Amp channel switch, bypass loop, combined - first try

[ralff]

I whipped this up in paint during some downtime at work (the website is blocked for some reason, so I just went with what I had).  I've been looking for something like this for a long time, but haven't been able to find it.  So I figured why not try to build it myself.  I'd love to get some feedback, even if it's some laughs at my expense.  Apologies for the format, but it should be simple enough to understand.

What I've attempted to create is a box with 3 switches. 
Switch 1:  toggles the amp channel (clean/dirty) and loop simultaneously (if one is off and one is on, they will just swap)
Switch 2:  toggles the amp channel only
Switch 3:  toggles the loop only

I may try to work in LEDs at some point, but at this stage I'll be happy with some semblance of a working device.

Is there any hope for me?

[ralff]

I've been experimenting a bit, and think I may have figured out how to implement LEDs with this build.  My channel footswitch confused me a bit, so maybe someone can explain it better to me.

I'm using a Blackstar HT-5(R) with a FS-1 footswitch.  Fairly simple footswitch.  In my drawing I have it basically the same as the original footswitch, except I'm using SPDT switches to be able to toggle it from 2 separate switches.  The original uses a SPDT switch as well, but nothing is hooked up to the other terminal, so I assume it acts as a SPST? 

With the original footswitch that came with the amp, when the circuit is open, the amp is overdriven and the LED is on.  When the circuit is closed, the amp is clean and the LED is off.  Here is what confused me.  The LED is connected to the 2 leads that the wires are connected to.  What I'm thinking is this, and I could very well be completely wrong:  when the circuit is closed (clean), power takes the path of least resistance and bypasses the LED and goes directly back to the amp.  When the circuit is open (dirty, overdrive is on), the only path is through the LED.  However, I was not aware that LEDs have resistance and there are no (visible) resistors anywhere inside the original footswitch.  I'm not sure how the circuit stays open for the overdrive if there is voltage flowing through the LED. 

I have attached a drawing (again, apologies for mspaint, but should be easy to understand) of the FS-1.  Maybe someone has a better explanation than I do.  Keep in mind I'm ONLY drawing what is inside the footswitch.  I have no idea what's going on inside the amp.  Let me know if these pics are not viewable - I'm pretty new to hosting photos.



And here is my new drawing with the LEDs added.  To add an LED for the loop, I just mirrored the circuit that enables the loop.  I *think* this should work, but I have done no physical testing as of yet and implementation is a whole different ballgame.  Criticism is greatly appreciated. 

[PRR]

> I was not aware that LEDs have resistance

They do; but more significantly, they drop 1.6 Volts.

Say the amplifier feeds 12V through a 1K resistor.

If the switch is *closed*, its resistance is near-zero. The voltage across the switch is near-zero. As you say, the LED must be off. Counting a few ohms in the wire, the amplifier may sense about 0.01V across the cable.

If the switch is *open*, the LED drops about 1.6V, the amplifier senses 1.6V.

A simple BJT in the amplifier will be dead-off at 0.5V and full-on at 0.8V. A TTL logic gate in the amplifier will be dead-off at 1.0V and full-on at 1.4V. An opamp biased to 1.2V will flop at 1.2V. Any of these will easily sense the difference 0.01V or 1.6V.

[ralff]

Sorry to bump an old post, but I've come across a problem that hopefully someone can help me with.

I finally got off my butt, got parts, and put this thing together.  It functions as I intended with one rather large exception:  bypass mode does not work.  When I activate the loop, everything works fine.  When I click the loop off for bypass, I get a very faint signal (as in barely audible).  The only thing my novice brain can come up with is that some of the signal could be flowing backwards up the loop somehow instead of entirely to the guitar, but I don't even know if that's possible.  Connections seem fine when I pin them out with a multimeter.

This bypass circuit I've attempted has 2 switches instead of one like most, so I haven't had much luck finding other drawings or examples that may help.  I've attached a drawing of the "problem area" of my build.  I will work on a more conventional drawing but for now, this is what I've got.  It shouldn't be too hard to understand, although the logic of the circuit could very well be flawed.

[ralff]

I've done some looking around at other bypass schematics, and some of them have the tip of the loop shorted to the return signal when it's not in use.  Could this be my problem?