He might be concerned with the current consumption, which will be inherently higher if the IC has more circuits to bias.

Normally not a factor with a CMOS circuit, since it consumes only a very small leakage current when static.

 

Is it not the output impedance load that you want to be >20kΩ?

Long form answer for the TS . . .

Per the datasheet, the 4066 switch typical ON resistance can vary from 125 to 180 ohms when operating on 10 V at +25C. That resistance increases as the operating voltage decreases, so I'm guessing around 200 ohms max when running on 9 V (a common effects pedal operating voltage). Assuming the source has a low output impedance (because the signal source is the output of an effects pedal, not the guitar pickup directly), this resistance forms a voltage divider with the input impedance of the "analogue inputs". Because the switch resistance varies with the instantaneous signal voltage, this resistance variation appears in the output signal as a form of harmonic distortion.

One way to reduce this is to choose a switch such that its series resistance is a very small percentage of the downstream input impedances. I chose a target threshold of 1%, and the 4066 meets this if the analogue input impedances are greater than 20K ohms.

https://www.ti.com/lit/ds/symlink/cd4066b.pdf

ak

 

Normally not a factor with a CMOS circuit, since it consumes only a very small leakage current when static.

I know, but I assume that even in CMOS there are biasing circuits that consume more for more channels.

 

I know, but I assume that even in CMOS there are biasing circuits that consume more for more channels.

If I recall correctly, as long as the unused input pins are tied to a solid one or zero level, and the outputs unconnected, those unused gates would only consume leakage current in the nanoamp range.

 

If I recall correctly, as long as the unused input pins are tied to a solid one or zero level, and the outputs unconnected, those unused gates would only consume leakage current in the nanoamp range.

Good to know. I was assuming the worst case scenario.

 

That is the beauty of static logic, nano-amps leakage at idle. And at 25C of course. At higher temperatures the leakage increases very rapidly.

 

One way to reduce this is to choose a switch such that its series resistance is a very small percentage of the downstream input impedances. I chose a target threshold of 1%, and the 4066 meets this if the analogue input impedances are greater than 20K ohms.

Yes, but then the output impedance needs to be very high to not attenuate the signal.
It would seem better to not mess with the signal output impedance, and just have a ≥20KΩ load for the switch output.

 

Relays for low current applications are not recommended, unless it's a solid-state relay. The contacts oxidize and start to not conduct with time.

Use the correct relay for the application if you chose to use a relay.

I use low-signal rated relays with gold contacts for line level signals. They been reliable for decades in gear running 24/7.
https://www.mouser.com/catalog/specsheets/Pansonic_12-15-2025_TQ_Relays.pdf

 

Use the correct relay for the application if you chose to use a relay.

I use low-signal rated relays with gold contacts for line level signals. They been reliable for decades in gear running 24/7.
https://www.mouser.com/catalog/specsheets/Pansonic_12-15-2025_TQ_Relays.pdf
View attachment 371185

Good to know there's these types of relays. A professor of mine once said what I said above, but didn't mention relays with gold contacts. Seems obvious now, but I didn't know it was a thing being sold.

 

Has the TS returned to comment?? I just read thru them and I am wondering. AND WHY is there even an issue about using an IC that can provide more than two inputs??
The post with the CD4066 putting switches in parallel is the very best scheme because of the lower series resistance.
BUT there can be voltage range issues using analog switch ICs. I think that was addressed but ignored. BUT with the standard CMOS analog switches the input voltage range MUST NEVER BE IGNORED!!
FORTUNATELY the work-arounds are simple and cheap!!

 

The TS wanted a thru-hole, SPDT switch designed around bipolar transistors.
He may have left AAC already.