Autoswitch between three dynamic microphones for instrument

[turbozob]

It seems that transisotr as a analog switch does not work as expected. When turned on the output voltage increases like it is also acting as a amplifier. I read about analog switched like MAX313 and ADG511 but am not sure what which one to use.

[turbozob]

The project has made a good progress, but the last problem I have is with DG412DJ analog switch.

There is a little pop-click noise heared on speakers when is switching and is also seen on scope. I tried everything to suppress it with capacitors and resistors, also used another analog switch to close-loop of amplifier before changing source of input, but again without success. Whenever the amp signal is released over analog switch the noise is there.

I read somewhere that optoisolator with MOSFET is a good choice for analog switching as Fairchild H11F1M
If anyone has more experiance and feedback what is the best for audio switching I would be much appreciated.

[turbozob]

Does anyone know why there is audible click pop noise to amplifier whenever I turn on LED or opto element? I tought that switching analog signal was making this noise, but now I see that whenever output is high or turning LED on the pop sound is there, it is also seen on the scope at amplifier output

[gilshultz]

First and foremost a Beta 58 is a dynamic supercardioid microphone it does not need or tolerate any external power.  I will admit it is one of the best vocal mic you can purchase.  Any DC applied to it will cause distortion and possibly burn it out.  Your Beta58A drawing shows that it is transformer coupled. You will need a Differential front end to amplify the microphones output, not single ended as in your drawing. You will need about 24 bit analog converter to pick up the quality of the microphone and convert it to digital where you will have to do processing. Multiply the A/D bits times the conversion rate required times 3.  For 44Khz 24 Bits 3 channels you need to process 3,168,000 bits per second or 395000 bytes a second.  A sigma delta converter may work better for you. Try this link: https://www.ti.com/europe/downloads/Choose%20the%20right%20data%20converter%20for%20your%20application.pdf

Take a look at this link: https://www.rane.com/note137.html it will give you some background information.  The simplest solution I can see at this point is to get a mixer that you can gate the outputs. These will have the ability to direct each channel to an effects processor (FX). Connect that to a AC/DC conversion circuit via a 600 Ohm isolation transformer.  You can then read the output of the conversion circuit with the arduino A/D inputs.  Then do some software to determine which is to be turned on and control the gates accordingly. You can use a inexpensive condenser microphones placed close to the Shure and use them for level measurement only,
Good Luck & Have Fun!
Gil

[turbozob]

Thanks for the info, the op amp circuit does is updated and does not have power to microphone and also uses TL074 op amp, but still my question was why when turning on/off led or opto I can hear click pop noise on op amp output? This happens even in op amp circuit with power led only.

[GoForSmoke]

Is something in the circuit inducing the microphone to produce that click-pop?

BTW, what led? What opto? I see resistors, caps, an opamp, a mic and a pot.

[turbozob]

Full drawing:


Sample opamp drawing powering led:


Opamp alone seems to be working fine, almost no noise with 2x AA batteries, but whenever I set output on/off to opto or led from arduino it makes a pop noise and also without analog signal switching. That is why I test the 2nd circuit just to turn on led or resistor as load for testing and it makes pop noise. Now 1000uF capacitor helps in that case but I do not know what to do at arduino output.

[GoForSmoke]

Going from mic to mic, the level won't quite be the same. What you hear is amplified, could it be filtered?

After looking at your drawing again, contact buttons bounce... does that affect your sound?

[turbozob]

The level seems to be the same but I did not go so deep. The thing is whenever I press/release the test button to turn led on/off or just trough the resistor, or turn opto led on/off with arduino output I can hear the pop noise.

I can filter this noise by putting large capactior across power supply form led, but dont know how to solve issue with arduino output.

[GoForSmoke]

The noise is a little thing that gets amplified.

When a contact switch closes or opens there is a short period where sparks jump the gap. For every voltage there is such a gap.

The sparks make what is called bounce and you MAY be hearing that. With Arduino you put the switch on one pin and watch that pin to detect transition from one state to another, that isolates the switch from your audio circuit.