TL072 based Electret mic pre-amp not working correctly... Tinny and quiet. - diyAudio
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Old 11th May 2014, 12:00 AM   #1
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Default TL072 based Electret mic pre-amp not working correctly... Tinny and quiet.

I wanted a pre-amp for electret capsules which allowed for higher SPLs and lower noise levels. I came across this design: Simple Stereo Electret Mic Preamp and it seemed like it would fit the bill.

Not sure what I did wrong but the output is really really quiet and sounds very tinny. There's also quite a lot of noise. I've removed the 27k resistor so the gain should be 23.

This is pretty much my first circuit so I'm not entirely sure what's going on here. I probably did something stupid.

Maybe these photos will help. Excuse the terrible soldering:

Click the image to open in full size.

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Old 11th May 2014, 12:29 AM   #2
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Schematic would help.
You should have cleaned yopur board before you soldered any thing to it.
I scrub mine down with a green scrubby or some steel wool.

What type of mic. element are you using, They are not exactly quiet anyhow ,but some are better than others.

jer

P.S. The links do not work.
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Old 11th May 2014, 12:37 AM   #3
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There's a schematic in the link, I'll embed it here:

Click the image to open in full size.

The element I'm using is by no means hi-fi. Cost me like $3. I'm not actually sure what it is tbh... I'm trying to get as much performance as I can out of it but I'm not expecting it to suddenly become amazing. It sounds much better with a simple one resistor, one capacitor, and a 9v battery circuit than with this though, so something is definitely not right.

What does cleaning the board achieve?

Thanks.
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Old 11th May 2014, 01:05 AM   #4
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I think if you reduce the gain of the preamp you may have better luck as it is also amplifying the noise that Mic. is producing as well.

I tried doing this a long while back hoping that I could have decent mic to do some recording with.
The capsule I had got did have a good and clean sound to it, but in my case it was to noisy for me to work with on my recording equipment.

There just wasn't any way to get rid of the hiss.

The gain of your circuit is more around 34, this is much higher than you probably had expected.

Try reducing the gain significantly and maybe you can find a happy range.

You can replace the 1k with a Pot to make it adjustable and then when you find the proper range replace it with a resistor with the corrected value.

jer
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Old 11th May 2014, 01:09 AM   #5
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"What does cleaning the board achieve?"

Better solder connection!

A bad solder connection can also create a lot of noise, sometime more than you can imagine!!

FWIW

jer
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Old 11th May 2014, 01:24 AM   #6
AJT is offline AJT  Philippines
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@fraseyboy, did you have permission to post that schematic? if not please edit your post to show links instead.....thank you...
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Old 11th May 2014, 01:30 AM   #7
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I missed that the 1k is actually a 1.5k so you are corrected the gain is 23.
Sorry for the confusion.

jer
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Old 11th May 2014, 01:38 AM   #8
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AJT, the schematic is in the link he had posted, I just failed to scroll down far enough to see it.
Sorry about that, my bad!!
jer
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Old 11th May 2014, 01:41 AM   #9
AJT is offline AJT  Philippines
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my concern is is he the author of that article? if so then fine....
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Old 11th May 2014, 01:46 AM   #10
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Quote:
Originally Posted by AJT View Post
my concern is is he the author of that article? if so then fine....
The schematic is in the link I had in the OP (Simple Stereo Electret Mic Preamp), pretty sure that's the original author.

I don't think it's a result of the mic. Something definitely sounds 'wrong'. Like it's being recorded underwater...

Edit: I tried putting in a resistor to reduce the gain and it sounds pretty much the same... Also the pot I have doesn't seem to affect the volume at all.

Last edited by fraseyboy; 11th May 2014 at 02:02 AM.
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