Relay Bypass with optocoupler muting | TLP222G versus TLP181, which is better?

[Gui113m]

Hi,

I want to build all my pedals with soft switching from now on. I have been experimenting a lot with true bypass relay kits but all of them had an issue: switching "pop" noises, so I have been researching and seems like everybody says that using optocouplers are the best option for muting the output signal while relay is switching.

Problem is that some optocouplers, even if on the "OFF" position, can degrade the output signal (eating highs, distorting... Mosfets especially) I want to keep my output signal as clean as possible, as unaffected as possible, and surfing the web I came across two options, a circuit using a TLP222G and a circuit using a TLP181.

Below I attached the schematics and characteristics of both.

In words of one of the kit suppliers, "The use of an optical MOSFET Solid State Relay is critical. Other types of solid state
relays, transistor, and FET designs degrade the audio output signal. The recommended Opto-MOSFET is the 4-pin Toshiba TLP222G". But looking at its characteristics compared to the TLP181, seems like TLP181 is a better option to me, in terms of affecting output signal (Lower capacitance, for example)

But I'm not an expert, I can be wrong. So... what do you guys think?

- Which of them will affect less the signal?
- Will any of them increase the output impedance?

[PRR]

The difference between 30pFd and 10pFd is like 8 inches of cable.

I'm sure you don't obsess about a cable 8 inches longer than it absolutely has to be.

However the main reasons switches POP is stray DC on the signal. Find and fix that, much of it goes away.

The other thing is that when you switch between two different signals (same sound processed two ways), there is usually a butt-splice glitch. The fix for that is a slow cross-fade, not a mute (which actually introduces two butt-splices). Another approach seen is "zero crossing": find a point where both signals happen to cross through zero. But this may not happen before you get impatient. And there is still a disjoint because it is unlikely both signals have the same slope where they go through zero.

[Gui113m]

Thanks PRR