BOSS DM-2 Modification - Wet Only Signal

I'm looking to modify a Boss DM-2 so I can use it as pre-delay unit.

This should be a fairly simple job - just to install a switch that cuts the dry signal.. But I'm unsure of where in the circuit to install the switch without interrupting the rest of the pedal.

On the schematic attached I've added a couple of potential points in the bottom left. Is this possible or will it upset the op-amp IC1 ?
Thanks!
Jamie

hopefully someone will correct me if I 'm mistaken, but I believe you can just lift r32.

I would agree R32 is the spot but it might be important for noise reasons that you leave the resistor close to the op amp. So ideally you might unsolder just the input lead of R32 and then insert the wires to the toggle there.

Thanks for the help Andy and Squarewave !

As it turns out, there's a jumper between Leg 7 of IC1 and R32 anyway. I removed this which works, but gives a bit of noise. To reduce this I put a jumper between the output of R4 and R9 and the input of R32, so the op-amp see's the dry signal at both inputs.

Only issue now is there's no sound when the pedal is off, as I've cut the direct feed. Initially I thought I could use the inbuilt foot-switch as a dry on/off switch and always have the echo there but the switch is linked to the power in some way - possibly a ground connection for the circuit.

Either way it works! I'll update with some photos for anyone else who's interested when I next do some work on it.. It's quite a cool effect, playing without the dry signal.

cool, you're welcome!  That's a nice pedal   I like the 80s analog delays, I have two Ibanez AD9s incase one craps out.

The switch is a momentary for a flip flop circuit (friends, please correct me if mistaken) https://en.wikipedia.org/wiki/Flip-flop_(electronics).  I'm only saying that for my own educational benefit.  I believe you'll need a spst on off toggle foot switch.

Also, I have a question for the designers.  Would it be more elegant/ beneficial to also bypass R37 (the other mix resistor)?

Thanks!

andyfromdenver said:

cool, you're welcome!  That's a nice pedal   I like the 80s analog delays, I have two Ibanez AD9s incase one craps out.

The switch is a momentary for a flip flop circuit (friends, please correct me if mistaken) https://en.wikipedia.org/wiki/Flip-flop_(electronics).  I'm only saying that for my own educational benefit.  I believe you'll need a spst on off toggle foot switch.

Click to expand...

Yes a bistable alternating FF.  It should be easy enough to force it into the desired mode.

Also, I have a question for the designers.  Would it be more elegant/ beneficial to also bypass R37 (the other mix resistor)?

Thanks!

Click to expand...

R37 is the wet signal.. the OP wants wet...

JR

Well looking at the schematic I think you can achieve what you want by just lifting C8

Maybe you find a more elegant way of doing it in Diystompboxes or freestompboxes forums

JohnRoberts said:

Yes a bistable alternating FF.  It should be easy enough to force it into the desired mode.R37 is the wet signal.. the OP wants wet...

JR

Click to expand...

Hi John, I did some opamp reading and realized that I was neglecting the opamp feedback resistor.
I'll rephrase my question though!  If there are two signals being mixed by 47k resistors, and you eliminate one signal, then I thought couldn't you also replace the remaining mixing resistor with a jumper.  But I was neglecting how the gain was set with the feedback resistor.

anyway, clear as mud and stupid (my question) 

Thanks!

andyfromdenver said:

Hi John, I did some opamp reading and realized that I was neglecting the opamp feedback resistor.
I'll rephrase my question though!  If there are two signals being mixed by 47k resistors, and you eliminate one signal, then I thought couldn't you also replace the remaining mixing resistor with a jumper.  But I was neglecting how the gain was set with the feedback resistor.

anyway, clear as mud and stupid (my question) 

Thanks!

Click to expand...

I thought this was already answered... feedback resistor stays unchanged, the one input resistor you no longer want just gets removed.

JR

Thanks for everyone's contributions.

The DM-2 is still working well in wet only mode - just wondering if anyone has an idea how I can change the Flip Flop circuit so that it switches from Wet only signal to dry (off) ?