Noise in Amplifier.

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A while back, with the help of regulars on this newsgroup, I made a Sooper
Snooper microphone in a parabolic dish for a bird-watching friend. The dish
and the amplifier kit came from Oakley Electronics and was described in the
September 2001 issue of Silicon Chip.
It worked well and he has made a couple of ground-breaking recordings of
local lyrebirds.
He uses a program called Audacity on a laptop and plugs the output from the
amp into the microphone input on the laptop. The output from the amp is such
that its volume control must be set at just above the minimum or its signal
swamps the laptop.
There is a problem with background noise. At first it was masked by
wind-in-the-trees noise and the sound of the surf from about 5K away, but
now that he is recording in remote and very quiet places, it is sadly
obvious that there is hiss coming from the amp itself.
The hiss is there at the very lowest volume, and is present whether  the
electret microphone is plugged in or not.
If I could reduce the hiss I could replace the volume control with one that
uses most of its travel to do what a quarter turn does on the existing
volume control.
It seems that a microphone plugged directly into the laptop is a bit too
faint, and the output from the amp, plugged into the laptop input is too
strong.
Are we a bit too ambitious in expecting the little amp to be free of hiss?
(Or almost?)
Are we taking the wrong tack in using such an amp anyway?
Is there a stand-alone microphone that we could fit into the parabolic dish
that would have enough grunt to record the birdcalls directly to the laptop,
without having too much inherent noise? Something like an upmarket desktop
microphone that records voice beautifully, doesn't seem to be powerful
enough, designed as it is to sit on a desktop. Something of similar quality
with a bit more output would be perfect.
I had such helpful comments last time that I expect that I will be equally
grateful this time.



Re: Noise in Amplifier.
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Most laptops have quite noisy audio hardware. A computer is an
electrically noisy environment and it's hard to mask that noise,
especially when dealing with a low-level signal like a microphone.

You should find a laptop with a "Line in" input and/or better
sound hardware, or use external sound hardware that's quieter,
perhaps an M-Box or one of the better USB devices if you can find one.

Re: Noise in Amplifier.

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Sooper
the

Stop using the laptop's crappy mic input then.

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True.


Not really, there are plenty of pro level internal soundcards with decent
quality microphone inputs.
Sadly however, the standard microphone inputs on laptops and most desktops
for that matter, are universally (or very nearly) total crap, and the OP's
is no different it seems.

MrT.



Re: Noise in Amplifier.

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.....The noise is coming from the amp. When the cable is plugged into the
laptop but not the amp the hiss is not there.
.....No doubt if the hiss is eventually cured the shortcomings of the laptop
(Toshiba Satellite) will then become evident.
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.......He can't afford another laptop. The challenge is to get the best
input available into the existing laptop.
.......The quality of the sound from something like a logitek
headphone/microphone, if loud enough, would be adequate.
.......This makes me believe that if the sooper snooper is unfixable, there
is something out there that is adequate and affordable.



Re: Noise in Amplifier.
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Logitech use a cheap 20 cent electret mic like all the others do.

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You need a unidirectional electret mic element and a good low noise
pre-amp with the desired gain. Almost any electret mic element will be
good enough, but they do come with different gains. This can easily be
battery powered.
This must be connected to the line-in on the notebook, not the "mic"
input. If you don't have a "line-in" then your only option is a USB
preamp, or a USB microphone (which has it's own preamp and ADC built-
in), but that might not be physically suitable for your dish. As
others have said, the mic input on notebooks and PC are atrocious.

Dave.

Re: Noise in Amplifier.

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The notebook has no line-in
I'm sure you are right about the USB input. Using a desk microphone into the
laptop's USB port gives better sound than using a similar mic into the mic
input. The existing mic and dish with a battery powered pre-amp into the USB
port would be ideal. If I can find an affordable one, or find a suitable
circuit.
Googling this kind of thing is frustrating. Of the multitude of hits (dare I
say it), the signal-to-noise ratio is not good.
But at the moment our problem is hiss, not audio quality. That is the next
hurdle. Reading the literature, it is evident that lots of money can be
spent on this innocent endeavour, and with diminishing returns.



