9V source. When starved, one gets a nice synthy tone. Think robot blues.

    2. Instead of a toggle, I used a pot to give a wider range. Although I found the setting with the smallest calculated input cap to be the most interesting (and most Os Mutante sounding).

    3. I wired up Log 50K pot between the diode (cathode facing ground) and ground for a bit of asymmetric clipping. When fully open, it behaves as if there is no clipping at all.

    Hope that helps.

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  5. can't find any 15k pot, is there any substitute?

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    1. Along that line, I was wondering if it's better to go up to a 25k or down to a 10k

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    2. Use 50K pot and stick 22K resistor between lugs 1 and 3. That gives you 15K2 pot.
      +m

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    3. Yep, like Miro said you can make up a specific value by just using a resistor, or in the case of this being just the volume control if you use a 20K pot it should be fine.

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  6. Has this been verified? I can't get mine to work yet. Thanks

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    1. Well it wouldn't. I just looked at it and straight away I could see that it wouldn't work as is, shame I didn't spot it before I posted the layout! :o) Put a cut to the right hand side of the top of the 100n cap to separate the collectors. Layout updated

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    2. Well, that did the trick. You can color this one verified.

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    3. Top man, cheers for that!

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  7. This thing is a beauty! Many thanks Mark. Really reacts to guitars tone/volume controls and pickup selector making it way more versatile than you might imagine. Made mine up with 2N222s which I like better than BC109s, and I'm going to replace the toggle switch with a footswitch.

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    1. 1M pulldown resistor at the input is there to kill possible pop sounds from switching. It's usually just easier to explain that extra resistor than to debug the popping sound on these comments.

      For the switch, you'll want DPDT on-on type.
      +m

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  9. Thank you very much !
    Do I need to put this !m resistor in all circuits that I will build ?

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    1. you don't it's just done as a preventative measure. if you don't put one in, and you put it all together and get a popping sound when you engage/disengage the stomp switch, you can go back and add it later.

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    1. i don't have much info to help, but first of all, bc109 is at 200-800hfe, while 2n2222 you've used is only at 30-300hfe. so you could start from there.
      don't you have any bc550,or bc549 to see if that could cause the volume and gain drop??

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    2. Well the good news is that low volume is normal for this pedal, so you have not done anything wrong. The bad news is that it cannot be corrected by using different transistors.

      This is one on my favourite fuzzes, and I have built several of them and there is a solution, that works with almost any pedal that does not reach unity gain.

      Build a LPB-1 with trimmer and add it to the circuit. Loads of volume on tap now.

      http://tagboardeffects.blogspot.co.uk/2013/01/electro-harmonix-lpb1-with-trimmer.html

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    4. Try other transistors if you want, but it will not get loud enough to reach unity.

      To hook up the LPB-1 (with trimmer) run the output wire from the volume pot lug 2 and connect to the "input" location on the LPB-1 (with trimmer) board. Take a wire from the output location on the LPB-1 (with trimmer) board to the "board output" lug on the 3PDT switch.
      It also needs hooking up to ground, and to 9V.

      Yes the trimmer is used to set the volume level.

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    7. Is the LPB1 noisy if you use it on its own?

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  12. Managed to quickly build this this morning before all the family arrived for Easter food. Quite a nice fuzz. May mess with the Trannies though as its not the loudest. Happy Easter all.

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  13. I haven't built this, but I think lowering the value of the 22K resistor should give you more output. You could even replace it with a link, not sure how that will affect the sound, maybe socket that resistor and play around

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