Thrown for a "loop"...

[lotsolowend]

i couldn't resist the cheesy joke... down to business!

I'm building a custom looper pedal for a keyboard player friend of mine and I have one problem that I can't think of a way to overcome : /

Here is a quick sketch of what I've done so far:



The idea of this pedal is to have 2 keyboards running (respectively) to 2 DI boxes and these send/return to one pedalboard.  Stomping switch 1 should send in1 -> send -> return -> out1 and deactivating it should just be TB in1 -> out1.  The problem is coming from having 1 send/return and soldering both switches to it.  I'm new to this so I thought diodes could just work like a one way street but someone with a little more intelligence than I said that would cause tone loss because of too much resistance if it even worked (keyboards output tons more voltage than guitars he claims?).  Any ideas? I have an idea of how I could do it with 1-2 more toggle switches but I'd like to keep it simple.  It's okay if the keyboards cannot go to the send/return simultaneously. 1 on the other off, or both off, is enough.

Good luck!
-Jonathan

[petemoore]

  I can suggest a different approach because I can't quite follow the flow, reading other looper pedal schematics, understanding how to recognize the various 'flow patterns' of the signal, this may make it easier to discuss, choose, inquire, and write about the switching circuits, because they are cleanly drawn and the components are labeled.
   

[lotsolowend]

Hah, understandable.

I drew that at work and the best i could think to do was color code it.
Blue - Input
Brown - Ground
Black - Send
Red - Return
Orange - 9v+
Purple - Output

I'll try to get a better drawing.  I could take a picture of the assembled pedal also if you'd like

[lotsolowend]

Okay, my first time to draw a schematic, hopefully this makes reading it a little easier but i'm sure with more experience i'll find a more efficient way to draw it.



i know it is still cluttered but between the 2 sketches maybe someone can get an idea of what is going on.

<- accepting constructive criticism on schematic drawing

[lotsolowend]

bump while i drive down to the electronics store to see if they have some input

[sean k]

Looks fine except when you bypass the send on 1 and go straight to out then if 2 is on send and return it won't work because the send is tied to 1's switch and is grounded so just disconnect the ground switching on the sends... oh, and reverse the diodes as they are round the wrong way.

[lotsolowend]

okay, i'll give that a try when i get off work.
should i disconnect the ground from the send and return or just send?

and those are supposed to be LEDs so they can run either way (i think...)

[petemoore]

  Not sure what it's really intended to use as...
  But both inputs can tie to the send, that means it's an unbuffered mixer, whether both sources are in phase or impedance problems arise are questions for 'raw mixing' though.

[lotsolowend]

so do you agree that disconnecting the send/return grounds will make it work?

what kind of problems could come up with the whole "raw mixing" thing?

[petemoore]

what kind of problems could come up with the whole "raw mixing" thing?
  One tends to come through better than the other, neither comes through as good as when actively mixed? Try two guitars into a Y cable > amp, keyboard outputs are probably much lower impedance than guitar outputs though, try two keyboards, Y'd into an amp, loading problems?
  Calculate the Impedances, make it so it doesn't matter [active mixing ?], or decide how much it matters.
 
   

[lotsolowend]

snipped the grounds and it still didnt work, outputs were being crossed etc so i'm going to start from scratch and go back to the drawing board.

I found this, it is pretty much exactly what i need but rather than one 4p3t rotary, 2 3pdt toggles

http://www.bluesmothers.de/download/Share-A-Loop.pdf

any ideas?

[sean k]

I don't get the switch on the link, maybe because I'm thinking of a normal rotary switch, and I find those things somewhat problematic at the best of times.

I think that you have to tell us what you want to acheive.

If you were playing one keyboard at a time through the fx loop it shouldn't be to hard to acheive but as the other guys say you are mixing impedances and even grounds between keyboards, fx and amps if you want to use both sets of keys at the same time on the fx loop... and that could be quite problematic and need solving with buffers and mixing ladders and possibly signal transformers to isolate grounds.

