I am a guitarist. I recently wanted to figure out how to power an internal mic for a guitar, so I started digging into it over on the Acoustic Guitar Forum. I eventually made my way over here and continued to developed an internal mic preamp with some help from this forum, very similar to a circuit that @Audioguru again originally developed. The max gain in the circuit below is 11x (100/10 +1), or about 21 dB (see below). I have been using it on two condenser (2 conductor) mics I have: Shure WL50 (1.7kΩ) and the Rodes GO (3kΩ). For these two mics, I don't need much gain, the Shure takes a little, maybe 3-5 dB while the Rodes GO doesn't take ANY gain, volume pot all the way down.

There are 2 other very popular mics that guitarist use for this application (internal mic), a bit more expensive than the ones above: Audix L5 (200Ω) and DPA 4061 (30Ω). The DPA 4061, for example, has an impedance of 100x less than the Rodes GO. Am I right in thinking that because the DPA has 100x less impedance than the Rodes GO that it will take 100x more gain?

 

The DPA 4061 lavalier mic costs $500US (!). It has a normal electret mic frequency response and low noise level.
Its sensitivity is exactly the same as a normal electret mic.
Then it will sound the same as a $2.00US electret mic cartridge.

BUT, its max sound level with low distortion is a blasting 134dB (!) for use inside a drum or maybe inside a loud piano.
The common cheap electret mic cartridges can be easily modified (Linkwitz mic mod in Google) for low distortion at very high sound levels but with less sensitivity, then the preamp needs more gain.

What is "take more gain"? More gain produces a higher output sound level. If playing live then too much gain creates acoustical feedback howling or amplifier clipping. If an electret mic cartridge is mounted inside your acoustic guitar and you strum very hard then it needs the Linkwitz mod and more gain to make-up for the mod's reduced sensitivity.

The DPA4061 replaces the simple Jfet in an ordinary electret mic with a circuit that has a very low output impedance BUT it draws a much higher DC current. The mic preamp circuit must be modified for it.

The Rodes GO mic uses an ordinary cheap little electret mic cartridge with an expensive radio wireless system. It produces the normal distortion at and above 95dB or 100dB sound pressure level.

 

I am a guitarist. I recently wanted to figure out how to power an internal mic for a guitar, so I started digging into it over on the Acoustic Guitar Forum. I eventually made my way over here and continued to developed an internal mic preamp with some help from this forum, very similar to a circuit that @Audioguru again originally developed. The max gain in the circuit below is 11x (100/10 +1), or about 21 dB (see below). I have been using it on two condenser (2 conductor) mics I have: Shure WL50 (1.7kΩ) and the Rodes GO (3kΩ). For these two mics, I don't need much gain, the Shure takes a little, maybe 3-5 dB while the Rodes GO doesn't take ANY gain, volume pot all the way down.

There are 2 other very popular mics that guitarist use for this application (internal mic), a bit more expensive than the ones above: Audix L5 (200Ω) and DPA 4061 (30Ω). The DPA 4061, for example, has an impedance of 100x less than the Rodes GO. Am I right in thinking that because the DPA has 100x less impedance than the Rodes GO that it will take 100x more gain?

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The voltage use relative solely to impedances is dependant on the impedances of source and load.
ie., in your case, you have an input impedance of around 8,33 kOhms, and the DPA has 30 ohms output impedance, so your use factor will be 8333/(8333+30), which is pretty close to 100% (the maximum you can have). With 3 kOhm mic, you'll have 8333/(8333+3000), which is 73,5%. So you'll end up going from 73,5% to close to 100%, which is a gain of 36%, which is around 2,67 dB if I didn't any mistakes.

 

So you'll end up going from 73,5% to close to 100%, which is a gain of 36%, which is around 2,67 dB if I didn't any mistakes.

Do the DPA will be louder than the Rodes GO?

 

Do the DPA will be louder than the Rodes GO?

Provided they won't saturate within a certain range, yes, DPA will be a bit louder.
Edit: If their sensitivity isn't equal, you won't have this gain relation. If a mic is less sensitive, it'll produce less voltage and therefore less voltage drive on the speaker. If you need more gain, you can adjust the resistors near the operational amplifier. This will get you to gains up to thousands of times easily.

 

Loudness of a mic is spec'd by its sensitivity rating. The DPA mic has an impedance of only 30 ohms which must be created with an electronic circuit but it has the same sensitivity as many other higher impedance mics.

The Rodes Go wired electret mic has more sensitivity than most other simple electret mics then it will sound louder. Its specs are 9dB more sensitivity than a DPA 4061 mic that is provided with its more DC current than most other electret mics.

 

The DPA mic has an impedance of only 30 ohms which must be created with an electronic circuit but it has the same sensitivity as many other higher impedance mics.

I think you meant that gain must be created through an electronic circuit.

 

I think you meant that gain must be created through an electronic circuit.

