Question about wiring DPDT on/on switch (EA Tremolo pseudo-waveform selector)

[davidjnichols]

I'm building an EA Tremolo and want to do a depth mod.  I'm building this one.

http://www.generalguitargadgets.com/pdf/ggg_eat_sc_improved.pdf

I want to add a switch in place of r19 and on one side of the switch be a 68k resistor and the other side of switch be 1m to get choppy, square wave style depth.  My problem: I have no idea how to wire a DPDT switch for this.  I have one of the 6 prong switches.  If I understand correctly, the center two poles are input, and the end poles correspond with that side of the switch.  Since my circuit that's running through the switch only has one signal (not a neg/pos), do I need to wire both lugs for center left and right, or should I jumper them?  Help!  Thanks.

[slacker]

There's a few ways you could do it.

If you imagine the switch lugs like this

1    2
3    4
5    6

then what you have is two separate switches lugs 1,2 and 3 are one switch and 2,4 and 6. For the left hand one lug 3 is the input and 1 and 5 are the outputs depending on which way the switch is set, same for the other side. You could just use half the switch and connect one end of each resistor to say lugs 1 and 5, connect the other ends of the resistors together. The lug 3 would go to where the top of R19 went on the schematic and the joined ends of the resistors go the the bottom, ground.
Or you can use both halves of the switch, connect one resistor between lugs 1 and 2, the other between 5 and 6, 3 to where the top of R19 went and 4 to the bottom.

There's at least a couple of other ways to do it.

Hope that makes sense.

[davidjnichols]

There's a few ways you could do it.

If you imagine the switch lugs like this

1    2
3    4
5    6

then what you have is two separate switches lugs 1,2 and 3 are one switch and 2,4 and 6. For the left hand one lug 3 is the input and 1 and 5 are the outputs depending on which way the switch is set, same for the other side. You could just use half the switch and connect one end of each resistor to say lugs 1 and 5, connect the other ends of the resistors together. The lug 3 would go to where the top of R19 went on the schematic and the joined ends of the resistors go the the bottom, ground.
Or you can use both halves of the switch, connect one resistor between lugs 1 and 2, the other between 5 and 6, 3 to where the top of R19 went and 4 to the bottom.

There's at least a couple of other ways to do it.

Hope that makes sense.

That makes a lot of sense.  I think to keep it simple, I'll just use one half of the switch.  Thanks a lot!

[GGBB]

I did something similar with mine but in a much simpler way.  Make R7 100K and R19 18K, and join pins 2 & 3 of the 250K depth control.  Then to go to max depth just have your switch short out R7.  You will only need an SPST.

[davidjnichols]

I did something similar with mine but in a much simpler way.  Make R7 100K and R19 18K, and join pins 2 & 3 of the 250K depth control.  Then to go to max depth just have your switch short out R7.  You will only need an SPST.

So I did it the more complicated way I guess.  I left R7 at 120k and on one side of the switch I had the 68k resistor and the other side 1m.  When I'm switched to the 68k side, the depth control acts as it would without the DPDT, but when I switch to the 1m side, it's at max depth and the depth knob does nothing.  I was hoping the 1m side would make a choppier wave sound but would still be controllable.  How should I fix this?  My goal is to have one side of the switch sound like a sine wave and the other a square wave (because I don't know how to change the actual waveform). 

[davidjnichols]

Wait a second!  What if I use the switch to run the signal through a diode or something to get a sawtooth style wave?  Could I use the switch to go through a "ramp up" dealy like this schematic?  http://fuzzcentral.ssguitar.com/tremulus.php  I just really want a switch that will change the sound of the wave but still retain all controls (speed, depth).

[GGBB]

R7 R13 R19 are working as a voltage divider.  R7 sets the max depth, and R19 the min depth.  The range of depth adjustment is provide by the pot R13, and its wiper position determines the Vin/Vout ratio.  Max depth is achieved when Vin = Vout - in other words at the other end (C4) of R7.  So the stock configuration doesn't allow you to go to max depth because of R7.  Even with the pot at full depth, the ratio is ((68 + 250) / (68 + 250 + 120)) =  72.6%.  By swapping R19 to 1M, your are changing the ratio quite a bit but you are not maxing out the depth because you still have R7 and some of R13 (according to where you have the pot set).  You would still only be able to get up to 91.2% max depth.  (This is the math of course - audibly 91.2% might sound like 100% - I don't know.)  To achieve absolute max depth on a switch, all you have to do is provide a direct connection between C4 and Q2 gate.  So there is more than one way to achieve that - my way is one that I know works.  In my case the 100K R7 was implemented as a variable resistor (pot) so that when switched on I could have either max depth with the pot full up or an intermediate setting anywhere between the original depth setting and max depth.  To do this I had to make the depth pot a variable resistor and change R19.  But you could just jumper those two points on a switch to kick in max depth or perhaps more elegantly switch the Q2 gate between the depth pot wiper and C4/R7.  No additional resistors or value changes are necessary.

[davidjnichols]

Wait a second!  What if I use the switch to run the signal through a diode or something to get a sawtooth style wave?  Could I use the switch to go through a "ramp up" dealy like this schematic?  http://fuzzcentral.ssguitar.com/tremulus.php  I just really want a switch that will change the sound of the wave but still retain all controls (speed, depth).

Wait, maybe that won't work.  But I feel like I'm on the right track.  I basically want to add a switch to my EA Trem that does this: http://youtu.be/xdrqkZlWtMI?t=3m

[davidjnichols]

R7 R13 R19 are working as a voltage divider.  R7 sets the max depth, and R19 the min depth.  The range of depth adjustment is provide by the pot R13, and its wiper position determines the Vin/Vout ratio.  Max depth is achieved when Vin = Vout - in other words at the other end (C4) of R7.  So the stock configuration doesn't allow you to go to max depth because of R7.  Even with the pot at full depth, the ratio is ((68 + 250) / (68 + 250 + 120)) =  72.6%.  By swapping R19 to 1M, your are changing the ratio quite a bit but you are not maxing out the depth because you still have R7 and some of R13 (according to where you have the pot set).  You would still only be able to get up to 91.2% max depth.  (This is the math of course - audibly 91.2% might sound like 100% - I don't know.)  To achieve absolute max depth on a switch, all you have to do is provide a direct connection between C4 and Q2 gate.  So there is more than one way to achieve that - my way is one that I know works.  In my case the 100K R7 was implemented as a variable resistor (pot) so that when switched on I could have either max depth with the pot full up or an intermediate setting anywhere between the original depth setting and max depth.  To do this I had to make the depth pot a variable resistor and change R19.  But you could just jumper those two points on a switch to kick in max depth or perhaps more elegantly switch the Q2 gate between the depth pot wiper and C4/R7.  No additional resistors or value changes are necessary.

Yeah that makes sense.  I think I may want to try, rather than the depth increase mod, a "ramp up" sawtooth mod.  I don't know how well I could implement it on an EA Tremolo, but it works really well on the Tremulus Lune.  And it's more of the effect I'm going for rather than depth increase.  http://commonsound.org/tremulus/tremmods.pdf   No clue how to do it though.