Passive Line selector/ looper

[Toney]

....with grounded inputs for the non active side.

You know, after all this time i hadn't got around to making one of these.

I had a search, there's plenty on this, but I couldn't quite see what I wanted... maybe it's there...probably somewhere.
Anyhow, I always figuired "oh yeah, piece of cake" till I actually gave it some attention.

So, what I wanted is a loop selector that switches between two effects  (or chains of effects) that can also double as a true bypass box, using just one 3pdt.
To do this...simple ...use N/C MONO jacks for the input and output jacks of loop 1. Just wire those third 'N/C' lugs together.

When there's nothing inserted to loop1, the box becomes a single loop true bypass box, via loop2.

[Toney]

Obviously, just use a second 3pdt if you want a box selecting between two chains and bypass.

My only concern.... is it/is it not an issue not isolating the 9v- for the led switching from the common ground?
Search results for this were unclear.

Experiences?

[Toney]

   Ok a bit of further reading and thought...

I think the best way to switch a single loop is as follows. By keeping the common ground and 9v negative to the LED separate, the old popping problem should not be an issue. This will require a SPDT on/off switch for the LEDs when using a battery- no big deal to flip it on when you're setting up, or just direct power via the 9v jack.  Loop input is grounded on bypass.



To make multiple loops, obviously cascade as many outputs to inputs as you need.

[Gilles C]

I don't know if it can help, but this is the schematic on the AB/Loop box I've been using for 5 years.



I want to draw an updated schematic of it this year, but it will be the same schematic, with only a few changes for the LEDs because I never had any problem with this design. It would be mostly to make an easier to understand schematic or layout.

Bty, I use an isolated path for the LEDs in my box, with no connection to the box. But you have to use another kind of jack to switch the power on for the LEDs. Like in the following picture.



Gilles.

[Toney]

 Just noticed that in the 'True bypass looper' diagram, utilizing only input and the LOOP1 and LOOP2 inputs as A and B, the whole thing doubles as a simple A/B box with grounded inputs too.
Pretty neat.

Might be needing my first 4pdt to do the switching and keep the 9v and led negatives separate though.

Can anybody speak about the idea of isolating the 9volt for the LED switching?
Necessary? Opinions?

[Toney]

Gilles, if you have a jack that can switch the 9v negative without going through the common ground, that would be interesting...
Do you have an picture?

[Gilles C]

In fact, I like to use then everytime it is possible because I like the feeling of these jacks. They are smoother.  And I can't say for sure it it makes a difference, but I feel it does. The LED circuit is separated from the audio when connected that way.

Look for 1/4" enclosed phone jacks with isolated switch contacts. I can get them locally, so I can't suggest a place to buy them.

I always buy the stereo ones because that way, I have the choice of using them anyway I like.

Sorry, I don't have ano more photos for now. My site seems unavailable from time to time... like right now 


Gilles

[Toney]

Gilles,

Whats the small resistor on the input grounding of input ttwo up to there?
I've seen a few use this...what's the advantage?

[choklitlove]

maybe a millenium bypass would work.  maybe two, one for each loop.  that would free a pole of the 3pdt.  maybe it would help.

maybe not.  subjects like this just end up confusing me.

[Toney]

 Yeah, I think that would cover it. Just I'm too lazy to make them most of the time.

How big an issue is having the battery negative in with the common ground?

Anyone? I searched but kinda got unclear results...it seems some get by without it, though it may not be best practise.

To keep it out, in the dual loop diagram, I figure it's got to be milleniums or a 4pdt...unless someone has another idea?


Like so....

[Skreddy]

No grounding on non-selected loop, but works quite well...

[Toney]

Well, I'm just going to go ahead and make up a two loop box from that first diagram "true bypass looper".
I will use two milleniums and a 3pdt, this should be the best way to have grounded inputs AND the leds withouts the pops.

I understand that direct wiring the leds to the signal ground cab cause issues due to the inrush of current as the led fires up.

It occurs though....how does the millenium circuit avoid this??? I mean, the led is still ramping up with the same ground, just via a mosfet?

What difference is there? It should be the same I would think, and yet it doesn't pop. Why?

[Gilles C]

Gilles,

Whats the small resistor on the input grounding of input ttwo up to there?
I've seen a few use this...what's the advantage?

The 51 ohms resistor could be replaced by a jumper to short the unused input to ground, but using a resistor like this is supposed to eliminate any ground loop that could be produced by using only a jumper to ground.

That's what a company was using in their A/B boxes many years ago (can't remember the name...)

Gilles

[Toney]

Hmm, sounds plausible.
I guess in that case the cross jumper wires in my diagram can just as well be resistors.
Thanks.

[brett]

Hi.
I'm not sure if this is relevant, but might a "ground lift" switch help if ground loops are a problem.  Ground lifting in direct injection boxes switches the output (or is that input ?) between DC to ground and AC to ground (via a cap of about 100uF).
cheers