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Newbie question on dynamic mic circuit problems

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I did not and I won't be able to do so until January 3rd because of holidays. But I will (I don't have all this with me).

When I use any element I measure its values first - for capacitors and resistors. Also, I test transistors (when its required for the circuit) with a tester.
I wish I had an oscilloscope but they're freaking expensive!

The bypass capacitor is C1. Oh, sorry, this is the schematic I used:

OPA322 preamp.png
 

Hi,

As already recommended I'd use a series resistor at the input.

Now some thoughts ...
You use a very high quality, low distortion Opamp...
If you want to maintain signal quality I recommend to replace the tantal capacitors in the signal path with foil capacitors.
Tantals and electrolytics, but also ceramics capacitors will add distortion.

Instead of buying a scope you could use a PC's audio input. It usually has less noise and higher resolution than a scope.
But it's frequency range usually can't go down to DC ... but you don't need this anyway.
There also is PC software available for scope view as well as signal analysis like FFT.

Klaus
 

I was right. Since you used a polarized capacitor for C3 then its polarity is backwards without an electret mic maybe holding down the input voltage low enough.

- - - Updated - - -

In the inverting opamp circuit provided by Texas Instruments, the input resistance is produced by the output impedance (about 3.9k) of the electret mic parallel with R1.
A "foil" capacitor is 100 years old. A more modern film capacitor is smaller and has metal vaporized onto the plastic film.
 

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A ceramic capacitor is microphonic, it produces a sound when it is touched, bumped or vibrated. A film capacitor is used to properly and quietly couple audio signals.
The Mouser film surface-mount capacitor will be fine. It might melt and be a short circuit if you overheat it while soldering.

C3 is the only capacitor that has an unknown polarity when there is an electret mic connected to it. C3 also is the only capacitor in the circuit that is very sensitive to being bumped.
 

Turns out I don't have some tools to make double sided PCB... and time. But I made a PCB in Circuit Maker, made all the bypass capacitors closer to the op apm and the traces should be shorter overall. Not sure about less loops though...

Well, I'll keep trying when the tools delivered.
 

So I was learning to make double sided PCB's and I chose to work on the 2x transformers circuit. I learned some things about PCB design... and I made a "sparking circuit"! Well, at least I'm good at something as consistency is the key! :)

 

Made double layer PCB for the circuit with electrec mic, the opamp is heating up :/ Double checked shortages, found one and fixed it. But it's still heating up very quickly... But I all my components are used (from my previous attempt), even though I checked all of them except the opamp. I don't know, should I make a new PCB and use everything new?

Good news I made progress on making PCB's though, now with solder mask. I think...
 

ok, it's been a while. So I found the cause of all my circuits problems - since I make PCB's myself (double-sided) I did not pay attention to its orientation. For some reason when I make a PCB I've always had it flipped horizontally. Yes, when all soldered it looks valid but the problem is any IC is then mirrored too, thus pins are not connecting to the right tracks on PCB! I probably build ~15 PCB's until I realized that... damn!

ok, the TI reference board works like a charm! I also built a simple LM386 amp, also works.
The only circuit that doesn't work is TI's pre-amp modification with 5V op amp. But that one I tried with 0402 components and honestly I couldn't solder them properly. I have no right tools for that. So I'll try again later.

Anyway, it seems I got to the right path finally! I'll probably try to make this transformer circuit again, just for fun :)
 

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