Klon output mixer circuit

[disorder]

Always wondered how the Klon output mixer works. I've seen others struggle to comprehend this as well so I figured I'd start the discussion. When it is set to bypass, the effected signal get's grounded at one of the amplifier stages so there is no effected signal at this output mixer in bypass mode. But in effected mode, you're clean signal is still sitting at R26.

What are those 68k resistors doing? And why the 68k value?



And full schem: https://aionelectronics.com/wp-content/uploads/2013/11/klon-centaur-schematic.png

[mremic01]

Those resistors at the output are to prevent popping. In the first and 2nd versions of the circuit, there were no 68k or 100k resistors there. Bill added these parts in the 3rd revision. When in bypass, the output jack was connected directly to the buffer's output. When the pedal was switched on, the jack was connected directly to the output pot. In the 3rd version of the circuit, the direct connections are still present, whether it's on or bypassed, but the 68k resistors bridge the fx output and buffer's output and then connect that node of the circuit to ground with the 100k. Either output can then bleed potential poppiness to ground through the 100k, at least that's my rudimentary (and likely wrong) understanding of it. Since your signal is going to take the path of least resistance, the value of 68k is probably high enough to block anything audible from the side that's not supposed to be switched on.

[PRR]

The 68K are just mix resistors. You can't short two outputs together; they fight. The mix resistor values will generally be higher than the source impedances and lower than the load impedance.

The evident intention is to mix some clean with the dirty.

IMHO, there's no pop here. Both sources are well DC referenced.

[mremic01]

Why would the outputs be shorted? In the first two versions of the circuit, they're just absent (not shorted).


This is what the Centura build docs says:

"* - Anti-pop resistor network. Absent in early spec units, no sonic impact."

"Note also the missing R26,R27,R28 makes the switching a bit poppy, thus you might want to have these still, and wire per Later Circuit, even if you opt for Early Circuit for the other differences (ie, the wire from stomp switch to Tip of Out Jack)."

[anotherjim]

I'm with Paul, the 68k are mixers.
Although there are those 560R resistors already in circuit, they would be too small and the low output impedance of the opposite amp would make the 4u7 coupling caps on the amp outputs (a path with those caps in series) too small for the lower end of the frequency response.
If they are helping reduce switch pop, they "might" be reducing the effect of capacitive coupling at the stomp switch - picking up the LED current on-off across the contacts.

[Ben N]

Like the 220ks in any classic BF/SF Fender amp.

[antonis]

Don't ask me why  but 68k is a "typical" value for mixer resistors.. 
(as also for High/Low Input selectors..)