OK, so here's an irritating problem...

A while back I bought an external sound card. I'm very happy with it by 
the way. But then I unplugged my microphone from my PC's built-in sound 
card and plugged it into the external one. I can't hear a damned thing.

"OK, so it needs a line input" I thought. So I went out and bought a 
microphone preamp. And you know what?

I still can't hear anything.

To be fair, without the preamp, if I amplify the digital signal all I 
get is noise. But with the amp, if you apply about 90 dB of 
amplification, you can very faintly detect any loud noises made directly 
in front of the mic.

Can anybody explain to me (A) why the mic is still too damned quiet, and 
(B) how to make it loud enough to be useable?

[Remember, if I plug it into my motherboard sound card and turn on the 
"boost mic" option, it works perfectly. But the outboard sound card has 
no such option.]

Just as a point of interest... I have a knackered old mic that I got for 

just fine. [Although it's still a little on the quiet side. And that mic 
never did have any treble response at all.] The mic I'm trying to use 
was sold as a PC microphone, and indeed if you plug it into any PC and 
turn on the mic boost option, it works just dandy. [And gives a vastly 
superior sound quality to my ancient mic.]

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

My guess is that it's just picking up the wrong input in the app.  The 
mic probably works fine (try plugging it into the mobo mic jack and see 
if it behaves properly).

Jim

Post a reply to this message

48501913$1@news.povray.org...
> OK, so here's an irritating problem...
>
Maybe this microphone is an electret one and need to be powered (whitch your 
motherboard microphone input does but not your additionnal soundcard)
Maybe you need to switch something like 'plugin power' somewhere (either 
hardware or software switch).
Be careful your preamp may have a ' 48v phantom power' option but it is way 
too much for a PC microphone.

Marc

Post a reply to this message

> A while back I bought an external sound card. I'm very happy with it by 
> the way. But then I unplugged my microphone from my PC's built-in sound 
> card and plugged it into the external one. I can't hear a damned thing.

As Marc said, your microphone is probably a powered one, and PC sound cards 
normally provide power on the mic socket.

> "OK, so it needs a line input" I thought. So I went out and bought a 
> microphone preamp. And you know what?
>
> I still can't hear anything.

The pre-amp is probably expecting a real microphone, not one that needs 
power.

Post a reply to this message

4850cbf8$1@news.povray.org...
>
> The pre-amp is probably expecting a real microphone, not one that needs 
> power.
>
Some top-notch microphones need power :-)
on professionnal equipment 48V DC phantom power through ballanced wiring is 
commonly used.
http://en.wikipedia.org/wiki/Phantom_power
But as I said it does not fit to PC microphones that use plugin power
A detailed arcticle :
http://www.epanorama.net/circuits/microphone_powering.html

Marc

Post a reply to this message

>> OK, so here's an irritating problem...
>>
> Maybe this microphone is an electret one and need to be powered (whitch your 
> motherboard microphone input does but not your additionnal soundcard)
> Maybe you need to switch something like 'plugin power' somewhere (either 
> hardware or software switch).

Actually I'm pretty sure my PC microphone is a crystal mic...

[The microphone that works is marked as "dynamic", whatever that means.]

I had a go with my dad's test meter. At 0 Hz, the working mic has a 
resistence of about 600 Ω, whereas the non-working one is about 1.2 kΩ. 
I don't know whether that has anything to do with anything. [I don't 
have the specifications for my outboard sound card to hand...]

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

4850f855@news.povray.org...
> Actually I'm pretty sure my PC microphone is a crystal mic...
UH? do they still sell that? Usually they are electrets
>
> [The microphone that works is marked as "dynamic", whatever that means.]

It means a moving coil microphone, no need for power

>
> I had a go with my dad's test meter. At 0 Hz, the working mic has a 
> resistence of about 600 ?, whereas the non-working one is about 1.2 k?. I 
> don't know whether that has anything to do with anything. [I don't have 
> the specifications for my outboard sound card to hand...]
For the dynamic microphone you measure the DC resistance of the coil .
Electret microphone are buffered by a FET and insulated from DC by a 
capacitor.
You can't measure a useable impedence at 0 Hz :-)
maybe you measured between rim (power +) and sleeve (ground)
http://en.wikipedia.org/wiki/Electret_microphone

Marc

Post a reply to this message

>> Actually I'm pretty sure my PC microphone is a crystal mic...

> UH? do they still sell that? Usually they are electrets

Sure - why not? They sell crystal ear pieces too - very useful with 
home-made crystal radio sets. And let's not forget, picture speakers use 
crystals too...

>> [The microphone that works is marked as "dynamic", whatever that means.]
> 
> It means a moving coil microphone, no need for power

Right. So a reverse speaker then?

>> I had a go with my dad's test meter. At 0 Hz, the working mic has a 
>> resistence of about 600 ?, whereas the non-working one is about 1.2 k?. I 
>> don't know whether that has anything to do with anything. [I don't have 
>> the specifications for my outboard sound card to hand...]

> For the dynamic microphone you measure the DC resistance of the coil.

Right. So the working mic has a DC resistence of 600 Ω.

> Electret microphone are buffered by a FET and insulated from DC by a 
> capacitor.
> You can't measure a useable impedence at 0 Hz :-)

OK. So assuming it really is electret, I can't measure its impedence 
meaningfully.

I'm 70% sure this is the guy BTW:

http://www.maplin.co.uk/module.aspx?ITAG=SPEC&ModuleNo=24698&doy=12m6#spec

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

4850ff36$1@news.povray.org...
>>> Actually I'm pretty sure my PC microphone is a crystal mic...
>
>> UH? do they still sell that? Usually they are electrets
>
> Sure - why not? They sell crystal ear pieces too - very useful with 
> home-made crystal radio sets. And let's not forget, picture speakers use 
> crystals too...
The frequency response of crystal microphones is often limited to a 
relatively narrow band . They boost treeble and have poor basses.
It may be good for a close-miking of voice to enhance speach recognition but 
they are far from all-purpose applications.
>
>> It means a moving coil microphone, no need for power
>
> Right. So a reverse speaker then?

Exactly but not optimized for that use :-)
>
>
> OK. So assuming it really is electret, I can't measure its impedence 
> meaningfully.
>
> I'm 70% sure this is the guy BTW:
>
> http://www.maplin.co.uk/module.aspx?ITAG=SPEC&ModuleNo=24698&doy=12m6#spec

The *stereo* (the exact name is TRS for Tip/Rim/Sleeve) jack for a mono 
microphone makes me suspect it is an elecret.
The rim is for power +.

Marc

Post a reply to this message

>>> It means a moving coil microphone, no need for power
>> Right. So a reverse speaker then?
> 
> Exactly but not optimized for that use :-)

Mmm - I understand you can also make a mic out of a speaker. But it 
tends not to work well. ;-)

Hey, I wonder - can I use the alternator on my car to drive the car 
instead of recharge the battery? :-D

>> I'm 70% sure this is the guy BTW:
>>
>> http://www.maplin.co.uk/module.aspx?ITAG=SPEC&ModuleNo=24698&doy=12m6#spec
> 
> The *stereo* (the exact name is TRS for Tip/Rim/Sleeve) jack for a mono 
> microphone makes me suspect it is an elecret.
> The rim is for power +.

Hmm... a stereo jack on a mono microphone... yeah, that does seem a 
little suspect.

Oh goodie. Now I need to find some power from somewhere. :-/

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message