Quick CD4053 question

[JP19]

Hi,

I'm planning to use a CD4053 to bypass my pedal (As described in this article http://www.geofex.com/article_folders/cd4053/cd4053.htm).

This suggests I want all the points of the switch biased to 4.5v. If the first stage of my effect is an non-inverting opamp buffer (which also wants biasing to 4.5v), can I connect them directly, or is the capacitor in between serving some purpose other than just blocking DC?

In other words, looking at this picture - can I just remove the parts circled in yellow?

Thanks!

[ElectricDruid]

In theory, yes, you can remove them and it doesn't make any difference. The two sides of the cap are biased at the same level after all, so there should be no DC across the cap.

In practice, I've found that I've *sometimes* had trouble by doing so. The only reason I can see for this to be the case is that there's an offset on the input of the op-amp which is then allowed to feed back to the switch. The extra cap blocks this and makes sure that the switch really is biased at Vref. The op-amp is actually biased at Vref+offset, whatever "offset" is. I assume on the occasions I've removed those parts with no problems, offset was close enough to zero to not matter.

Assuming that's true (and I've never tested the theory with any rigor) using an op-amp with a low input offset for your buffer would allow you to get rid of those parts with more safety.

I recommend you give it a try and see how it goes. I'm not talking about any huge failure or anything like that, but merely a bit of a click when you switch. If you can live with that in any case, you'll be fine. If not, you might need to choose a different op-amp of put the parts back.

[JP19]

Thanks! That makes sense. I've got room on my board so I'll probably just keep the extra parts to be safe.