Popping from EQ in/out switch

[Potato Cakes]

Hello,

I have several of the Audiox's 169 preamp/EQ modules I built a while back where I added all the options I could in a single 500 series module. All of the features work as intended, but there is a bit of a thump/pop when switching the EQ in and out (EQ bypass is not built into the original circuit). I know there's a simple way of solving this with either a resistor or capacitor either between switch poles or between a pole and ground I just don't know exactly. These modules are working and I'm wanting to avoid what sometimes does in my DIY world where I cause more problems and headaches while trying to find what should be the simplest solution. If someone who knows could give me a hint I think that would allow me to avoid potential unnecessary frustration.

Thanks!

Paul

 

[john12ax7]

How are you switching,  a true bypass relay or something else? It's important to make sure there is no DC on the line.

 

[Potato Cakes]

I'm using a toggle switch to jump around the EQ circuit as the preamp section still has to be in play. I think I might be getting DC from somewhere, but didn't know where the best place to do the blocking would be. I'll look around for the overlay and the points I used for signal to the switch to see if that clarifies what I'm doing.

Thanks!

Paul

 

[Bo Deadly]

There is no one single common cause for a switch causing popping. Post a schematic of the switch and the components connected to it.

 

[Potato Cakes]

Here is the schematic.

 

[Potato Cakes]

And here are the board edits.

Upon looking at this, I'm not sure why I removed C15 and put it at the end. I probably should have just left it in there and added another coupling cap. I was some time ago and I've worked on a bunch of stuff since then so I can't quite recall my thought process during this project.

Thanks!

Paul

 

[JohnRoberts]

Here is the schematic.

How about showing where your in/out switch is connected?

JR

 

[Potato Cakes]

Since I have raised the question, I believe I have found the error of my ways. I've learned a couple more things since I built these, and looking at the schematic now I have no idea how I ended up with what I did to insert an EQ bypass let alone how it even worked.

I pulled C15 and put in a jumper and then picked off from the + connection of C15 and went to the switch pole. From there the two toggle positions  went to the output of U2 and the other went to a negative connection of what was C15 and the positive side of that connected to the junction of R34 and R32. I don't know why but looking at this now I can see this is very wrong.

I'll do a drawing of the schematic of what I think I should do and post that for review.

Thanks!

Paul

 

[Potato Cakes]

Here is photo of the (erroneous) work done to the board.

 

[Whoops]

This is whats done in true bypass guitar pedals,
adding 1Mega resistors to gound, maybe you could try that out:

check the full article here:

http://www.muzique.com/lab/pop.htm

 

[Potato Cakes]

This is whats done in true bypass guitar pedals,
adding 1Mega resistors to gound, maybe you could try that out:

check the full article here:

http://www.muzique.com/lab/pop.htm

That was going to be my next thing to try after I make corrections to my initial work.

Thanks!

Paul

 

[abbey road d enfer]

This is whats done in true bypass guitar pedals,
adding 1Mega resistors to gound, maybe you could try that out:

check the full article here:

http://www.muzique.com/lab/pop.htm

This is unapplicable here.

 

[abbey road d enfer]

.I pulled C15

That's your first mistake. You should have left it there.

and put in a jumper and then picked off from the + connection of C15 and went to the switch pole.

You should take the PRE-EQ signal from junction of C14 and C15. BUT...

  I don't know why but looking at this now I can see this is very wrong.

Indeed. I would recommend you put it in its original state because the second EQ stage is also one -half of the output stage. You would need an extensive mod of the topology to achieve your goal.




[/quote]

 

[Potato Cakes]

Yes, all very wrong indeed.

As I mentioned as stared at the schematic again and it became clear what the majority of my mistakes were. I'm going to try to get at these this weekend and correct my mistakes and see if that solves the switching noise.

Thanks!

Paul

 

[Potato Cakes]

I've gone back and reinstalled C15 from the schematic and made the switch connections as attached. The popping seems to have been solved, however I now have a noticeable gain difference between EQ in and out as well having a high frequency roll off starting around 1k no matter if the EQ section is in or out. With the other builds that still have the incorrectly wired bypass mod, I get a roll off starting around 16k. The EQ still seems to function as it should, but for some reason their is a fixed HF attenuation around 1k. I'm afraid I may have opened a whole can of worms. I'm going to make corrections to one of the other modules and see if I get the same results.

Thanks!

Paul

 

[Potato Cakes]

I think I found it. Standby...

I thought I found it. It was not it. Time to start poking around till I find it.

 

[abbey road d enfer]

I've gone back and reinstalled C15 from the schematic and made the switch connections as attached.

It's just not the way bypass is done. Your bypass position actually loads the preamp's output with the EQ's output. You would need to disconnect the 100uF that's close to C24 to fix that. However, the EQ network would still interact with the frequency response. As I said earlier, proper bypass needs a significant change of topology.

 

[Potato Cakes]

It's just not the way bypass is done. Your bypass position actually loads the preamp's output with the EQ's output. You would need to disconnect the 100uF that's close to C24 to fix that. However, the EQ network would still interact with the frequency response. As I said earlier, proper bypass needs a significant change of topology.

I agree that isn't ideal as I am trying to find a way to do this without ripping apart the whole board and starting over. I've started a new thread that pertains to creating a bypass since the popping sound has been resolved.

https://groupdiy.com/index.php?topic=72410.0


Thanks!

Paul