op amp buffer phase switching

[Kipper4]

I feel sure I've come across this before and should already know the answer but I'm having a total brain fart about it.

I have a spare half of an op amp in my circuit.

I would like to make one of the input NI buffers (coming from another Effect) and be able to switch the phase to an inverting.

How'd I do that?

I'm thinking DPDT switch.

Any links or help would help me dispel the proverbial brain gas.
Thanks
Rich

[Kipper4]

Just for clarity this is AC signal.

[KarenColumbo]

If it's okay to post a link:

http://sound.whsites.net/project107.htm

[Kipper4]

Sounds a bit Irish answering my own question but would this work, so it would....



Happy St Patricks day everyone.

[bluebunny]

There's a circuit at Geofex that does it with a single opamp and an SPST switch. I'm a bit "mobile" atm, so I can't do the search for you mate. :-}

[Kipper4]

Yep I know the one Marc. I'll try both later today.
All solutions gladly received.

[Kipper4]

The GeoFx idea doesnt work for this since there's a gain change on switching but it was worth a punt.

I've dropped the idea since it causes more problems than answers and I'll probably just use the spare op amp to buffer the Vbias.

Thanks anyway guys and girls.
Rich

[anotherjim]

The single amp idea should work without gain change...
Inverting input with x1 gain = Inverted output x1 gain.
Connect to the + input as well as the - input = Non-inverted output x1 gain.
Because if both + and - inputs of an op-amp have the same signal, if makes it a unity non-inverting buffer.


You are keeping the first op-amp to buffer it? It needs to be there.
Rbias and the input cap are not needed as the buffer outputs at Vref. R1,2 & 3 are the same (10k)

[Kipper4]

Ok thanks Jim I ditched the original buffer and implemented it without.

I'll put a buffer before it and try it.

The issue I found when I tried the kipper buffer (post3) Credit to SamHay there too.
Was that it caused a phase issue with the input buffer in the enveloped looper.