Switch Pop/Bang in a Distortion Circuit

[Karlsbad_kontradiction]

Hi All,



I'm working on the above distortion circuit (simplified) with a high/low gain switch. The problem is that it makes a big old bang every time I flip the switch. I know that this is generally an issue and I found a number of different discussion on the board here, but they all refer to non-existent schematics (or that I can't find, I'm new here), so it's tough to figure out what they're talking about.

R.G.Keen has a faq posting (http://www.geofex.com/Article_Folders/box_pop.htm) that hints at the problem, but also says it's not really fixable. Basically, because I'm jumping between gain levels, the opamp is having to make non-continuous changes, which translates into a pop when the speaker tries to reproduce it. I've tried various values of capacitor in various places, thinking to use it as a super high-frequency RC filter, but no dice.

Does anyone had a fix/solution/magic bullet? I've seen reference to FET switching circuits, but haven't had the chance to research them at all yet.

Thanks in advance.

[duck_arse]

hello K_k, welcome to the forum.

hard wire your 560k resistor to the 500k pot. then switch the 110k in parallel w/ the 560k, that way you will always have the feedback loop closed, to some extent.

[Karlsbad_kontradiction]

Short and sweet. Genius. Thank you.

p.s. I am very fond of your nickname.

[antonis]

IMHO, a make-before-break SPDT switch should eliminate your issue..
(it shouldn't leave no time for the op-amp to pass into open-loop gain..)

Alternatively, you can connect each "open" feedback resistor leg to op-amp inverting input via a BIG resistor (1M, say) and make gain pot value 1M (instead of 500k)...
(don't bother k_k.. just a temporary mind trouble..)

edit: Down-under connection is by far faster..
(both for welcome & suggestions..)

[GGBB]

Everything in series - switch jumpers either 110k or 560k:

[Karlsbad_kontradiction]

Down-under connection is by far faster..

Down-under connection?

[Karlsbad_kontradiction]

Everything in series - switch jumpers either 110k or 560k:

That one makes my brain go sideways. I'll cut myself some slack for not thinking of it. Cool idea, though, thanks.

[antonis]

Down-under connection?

It refers on mr. duck_arse way of thinking..