Re: Noise in Amplifier.
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Ah yes, the old Google S/N ratio!
Perhaps you are better off searching for a "USB sound card", and then
you find stuff like this:
http://www.techbuy.com.au/p/48770/SOUNDCARD/Creative/ACSB0271.asp
Proper USB mic pre-amps are fairly expensive and have balanced inputs
and phantom power etc for professional mics, you don't need that stuff
unless you use a professional mic. Just getting yourself a line-in on
a good quality sound card it plenty good enough. Then build your own
mic pre-amp as they are simple.

You can also use a PCMCIA sound card if the norebook has one, and you
can get real good quality ones like this one for a reasonable price:
http://cgi.ebay.com.au/7-1-PCMCIA-Audigy-Sound-Card-For-Notebook-IBM-Sony-HP_W0QQitemZ350036326070QQihZ022QQcategoryZ150128QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

eBay has plenty of both types.

Dave.

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http://cgi.ebay.com.au/7-1-PCMCIA-Audigy-Sound-Card-For-Notebook-IBM-Sony-HP_W0QQitemZ350036326070QQihZ022QQcategoryZ150128QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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All this is surely too hard ! The laptop mic input is simply being
driven far too hard, that's why the laptop gain control is so "savage" -
it just needs an input pad, or most basically a series resistor.

These directional mic units work fine into headphones but obviously this
level is far too high for a mic input. A series resistor will be enough
to drop the level but the 1/2 rail on the LM386 could hurt the mic input
on turn-on hence the suggestion for a pad.

The LM386 used in this way is wasteful of battery power, so why not
remove it and connect the cable to the laptop mic input via a suitable
series resistor to the input of the (now removed) LM386 - or the wiper
of the local gain control pot ? The series resistor may not be required
as many microphones suitable for laptops are already electrets.

Of course the right kind of electret could just be driven by the B+
appearing at the laptop mic input, then the electret would be wired
direct to the laptop input and the user would not even need the
jiffy-box hanging off the parabola assembly (except for the loss of the
local gain control). Much simpler - he's only listening to bird noises !

Re: Noise in Amplifier.
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Yes, which is why he wants it as quiet as possible. Have you been out
into the bush and listened to bird calls? It's not like they fly up to
the mic and sing into it, you need a big SNR.
PC mic input pre-amps are notoriously bad, you often can't even record
*decent quality* speech with it. Compare it with a good quality USB
mic in a quiet room and you'll hear the difference plain as day. You
can also see the noise floor in real time with programs like Audacity.
Check out pod-casting and why hardly anyone recommends using the mic
input on a PC, and that's just regular speech.

Dave.

Re: Noise in Amplifier.
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All understood Dave, and for info I live in the bush with no town sounds.

The user wants a cheap (toy !) and I suggested a way he can use the one
he purchased.

You are correct in your statements, I am not arguing at all.

If the user wanted to be serious in his pursuit of bird noises he would
use a "proper" system, yet the device he has can work remarkably well
for its simplicity.

As an aside - I built an RF transmitter on ~ 106MHz for my old man which
could be placed in a tree or at a bird bath/feeder. This could be
received on any FM broadcast receiver with excellent results, and one
could hear all the scuffling and eating noises for a 'different'
experience. The transmitter is still here somewhere, built "dead bug"
style on a scrap of PCB.

Birds actually "talk amongst themselves" at a feeder, akin to human
"birds" in the dunny of a pub (but with less bullshit).

Translation of that last sentence may be required for readers outside of
Astraya.

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the
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the
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USB
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(dare I
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Given that the OP's friend has moved on to "remote and quiet" places,
I'd say he's getting fairly serious about this.
That means ditching the microphone input. Unless the notebook mic
input has been characterised as having acceptable performance for the
job (unlikely), then he must get a proper pre-amp designed for the
job. The whole upgrade can be done for well under $100, including a
USB sound card and a pre-amp, it's a no-brainer.

