Simple electret/dynamic mic preamp

[Crontox102098]

Just that, need help... I'm looking for the best and simple electret/dynamic preamp. Hope you can help me...

Cheers!

[GibsonGM]

search online - there are many out there, including one I've seen based on ONE transistor!  I don't have time to upload it to Photobucket at the moment - if you can't find anything, I will put it up for you tomorrow. 

[Crontox102098]

search online - there are many out there, including one I've seen based on ONE transistor!  I don't have time to upload it to Photobucket at the moment - if you can't find anything, I will put it up for you tomorrow. 

These preamps got bad results for me, so I want one with your approval.

[PRR]

> the best and simple

Which is it? Best? or Simple?

To do what? Harpsichord? Singing on stage?

How long is the cord from mike to preamp??

To drive what? A guitar input? A long line?

What power is available? D-cell? 9V wall-wart? +/-18V? 250V?

In general, for not-tiny sound levels, short lines in and out, and reasonable modern voltages, it is hard to beat a 5532.

Since you don't know (almost never know) what you are doing level-wise, it needs a gain knob.

[Crontox102098]

> the best and simple

1.Which is it? Best? or Simple?

2.To do what? Harpsichord? Singing on stage?

3.How long is the cord from mike to preamp??

4.To drive what? A guitar input? A long line?

5.What power is available? D-cell? 9V wall-wart? +/-18V? 250V?

In general, for not-tiny sound levels, short lines in and out, and reasonable modern voltages, it is hard to beat a 5532.

Since you don't know (almost never know) what you are doing level-wise, it needs a gain knob.

1. Both if it can be...

2. Home recording, singing on stage and "/experimentation/"

3. 20 ft(6meters) as much.

4. To drive a Behringer Mixer and directly to my sound processor.

5. 9V wall wart (common pedals power supply) and 110V.

I've got a pair of 5532 (hard to found here).

[PRR]

> drive a Behringer Mixer

Don't those have MIC inputs already?

Oh, I see... the Bee-ringer is set up for XLR "Balanced". Most modern Dynamics should plug right in. Electret capsules will need a circuit.

[Crontox102098]

> drive a Behringer Mixer

Don't those have MIC inputs already?

Oh, I see... the Bee-ringer is set up for XLR "Balanced". Most modern Dynamics should plug right in. Electret capsules will need a circuit.

That's why i need one... And when i need to go to gig I'm too lazy to disconnect all cables from the mixer and pack it. I've been recording my own demos and sometimes I have no place for another microphone in that little mixer.

Cheap electret mics have a special sound for me 

[anotherjim]

Does the Mixer have Phantom Power that you want the electrets to work off?

With the electret capsules, find out if they are directional or not. Directional ones are better for stage and those will have one or more holes in the back of the capsule. Having said they are better, some are only built for telephone grade speech so don't expect a pre-amp to improve that. The very best of these get to 18Khz which is more than good enough for live work. 12Khz top is typical for most of them.

If there are no holes in the back of the capsule, they are omni-directional. These will have the better frequency response (some are usable up to 30Khz) but pick up everything. On stage, they get used for drum kit overheads, but not much else.

For battery power, the type of preamp that use one transistor but increases the battery to 9volt (standard for electret is only 1.5Volt)  would do well enough. The dynamic range of a typical electret is limited by the internal JFET amplifier. This can be improved by converting it (a simple mod in most cases) to a unity gain buffer and following that with an amplifer in the mic body.

[bool]

Try building a compound pair type preamp.

They usually have a good "sound signature".

for example:
http://circuitdiagram.net/portable-mic-pre-amp-circuit.html

for more design ideas:
http://www.sound.westhost.com/project13.htm
http://sound.westhost.com/project134.htm
http://sound.westhost.com/project93.htm

[GibsonGM]

+1 Bool and PRR.   

If you want simple for home use, then Bool's or the one I'm thinking of will be fine...but for onstage, "real" work, you probably need to invest some time in the amp you build, and also the quality of the capsule you get.     Or not, if you like grungy  

Try the one in Bool's link, that is probably the only way you will know what level to take this to.

[Crontox102098]

Basing in all that information you gave me, I ventured to develop my own preamp... It will explode in my face?


SW1: Electret/Dynamic selector
SW2: 2dB/23dB selector

C2: 200khz cutoff frequency
R7: Little noise filter

[bool]

You have an error in the schem. This won't amplify, it's only a buffer now.

R5 should be connected to the "-" opamp input (pin 2) not the way you have done it in your drawing.

[PRR]

> R5 should be...

What he said.

