Quick switch question

[FingerBlisters]

Howdy,

I'd like to add a switchable pair of diodes to the feedback loop of an op amp. Nothing crazy- with switch one way the diodes are bypassed, switch the other and they're brought in for some soft clipping. In either position the cap/resistor are still in circuit.

Would I do this?



Or something like this?



Thank you kindly.

[antonis]

The first one..!! 
( the second one also shorts everything else inside NFB loop - unless, of course, we want a buffer when diode pair set "off".. )

[FingerBlisters]

The first one..!! 
( the second one also shorts everything else inside NFB loop - unless, of course, we want a buffer when diode pair set "off".. )

Thank you man, I appreciate the help.

[iainpunk]

The first one..!! 
( the second one also shorts everything else inside NFB loop - unless, of course, we want a buffer when diode pair set "off".. )

that will buffer the Vref!
its an inverting gain stage, so shorting out means silence!!!
also, in an inverting gain stage, diodes are hard clipping, not soft. add a resistor to make it soft, the resistor should be larger than the input resistor of that gain stage.

cheers

[antonis]

its an inverting gain stage,

Eagle eye, Iain..

[FingerBlisters]

The first one..!! 
( the second one also shorts everything else inside NFB loop - unless, of course, we want a buffer when diode pair set "off".. )

that will buffer the Vref!
its an inverting gain stage, so shorting out means silence!!!
also, in an inverting gain stage, diodes are hard clipping, not soft. add a resistor to make it soft, the resistor should be larger than the input resistor of that gain stage.

cheers

Alrighty. Thanks fkr the clarification. But so we're clear, the switching method in the first diagram will work to switch the diodes in/out of the circuit while leaving the other stuff intact?

[iainpunk]

Alrighty. Thanks fkr the clarification. But so we're clear, the switching method in the first diagram will work to switch the diodes in/out of the circuit while leaving the other stuff intact?

you're welcome and yes, the first one is perfect!

cheers

[duck_arse]

if I may, I'd like to point out you are using the/a wrong switch diagram. as shown, the flinger/dinger/common/2/[can't think the right term for the moving part] is shown in a centre-off position, as it is drawn pointing at nothing (making both throws normally off). if it were a simple on/on switch, the flinger would be drawn pointing to one of either "1" or "3" (and making one of those normally closed, the other normally open).

this all helps you, however, not at all. carry on.

[antonis]

Picture might have been taken during switching transition between throws with a shutter speed of 1/8000 sec.. 

[FingerBlisters]

if I may, I'd like to point out you are using the/a wrong switch diagram. as shown, the flinger/dinger/common/2/[can't think the right term for the moving part] is shown in a centre-off position, as it is drawn pointing at nothing (making both throws normally off). if it were a simple on/on switch, the flinger would be drawn pointing to one of either "1" or "3" (and making one of those normally closed, the other normally open).

this all helps you, however, not at all. carry on.

Well you're not wrong but it does the job. It's the Madbean Eagle library and I think we can all mentally extrapolate that the finger will move back and forth. Maybe they didn't want the diagram to show it pointing to one side lest people then presume it's hardwired to that position? That'd be my guess but I get what you're saying since that switch technically doesn't have an off position but it kinda looks like it.

[r080]

If you have an on/off/on switch, I don't think you need a DPDT. You should be able to have the middle lug of an SPDT connected to the output, then put the diode pairs on the outer lugs. The middle off position is no diodes.

[FingerBlisters]

If you have an on/off/on switch, I don't think you need a DPDT. You should be able to have the middle lug of an SPDT connected to the output, then put the diode pairs on the outer lugs. The middle off position is no diodes.

Yeah dude, that's the thinking I've come to. Weirdly the MB Library doesn't have any on/off/on toggles so I'm neck deep in the library editor trying to make a suitable part.

Opted for a SPDT on/off/on in the end.