Microphones in parallel to reduce noise
in [Design]
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From: krw on 16 Dec 2009 19:05 On Wed, 16 Dec 2009 17:01:24 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote: >On Wed, 16 Dec 2009 17:58:19 -0600, Vladimir Vassilevsky ><nospam(a)nowhere.com> wrote: > >> >> >>osr(a)uakron.edu wrote: >>> My boss laid a unit on my desk today. Its got ten electret mics fed >>> into one low noise opamp. Any ideas how they did this without a ton >>> of noise. All I can see from the board layout is it is NOT the classic >>> op amp summer. >> >>Electret mikes usually have built-in FET stage. Are you sure they are >>combined in parallel, not in series? >> >> >>Vladimir Vassilevsky >>DSP and Mixed Signal Design Consultant >>http://www.abvolt.com >> > >They are available WITHOUT the FET. I have an RFQ on my desk >requesting a complex chip that will use Electrets sans FET's. Right. Some of ours come with FETs, some not. Some "dynamics" are really electrets in drag.
From: Phil Allison on 16 Dec 2009 19:07 "Jim Thompson" Vladimir Vassilevsky <osr(a)uakron.edu> >> >>> My boss laid a unit on my desk today. Its got ten electret mics fed >>> into one low noise opamp. Any ideas how they did this without a ton >>> of noise. All I can see from the board layout is it is NOT the classic >>> op amp summer. >> >>Electret mikes usually have built-in FET stage. Are you sure they are >>combined in parallel, not in series? >> > > They are available WITHOUT the FET. ** So what ?? The kind with inbuilt JFET pre-amps are about a million times more common. PLUS, to comply with the OPs post they cannot be naked condenser capsules. .... Phil
From: osr on 16 Dec 2009 19:09 Ok, each mic has a surface mount network around it for frequency shaping. and each one has a internal fet. Until I can dig into it in the morning I don't know the values, 805 parts that I cant see until I get a microscope. A bit of probing reveals the outer ones are tailored to low freqs, inner ones to highs, and gain increases towards the centers of the array. Steve
From: osr on 16 Dec 2009 19:12 So tomorrow I look at the bias string.. Ok. I didn't have time to do much probing. I did sweep the response of each one by injecting a sweep. Steve
From: Phil Allison on 16 Dec 2009 19:29
"krw" > > Some "dynamics" are really electrets in drag. ** Totally stupid bullshit. .... Phil |