Pop with opamp buffer circuit

[joulupukki]

i'm working on a buffer inside of my pedal using a TL072 (or other opamp). I've got the input impedance dialed in, but have been experimenting with the output impedance.

Coming out of the opamp, I've got an electrolytic cap C3 and a 100nF cap C4 and then a pull down resistor (RPDO).

Initially I was trying a 47uF for C3 because it looks like in LTspice that the output impedance is nice and low:

But, it resulted in some pretty serious pop when I switch to and from bypass.

So I experimented changing RPDO to 100K. Still had a pop.

Then, I changed C3 to 10uF and put RPDO back to 2M. Still had a pop, but less.

Then, I changed RPDO to 100K. The initial pop after power-up of the pedal is almost good, but still a tiny bit of pop left. After switching a few times between bypass the pop virtually disappears.

Here's the impedance simulation for 10uF:

I haven't tried yet, but my next test will be to try RPDO at 10K similar to the TS's buffer output.

The high pass filter formed by C3 and RPDO is:

10u + 100K: 0.159 Hz
10u + 10K: 1.59 Hz

Couple of questions...

Can someone tell me if there'd be a detriment of switching to 10K?

Also, incidentally, I notice that the Klon uses 4.7u + 100K but then also has a 560R resistor in-line after the 4.7u + 100K. What's the purpose of the 560R?

 

[joulupukki]

Update. I tried 10u + 10k and the pop no longer exists (yay!) and seems to still sound the same. Still curious about the 560R in the Klon. Is that just a mixing resistor used for when the pedal effect is engaged and you're basically blending the buffered and wet signals together?