Filter range mod? MXR

[jimbob]

http://www.tonepad.com/getFile.asp?id=5

Im wanting to add the filter range mod to the MXR envelope filter but Im not sure how to wire it to the dpdt switch. It is supposed to switch between "A and B" and "I and J" pads but where do those wires go on the switch?. Theres a total of 4 wires from the board to do this but there are 6 lugs on the dpdt switch.

Can someone either explain where I would place theres wires or draw up a quicky diagram?

Thanks

James

[jimbob]

anyone?

[Mark Hammer]

I think the best advice is to do something similar to what is done with the Zombie Chours, except doubled up. 

Remember that caps in series are treated indentically to resistors in parallel.  So, a pair of 1000pf caps in series gets you 500pf.  Remember as well that filter frequencies are generally proportional to capacitance change.  So, cutting the capacitance in half moves you up an octave.

Okay, let's translate this into practical action.  The Tonepad layout presumes you will switch a second capacitor in parallel.  That works, but if you do your range-switching while the effect is on, you WILL hear popping.  Using caps in series will get around that problem.

Francisco's layout shows a C6 and C7, plus pads for a Ca1 and Ca2 for switching in parallel.  Using the pads already provided, you can install a second 1000pf cap in series with C6 and another in series with C7.  Here's a picture showing you how to re-orient the 1000pf caps using the existing pads: http://img.photobucket.com/albums/v474/mhammer/A-GuaFilterRangeswitch.png

The purple dots are where the wire leads go.  It doesn't really matter which purple dot you run to which solder lug, as long as the two purple dots for each pair of caps is wired to the same side of the switch.  The idea is that your DPDT or DPST toggle will shunt one of the caps in each pair in one of its positions.  Whether purple dot A or B goes to the common is immaterial because a shunt is a shunt.

Keep in mind this assumes you use equal-value caps (1000 + 1000).  Should you decide, for whatever reasons, that you would prefer to have more than an octave shift (e.g., 1200pf and 820pf in series), the scheme will still work, but you'll need to be mindful of which cap values go where so that you shunt the same-value cap in each pair.

[jimbob]

Very cool. Thanks.