Re: Cell phone noise into opamps

Yes, and also in the supply path.

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Regards, Joerg

http://www.analogconsultants.com/

Mail me the schematic and layout, and I'll do some hand-waving.

John

Then I'll get shot :-)

I already did the convincing session (thou shalt not split grounds etc.). The layout is going to be pretty good and with some extra shield cans and stuff I am sure we can make it work. But no matter how much filtering there comes a point where something without a b-e junction would be kind of nice. This is an app where a cell phone right next to the unit is something to be reckoned with. Almost like good ole mil stuff.

--
Regards, Joerg

http://www.analogconsultants.com/

Just an observation:

These tiny Bluetooth headsets seem to get away with this sort of stuff. I have one which happily works without any audible interference with the cell phone sending Bluetooth data , and of course its own radiation at 8-900 MHz, with the phone effectively right on top of the earpiece. And its all in a plastic moulding.

--
Regards,

Adrian Jansen           adrianjansen at internode dot on dot net
Design Engineer         J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.

It's ok for simple audio stuff. But we have to extricate signals in the uV region.

--
Regards, Joerg

http://www.analogconsultants.com/

"Joerg"

** What the heck do you imagine all microphone, tape head and phono pre-amps have been doing for the last 70 years - PAL ????

Grrrrrrrrrrr..........

....... Phil

Yes, electret microphones. I only know the cheaper ones and they had rather mundane JFETs in there, not good enough here.

70 years, hmm, maybe I should check out nuvistors as well :-)

--
Regards, Joerg

http://www.analogconsultants.com/

"Joerg"

** NO !! All microphones.

Originating audio signal sources have sub uV noise levels at their utputs - so their associated pre-amps all have to " extricate signals in the uV region " .

** Don't try be smart about stuff you have no comprehension of - or you will fall flat every time.

...... Phil

Yeah, I guess that's why you guys use all those low noise opamps like the LM833 or the NE series.

I did build audio gear with tubes, back when even Ge transistors were expensive. Pre-amps, compressors, bigger amps, and one really big amp. That one had six color-TV H-tubes in it. You could make the plaster rain down from the ceiling with a few cords on the E-guitar. Sure enough, shortly after we fired it up the laws came. Luckily they did not check out how I had done the power transformer. There was none ...

--
Regards, Joerg

http://www.analogconsultants.com/

On a sunny day (Wed, 14 Nov 2007 09:34:38 +1100) it happened "Phil Allison" wrote in :

Bullshit, carbon mikes, throat mikes (or whatever you English care to call these), dynamic mikes, and a ton of other ones, have much higher output.

"Joerg"

** They will all "extricate signals in the uV region". ** Yawn....

What an appalling web site.

Cleary, Joerg = another rabid nut case.

...... Phil

"Jan Panteltje"

** FUCK OFF -

you ASININE WOG MORON

....... Phil

Adrian Jansen snipped-for-privacy@qq.vv.net posted to sci.electronics.design:

I saw your frequencies and thought "that's not right". So i googled and the correct frequencies are 2400 to 2500 MHz pretty much worldwide. Right there with 802.11b/g network equipment.

Jan Panteltje snipped-for-privacy@yahoo.com posted to sci.electronics.design:

Phil aside, low Z dynamic microphones have maximum outputs on the order of 10s of mV, magnetic phonograph pickups have full amplitude ratings of a few mV. This means if there is a quiet passage the output is in the 10's of uV range, and the noise floor is at least 40 dB below that (fractional uV). This is one of the reasons that high futility (Hi-Fi) used to be very hard.

"JosephKK"

** Big mistake, that.

** Probably the smallest voltage signal encountered in audio is that produced from the tiny diaphragm of a ribbon mic.

Such a ribbon has a resistance of about 0.1 ohm !!!!

Thermal self noise is a mere ** 5nV ** over the audio band.

Even in the early valve era, by using two stages of transformer impedance matching, the signal to noise ratio achieved was within a very few dB of the theoretical limit.

...... Phil

On a sunny day (Tue, 13 Nov 2007 21:34:26 -0800) it happened JosephKK wrote in :

Yes true, especially if you are in the Australian outback with a dynamic mike listening for ants moving ;-)

As to the dynamic mike, I remember getting into an argument with somebody, but what it came down to was: the person told me the dynamic mikes were mainly used for on stage vocals, where it is used close to the food opening, and the membrane is a bit heavy, so it probably will not react a lot to the ant noises, and should not pick up anything further away. Capacitor mikes, and electrets, have a much lighter membrane, and are more suitable to pick up those ant noises. There were also ceramic mikes, usin gsome crystal, Ronette is what I remember, those had quite a bit of output voltage too. Same difficult to move membrane.

4.5mV/µb at 1KHz

I have used the Ronettes :-)

Jan Panteltje a écrit :

Which end?

Hope there aren't any ant there!

Hope so too :-)

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Thanks,
Fred.

I know the bluetooth frequencies are 2.4 GHz, I was referring to the cell phone frequencies. Bluetooth power is miniscule, but cell phone transmission is not.

--
Regards,

Adrian Jansen           adrianjansen at internode dot on dot net
Design Engineer         J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.

Adrian Jansen snipped-for-privacy@qq.vv.net posted to sci.electronics.design:

It got lost in the snippage.