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teopoz 27th April 2007 10:18 AM

electret Mic preamp
Hi to all I'm new in the forum or better I have used it some ago to make a diy projector!I do not know electronics so much (I'm reading books and tutorial) but ...
now I want to build a cheap portable preamp
I've searched the forum but due to my ignorance in electonic I dont know if what I've found is usefull to sorry for it
Let's show my problem:
I've got a Sony ECM-959A Electret Condenser Stereo Microphone that have a AA battery inside to power it but recording with a minidisk by sharp that I've bought on ebay (mt88) it have line in and mic in but recording with mic in (even at the max sensibility) the clip have a very low level and a lot of noise.
so I think I need a preamp ...looking on the net I've found
theese :
and now some question:
-did you think that suit my need?
-what are the difference in a preamp from an electret mic preamp an and a normal one?
-my microphone have a AA power battery inside it did you think I'll damage it if I use one of these scheme?
-did you know some open source scheme for a preamp?

for now many thanks and best reguards to all

sek 27th April 2007 10:42 AM

Hi Matteo,

and welcome to the forums. :cool:

I would first make sure that both units are in 'a working condition'. ;)

It would help a lot if you can make sure both the microphone and the mini-disc recorder actually work. Perhaps you have the possibility to connect another (known good) mic to the recorder and - vice versa - the mic to a (known good) preamp?

I am writing this recommendation because you state that you aquired the recorder used, and it sounds like you never might have checked the mic before.

Other than that, the AA battery inside the microphone is not to power a built-in preamp, but to charge it's condenser diaphragm. Different story.

Your microphone looks suitable for your recorder. And as you have some input signal recorded, it might be possible that the loudness of the sound you picked up was just less than you expected. ;)


teopoz 27th April 2007 10:59 AM

thanks Sebastian

For the minidisk I think it is in working condition because if I plug a cheap microphone in the mic in, it work and with not as noisy as with the sony mic ...and I've to set at not high sensibility
and also for the mic (the sony one) I've plug it in a guitar amplifier and works good
if I plug it in the stereo(radio cd) that have a mic in or in the pc mic in (audacity) I've got the same problem of the minidisk ...low level clips

I haven't no more audio hardware to test I think

teopoz 27th April 2007 12:19 PM

....What I think to do is to avoid the mic in of the minidisk and use the line input that I know it is working fine :-)

sek 27th April 2007 12:55 PM

Okay then, the microphone you've got looks fairly professional, although I haven't got any datasheet to go into the details.

The circuit you linked to could be your solution I guess, I just can't tell for sure without any information about the microphone's impedance and sensitivity.

So the preamp schematics you mentioned will work, but are only one solution. And because I know of the difficulty in finding a good mic preamp, I recommend reading the technical note about it by Rane. They're not the only manufacturer in the world, but their MS1b is a good example of a very simple, yet very good preamp. Please report about the findings for your microphone.

I found it to be difficult to actually find projects with PCBs for portable stereo mic preamps...


PS: Wouldn't your question be fitting better in a forum about minidisc recording than here in 'Chipamps'? ;)

teopoz 27th April 2007 02:14 PM

hi Sebastian
I'm at work and on the net I haven't found the info about my microphone (only this site )
When I came back home I'll post them
I've looked at the Rane link and their MS1b
but is too big for me
I need a portable setup because I have to record live sound (a short movie) and I want to stay on the cheap (100euros)

I've lookad at some mini disk forum but
I have in mind to learn electronics so I want to try to Do It by mYself ...if I can ....and looking at the pcbs online that reguards preamp I think that are not so impossible to build (not so many soldering) :-)

sek 27th April 2007 02:38 PM

Hi Matteo,


Originally posted by teopoz
I've looked at the Rane link and their MS1b but is too big for me
I was only referring to the Rane article, note the product, sorry. Just read the document and tell us what values apply to your microphone - or what values you want. ;)


teopoz 27th April 2007 07:12 PM

2 Attachment(s)
I'm Back here is the photo of the spec of the microphone I'm reading the article you gave me ...very explanatory many thanks

teopoz 27th April 2007 09:46 PM

2 Attachment(s)
looking at the md spec I realized to have understand nothing

here are the spec of my minidisc!
tomorrow until 2 may I'll be out so sorry if I do not reply in this period
for now many thanks
best reguards

ee_lagan 21st June 2007 06:54 AM

electret mic
hi i'm new here..i need an electret mic for my project..where can i get a free electret mic?...tnx:)

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