Effect loop selector box

[xad001x0w]

Hi,

As the title suggests i am trying to build an effects loop selector box. That is you have two sets of loop sockects (send and return). an input and output. A DPDT switch switches the input between between the two send sockets and then the return sockects are both directly wired up to the output socket. This works fine in prototype however when both loops are connected the signal becomes very very quiet. I am sure this is due to the fact that the "recieve" connections are basically wired together with the output socket. So when both loops are plugged in, the active loop's output just drains back into the inactive loop's output which is earthed at the switch. Anyway, I am unsure of how to fix this problem whilst still keeping the box passive. I am wondering if an XOR gate could be my answer if i HAVE to go active. With the live connections of both "recieve" terminals wired to both the inputs and the output wired to the output jack socket. Any help would be much appreciated, I know this isnt perhaps the clearest of explanations and i will try and provide a diagram of what i am trying to do at some point as well.

Many thanks

EDIT:
Here is the picture i promised:

[Lukas]

Instead of just switching the sends why not just switch both the send and the returns. Something like this should work:

Code Select Expand

             ______
Send 1 -------+  +------Return 1
            |      |
In -----------+  +------Ouput
            |      |
Send 2 -------+  +------Return 2 
            |------|


Probably won't be silent when switching but it will do what you want it to.

Lukas

[xad001x0w]

thanks i will try this out when my next load of parts comes in and will report back on my hopeful success

EDIT:
Added picture



Is this the correct wiring then? I believe i used your diagram correctly

[scaesic]

why can't you just use?

send 1     __   __ return 1
signal in   __   __ signal out
send 2     __   __ return 2

[scaesic]

oh wait, thats what the guy before me said.

the amended diagram isn't that, just have all the grounds connected common, then wire up the "signal" lines like it says above.

[lethargytartare]

Yup.  But it will pop when you switch.  Something about the caps in the effects themselves, I think...

Anyway, I built one like that a while back too.  Here was my diagram:
http://www.lethargytartare.com/caves/gerbcave/diystory/diy-2.html (near bottom)
and here's what the wiring looked like:
http://www.lethargytartare.com/caves/gerbcave/diystory/index.html (near middle)
The switch was added so you could leave the second loop empty, and then the box acted like a simple true-bypass box.

Really simple, really fast to whip up, but not a great live solution because of the popping.  It's also a quick way to experiment with and nail down your understanding of some routine wiring and switching tasks that come up in every pedal project.  Of course, the ideal way to go is to get the aby project from GeoFX, or go easy and buy a commercial one (which can be pretty cheap these days) :-)

Best of luck!

ltt

thanks i will try this out when my next load of parts comes in and will report back on my hopeful success

EDIT:
Added picture



Is this the correct wiring then? I believe i used your diagram correctly

[scaesic]

whats a better non-popping alternative?

[slacker]

you might be able to stop the pops using pulldown resistors on the send and return sockets.

[xad001x0w]

I thought about using resistors to try and remove any popping, but what kind of value am i going to be looking at to do so?

[Peter Snowberg]

Anti-pop resistors are generally 1 to 2.2 megs.

Somebody asked about a similar thing a couple of days ago.

Check out The Tone God's Wicked Switches article.
http://www.geocities.com/thetonegod/switches/switches.html

Also check out the 4053 article on GEO:
http://www.geofex.com/Article_Folders/cd4053/cd4053.htm

[scaesic]

is it possible to just have two  2.2m connecting signal to ground on both returns?

will this compromise high end?

[lethargytartare]

What you should do is build it and then try stuff out like this:  instead of a resistor, put a 10M pot in there, and see what happens when you change the value -- compare the pop when you switch, listen for tonal changes, etc.  When you dial it to a place you like, measure the resistance.  ANd then when you see other opinions, build them in.  The box, as you initially designed it, is a really easy thing to tinker with -- you'll learn a lot, pretty quickly.

But if your goal is a show-ready looper, give serious consideration to the designs that are already out there (like hte one at geofx) -- those are the product of different iterations, commentary, and upgrades.  They're slick and refined, and you'll surely be happy with the result!

[Peter Snowberg]

is it possible to just have two  2.2m connecting signal to ground on both returns?

will this compromise high end?

Effects returns are generally quite low impedance so resistors there will just disappear in the scheme of things.

With a muted input, measure the output signal of your effects. If you see any DC voltage on the outputs, you will get a pop. The same goes for inputs, they should all reference to ground. If you has an effect with DC voltage on the input or output, adding a coupling capacitor internally will solve that problem.

[Skreddy]

I've made a bunch of Dual Loops, just switching both sends and returns like Lukas and scaesic drew.

Popping is really not as much of a problem as you might imagine.  In fact, I've had no complaints even from cork-sniffing users.  You are leaving the input of the unused loop floating, but this has not resulted in any audible poppage or problems I've encountered.  It is really that simple and does not need to be fixed any further. 

(Oh yeah; use Switchcraft 12A closed-tip jacks for the return line, with the switched contact wired to the send line)