An ordinary simple electret mic has one Jfet that is selected for a current of 0.5mA max. Then its output impedance at its drain wire is about 5k ohms parallel with the 10k resistor that powers it making 3.3k total output impedance. The DPA mic has an output impedance that is only 30 ohms and uses a higher operating current which is probably produced by an electronic circuit.
The DPA mic has the same sensitivity as a simple electret mic.
A mic preamp has plenty of gain which can be adjusted for low gain (mic is used inside a musical instrument) or high gain (mic is used for normal acoustical voice and away from an instrument).

 

I should have specified in the circuit, the 100k VOL is a pot. But all things equal, I should compare their sensitivity, not their impedances, right?

 

A volume control is usually at the input of the power amplifier, not the negative feedback resistor. The negative feedback can be a preset set one time trimpot.

The DPA mic is odd with a very low impedance and a high idle current.

You care about mic sensitivity, not impedance.

 

An ordinary simple electret mic has one Jfet that is selected for a current of 0.5mA max. Then its output impedance at its drain wire is about 5k ohms parallel with the 10k resistor that powers it making 3.3k total output impedance. The DPA mic has an output impedance that is only 30 ohms and uses a higher operating current which is probably produced by an electronic circuit.
The DPA mic has the same sensitivity as a simple electret mic.
A mic preamp has plenty of gain which can be adjusted for low gain (mic is used inside a musical instrument) or high gain (mic is used for normal acoustical voice and away from an instrument).

You just explained the circuit, but you said something different, which was something like "create the impedance with electronic circuit", which I don't see an application here.

You care about mic sensitivity, not impedance.

Because it gives you more gain alone than the impedance alone, right?

 

In a DPA mic, there is probably an electronic circuit that allows it to withstand an extremely high sound level of 134dB which occurs inside a drum or piano. The electronic circuit happens to produce a very low output impedance that only slightly affects its sensitivity. The electronic circuit also has a supply current that is much higher than a simple common electret mic needing the preamp to be modified to power it.

I do not know the max sound levels inside your guitar. I assume that you do not want the extreme distortion produced by electric guitars.

 

Internally micing an acoustic guitar would be very similar to micing a piano. Strings and wood. Guitar goes down to 80hz, pianos go another couple octaves below that.

 

I am a guitarist. I recently wanted to figure out how to power an internal mic for a guitar, so I started digging into it over on the Acoustic Guitar Forum. I eventually made my way over here and continued to developed an internal mic preamp with some help from this forum, very similar to a circuit that @Audioguru again originally developed. The max gain in the circuit below is 11x (100/10 +1), or about 21 dB (see below). I have been using it on two condenser (2 conductor) mics I have: Shure WL50 (1.7kΩ) and the Rodes GO (3kΩ). For these two mics, I don't need much gain, the Shure takes a little, maybe 3-5 dB while the Rodes GO doesn't take ANY gain, volume pot all the way down.

There are 2 other very popular mics that guitarist use for this application (internal mic), a bit more expensive than the ones above: Audix L5 (200Ω) and DPA 4061 (30Ω). The DPA 4061, for example, has an impedance of 100x less than the Rodes GO. Am I right in thinking that because the DPA has 100x less impedance than the Rodes GO that it will take 100x more gain?

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I suggest investigating what is called "Phantom Power" as a well developed commonly used means to power the amplifier in the guitar. That scheme will avoid the internal battery and also provide a more noise resistant connection scheme. Many phantom power amplifier circuits are published, in addition to complete assemblies being available for purchase.

 

Electric guitars would be SO much better if they were balanced line, with a phantom powered buffer amplifier.
None of the hum problems, none of the problems with treble response that changes with lead length etc. They could even have a tone control that actually works, instead of three pots bodged on to the output of the pickup.

 

Electric guitars would be SO much better if they were balanced line, with a phantom powered buffer amplifier.
None of the hum problems, none of the problems with treble response that changes with lead length etc. They could even have a tone control that actually works, instead of three pots bodged on to the output of the pickup.

There are certainly quite a few circuits published that would work. "Schematics for free is the website. It will take a bit of looking, because the site has recently been very much revised.

 

This application is an internal condenser mic, 5-9v is all that is required. Powered externally.

 

The two advantages from phantom power are: first, the output is a low impedance balanced line, which is noise and hum resistant, and usually a much higher voltage level signal., and second, that a battery rundown fault is not possible. These benefits are usually worth the effort.

 

The two advantages from phantom power are: first, the output is a low impedance balanced line, which is noise and hum resistant, and usually a much higher voltage level signal., and second, that a battery rundown fault is not possible. These benefits are usually worth the effort.

yes thanks for the explanation. In the acoustic guitar world, for this application, a TRS cable is common, readily available, but that has to carry 2 signals… so both would be unbalanced.

what you suggest is no doubt better… and more technically correct, but much more difficult/expensive to do.

 

Electric guitars would be SO much better if they were balanced line, with a phantom powered buffer amplifier.
None of the hum problems, none of the problems with treble response that changes with lead length etc. They could even have a tone control that actually works, instead of three pots bodged on to the output of the pickup.

this is interesting. Dual coil pickups are suppose to get rid of the hum… mostly do. But using a TRS cable/jack is very possible. Show me a circuit of what this would look like, maybe I could modify one of my electrics and try it out.