Any idea where I went wrong on a bypassable buffered bypass?

[swyse]

I recently tried to make a breakout board with optional buffered bypass. The buffered bypass worked great, but the true bypass didn't. Below is the buffer section of my schematic. Here is the datasheet for my switch. Additionally, not using the switch and bridging pins 5 and 6 on the switch still caused my bypass to not work until I removed C24 from my board.

 

[benny_profane]

I’m surprise that switching sent the signal to the circuit if I’m reading it correctly. It looks like it’s sending the circuit input to ground.

Try this:

1. Input Jack (Connect to 6)	4. Circuit output
2. Circuit input	5. Output jack
3. Ground	6. Connect to 1

 

[swyse]

It was meant to send the buffer input to ground and bypass the input completely in the down position and in the up position it would send it to the circuit input and disconnect the straight line from input to output.
Looking at your switch vs mine I see yours effectively disconnects the output from the output jack which makes a lot of sense, I can't remember why I designed it how I did in all honesty, I remember I had a really bad fever that day but in my head it was correct as I thought you could just have an op amp connect to the output through a capacitor and it wouldn't affect anything as long as the input was grounded to avoid noise, but I suppose I may have grounded out my signal doing this?
Edit: Actually I'm still confused why just bridging 5 and 6 (input jack to output jack) and leaving the input to the buffer floating with nothing grounded would kill my signal.

 

[Feral Feline]

Silly idea, I have.


What if you use a 3PDT and use the 3rd pole to disconnect/connect the output cap in concert with the rest of the circuit. Could it be the signal was grounding out by "swimming upstream"? [I just re-read the OP and indeed C24 is the output cap, so maybe my idea isn't so silly after all...?]



Check out Aion's Cygnus PDF, It shows an optional buffered-bypass switching system using a 4PDT.




ARGHH Everybody has to have their own way of labelling things... and here Aion uses two ways:

Footswitch "FS" 3PDT (pole B, used for LED, not shown above)
A B C — poles
1 1 1
2 2 2
3 3 3

Buffered Bypass 4PDT "SW"
A B C D
1 4 7 10
2 5 8 11
3 6 9 12


Why not FS
A B C
1 4 7
2 5 8
3 6 9
?


I gotta work tomorrow today, gotta get some sleep. Maybe this'll all make more sense after work.

 

[Robert]

Yep, your buffer is connected to the output all the time.

When the switch is in bypass the buffer is still "buffering", but it's input is connected to ground so it's doing it's job, enforcing the output to silence.

Try one of these methods:

 

[swyse]

Appreciate the education guys. I'll revise my schematic. I think the reason I thought this would work was because of a parallel effect I saw where the volumes were independent, but I think that is a bit of a different animal.