Friday, 14 December 2012

Runoffgroove 22/7

Phew. This board almost made me crazy. There is "only" 28 cuts and 11 links, but i got down to only one resistor over one strip. This one is quite interesting. CMOS Hex inverter based BMP adaptation.

A word about the circuit from ROG:
This circuit was born with the idea of making a CMOS workalike of the well known Electro-Harmonix Big Muff Pi (BMP). We chose the name Twenty-two Sevenths or 22/7 since it is a rational approximation of pi.

The gain and frequency response of each stage were adjusted to match the corresponding stage on a BMP. The result is a rich and full sounding pedal that evokes some of the fuzz sounds circa 1969, as well as some classic singing leads.

Through the years several variations on the tonestack have appeared, but after studying their variants we concluded that these differences correspond more to parts value availability rather than a significant difference in sound. So, the tonestack components were chosen to obtain an "average" BMP sound, which is referred to as CLASSIC mode in this implementation. In addition, a center-off DPDT switch was added in order to obtain two additional sought after sounds from the tonestack: a FLAT setting and a deeper SCOOP mode. In this way, the sonic palette of the 22/7 is greatly expanded.

The interstage coupling caps have been observed to vary between 100nF and 1uF in different versions of the BMP. In this implementation we chose 100n, which produces a more balanced bass/treble mix that works well for chords as well as soloing. If you want heavier and fuzzier bottom end as found in some BMP versions, you may want to replace the five 100nF caps with 1uF.

As this is a high gain circuit, good layout and cabling practices are critical for good performance. Apart from recommending shielded cable for input and output wiring, the entire circuit should be well shielded inside a metallic enclosure so as to reduce AC mains hum pickup to a minimum.




13 comments:

  1. I just might have to give this one a try.

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  2. Built this one from the ROG original prefboard layout.
    A very rewarding built with a lot of options and a smooth sounding fuzz for some cool Smashing Pumpkins riffs. Not as rich and powerful as the original BMP but it's close and has a unique sweet flavor to it.

    http://fuzzquest.blogspot.co.il/2012/07/the-fluffy-fuzz-cake.html

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    1. Great blog, I'll add a link to the list

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    2. Oh and 101 Greatest Fuzz Songs of All Time. Everyone may laugh at me, but just go and listen to Goodbye to Love by the Carpenters. That's the first song to make me sit up and think WTF was that! Not only fantastic fuzz solos, but one of my favourite solos ever.

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  3. This is a great layout, it takes a hell of a lot of thought to keep the components apart enough to satisfy flat lying OCD :), and sometimes you just can't avoid 3 row resistors (like in some of the muamp layouts), but that's why everyone should buy a full set of 1/8W resistors as well! I love 'em! :o)

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  4. Hmm. I am going through some old stock that I acquired from my school daze. Found a 7404 type Hex Inverter. I might try this out on a proto board. The pin out isn't the same as a 4049, but it has the same amount of inverters... Where's the Schem?

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  5. Miro, I've got to say, I built this over an hour ago and I don't want to put the guitar down! This is fantastic; taking me into Frippish, " Lark's Tongues In Aspic" territory. A nice take on a big muff. Well done ROG, excellent, tag it. cheers, my friend!

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    1. Cool! Thanks man! Taggin' it right away!
      +m

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  6. This thing is freakin fantastic, love it, build this and you wont need to build anyother muff design. Thanks for the excellent layout as per usual chaps.
    Thanks
    Dave

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    1. Yea It is freakin fantastic indeed i just made it and have been playing it for a couple of hours now, great muff variant.

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  7. This comment has been removed by the author.

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  8. Just built this awesome pedal. Can't stop using this one its a mighty beast, love it!

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