Best approach to switching two effects w/ one switch?

[mdcmdcmdc]

Hi folks,

I'm working on an overdrive/boost circuit and I'm having some issues with switching; some insight into a better approach would be greatly appreciated.

Basically, I have an overdrive circuit and I would like to switch two separate boost stages on and off with a single switch - one boost BEFORE the OD and one boost AFTER.

This was my original approach using a 3PDT:


The switching worked well enough, but I was getting a lot of switch pop. A lot seemed to be coming from the LED (popping decreased substantially with the LED out of the circuit).

I assume a lot of the problem is insufficient R/C networks around the switches - any help with where to stick pull down resistors and additional caps would be greatly appreciated.

Similarly, I'm unsure if tying the inputs together and switching between outputs is the best way to go here? Is there a more sensible arrangement using a 3PDT or 4PDT?

I'm using optical switching a la voodoolabs for the global ON/OFF, but any help or advice for how to snake around these three building blocks would be greatly appreciated!

Thanks in advance!!

[bluelagoon]

To Avoid Switch pop could be easily achieved with a little extra circuitry and a DPDT Single Coil Relay,
See the 2 methods shown below that work well for myself, they both have muting built in that sends the signal momentarily to ground when switching, which usually inhibits and gets rid of all the switch click unwanted noise.
This also allows an LED indicator within the circuit to identify which switch side is in or out.
It also allows for use of a momentary switch, (normally open) All thats needed is replace your 2PDT or 3PDT with the 2PDT Relay. As it appears from your schematic you only used as much as 2PDT to get your effect working.





https://www.diystompboxes.com/smfforum/index.php?topic=118021.0

There is also the potential to get a similar or same result using a Microchip programmed to run a similar relay.

https://www.diystompboxes.com/smfforum/index.php?topic=129895.40

[bluelagoon]

Alternatively if you just need to silence your LED. There are some methods to do that. Plenty has been discussed already on this forum in previous topics.
Here is a diagram I picked up from one of those earlier DIY Stomp topics -

[mdcmdcmdc]

I appreciate the suggestions - thank you!

You're correct - I'm using 2 poles of a 3PDT for the switching and a third for the indicator LED.

My general approach to solving LED pop that won't go away through other means is optical switching - it's much less complicated than relays or microcontrollers, the parts are cheap(er), and I don't need soft/silent switches. I could implement that here but it would involve 3 sets of switching circuitry - I'm using it for the main ON/OFF, but I was hoping to avoid it on the boost stage.

I'm wondering particularly, with regards to the schematic above

a)if there are any obvious places to add extra r/c networks to fight switch pop.

b)if switching the outputs of the gain stages while leaving the inputs tied together is the best way to go. Perhaps there's a 4DPT arrangement that would allow for things to be tied to ground when not connected?

Again - thank you for the suggestions!

[mdcmdcmdc]

Perhaps better?
Would decreasing those 10M gate resistors to 1-2M be of any help? I don't think the value is super critical there, I just went with 10M as a default...

EDIT - just noticed a mis-drawn connection in the tone stack oops, edited to fix

[antonis]

Would decreasing those 10M gate resistors to 1-2M be of any help?

No..
(brute answer..)

[mdcmdcmdc]

Thanks @antonis - you're always very helpful with these things! Is there anything in your opinion I could do per the 2nd schematic to improve the switching/minimize popping?

[antonis]

It strongly depends on popping "source"..

Disregarding LED popping, the only suspect point is C45 (220nF) OUT cap (its right leg is floating..)
Try to move R21 (470k) right after C45..
(its left leg should always be grounded either via VOL pot or via R18..)

P.S.
Is the absence of input cap for Q4 stage intenional..??

[mdcmdcmdc]

The last boost stage? It seemed to work fine without a cap there, but no harm in adding one between VOL and BOOST VOL.

Thanks again!

[duck_arse]

I think antonis is driving at that very first stage, the one without an input cap. it seems pointless to add that last last output cap, especially when it has hanging output, when all before it is already DC isolated and pulled down.

wouldn't the boost volume pot connect to the full signal at R13 instead of "some level" set by the volume pot?

[mdcmdcmdc]

Ah, gotcha. I did add an input cap to that first boost stage at one point while trying to solve the popping, and must've not added it in the schem.

That said, it seems to be a convention of LND150 designs that they're not really necessary (see: moonlandr, spaceman saturn).

[mdcmdcmdc]

This is where I landed with it earlier:



Would you say C17, C15, R21 are all redundant?

Good call about swapping that junction from VOL2 to R13. That makes a lot more sense.

[antonis]

Caps are almost never redundant - in the mean of better safe than sorry..