#1
Hello all!
I recently constructed a loop switcher (aka line selector) pedal. It's a passive circuit for switching between [guitar > amp] for clean sounds, and [guitar > effects processor > amp] for effects etc. This is my first DIY build, and I designed the device myself, since I couldn't find any schematics on the web. I'm really quite new to electronics.

Here's what it looks like. The housing is temporary.





Now the guts. Here you see the true crappiness of my workmanship



It works fine, except for one problem, there's some amount of noise being added by the switcher. It's not so much that it makes the thing unusable, but it is noticable, and it's pissing me off! If I lift the device off the floor, the noise decreases noticably
I'm guessing when I add a dirt pedal and a wah to the signal path, the overall noise might increase, so I really want to minimize the noise caused by the switcher.

Can anyone give me some ideas about what might be causing the noise, and what I could do to get rid of it?
Any help would really be appreciated!

PS:
Here's a rough paint image of the design.

Shaafi Shaikh
#2
my first thought was, what the heck is going on in that drawing?

second thought was, why they heck did you use a 4pdt switch when a dpdt switch would suffice?

i would assume the problems you are having are arising from the fact that you have a lot of extra wiring, and youve got some really funky wiring going on. 2 wires taped together? thats just screaming for noise. also, metal enclosures provide some nice shielding so you dont get noise from EMI.

i suggest you start over with a DPDT switch (or half your switch) and see if that clears up a lot of your stuff. my guess is it will help, and good wiring practices will help some more.
#3
Lol. Yeah I thought the diagram wouldn't make much sense to anyone but me.

I dont see how I could achieve the same function with a DPDT switch. Can you please explain?

Okay thanks! I'll fix it into a metal enclosure, and see if that helps.
Shaafi Shaikh
#4
Probably just faulty wiring and/or poorly made connections. Use as little wire as possible. I can't see your diagram but essentially you just need a DPDT and 3 jacks.
"Experience is not what happens to you. It is what you do with what happens to you." - Aldous Huxley
#5
I think the biggest problem is that your box isn't conductive and therefore doesn't shield the wires. I think I can see why you were doing what you were doing with the 4pdt switch. Am I correct that you used it to compleatly ground out the loop when the loop wasn't in use? Doe it do anything else that I'm not seeing? Grounding out the loop when not in use and that is a good idea, however you could do it with a 3pdt too. Unless I'm mistaken this should work.
Attachments:
loop.JPG
Last edited by CorduroyEW at Jun 9, 2010,
#6
Thank you all for your replies! I'm very grateful for the help!

Okay CorduroyEW, you obviously understand how these devices work alot better than I do! My design came about from putting two A/B switches together, like so.



I'm not quite sure how the ground loops work, but your design seems to make sense. Can you please explain how the ground part of the circuit would work?


Okay I transferred the guts from the particle board casing to a metal enclosure.
Here's what it looks like now.





Now when I plugged it into my rig and tried it out, it didn't work. I couldn't hear the guitar signal at all, just static.
I then insulated the Input jack from the metal casing, and it starts working again





I think the noise has been reduced a bit, but it is still there, and audible.
What now? I think replacing the sloppy wiring might be my next step.
Shaafi Shaikh
#7
Quote by saqi


Okay CorduroyEW, you obviously understand how these devices work alot better than I do!


I wouldn't say that. I've build an A/B switch before but never a loop switch so my layout was simply a guess.

My design came about from putting two A/B switches together, like so.



I'm not quite sure how the ground loops work, but your design seems to make sense. Can you please explain how the ground part of the circuit would work?


That is pretty much the concept of the AB switch that I've built in the past. When the hot from 1 out is connected to the input hot the hot from the unused jack is grounded. With my loop design I've simply set it up so that the hot from both the send and return go to ground when the loop is "off". The switch I laid out doesn't really take ground loops into account because to do that I would actually need to isolate the grounds and to do that you need a much more sophisticated circuit.


Okay I transferred the guts from the particle board casing to a metal enclosure.
Here's what it looks like now.




Now when I plugged it into my rig and tried it out, it didn't work. I couldn't hear the guitar signal at all, just static.
I then insulated the Input jack from the metal casing, and it starts working again



It looks you are using the switching jacks. Is it possible soldered your ground (or hot) wires to the switch by accedent?
Last edited by CorduroyEW at Jun 9, 2010,
#9
im lazy so i didnt draw the actual jacks. but this is a simple sketch of how to do it with a DPDT switch.


the pedals in the loop are completly removed from your signal chain when you arent using them, so i dont see any point in grounding the input/output. instead you could use the extra poles for LED indicators or something.
#10
this should help a lot


Thank you! I've been to this site! I wish I had seen this page before!

It looks you are using the switching jacks. Is it possible soldered your ground (or hot) wires to the switch by accedent?


I just checked, and traced the conductors in the jack. The hot wire is on the tip and the other wire is on the ring. That seems alright to me
Also, what are switching jacks? When I was buying these I just asked for mono input jacks and this is what I got. I'm sorry I'm quite clueless


I'm really quite confused now!
I have three different circuit diagrams, and they all seem to be more efficient than the one I made. Which one do I build?
Shaafi Shaikh
#11
Quote by saqi


I just checked, and traced the conductors in the jack. The hot wire is on the tip and the other wire is on the ring. That seems alright to me
Also, what are switching jacks? When I was buying these I just asked for mono input jacks and this is what I got. I'm sorry I'm quite clueless :


The switching jack is still a mono jack but it's got 3 lugs you can solder to instead of just 2. The extra lug is connected to a bit of metal that makes contact with the "hot" lug when nothing is plugged in but contact is broken as soon as you plug a jack in. This type of jack will work in any situation that a normal mono jack will work so no worries there, you just have to be sure you soldered it all together correctly.

On switchcraft, mojo, Fender, and Allparts brand switching jacks, if you look at the back of the jack with the 3 soldering lugs on top then this is the order of the lugs
Left=ground
Middle=switch
right=hot

If your jacks are not one of these brands then just look at them closely. Usually the ground lug is on top (when looking from the back of the jack) and you can see that there is a metal ribbon that connects the grounding lug to the sleeve of the jack. Typically the switch is in the middle layer between the hot and ground layers. The hot lug is typically the deepest layer and often times if you look closely you can see where it physically connects to the tip of the jack.

1 jack with either hot or ground wired to the wrong lug can cause the problems you are having.
#12
Success! To some extent.

I built the circuit from Beavis Audio. The link that was referred to earlier.
I used new jacks without the switching mechanism (thanks for the tutorial CorduroyEW) and shielded wire. It looks like this now.



The noise is almost gone. Not completely, but its much more usable now.
Theres still some amount of hiss when I run something with higher gain levels through it, but perhaps that will go away when I get an enclosure that is closed on all sides.
Thanks guys!
Shaafi Shaikh
#13
Im thinking ahead to how to finish the enclosure, once its done. Does paint effect grounding or shielding in any way?
Any ideas on a colour scheme?
Shaafi Shaikh