John Curl's Blowtorch preamplifier part II - Page 2861 - diyAudio
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Old 29th October 2012, 03:02 AM   #28601
morinix is offline morinix  United States
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As a kinda' stupid but practical person I wonder how to let the sound waves in and keep the background light out. Or is this a mic for only dark, smoky club live recording.
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Old 29th October 2012, 03:13 AM   #28602
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You can think of the ambient light as a DC signal, while the proposed f.o. circuitry only responds to AC.
It seems to me that as described the circuit could pickup/send both electrical and f.o. signals, therefore easy to do a side-by-side comparison of the results.

edit: Although the diaphragm optimized for one probably won't be optimized for the other...
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Old 29th October 2012, 03:21 AM   #28603
RNMarsh is offline RNMarsh  United States
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Default Optical microphones have advantages --

There are several makers -- try OPTIMIC by Optoacoustics. One of the leaders.
You guys get out much? Out of your box? It's well into the 21st century. I may be an old geezer But I'll never be that old ! try to keep up. -RNM

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Old 29th October 2012, 03:35 AM   #28604
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Quote:
Originally Posted by RNMarsh View Post
Too broad.
The question was too broad.

It depend of what kind of device (FET or BJT), thermal resistance, quiescent current etc...

As an example, the variation of the quiescent current of a BJT Vs temp depends of the way it is used.
For an emitter feedback, it is an order of 15% for 40°. It seems enormous, but, it will be compensated by the feedback or error correction (if any).
The real difference ? You can have an idea, looking at the distortion curve of your amp at various output power, they include the same temp variation.
In your example, you double the voltage, so you X4 the power of half a period while 0 for the other.
The difference introduced by offset will be mainly in the harmonic figure, because less symetry so more percent of even-order harmonics in the total harmonic distortion.

Nothing to worry, i believe, when your amp is < 0.005% ?

Note that Class D amps will ask-you: "What are-you talking about ?"
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Old 29th October 2012, 03:39 AM   #28605
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Quote:
I may be an old geezer
No fair... you had a head start! I have to catch up before I can keep up
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Old 29th October 2012, 04:19 AM   #28606
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Esperado View Post
The question was too broad.

It depend of what kind of device (FET or BJT), thermal resistance, quiescent current etc...


The difference introduced by offset will be mainly in the harmonic figure, because less symetry so more percent of even-order harmonics in the total harmonic distortion.

Nothing to worry, i believe, when your amp is < 0.005% ?
????? What?
I could have sworn I mentioned CM relates to THD production.... especially in asymmetrical topologies, in particular. And, that tests using asym waveforms have a CM component to them to deal with. Thus, whats the CMR... doesnt anyone care about this aspect of amp design. You should. Thx-RNM
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Old 29th October 2012, 04:21 AM   #28607
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Fiber-Optic microphones: If you shine a light on a vibrating diaphram and pick up the reflected light via a f.o. to a detector.... you pretty much dont have to worry about noise, amps and Z and cable pick up of hum emi/rfi et al. Why arent more using them and developing them further for more recording appl? Why, why, why? -RNM
Noise of the light emitter ? Noise of the receptor ? How did they analyses the membrane displacement ?
Digital ? You need a line of 36mm for 1000000 pixels in the actual density of photosites in the best photo captors. For 120db of dynamic (in the nature) and 1db step (not enough).
Analog ? How ?
One thing is for sure, we could get rid of the inertia of a moving coil , like in electrostatic capsules. And if captor is digital, get rid of any analog problems, and converters, yes.
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Old 29th October 2012, 04:27 AM   #28608
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especially in asymmetrical topologies
I prefer symmetrical amps to play music to symmetrical girls.
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Old 29th October 2012, 04:36 AM   #28609
morinix is offline morinix  United States
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Originally Posted by RNMarsh View Post
There are several makers -- try OPTIMIC by Optoacoustics. One of the leaders.
You guys get out much? Out of your box? It's well into the 21st century. I may be an old geezer But I'll never be that old ! try to keep up. -RNM
Those are for industrial applications. I was wondering because couldn't recall seeing a review in the recording magazines.
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Old 29th October 2012, 04:54 AM   #28610
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About mikes, there are some omni-directional Electrets capsules, with very flat response curves and a diameter of 5 millimeters.
Glued on the branches of my glasses, above the ears, i used them to record ambiances for movies, without nobody can notice.
Kinda very good "Stereo natural head" recordings :-)
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