Pop noise in buffer

[juan_felt]

Hi!

I built an A/B-Y box with a buffer right after the input.
The box works perfectly, and the buffer too. I have a 3PDT toggle switch for the buffer. I have the following issue:
When I turn the buffer on I hear a loud pop, and also when I switch A/B or Y (this does not happen with the buffer bypassed).
I put a pulldown resistor on the output of the buffer, still have the same problem.

This is the buffer:

http://4.bp.blogspot.com/-fB4GdAOjhnE/U2fUkMsSluI/AAAAAAAAHGA/Adh1X3UOXUQ/s1600/JHS+Little+Black+Buffer.png

Any ideas?
Thanks!

[nonoxxx]

Did you try a 1 Mhoms resistor at the input ?

[Kipper4]

Did you put an anti pop resistor on the input too?

[Kipper4]

Thats a big ass cap for a buffer output. maybe try a 100nf instead of a 10uf.

[juan_felt]

Thanks for the replies,

I added the pulldown resistor at the input, and the pop is slightly lower.

I measured the DC voltage at the output, and when the buffer is bypassed its nearly 0V, but when it's on it goes up to around 700mV.

[Kipper4]

leaky output cap?

[juan_felt]

Hi,

I changed the output cap and the pop was almost gone, but I ended up making a different buffer.

(If anyone is interested is this one and it is great: http://tagboardeffects.blogspot.com.ar/2011/04/klon-buffer.html)

Thanks people! Have a good weekend

[amz-fx]

Thats a big ass cap for a buffer output. maybe try a 100nf instead of a 10uf.

Since the circuit mentioned is modeled after one on my basic buffers page, which has the 10uF output, I'll explain why the output cap is so large.

The circuit is a buffer and meant to drive low impedance inputs with an even lower output Z.  Since we cannot know what kind of load is going to be put on the buffer, especially if it is a standalone circuit, we have to allow for variations by selecting an output capacitor that will give full bass response with any load that the opamp can drive. The 10uF is good for 1k loads or greater.

If I were using the buffer as part of a larger circuit and I knew what load was on it, I would most likely use a smaller value capacitor on the buffer output.

Also note that sometimes circuits in my articles are just building blocks used as examples and do not have all the components shown that a good design would use. This makes the examples more clear to review in the context of the article. For use in a proper pedal, I would add pulldown resistors and power supply filtering for the buffers, and probably a build-out resistor as well. (My buffer boards for sale are designed with those extra options.)

Best regards, Jack