spdt in the TS... maybe...?

[flavourful]

I'm just finishing up my first stompbox, which so happens to be a TS808. I used mostly the stock schematics changing only a few caps and whatnot on the layout to the specs of the Robert Keeley ts808 mod, (which actually lists all the replaced parts on the site) I was browsing the other mods and the DS-1 'seeing eye' one caught my eye. thats just adding another clipping diode to the circuit using a spdt switch, isn't it? at least thats what I got out of it....  Anyways, now for the real question. Could I do thtat with the TS808 to switch between standard symmetrical to an asymmetrical clipping circuit using a spdt switch with a diode on one side and nothing on the other? better yet is it possibe to use the spdt to switch that critical cap (the one in the clipping stage. ~.047uf stock and .1uf in the keeley mod) between one that gives the stock freq. reponse and one that gives more bass?

[comfortably_numb]

As a matter of fact, both of those things are possible.  I think you may need a dpdt switch for the diode, as you would be adding it in series with another.  One side of the switch would be a bypass to the other diode, the opposite side of the switch would have the additional diode in it. 

The cap you can do with a spst switch.  Since you add the values of caps in parallel, you can put the .047uF cap in permanently, and add in another .047uF (or .053 technically, but I don't think they're made) on an spst switch.  First, switch the 4k7 resistor with the .047uF (you SHOULD be able to do this, you pros check on me!) Wire one side of the switch to the resistor (where it meets the .047cap), and the other side to the cap, with the cap to ground.  That way when the switch is out, you have .047uF, when the switch is in, you have .094uF, or .1uF (and given tolerances of capacitors, this is probably just as close).

Someone check me on this, but I think it should work fine.

[petemoore]

  changing from two diodes in one direction, to one diode, short across one of the two diodes.
 Since a lower threshold diode will do all the clipping if two are across the clipping connections [OA output and -input in TS] lifting the low threshold diode [with a switch to take it out of the circuit on one end] leaves the higher threshold diode to do any clipping.

[flavourful]

big thanks to y'all. most of it makes sense now, except for that little bit "switch the 4k7 resistor with the .047uF". wouldn't that make a simple low pass filter as opposed to the high pass thats there? seems like it would mess up the freq. response, though I really don't know. Also, now that I can do a bit of diode switching which diodes do you think I should add? I'd like to have symmetrical clipping on it somewhere, so I'm thinking either have an led in permanently (louder with less gain??) and have the matching diode on the switch, that or have the matching diode in permanently and have something with a bit less threshold voltage on the switch, or even a geranium (more fuzzy??). any other ideas?     -thanks

[comfortably_numb]

The resistor/capacitor to ground in this situation doesn't work like a standard RC network.  It doesn't give you the low pass, or high pass filter that you're refering to.  What happens here is that the opamps gain is set by the amount of signal that is fedback to it from it's output.  The signal going in basically suppresses what comes out.  So in this case, your .047uF capacitor bleeds high content to ground, sending more low end to the opamp, which has the effect of supressing low end in the output.  Make sense?  The math is the same, regardless of the position of the cap/resistor.  There may be a small difference, but it is a neglegible one.

[flavourful]

it all makes sense now. thank you! now I just have to finish the wrapper and I'll be finished, at least until I get the switches.