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What's the minimum mW necessary for an electret mic preamp?

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School

New Member
I'm wanting to use a Panasonic electret capsule for an acoustic guitar mic.

And i've read about some really small tubes that can be used off of battery power. So I thought I might try and see how these things would sound with an electret capsule.

I found some random references to a 6088 tube, a 5672 pentode tube, and I think that the DL69/CV2361 is also one of the miniature tubes.

So i'm wondering what the minimum output is for a typical electret preamp.

And better yet, I would be extremely interested if someone already knew of a design like this.
 

mneary

New Member
What are you driving? All capsules have driven every amp I've used with no amplification (aside from that inside the capsule).

Find a lot of tube specs at Frank's electron Tube Data sheets

I remember when a 'portable' radio had 1 lb. of batteries, which barely lasted a week.
 

audioguru

Well-Known Member
Most Helpful Member
Why use a distorting old vacuum tube? Instead use an opamp. Then the sound will be exactly the same as without the amplifier but louder.

The output of an electret mic is 10mV into a load of 50k ohms or higher when somebody is talking at a normal loudness about 20cm away. The loudness from an acoustic guitar varies depending on how hard it is played but could be much higher.
Simply make the preamp with enough gain for playing softly and use a volume control to reduce it when playing hard.

Electret mics are usually omni-directional and are blamed for causing acoustical feedback howling.
 

School

New Member
Terrible things - I refuse to do the PA for my daughters band if they are using acoustic instruments with electret mikes! :p

The alternatives aren't so hot either. Piezo mics under the bridge, on sticky pads, etc., sound wrong to my ears. They remind me of that Ovation guitar sound.
It's really not bad at all, but it's not right either.

So to fill in some more details, the guitar already has a piezo saddle now. And what I would like to do is put one or a few Panasonic capsules near the soundhole, maybe on the soundboard by the back end of the neck, maybe even inside the soundhole, who knows.
Then what I would do, is cut the highs from the piezo saddle, and cut the lows from the electret capsule(s).

That's it in a nutshell, and any different approach that anyone wants to pipe in on will get my attention.

TIA




.
 
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School

New Member
Why use a distorting old vacuum tube? Instead use an opamp. Then the sound will be exactly the same as without the amplifier but louder.

The output of an electret mic is 10mV into a load of 50k ohms or higher when somebody is talking at a normal loudness about 20cm away. The loudness from an acoustic guitar varies depending on how hard it is played but could be much higher.
Simply make the preamp with enough gain for playing softly and use a volume control to reduce it when playing hard.

Electret mics are usually omni-directional and are blamed for causing acoustical feedback howling.

Well i'm not wanting to boost the signal all that hot.
Just enough to get a bit of a tube effect.
But besides that, i'm not really dead set on using the tubes, either.
I just ran across some info on them and thought it might be cool to use one.
 

Bob Scott

New Member
Well, as an alternative you might consider using a regular mic on a mic stand.

Electret mics don't need tube amplifiers. Just plug them into a regular mixer input that has phantom power.

Bob
 

School

New Member
Well, as an alternative you might consider using a regular mic on a mic stand.

Electret mics don't need tube amplifiers. Just plug them into a regular mixer input that has phantom power.

Bob

That wouldn't be so bad, but I'm most likely going to use more than one of them. So I need to do that before it all gets mixed together.

And i'm hoping to introduce some low filter on them, as well as high filter on the piezo saddle.
 

School

New Member
I found something interesting when I was digging around on this.
Apparently Takimine has an acoustic guitar where they did something similar to what i'm thinking about.

EDIT*
Nevermind. Apparently that preamp eats up four AA batteries per day.
 
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mneary

New Member
EDIT*
Nevermind. Apparently that preamp eats up four AA batteries per day.
Sounds about right. The smallest tube I saw in my brief search used 60mW for the heater alone.
 
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