The Double Filter Revisited: Junction Machine

Alright so I've come back around to working on the double filter pedal and have made it much simpler on myself.  Basically I have implemented a variable capacitor at the beginning of an LPB-1 with a footswitchable potentiometer to let me switch between boosting frequencies.  I socketed the two input capacitors and the output capacitor of the LPB-1. This basically makes it so that I can switch out the range of the frequency at a later date.  At the moment I need to go back in modify the range of the pedal.  Its looking like I need larger output capacitors to let more bass go though, as well as larger capacitors on one end of my variable capacitor.

If you've seen Kit Rae's big muff page, he has a lot of schematics on there.  The idea of using an input "Depth" or "Focus" is where this originated.  A quick glimpse at the Supercolyder is where I'll be heading next with the Capacitor selection.  I think having a 10uF capacitor at the output should be good enough to let all frequencies pass through, and having a 10uF and 0.01uF at the input capacitor will allow for a drastic range across the frequency sweep.

Much thanks to Micah over at Glass Hero for his help.  His website is down, but he makes some awesome pedals!! Check out his facebook in the meantime.

A little bit of a lesson

Alright, so I have not quite got the current Binary Filter to work.  I messed around with the wires, testing just one capacitor per filter, and still it just goes from Farty to clear sounding, with little variation on the sweep of the potentiometer. It sounds interesting, but not quite what I had in mind.  All of the PCB and wires makes up a giant rats nest which is hard for me to diagnose where I've gone wrong.  Ultimately I think that due to my lack of knowledge in this area I'll have a hard time going through and assessing where things are going wrong.  Heh I'll admit it was quite frustrating, this is the 3rd time I've attempted to make this circuit.  Which leads me a very crucial tip.
MAKE SURE YOUR CIRCUIT WORKS EXACTLY AS YOU LIKE BEFORE YOU PUT IT IN THE ENCLOSURE!!!

Unfortunately for me I get too excited and map out the graphics for the enclosure before I have the circuit done and pretty much finish the enclosure before I've even tested the complete circuit.  So now I am left with this metal box with wholes in it that I've got to make work for me, otherwise I end up with well, just another metal box with holes in it.  Big picture here is to not get too ambitious with your first couple of circuits.  On the positive side of things, my 3PDT switching has worked for my past 2 failed attempts.

Ultimately the idea is to create a dual boost pedal, where I can choose to either boost the bass or treble side of a signal. Which would allow it to work great with most any other pedal.  I see this as a great sort of "support system" type of pedal.

So I'm going with the idea of just keeping things simple.  Lets go caveman style!  This should be a positive distraction to keep me from thinking about how much desoldering I'm going to have to do in order to salvage the components and the PCB.  Since the first pedal was an LPB-1 in a pedal, I figured I'd extend my abilities from there.  Apparently switching out the input capacitors on this circuit changes the frequencies that are allowed to pass.  If i could load up a good number of those on a rotary switch then I think it would kind of function like a tone knob from the LPB-1/my signal.  Add on a 3PDT switching system and I'm already getting started.  For further tailoring I think I'll follow it by a Tone Stack and a recovery stage.
This is what I've drawn up so far.

I apologize for the blurry image, but my camera is messed up, and besides there are not values or even a tested version that I can tell you works at all. But you get the idea of what I'm going for.  I think this should be more straight forward than the previous design and I believe should operate in a similar manner.  The other issue is what to do with the two extra holes in the front of the enclosure.  Previously these were for the High and Low pass capacitors, but now I'll have to come up with something else. (Once again this is where I'll have to continue testing out my circuit ideas...)  But in the meantime onto the next paragraph.

Tone clipping is the focus here!!!  For those of you who haven't been to the AMZ site, take some time and go over there to absorb some knowledge. I've found it to be chock full of resources.  Here I'll direct you to his discussion of Tone clipping.  The idea is that you can place clipping diodes (i.e. Silicon, LED, etc) after your filters and they will clip that portion of the filter.

So If I add clipping diodes after the low pass filter, then it will make the low frequencies fuzzy with a somewhat preserved high frequency response. The opposite will happen when I put clipping diodes after the high pass filter. Once I get it breadboarded I''ll have to test out the multiple combinations to see which  combinations sound best for each filter.

Well that's the basic idea.  I'll have to see how it goes.  I'm also planning on making a modded fuzz face in the near future as well.  I'll post some of my thoughts on that too.

Moving in and out of sound with Filters.

For all of you My Bloody Valentine fans out there,

This is Kevin Shields' supposed rig from the Loveless tour.  At the beginning of his chain he has his primary distortion unit followed by 2 graphic equalizer pedals.  This is in addition to the 3-band EQ that is already in the Marshall Shredmaster.  So it seems that he has 3-preset tones that he can utilize just at the beginning of his pedal chain.  One of my goals is to make something similar to this.  It has been essentially seen in the Death By Audio Kill Kill Filter.  However There are some things about filters that I've learned in the meantime which I think could be added.

The generic Big Muff Pi Tone is what I plan on using in most of my designs, from what I understand it is both a hi-pass and low-pass filter which can be sweeped between the two. One of it's characteristics is the Mid-Range Notch, which depending on the music style you're playing may cause you to get lost in the band's mix.  With out a proper equalizer you might not be able to hear yourself too well.  One thing I've seen from the BYOC big muff clone is that they have changed some of the capacitor values in order to achieve the mid range notch, a flat mids tone, as well as mid-range boost.  This option has already been applied to the distortion unit, but I'd like to take it further and apply it to the dual filter idea.

What I'd like to do is to be able to choose the general mid-range characteristic, and then be able to switch between two sweepable frequency equalizers to further characterize the tone.  I'd like to have a little bit more options in terms of mid-range characterizations, so instead of a single rotary switch to choose between 3 mid-range options, I'd like to implement 2 toggle switches to choose from 4 different tonal characteristics.

I'll have to see how I'd go about doing this, I think a set of DPDT switches in place of the capacitors in the filter would allow for me to make the toggle switches work properly. Some LED's would be nice as well, probably 3mm as indicators of which characteristic option is currently selected so they don't compete with the.  I've got a basic layout created for this pedal, I'll just need to upload it...another saga another day....Duplex Filter something or other...