[JHouser]

Does anyone in here know of what is needed for this? I need a (phantom Power) preamp for my little stereo condenser mics I plug into my MD recorder for live recordings. As the db levels go up the mics crap out, I would also need some type of bass roll off. The pre-amps themselves retail for about $160, however I'm sure it's not much more complicated than a simple Cmoy type design that send power back to the Mics. Am I being naive to think that there is a DIY solution?

Thanks in advance

J-

 

[drewd]

You can do it with a CMoy type amplifier, but you'll need gain - lots of gain. If you're using Tangent's guide, you'll need to adjust R3 by making it quite a bit smaller than the typical 1K value.

Power for the microphone typically goes from V+ to the microphone's signal pin. You'll need to block that DC from the input of the opamp with a cap - I see a lot of microphone amps with something around 10uF on the input. Connect V+ to the microphone's signal pin through a 1K resistor. It also wouldn't hurt to put a cap on the output of the opamp, just in case. And a 10K pot on the output of the opamp will let you adjust the output level to whatever you're driving with the microphone amp.

Incidentally, as far as I know, most electret condensor microphones run on 5 to 9VDC, so if you're going to use more than a 9V battery, you should beef up the resistor from V+ to the microphone to around 2.2K.

-Drew

 

[JHouser]

Quote:

Originally Posted by drewd You can do it with a CMoy type amplifier, but you'll need gain - lots of gain. If you're using Tangent's guide, you'll need to adjust R3 by making it quite a bit smaller than the typical 1K value. Power for the microphone typically goes from V+ to the microphone's signal pin. You'll need to block that DC from the input of the opamp with a cap - I see a lot of microphone amps with something around 10uF on the input. Connect V+ to the microphone's signal pin through a 1K resistor. It also wouldn't hurt to put a cap on the output of the opamp, just in case. And a 10K pot on the output of the opamp will let you adjust the output level to whatever you're driving with the microphone amp. Incidentally, as far as I know, most electret condensor microphones run on 5 to 9VDC, so if you're going to use more than a 9V battery, you should beef up the resistor from V+ to the microphone to around 2.2K. -Drew

Great, thanks. would it make my life eaisier to build this around a Mint with a single 9v power supply?

j-

 

[rickcr42]

what you are looking for is a "battery box" :

http://www.minidisc.org/homemade_mics.html

http://webpages.charter.net/tidmarsh/binmic/

And yes a bass rolloff is a good idea to prevent overloading the input stage of the mini disc.This cap not only acts as a DC blocking cap so the nine volts from the battery does not shoot straight into your MD but also sets the bass cut frequence F3.

For years i have been using one with all radio shack parts :

metal film resistor pack for the two 10K

small printed circuit project board

1uf X 2 in parallel per channel metal film caps,the big blue ones .

2X4X1 project box-black plastic

1/8 " stereo mini phone jacks X2 (1 input/1 output)

9V battery clip and connector.The clip is bolted down to the board and holds the battery in tight.

I even use the rat shack mics even though many report bad things.I never had a problem.

and if your MD is a sony you better think about adding an inline pot as a volume control for best results.

The preamp is nothing special and is as easy as either an jfet or transistor used as a single stage amplifier.Simple and effective without the hassle of soldering in a multipin IC.But it is rare i need this extra preamp stage.The mics have a jfet amp built in.That is why you need the bias box (battery box) to begin with-to power the amp/impedance matching jfet stage and a microphone puts out voltage according to the sound pressure hitting it.Soft sounds i preamp.Music no.

 

[erix]

What is phantom power?

Today a guy at worked asked me to build him a headphone distribution box for his basement studio and said it'd be cool if it ran off phantom power.

thx,
erix

 

[rickcr42]

well wouldn't it be ?

imagine the POWER !

Actually a very misunderstood area .Many do not even know WHY some mics need an external power source because they do not know there is actually an active device inside the mic element of a condeser mic-the FET

and even when they know they need it they also don't know to swtch "off" the bias when going to a dynamic mic element which pumps the bias right at the mic

 

[petrini_bigsmart]

Quote:

Originally Posted by JHouser /img/forum/go_quote.gif Great, thanks. would it make my life eaisier to build this around a Mint with a single 9v power supply? j-

Hi Houser,
Did you made this mic amp? I woud be interested to know how did your project worked. I'm also looking for a simple, small and handy microphone preamp for my small membran condensator microphones.
I just finished my first diy project ( a CMoy) and would be great to make also a mic preamp on this layout.
Greetings, Petrini.

 

[Fred_fred2004]

Do you realise how old this thread is?

 

[petrini_bigsmart]

Quote:

Originally Posted by Fred_fred2004 /img/forum/go_quote.gif Do you realise how old this thread is?

I have only asked if you made this amp. Whats the point if this thread is 6 years old?