I finally got around to implementing a mod to cmoy's modified linkwitz crossfeed circuit to enable it to use a 4 pole 3 position rotary switch rather than two DPDT toggle switches. I came up with such a scheme and sent it to Tangent. He kindly wrote up a section about the scheme here. Before I actually tested it, however, I began to worry. With a rotary switch, when switching between positions, all 4 switch locations would be disconnected for a moment. There would still be a path from Input to Output through C1/R3 but I wasn't sure if that would produce a noticeable click or not. Tangent has confirmed that there is indeed a click in such a situation. To circumvent this I came up with a new scheme. R1a is now always connected and hence there will be less of a click in the sound when changing positions on the rotary switch. Usually it is silent. An added benefit is that you use 2 less wires to the rotary switch. Tangent has included this new scheme as well in the link above. Below is cmoy's schematic modified to show the new circuit and switch connections:
As you can see, R1a is now always connected between the Input and Output. The crossfeed portion of the rotary switch (poles A and D) is wired such that it connects R1b in parallel to R1a in the 2nd position, and disconnects R1b in the 1st and 3rd positions. R1b is now 600 ohms (6k for the Hi-Z) which when paralleled with R1a gives you 150 ohms (1.5k for the Hi-Z). Thus, the 2nd position is less crossfeed, the 1st and 3rd more. The bypass portion of the rotary switch (poles B and C) is wired such that the 1st position is bypass mode, the 2nd and 3rd positions are crossfeed engaged. When put all together, that gives you position 1 = bypass, position 2 = normal crossfeed, position 3 = perspective crossfeed. I hooked this up using the modified linkwitz board that Tangent sells, and it worked perfectly. The switch I used was Digikey part number EG1958-ND. Here's a picture:
Of course the main benefit to this is cosmetic -- I prefer the look of a big fat shiny knob to that of two toggle switches. One less hole to drill is always nice too.
I would appreciate any questions and comments. If I've made any glaring mistakes I would appreciate the feedback. Thanks!
As you can see, R1a is now always connected between the Input and Output. The crossfeed portion of the rotary switch (poles A and D) is wired such that it connects R1b in parallel to R1a in the 2nd position, and disconnects R1b in the 1st and 3rd positions. R1b is now 600 ohms (6k for the Hi-Z) which when paralleled with R1a gives you 150 ohms (1.5k for the Hi-Z). Thus, the 2nd position is less crossfeed, the 1st and 3rd more. The bypass portion of the rotary switch (poles B and C) is wired such that the 1st position is bypass mode, the 2nd and 3rd positions are crossfeed engaged. When put all together, that gives you position 1 = bypass, position 2 = normal crossfeed, position 3 = perspective crossfeed. I hooked this up using the modified linkwitz board that Tangent sells, and it worked perfectly. The switch I used was Digikey part number EG1958-ND. Here's a picture:
Of course the main benefit to this is cosmetic -- I prefer the look of a big fat shiny knob to that of two toggle switches. One less hole to drill is always nice too.
I would appreciate any questions and comments. If I've made any glaring mistakes I would appreciate the feedback. Thanks!
