CMOS 4066 + 4049 inverter question

[dataplex]

hello!

this is my first post here, although i have been reading the forums for years now 

so for my first question, here goes;

as a part of a bigger circuit - i am trying to build a simple guitar preamp / phase flipping circuit that allows me to:

• amplify a signal from a single-string pickup (its around 2.5kohms)
• flip the phase using a single switch
• bypass the signal from the output, or rather cutting it off using a single switch

here is my circuit;


(first switch to the right flips the phase, second is the bypass switch)

the circuit works great when i do the switching manually with physical spdt switches, however i need to be able to do the switching electronically - preferably using the quad CMOS 4066 switch and the 4049 HEX inverter (so that by default, the switches are ON).

so my problem is that if i power the 4066 with a single ended supply (let's say, 0 - 15v) it wont pass any negative voltages through the switches, and effectively clips the negative swing of the input signal off. it sounds pretty nasty, and looks like this on the oscilloscope.



appearantly the 4066 can handle dual ended power supplies(let's say -5 to +5), and then it will pass the signal unaltered(no clipping) - but my understanding is that this also means the incoming logic signal has to be pulled to the VSS (-5v) to turn the switches off. so a 0v logic signal will still be seen as "high"... right? i think thats what the datasheet says...

4066 datasheet is here::http://www.ti.com/lit/ds/symlink/cd4066b.pdf

maybe all i need is a capacitor between the signal and CMOS, im not sure... there seems to be a plethora of circuits online that use the 4066 in a single ended configuration to switch audio with no problems at all... maybe i can configure the 4049 inverter to swing the logic signal to negative, even though the input logic still is 0v - 5v?

any thoughts on this would be greatly appreciated!
thank you,
úlfur

[PRR]

> (let's say -5 to +5)

No "let's say". What IS the power to the opamps?? Not shown on your large drawing. It matters.

If it is bi-polar power to the opamps, the problem is that signal is swinging negative but the zero/+V powered switches can't swing below zero.

Look at CD4053. Unlike the simple switches, the CD405x series can take 0/+5V logic and control analog at other voltages (say -5 to +5).

Also the 2-throw function of the '53 allows you to fix a potential trouble-spot in your cut-off funtion: the amplifier input is left open to pick-up hash hum and radio from thin air. With the 2T function you can ground the amp input when not wanted.

> a plethora of circuits online that use the 4066 in a single ended configuration to switch audio with no problems at all

I think you will find that most of them bias-up the audio on a positive DC level.

A few very-small signal applications get away with it because they don't swing more than 0.5V negative, the point where the CMOS chip becomes a diode.

There are also tricks of inserting the CMOS at a summing-node, a virtual ground, using diodes to catch it when the switch is open.

Welcome to the Forum!!