A/B switchbox question

[Axmanjr]

What are the part lists for this schematic?
http://www.fortunecity.com/tinpan/humperdinck/223/swbox.jpg

To me, it looks like there are 2 different resistors being used:
1. 1500 ohms (is it the same as a 1.5k resistor?)
2. 3 meg

However, I can't find a 3 meg resistor!  Can I substitute a bunch of different resistors side-by-side to add up to the value?

So basically all I need are jacks, LEDs (can those be any value too? and don't they need a resistor in front of them?), DPDT switches and a battery, right?

Sorry for throwing my questions around all over the place :lol: .  Hope you guys can answer them all!

[Mike Burgundy]

1500Ohm=1.5k, or 1k5 (in Europe the multiplier is often used as decimal point for legibility). k stands for kilo, which means *1000 (see the FAQ).
the 3M (Mega, *1000000) reisitor is only there to prevent pops and nasties like that. You can use a 1M, 2.2M, 3x 1M in series, whatever's your fancy - or you can even omit it. You will run the risk of pops, but have a look-see.
LEDs come in all shapes and sizes, but the run-of-the-mill reds will work with a 1.5k resistor - hey look at that! They DO have a resistor on them, it's just before the switch. The middle lug switches between both leds, lighting the appropriate one. The other side does the same with input A or B into output.
If your particular LED is an ultra-bright and/or you want to bring power consumption down, use a higher-value resistor than 1k5. Experiment. Different colours might require different resistors, in which case you can replace the resistor to the middle lug (1k5) with a wire, and insert a different resistor between each LED and the switch.

So basically all I need are jacks, LEDs (can those be any value too? and don't they need a resistor in front of them?), DPDT switches and a battery, right?

and a box, LED-sockets, and wire, battery-clip, paint, and patience
Welcome to the building community.
Let us know how it turns out, and what your next project is going to be

[Axmanjr]

Cool, thanks!

the 3M (Mega, *1000000) reisitor is only there to prevent pops and nasties like that. You can use a 1M, 2.2M, 3x 1M in series, whatever's your fancy - or you can even omit it. You will run the risk of pops, but have a look-see.

What do you mean by "pop"?  :?  If you omit the 3M, then it may pop? Or if you use multiple resistors (that add up to 3M), then it may pop?  I'm figuring that you're referring to the first one (omitting).

[Axmanjr]

I tried breadboarding it first but I doubt that the pedal is actually working the way it's supposed to.  Channel A will go to my amp...however there is a dramatic loss of signal :shock: ! So that's not cool.  When I switch it to channel B, it seems to work decently- since it's going to my tuner.  I noticed that none of the LEDs are working and the effect will still switch between channels even after I unplug the battery!  So my analysis is that the circuit is complete (so that the signal is bypassing through to the desired output), but the intended effect is not working.  I'm guessing that the battery is used for boosting the signal.

I kind of scared about this schematic- I found so many other A/B/Y schematics on the net, but they all required at least 1 transformer/transistor/whatever else, whereas this one is very brief and plain.  So any help would be appreciated.

[Samuel]

Is it possible you've miswired the jacks? Or perhaps put that 3M (or whatever resistor you used) in the wrong place?

This design will switch the signal with no battery. The switching is purely mechanical, you only need the battery to light the LEDs. Check your wiring, check your soldering. If you're absolutely 150% sure they're perfect, the only option left is a malfunctioning switch. But miswiring is much much much more likely than faulty equipment. In particular make sure you're totally clear on which lugs on the jacks connect to which part of the jack. (IE which one is tip, ring, and sleeve). This can sometimes be a bit confusing and is likely the source of the trouble.

[Axmanjr]

Thanks, I'll look into it again.

So what would I have to do in order to prevent signal loss (I'm guessing the battery has nothing to do with it )?  Is that where all of the other fancy components come into play?

[Samuel]

The signal loss over a stompswitch should be hardly noticeable. Particularly if you're fairly conservative with cable lengths going to and from the device. If you're chaining 8 pedals together or something, it's time to start thinking about buffering, which is where you involve opamps or transistors or whatever to keep the signal healthy as it moves through your various effects. For a simple tuner mute, a plain old switch should work just fine.

[Axmanjr]

Okay, so in order to buffer my signal, I would have to buffer any pedal/effect. Or is there a particular one that I buffer (ie the first or last one, the dist pedal, ...)?  Could I just buffer the A/B box and place that first in my chain of effects?

I do have about 5 to 6 pedals running in between my guitar and amp (if that helps).

[Samuel]

It wouldn't be a bad thing to have a buffer built in to the switcher, but it's also probably not needed. If you want to hear the case for buffers check out Pete Cornish's article http://www.petecornish.co.uk/case_against_true_bypass.html.