Is it normal for the pedal to make a loud pop when you engage or disengage it?
We have added a pull-down resistor mod in the instructions, basically adding a 1M to 2.2M resistor from the input to ground so the C1 cap gets discharged and attenuates the pop when the pedal is engaged:
It helps but some engaging sounds are still present when the pedal is stomped, maybe as aalbinger mentioned, is worth to have a look to the software side and check if the current taken by the 2 LEDs are adding a current spike that makes all pop. Thanks for pointing it out.
Also, even with the mix volume all of the way up the pedal is sucking some of my volume.
I have been testing it these last 2 days, if you have a look at the output adder:
It works under the typical op-amp adder formula
-Vout = (R29/R25)Audio_in + (R29/R28)Taps
In theory R29 = R29=R28=R25=4.7K, so there should be no attenuation, BUT the analog switches (CD4066
) have a 300Ω Typical On-State Resistance. This resistance can inbalance the equation, resulting in a marginal attenuation.
That's an easy to fix issue, just making the R29 a bit bigger (instead of 4.7K, make it 5K or even bigger up to 6K) will make a bigger Vout.
Using an oscilloscope, with the standard circuit I measured:
So the output signal is 925mV, a 3.34% smaller than the original 957mVpp input signal
At this point, I changed the R29 for a 5K resistor:
And the output is exactly as big as the input, showing that the maths are correct.
It is a very small difference, and for the sake of a reduced (easier to source) bill of materials, I believe is better to keep R29 as 4.7K, but please feel free to experiment and make it bigger