1. Home
  2. Electronics Down Under
  3. Noise in Amplifier.

Noise in Amplifier.

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.

Reply to
L.A.T.
Loading thread data ...

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.

Reply to
Clifford Heath

"L.A.T."

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

On ABSE, or elsewhere please.

( ABSE = alt.binaries.schematics.electronic )

...... Phil

Reply to
Phil Allison

Sooper

the

Stop using the laptop's crappy mic input then.

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.

Reply to
Mr.T

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

Reply to
L.A.T.

.....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.

.......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.

Reply to
L.A.T.

Logitech use a cheap 20 cent electret mic like all the others do.

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.

Reply to
David L. Jones

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.

Reply to
L.A.T.

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

formatting link
You would need to AC couple the input to it to isolate the electret mic power.

Reply to
swanny

messagenews: snipped-for-privacy@s19g2000prg.googlegroups.com...

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:

formatting link
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:

formatting link

eBay has plenty of both types.

Dave.

Reply to
David L. Jones

messagenews: snipped-for-privacy@s19g2000prg.googlegroups.com...

formatting link

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 !

Reply to
Fun Tyme

messagenews: snipped-for-privacy@s19g2000prg.googlegroups.com...

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.

Reply to
David L. Jones

messagenews: snipped-for-privacy@s19g2000prg.googlegroups.com...

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.

Reply to
Fun Tyme

On Mon, 17 Mar 2008 08:01:46 GMT, "L.A.T." put finger to keyboard and composed:

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

formatting link
formatting link
formatting link
formatting link
formatting link

- Franc Zabkar

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

"L.A.T."

** Still not visible to me, but FZ has posted a link to the schem now.

OK, all you gotta do is modify the headphone output circuit.

  1. Replace the 22 ohm with a 2k2 ohms.

  1. Fit the 22 ohm in parallel with one of the 1N5817 diodes.

Then crank up the VOL pot to compensate for the 40 dB loss of signal.

Should improve the signal to noise by lots.

....... Phil

Reply to
Phil Allison

messagenews: snipped-for-privacy@s19g2000prg.googlegroups.com...

the

the

USB

(dare I

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.

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

Dave.

Reply to
David L. Jones

formatting link

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

Dave.

Reply to
David L. Jones

On Mon, 17 Mar 2008 19:59:46 -0700 (PDT), "David L. Jones" put finger to keyboard and composed:

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.
Reply to
Franc Zabkar

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?

Reply to
L.A.T.

Absolutely.

Most likely.

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

$50 + postage is pretty affordable.

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

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

Dave.

Reply to
David L. Jones

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.