Secondary point: now it works OK if power supply is dead-clean. If there is any crap on it, 95% of that crap comes right down the capsule bias and becomes "signal" to the amplifier. (In dynamic mode, 50% of PS crap comes in). The opamp has high power-crap rejection but these input networks do not. Since you have two lower-current things to feed, I would R-C filter a "clean power" node just for them. 1K and 100uFd is a starting point. I might also put 100 Ohms between +9V and C5. This gives C5 something to work-against if it tries to clean a crappy but stiff supply; it also is a "fuse" for reverse-voltage protection. (The 1N4007 will fight any battery, but won't win the war against a 2-Amp supply backward.)

[Seljer]

> drive a Behringer Mixer

Don't those have MIC inputs already?

Oh, I see... the Bee-ringer is set up for XLR "Balanced". Most modern Dynamics should plug right in. Electret capsules will need a circuit.

That's why i need one... And when i need to go to gig I'm too lazy to disconnect all cables from the mixer and pack it. I've been recording my own demos and sometimes I have no place for another microphone in that little mixer.

Cheap electret mics have a special sound for me 

I've used the balanced phantom powering circuit for electret capsules presented here http://www.epanorama.net/circuits/microphone_powering.html#phantom without any trouble on 60 foot cable runs

[bool]

A stripped-down Schoeps circuit should be fine for direct-to-XLR input.

another take on it

http://www.moosapotamus.net/mics.html

[GibsonGM]

The one I was talking about earlier is much like the one Bool just posted.  It only needed one transistor since it was a little more simple, but same diff.   Way simple solution.

[anotherjim]

I came up with an even easier balanced electret phantom power.

J201 JFET wired as a constant current diode. Gate tied to Source.
Hot > Capsule +ve
Cold > Capsule -ve
Capsule -ve > J201 Drain
J201 Gate & Source > Ground
Capsule case MUST not be grounded - screen should by an external metal mesh (cheap - tea strainers)
Also worked with 2N5457, but that's pushing it's voltage limits a bit too much. Tested with Panasonic capsules.

A Figure 8 mic can be done with 2 capsules mounted back to back. One connected to Hot and one to Cold. Both capsule -ve to the J201 Drain.
Sound from the sides is rejected.

But it doesn't look like Crontox has phantom power available?

[Quackzed]

I've used the balanced phantom powering circuit for electret capsules presented here http://www.epanorama.net/circuits/microphone_powering.html#phantom without any trouble on 60 foot cable runs

ive built a bunch of the battery powered mic ones, just a 2.2k and 10uf, used with just ratshack electret mic elements... love 'em for acoustic guitars and ambient recordings....  super cheap, super easy, super detailed and sensitivity...
i think they're super!!!
they put out a pretty big signal and can overload a line level input with loud sounds, so maybee a voltage divider after might be a good idea...
i think they're super!!!

[Crontox102098]

I came up with an even easier balanced electret phantom power.

J201 JFET wired as a constant current diode. Gate tied to Source.
Hot > Capsule +ve
Cold > Capsule -ve
Capsule -ve > J201 Drain
J201 Gate & Source > Ground
Capsule case MUST not be grounded - screen should by an external metal mesh (cheap - tea strainers)
Also worked with 2N5457, but that's pushing it's voltage limits a bit too much. Tested with Panasonic capsules.

A Figure 8 mic can be done with 2 capsules mounted back to back. One connected to Hot and one to Cold. Both capsule -ve to the J201 Drain.
Sound from the sides is rejected.

But it doesn't look like Crontox has phantom power available?

Thanks for all your answers peeps! After a LOT (really, a lot) of investigation, this circuit was the best worked out, it is deadly quiet and it's perfect to record voices and sounds great with clasical acoustic guitars, don't know if with measurement will work like in other cases, but works really good.

http://www.epanorama.net/circuits/ElectretMicBalanced.pdf

[anotherjim]

They don't let you ground the capsule either?
Crontox - those are Phantom powered circuits - I though you wanted to use line inputs of the mixer?

Something else to be careful of is relative polarity of your DIY mic's. I think the standard is with a positive going pressure wave on the element, the hot output wire should go positive, although the practical thing is to ensure mic's in close proximity to each other should have the same polarity. If they are opposite polarity you can seriously weaken the overall sound from the mixer due to phase cancellation

Watch out for electret circuits that require the so called " Linkwitz" mod - where the polarity is reversed by changing which output pin is connected to the can. This is done to preserve polarity of the can when using the built in JFET as a source follower.
Otherwise, where the can can't be grounded anyway, you can just reverse the connections since the electret and the JFET inside are electrically symmetrical.