MI Audio Crunchbox with Timmy EQ?

[Snare227]

I love the Crunchbox, I just wish it had a better EQ setup so I could dial in some extra low end when I use a small cab.  IVIark mentioned this in a thread on the open chat, and said it should be fairly easy (for him lol) but I am not experienced enough yet to know how to incorporate the EQ and combine different aspects of different circuits together.  Any help is appreciated!

[IvIark]

Give this a try and let us know how it turns out.  Bass and Treble control added and original Tone control removed.  I also omitted the presence trimmer.

The Timmy bass pot is a high pass filter which started cutting frequencies between 48hz and 1.23khz depending on the pot position.  The Crunch Box used a 1K resistor and 220n cap for its high pass filter in the same position which starts cutting bass frequencies from 723hz and down.  I've altered the caps in this bass control to 100n and 3.3uF which will alter the corner frequency of the high pass filter from 48hz to around 1.5khz and so close to the same range as the Timmy.  If you alter the 100n cap to a 120n then it will be exactly the same.  This range means when the Bass pot is approximately half way, you will be getting the same response as the original Crunch Box which should make it ideal, allowing you to tweak both ways.

I'm not sure how useful this entire range will be with the Crunch Box because it was done to allow you a bit more of a bass boost with the Timmy when using it with cleaner settings.  With the Crunch Box in high gain mode it will start to get a bit flubby in the low end, but at least you have the control to pull it back a bit as you need to.

The Treble control low pass filter, will cut high end around the same frequency range as in the Timmy (there is an additional 470R of resistance in series with the pot, but that won't change it too much).

The Timmy had the final opamp stage after the Treble pot whereas this goes straight to the volume pot, but that should be fine because it's how the original Crunch Box did it anyway, just with a different frequency range.

Anyway give it a go and let us know what you think.  If it's a good mod I'll add the layout to the main site.

[Snare227]

IVIark you are awesome man!  Today is my wedding anniversary, so I have to take the little lady out to dinner after work (though it would be interesting to see her reaction if I told her I wanted to stay home and smell solder fumes instead)... but I'll get on this as soon as I get a free evening and report back with findings.  Thanks!

[IvIark]

Oops I noticed it's only 17 columns wide, now corrected. And happy anniversary

[Snare227]

Well I did get around to building this up.  The bass does feel a bit flubby and exaggerated when it is bumped up with my humbuckers.   Most of the added bass is at the end of the pot, but I'm sure a different taper might even that out through the sweep. The bass and treble pots acted reverse one another, but I swapped the leads and it worked as intended.  Honestly I think MI Audio hit it pretty good with their version, and all this time I've wanted more bass in this circuit when in reality the original is right where it should be.  If I ever swap out my original on my board it will be for the four knob version I made from your layout with the outside mid pot. I appreciate your time in putting this up for me... and for all the other awesome layouts!

[Frank_NH]

I recently finished a Crunch Box and modified the circuit to use Jack Orman's version of the SWTC tone control:  

http://www.muzique.com/lab/swtc.htm

Sounds great(!) and permits a treble cut and boost.  (I also modded the second stage op amp to reduce the gain, identical to the Marshall Gov'nor on which the CB is based).

My modded CB will soon be my go to distortion - it's that good.