A/B loop with input and ouput buffer POP sound

[DeusM]

Hello everybody.
- I  made an input and ouput buffer with the posibility to use it as an bypass switch or and A/B swtich with an input after A. It's basicly an A/B switch with a bypass switch at the first ouput and the return or second input. Here is hot it works.
NORMAL: INPUT 1---> OUPUT 1  ---> INPUT 2 --- > OUPUT 2 (TO AMP OR WHATEVER)
ACTIVATED : INPUT 1---> OUPUT 2
So it bypasses the firts ouput
Hope it is clear.
- The problem is that it makes a pop sound and its not practical. It has a pull down resistor in both buffer circuits and the LED is not the problem beacause I already tried using it without it and the pop doens't go away. 
- The pop is not noticeable when playing but the problem is that for example if you want to use it to go from distorted to clean and you have a delay, the pop is goig to be delayed.
Hope you can help me.

Here is the schematic:

[antonis]

Delete S1B switch ..
(or better, wire LED ccathode to GND via switch..)

As it is, C6 is discharged through R10 & LED when OFF and shorts instantly +9V when ON..)

[DeusM]

Delete S1B switch ..
(or better, wire LED ccathode to GND via switch..)

As it is, C6 is discharged through R10 & LED when OFF and shorts instantly +9V when ON..)

I already said the LED is not the problem. I tried disconecting all that part out of the circuit.

[antonis]

I already said the LED is not the problem.

I never put the blame on LED..

[DeusM]

I already said the LED is not the problem.

I never put the blame on LED..

What I meant is that I already removed all the S1B section. It's the first thing I did. See if the LED section was the problem. Though it was clear. I mean the firts thing to do if you hear a pop sound is check the LED section.

[antonis]

Unfortunately, you can only have Input 1 grounded when OFF but I think it should worth a try..

[PRR]

It all looks OK from here.

Which suggests some mystery factor. Big DC leaking from the sources? Pull-down not really connected? R9 current surge even when LED is removed? Spend time with a DC meter and see what "jumps" when switched.

[DeusM]

Unfortunately, you can only have Input 1 grounded when OFF but I think it should worth a try..

What do you mean it can only be grounded whn OFF? There is a shared GND there. It is always gounded. Could the problem be a ground loop?

[DeusM]

It all looks OK from here.

Which suggests some mystery factor. Big DC leaking from the sources? Pull-down not really connected? R9 current surge even when LED is removed? Spend time with a DC meter and see what "jumps" when switched.

I checked the pull downs and they where conected. Gonna try again tomorrow. I already tryed removing the LED section of the circuit (including R9 and all the otrer components in that section). I'm not sure how to check the last thing you told me. Do I have to conect the multimeter in DC witch one probe to negative and the other in the components to se if DC jumps?

[antonis]

I mean directly (not via 2M2 resistor..) grounded Input ..
(left C1 leg shorted to GND)

Although, C5 is more suspicious both for been more prone to leakage and for about 5 times higher R8C5 time constant compared to C1R1 one..

[BJM]

Big DC leaking from the sources?

Too difficult for me..... But for what it's worth, isn't this schematic too complex? Stereo jacks and the power section appears to be double??? Wouldn't it be easier (or maybe even better...?) to ground the unused outputs? As explained here (the mute switch): http://www.muzique.com/lab/splitter.htm
I build something like this, although not with JFET's but with an op-amp and it didn't pop (although I used it only at home at low volumes), also not with a  Led. My Led was wired simpler btw, it didn't have a capacitor (C6) in parallel. What's the use of that?

Gr,

Bert

Bert

[PRR]

> didn't have a capacitor (C6) in parallel. What's the use of that?

It smooths the LED circuit on/off transition so there is no pop. Ironic?

However he has tried with all that disconnected.

> not with JFET's but with an op-amp

The plan in post #0 _is_ opamps not JFETs.

[BJM]

> didn't have a capacitor (C6) in parallel. What's the use of that?

It smooths the LED circuit on/off transition so there is no pop. Ironic?

However he has tried with all that disconnected.

> not with JFET's but with an op-amp

The plan in post #0 _is_ opamps not JFETs.

Hi PRR,

Thanks for the explanation about the capacitor  .

Yes, I noticed the schematic is for an opamp, I built my splitter with a TL072 but I don't think that would make any difference for muting the output, with pops or not, as explained om the AMZ website. In this schematic the audio input is interrupted while the rest of the components are still connected to the outputs. Maybe I'm mistaken but I thought also in most true-bypass 3PDT switches the output or input of the effect goes to ground? I don't see that here so maybe there's  some imrovement possible?

[DeusM]

Ok. I give up. I ended up trying diferent things and nothing seems to work. I'm still to noob at electronics to figure it out. Guess I'll end up having an input and ouput buffer and make some A B switch. Thanks guys!