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Old 12-21-2013, 08:24 PM   #1
Shelbien
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A/B/Y box help

I have this schematic of an A/B box
show

Can I use a DPDT with three positions (or another kind of switch) to go from A/B on either side and A+B in the center?
All A/B/Y switches that I've seen have a separate switch for A+B and A/B so I don't know if this would be possible.
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Old 12-22-2013, 10:55 AM   #2
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You could use a DPDT center-on (or SPDT center-on) switch but you won't ba able to ground the unused output, so you could have noise issues in the unused line.

If you could find a 3PDT center-on switch I think this could be done, or you could use a rotary switch (rotary switches with only 2 throws aren't too common last I checked).

But If you only want to use a stomp switch, you have to have two switches.
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Old 12-23-2013, 02:57 AM   #3
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I was originally thinking of something like this, but I can't find any 3PDT switches. http://www.mammothelectronics.com/4...p/810-1004.htm?

Would a 2 position dip switch work for this idea?
http://www.mammothelectronics.com/4...p/840-ds-02.htm
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Old 12-23-2013, 11:47 AM   #4
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A DIP switch is just a row of SPST switches. They are most useful in digital circuits as "option switches" to select various options/configurations of a device. Since digital inputs only require the presence or absence of a voltage, SPST switches are ideal.

To answer the question, yes you could use DIP switches--in theory. You would need 6 of them and they would have to be wired a certain way, and you would have to switch them in a certain way. Not at all practical. Aside from that, they mount directly to the PCB, they do not panel-mount. Switching them from outside the box would be a pain.

I don't know if they even still make 3PDT center-on switches. You'll probably have to use a rotary switch.
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Old 12-23-2013, 05:07 PM   #5
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The rotary switch looks like a good idea. Is there a spot for ground wires on the rotary switch, or can you ground it on the pedal enclosure?

Also, would this the correct way to wire it up ?
show

Thanks for all the help. I'm only beginning to scratch the surface in electronics and circuitry.
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Old 12-23-2013, 05:21 PM   #6
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The switch body will be grounded if it is on a metal box, but grounding the bodies of pots and switches and stuff is not necessary. That's just a guitar wiring-related thing.

Your diagram is not correct. The way it is shown, the three jacks are always connected. The switch has no effect.

Do you want to try to figure this out yourself or do you want me to draw a diagram for you?
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Old 12-23-2013, 06:13 PM   #7
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You could use a 3 position pickup selector switch, the style used for Gibson Les Pauls to route a 2 pickup system, each pickup or both to the output?

In this case you're just routing each output jack, or both, from the input jack. Use jacks that self ground when they are unused.

EDIT. Pic attached.
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Old 12-23-2013, 06:23 PM   #8
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An LP-style switch is a SPDT center-on type, which will work but won't ground the unused line.

How would the jacks "self-ground" if there is still a plug inserted in them?
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Old 12-23-2013, 06:36 PM   #9
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They won't self ground with a plug in them, only without a plug in them.

Wouldn't good quality shielded cabling throughout and a full metal box help eliminate hum, as a minimum shouldn't add anymore than what is already in the system without the A/B/Y?
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Old 12-23-2013, 06:43 PM   #10
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This is the switch I'm looking to use. It has one pole and is selectable from 2 to 12 positions. Since I'm going to be using three positions, I disregarded the others. http://www.mammothelectronics.com/A...820-1p2-12t.htm

I couldn't find any diagrams with a single pole, only ones with two, three or four poles. I assumed the wiring would be similar enough and ended up with what I drew previously.
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Old 12-23-2013, 06:47 PM   #11
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I guess that works in theory but I don't trust floating inputs. I've never built an A/B/Y so I don't have intimate experience of what can or can't be gotten away with.
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Old 12-23-2013, 07:22 PM   #12
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Quote:
Originally Posted by Invader Jim
I guess that works in theory but I don't trust floating inputs.


Tie a high value resistor from the input to ground. No longer floating
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Old 12-23-2013, 07:25 PM   #13
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I've been awake too long...
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Old 12-23-2013, 07:34 PM   #14
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hehe
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Old 12-23-2013, 09:08 PM   #15
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Can you help me with the diagram? Because the center is the common terminal, I thought it would be reasonable to have the input connected to it and, depending on which position the rotary switch is in, direct the signal from the input to A, A+B, or B.
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Old 12-24-2013, 03:47 AM   #16
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Quote:
Originally Posted by Shelbien
Can you help me with the diagram? Because the center is the common terminal, I thought it would be reasonable to have the input connected to it and, depending on which position the rotary switch is in, direct the signal from the input to A, A+B, or B.


Jim is right. The rotary switch diagram won't work. All outputs are connected together no matter which switch position you're in.

Have a look at the suggestion of the 3 position pickup selector switch, further back up the thread.
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Old 12-25-2013, 06:49 PM   #17
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I think I figured out the problem with my earlier diagram. I changed it from a single pole to a double pole.
show

I also tried using the three position pickup selector switch you suggested.
show

By "tie a high value resistor from the input to ground", did you mean a resistor on each of the jacks or only the input? There is most likely going to be a plug inserted into each jack at all times so this is just for my information.
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Old 12-25-2013, 07:27 PM   #18
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Your bottom diagram is right but the top one is still very wrong.

In this case you'd tie a high-value resistor across the outputs. You'll probably want a pretty high value because in y mode, the resistors will be in parallel, cutting the total value in half. Also, they will be parallel to the input resistors of the gear plugged into the box.

Long story short, 3.3M or higher would probably be good.
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Old 12-26-2013, 03:26 PM   #19
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This rotary switch diagram is a lot harder than I originally thought! Does the problem lie within the type of rotary switch e.g., number of poles, decks, and positions, or does it have to do with the way I connected the wires?

In any case, I'll mostly likely go with the three position pickup selector switch when I get around to ordering the parts.
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