Hi everyone, first post and real noob here, I hope is the right section

I'm trying to switch the phase of the TL072 using a CD4066 in the configuration shown in the attached schematic, the goal is to have a guitar buffer/booster using a digipot and eventually switch the phase with an analogswitch.
The circuit works fine except for the CD4066 switch, a lot of noise is introduced when pin 1 is floating.

Can you tell what I'm doing wrong here, if this is the correct approch, I'm open to any suggestions.

Thanks!

 

I think you are tying to achieve too much in too few stages.
Use one half of the TL072 as a preamp, non-inverting with gain, then do the invert-non-invert stage with unity gain.
Currently, the input impedance in inverting mode is 1k, and you really need 100k.

 

I think you are tying to achieve too much in too few stages.
Use one half of the TL072 as a preamp, non-inverting with gain, then do the invert-non-invert stage with unity gain.
Currently, the input impedance in inverting mode is 1k, and you really need 100k.

I actually don't need to reverse the phase, but since this is the 1 output stage of a stereo path, I need a "switch" to reverse the phase just in case one of the 2 output signal is out-phase.

Should I increase both R35 and R36 to 100k?

I have a couple of CD4051 around, maybe is this IC a better choice? At the end I need to just to tie a wire to ground (at least I think)

 

I’d use a real switch, and a unity gain Inverting amplifier, and switch between the main output and the inverted output using a changeover switch.
I‘d keep the 4066 as far as I could from the sensitive high-gain parts of the circuit, and keep the preamp as uncluttered as I can.
Signal processing can happen when there is a nice low impedance, line level signal to process.

 

IIRC, the 405x series has slightly better performance than the 4066, but it does not have the same signal voltage range. If you still do not want to go with a phase-invert stage that is separate from the gain stage, get a better analog switch. The 1960's were a looooong time ago, and better parts abound. There probably are others around here with more recent project experience, who can chime in on their favorite analog switch.

An alternative for digital control of an analog signal switch function is a small reed relay, driven with a controlled ramp waveform to prevent inducing clicks into the signal.

Is the phase-reversing function going to be used during music, or only during setups? If only during setups, you don't have to worry about clicks.

ak

 

Thank you all for your suggestion, I was able to switch the phase with an opto-coupler but then impedance problems arise, I choose then the @Ian0 way.
Can you please check if you see anything wrong?

 

Thank you all for your suggestion, I was able to switch the phase with an opto-coupler but then impedance problems arise, I choose then the @Ian0 way.
Can you please check if you see anything wrong?

Of course not! It's my circuit!

An observation on guitar preamps:
Everyone uses a 1MΩ load impedance.
Assuming that the pickup is 6kΩ+6H (which most of them are), then a 1MΩ input impedance puts a big resonance peak between the cable capacitance and the pickup inductance in the treble region, at an exact point that varies with the cable length.
100kΩ load impedance damps that resonance.

 

The digipot has a maximum allowed input signal voltage of -1V. It is being destroyed by the negative parts of the AC signal from the opamp that is driving it.
A CD4066 can use a +9V and -9V supply in this circuit.