I do what your trying to acheive because someone gave me a behinger mixer with a bum slider and I can twist knobs to thrown in or out two fx loops between several different instruments that may or may not be playing at the same time.

What I want to do though is switch one fx chain between send and returns and the output and my amp which in effect means I'm switching the fx loops from parallel to series.

so what I'm saying is that if we know exactly what you want to acheive then we can help with what you would actually need to do it.

[lotsolowend]

starting to think im trying to force this to work, looking like i might just have to let it die...

last call for ideas?

[sean k]

Nah Man, keep it going, it'll work.

[lotsolowend]

wow, last night i posted my reply without even seeing yours, stupid of me!

heres what i want to achieve preferably using only 2 3pdt switches and 6 jacks:

input 1 is always bound to output 1 and only output 1
input 2 is always bound to output 2 and only output 2
signal from input 1/2 always comes out of output 1/2 (inputs are always active, no muting)
switch 1 controls input 1 switch 2 controls input 2
if switch 1 is activated, the signal chain changes from
input 1 > output 1
input 2 > output 2
to
input 1 > send > (pedalboard) > return > output 1
input 2 > output 2
and LED 1 is lit (easy)
if switch 2 is activated, the signal chain changes from
input 1 > output 1
input 2 > output 2
to
input 1 > output 1
input 2 > send > (pedalboard) > return > output 2
and LED 2 is lit
it doesn't matter if they mess up if both switches are activated at the same time - he won't be using his pedalboard with both keyboards simultaneously (it would be nice if he could, but unnecessary)

so we need 2 keyboards to share 1 loop, but never at the same time if that's too difficult

let me know if you need any more info, i'm new to this if that hasn't been clarified yet.

thanks for all the help,
-Jon

[sean k]

Well there you go, thats answered the question. The keys don't share the fx loop.



What I've done is kept the earths together for 1 in/out and 2 in/out and switched them into the shared earth of s/r and then when the in/out isn't in that loop the earths are connecting the led... which should have a dropping resistor on it to +9.

Isolating jacks are required. That should work for you.

Also I'd build it in a box and only tie one channels earths to the box and put the switches close together and have then actuated with a plate that works both at the same time so while ones off the others on.

[lotsolowend]

okay i like this, but you lost me on the last little bit w/ the actuate plate stuff

also - where are the LEDs and where is the 9v ground to complete circuit for LED

[sean k]

Well my friend, the plate is about being able to have the switches work together so is essetially like a boss type plate on a hinge that when pressed acts on the switch so a regular door hinge pot riveted to the enclosure with a plate big enough to cover both switches would do the trick. Its merely to tie the switches together when pressed so as 1 goes to loop then 2 automatically goes direct... and vice versa.

LED's are at the bottom and just drawn as diodes, oops a bit of electronic shorthand there, and they switch on when the direct lines earths. Its all there except the dropping resistors for the LED's so just add some squiggly lines between the diode symbol and the +9 and write a figure between 330 and 1k ohms depending on how bright you want the LED's.

I wouldn't even bother with Leds 'cause the things going to be on the floor and have enough wires around it without having a power cable thrown in and the man'll be concentrating on playing with fx and will only see a changing LED as a distraction "cause he'll know which Keys are looped already. It'll be obvious.

[lotsolowend]

okay, thanks for all the help - i'll have to research the plate thing a bit when i get back and see what i can do

it would still work w/o the plate but he would have to be certain to turn one off as he turns the other one correct?

keep posted, if i have any more trouble i'll come looking for you - thanks a ton!

[sean k]

Well if the switches are close enough together then it'd be simple to hit them both at the same time but a plate would ensure that it happens. I don't know what would happen if both were in the loop at the same time but I would certainly try it to see what happened 

Good Luck!

Think about the lengths of the earth strands on the sheilded cable so you can make all the connections as well as which ones need to be connected where. Looks rather complicated in the drawing so you can imagine that the real world implimentation will be rather more difficult but it isn't insurmountable.

For instance, the in/out direct earths can be connected at the jacks and only one earth strand need go to the switch. Therefore the out hot is nearest to the point the earth goes to so the out earth connects to the switch.