did something wrong with opamps?

What are you doing with the OCM input to the amp? What are you using for input and feedback resistors? Do you have feedback resistors at all?

So I guess the answer is yes, we need more information. Answering the questions above will be a help, posting a schematic of what you're doing, either here in ascii art, on your website with a link, or on alt.binaries.schematics.electronic will be a big help.

Here's a schematic I drew up in paint. I've got nothing on the OCM input, though I've patched it to the Vcom pin on my analog to digital converter (PCM1804) and had the rest all hooked up, and the same thing happened.

What are you using it for that you need a diff output/input? I'd ground/common one mic input, so there goes the single batt. Right now, your mic/line is probably a big antenna picking up everything you see when you touch your scope probe, if you have a scope. Go beyond the first page of the spec sheet and note the filter caps on the supply and the output.

That "pop" is usually caused by not having a ground path for the inputs. The input caps which you don't show, but those feedback caps are probably the culprit, should have a path to ground/common on the mic side.

I've changed the schematic a bit.. added a 0v ground, however im still getting a pretty loud popping/static-ish noise comming from the mic see

Why are using it as a mic amp?

wrong choice AFAICS, they only spec it up a gain of 10 or so, whats the o/p level of mic, maybe 5mVpeak

a dynamic mic has a low source impedance, so you are really degrading the signal/noise by having those1Kohms in series.

Go for the SSM 2017 architecture, works fine, second sourced by TI and AD and Thatcorp( i furget the part nums)

martin

"An eye for an eye makes the whole world blind" Gandhi

Because it was suggested by Texas Instruments for use with my particular ADC (PCM1804). I've put in a samples order for the parts you've suggested however.

@ James Meyer: I'll work on those tests once I get home and report back =)

On 3 Mar 2005 19:32:14 -0800, snipped-for-privacy@gmail.com wroth:

It may be perfectly normal. A dynamic mike can be a very sensitive "speaker".

Try a couple of tests and report back.

Test 1, With the mike disconnected, use an ordinary multimeter to measure the voltage across the amplifier's input connections.

Test 2, Use a single 1.5 volt flashlight battery in series with a resistor to test the mike. Start with 10K or so for the resistor and keep increasing its value until the mike makes the same volume of "static" noise when you connect it to the battery that it does when it's connected to the amp.

Test 3, If you have access to an oscilloscope, measure various points on the amplifier to see if it is oscillating at some frequency much higher than ordinary audio.

Jim

Why did you choose the this opamp?

martin

"An eye for an eye makes the whole world blind" Gandhi

I'd start off with the circuit shown in fig 44 of the 1804 data sheet, its pretty standard . ( see the AKM and Cirrus datasheets) You could put lower THD opamp in , say AD797, but I doubt if you would hear any difference. You would still need a mic preamp to get the sensistivty ie 30 to 60dB of gain.

martin

"An eye for an eye makes the whole world blind" Gandhi