how to replace blend pot with button?

[Dr. Sherman Sticks M.D.]

i want to add a button to a pedal so that it will either replace or work in conjunction w/ the dry/wet blend pot.
the button would be 'OFF' = 100% dry or wherever the pot is set too, 'ON' = 100% wet.

is this possible?
here is my thoughts on replacing the pot. the 3 dots between the pot and the switch are where the pot is connected to the board currently.

Screen Shot 2015-09-30 at 10.45.27 PM.png (32.73 KiB) Viewed 3968 times

can i do it w/ a SPDT or do i need a DPDT like in the diagram?
is it necessary to send the dry to ground when the wet is connected? and vice versa?
do i need to add resistors to my switch?

how would you wire it up to have the pot still work in tandem w/ the button?

my knowledge is basic but i want to learn so i'd really appreciate any help!

[Nocentelli]

We'd probably be able to give better advice if we could see a schematic for the actual pedal you're planning to mod (blend pots work in different ways depending on the circuit). In principle, your switch idea could well work, I would suggest using a centre-off, three position spdt or dpdt so the centre position allows the blend pot to be active, and the outer throws give either 100% dry or 100% wet.

[Dr. Sherman Sticks M.D.]

its a MASF Possessed. i don't think there is a schematic? i couldn't find one.

heres a gut shot i dunno if that helps? the blend pot's 3 black wires are connected to the board in the bottom left corner where it says "P1"

2015-10-01 14.17.20.jpg (360.75 KiB) Viewed 3947 times

[Teej212]

So that's the spin chip which has three pot inputs labeled pot0 pot1and pot 2. The pot labeled p1 is suspiciously close to the locations of the pot input pins on the chip so just looking at that i would think the mixing is done digitally. If you can get a picture of the other side I can tell you for sure.

The problem with using a switch to connect the lugs on the pots on the spin is that there will be a slight lag which might bother you.

[Dr. Sherman Sticks M.D.]

thanks for the insight man. i'm not sure i can get a pic of the other side. the board is pretty solid in there w/ some plasti-dip or something on the sides and the wires and kinda short and don't seem super flexible. lemme inspect further.

[Teej212]

if you told me what the knobs did that might also let me know if the mix is being done analog or digitally.

[Dr. Sherman Sticks M.D.]

the top 3 are like size of the grain, pitch modulation of grain, and duration of glitchyness. not sure if the order of which knob is which is correct. (i can find out for sure if this matters)

the bottom two are blend and master volume

[Dr. Sherman Sticks M.D.]

also since its a pretty glitchy sounding effect, i dunno if a slight lag would bother me…do u have any idea how long of a lag we are talking? and does the lag cut out all signal?

[Dr. Sherman Sticks M.D.]

been thinking about this…just dawned on me. if the spin chip only allows 3 pots, then wouldn't the blend and master volume have to be done analog?
b/c the 3 pots to the spin chip have to be the three glitch parameter knobs at the top.

[Teej212]

yes sorry i didnt respond earlier. sounds like it has to be done analog. i wonder why they put the mix pot so near the pot inputs, very sneaky. so yeah you should just be able to jump the connections on the blend pot with a switch no problem.

[Dr. Sherman Sticks M.D.]

all good man no worries! rad!

umm so i tried just quickly jumping the connections w/ a wire to where the pot is connected to the board at PO. i dunno if i'm getting a wonky outcome because its all connected still, but when i jump the middle and wet (right). if I have the blend pot all the way dry. the signal cuts out entirely. like its getting the wet signal but its turned all the way down.

i think i'm missing something or i need to make some different or actual connections in order for it to work?

am i right in thinking that the left and right wires going from the board to the pot are carrying the input signal of dry and wet respectively to the pot? and that the middle lug on the pot is like an output carrying the mix of both signals depending on the position of the pot back to the board?

i guess i'm a lil confused as to exactly how the wiring should go between switch, board and pot.
if i do something like this will i get, 'OFF' position = pot position blend , 'ON' position = 100% wet?
i'd like to keep the blend pot in tact.

Screen Shot 2015-10-02 at 3.45.54 PM.png (22.96 KiB) Viewed 3912 times

[Dr. Sherman Sticks M.D.]

should i be worried about a button that only has a 250mA rating? i believe its rated at 48vDC, so at 9v the actual current rating would be higher, right?
http://www.mouser.com/ProductDetail/Swi ... d=23063929