Crunch Box - wow

[motterpaul]

I have built so many overdrives - but have seen IVIark and others mention the Crunch Box many times so I tried it. Normally I avoided LED overdrives because they sounded too hairy - I prefer a tighter distortion sound.

But the amount of gain on the Crunch is astounding. With the gain full on I can just barely crack the volume pot and it is at full volume. And the sound is fully saturated, compressed creaminess. I love it. It is the first OD I have built here that made me want to put down my humbuckers and see what it could do with a Strat. Perfect - it lets you get that Clapton Woman Tone or any 5-way switch position you want without it dropping down to that plunky, uninspiring cowboy pluck tone.

I am using the 5mm red LEDs (as in the layout). But I am really wondering, exactly where does all of this gain come from? It sounds similar to a RAT or Suhr Riot, but the Rat usually oscillates on me when I turn it up, and the Suhr Riot is fairly quiet. This one has all the gain and the volume, and no squeal.

It does have a fair amount of hum, but if you back off the gain it reduces substantially and you still get a very good tone. I doubt I would want to play this at full gain anyway because it is so gainy you can actually hear the notes start loud and go slightly lower in volume as the ADSR envelope compresses.

The only thing I might want is more low end - and John K mentions changing the input cap value to do that (if I read the notes correctly).

I just made this - but can someone tell me what is different about this circuit that makes it have so much gain? Is it because the gain pot is in the feedback loop?

(Note - a thank you to the fellows who supplied the images on their sites)

[nocentelli]

You have (very approximately) a gain of 100k/1k = x100 when the gain pot is cranked, but that goes into the second opamp with a fixed gain of 1M/10k = x 100, and cascaded gain stages multiply their gains, so max gain = theoretically x10,000. In reality, I imagine the second opamp clips pretty hard, but the diodes to ground and considerable treble roll-off from the tone pot and fixed cap to ground straight after IC2 willsmooth out that  "horrible opamp clipping" that some folks dislike so much.

[Beaker]

If you like this one, check out the Frantone Cream Puff. It's got 4 LEDs and it's a doozy!

http://tagboardeffects.blogspot.co.uk/2013/04/frantone-cream-puff.html

[clockman]

I made this for a friend and he likes it too. I can't answer about the low end mods but did try the presence trmmer as an external pot and glad I did. Very interactive with the tone control.
And if you dig it now, try hooking it up with a charge pump or 18volt supply.

[Suzukiscottie]

There is a version 2 of the schematic with the following alterations:

R6 - 470
C8 - 0.022u
R9 - replaced with the aforementioned Presence trimmer, 20k

edit - and now that i have looked at the layout above, it is V2!

[motterpaul]

Thanks you ALL for advice. I will follow up trying (probably) all of them as I build more of these. The presence should be a knob, I agree. It seems to have more control than the tone pot and there are some nice tones to be found when you dial it down although I seem to like it full on mostly.

[Heath]

Yep, Motts, everything you said AND it even sounds good at lower gain levels.  It's the definition of a "go-to pedal."

[iggy]

Hey guys thanks for bringing up this pedal. Not one I have built. But it's now on the short list. Always good to hear feedback on the different circuits.

[Heath]

Ignatius,

I think the Crunchbox was inspired by the video for AC/DC's Shake Your Foundations...




...and much like Angus, the CB will sound amazing while wrecking your shit.



It's also believed, amongst the denizens of the shadier parts of the internet, that the original Crunchbox design was developed by Dr. Emmet Brown (later known as Dr. BrownSound, but that's another story) himself!  GREAT SCOTT, 1.21 GIGWATTS OF ELECTRICITY?!?!



Further evidence is when Marty plugs his guitar in near the beginning of Back to the Future and gets blown backwards.  There exists convincing evidence that it was a prototype Crunchbox, at that time referred to varyingly as "Sonic Laxitive," "ohFUX!capacitor," and the less creative "Ohmygodican'tfeelmyballsanymore Device," rather than the speaker, itself.  You can see, briefly, when the speaker explodes, there's actually an early version of the CrunchBox back there with the volume turned up way too loud.

[Gentle_Jack_Jones]

This on my to-build list anyway, but with motterpaul's ringing endorsement, I pushed it to the top and finished it tonight. Yes, it does have mondo gain! It also has great lower gain sounds, but to get them, I have to turn the gain pot all the way down AND back my guitar volume almost all the way down. At that point, it sounds more plexi-like to me, and I can get a good Led Zep sound.

That's on a Tele. I haven't tried it with a Les Paul yet, but I wonder whether that guitar's volume knob will go low enough to get those great low gain sounds.

The newest version of the pedal, the "Super Crunch Box," has a low gain toggle to make accessing those sounds easier. Does anybody know what they use to get that? I'd think it would just be a resistor inline with the gain pot, but maybe it's something else? If it's just a resistor, I wonder what value.

Alternatively, I'm thinking I can just replace the specified gain pot with one that has more resistance. Does anybody have a suggestion about values if I go that route?

All and all though, a very box-worthy build!

[alltrax74]

I built a few of these and I love it, it's the only distortion (or high gain overdrive) I have on my pedalboard.
For heavier sounds I stack it with a Jan Ray before it sounds great.
I have no noise or hum even with the gain cranked up, but TBH I never go above half

[iggy]

Heath.
That's too damn funny. I almost had to go back and watch the movie again to see if i missed those scenes. Now my stomach hurts.