A "proper" system is nothing more than a decent pre-amp (can be easily
home built) and a $1 uni-directional electret mic.

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I've done that too. A simple two or three transistor bug circuit can
give amazing results.

Dave.

Re: Noise in Amplifier.
Sincere thanks to you all.
I am a little overwhelmed by the amount of help I have been given.

The first thing I will try is Phil's suggestion.

I believe that the parabolic dish is crucial to the scheme and that the
little mic is adequate..
I am now aware that line in would be better than the mic input but the
laptop hasn't got one and there is no suggestion of buying another laptop
just yet.
I believe there is a way of using the electret mic, the dish, and a preamp
that can plug into the USB port and I believe that this would eventually be
the best affordable means of recording, in the bush, to a laptop.

On the end of the cable of some mid-range and up-market USB desktop
headphone/microphone sets there is a little potted lump that must be an
analogue-to-digital converter. Is this what I need?



Re: Noise in Amplifier.
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Absolutely.


Most likely.


No need to, ever, plenty of cheap USB and PCMCIA sound cards around.

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$50 + postage is pretty affordable.

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Yes, it's a USB driver chip and a codec (ADC/DAC) with a preamp for
the mic.

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You need a USB or PCMCIA sound card with a line-in, simple as that.
Just like the one I posted earlier.

Dave.

Re: Noise in Amplifier.

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Thank you for your recommendation.
Mr. Lyrebirdman http://lyrebirdman.googlepages.com /
has bought this Creative soundcard and it works well. I have reset the
little Oatley amp to its previous specs and the output at full volume is now
enough to drive headphones and/or to drive the Creative soundcard but only
just. The quality of the recording is much improved as you promised. With
Audacity we can amplify the track after we get it home.
I am thinking of mounting the dish and its microphone in a little
eggcrate-lined box, firstly to diminish unwanted sound but more crucially to
protect it from knocks and mishaps in the pre-dawn, pre-birdcall darkness.
Is there a practical limit to the length of the cable from the mic to the
amp? At the moment it is about 4cm.
Would I suffer any adverse effects from making it, say, 10cm?
Thank you all, once again.



Re: Noise in Amplifier.

"L.A.T."

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** Can you ( or anyone here ) post the schematic of this unit ?

   On  ABSE,   or elsewhere please.

(  ABSE =  alt.binaries.schematics.electronic   )



......   Phil




Re: Noise in Amplifier.

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Done.
It's a tif. I hope that's OK.



Re: Noise in Amplifier.
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I'm not surprised you are having problems. The circuit has an LM386 power amp at
the output, for connecting to a speaker or headphones. For your application,
going into a laptop soundcard, you would be better off with a good preamp and no
power amp.

You could use a simple low-noise op-amp like the NE5534 to do what you want or
Phil's great little mic preamp (http://sound.westhost.com/project66.htm ). You
would need to AC couple the input to it to isolate the electret mic power.


Re: Noise in Amplifier.
finger to keyboard and composed:

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There are ways to get this info from SC's web site ;-)

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- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Noise in Amplifier.
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http://us1.webpublications.com.au/static/images/articles/i1017/101734...http://us1.webpublications.com.au/static/images/articles/i1017/101734...http://us1.webpublications.com.au/static/images/articles/i1017/101734...http://us1.webpublications.com.au/static/images/articles/i1017/101734...http://us1.webpublications.com.au/static/images/articles/i1017/101734 ...

That's sneaky.
Gunna tell us how you got those?

Dave.

Re: Noise in Amplifier.
On Mon, 17 Mar 2008 19:59:46 -0700 (PDT), "David L. Jones"


http://us1.webpublications.com.au/static/images/articles/i1017/101734 ...
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If I tell you, then SC may decide to kill the golden goose.

Check your mailbox.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

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