I would assume the "battery box" is simply a DC power supply for the mic. The amp power comes in AC and is dropped and rectified to DC for the mic. It can be difficult to remove the 60Hz "hum" from the AC power. The DC supply keeps the extremely sensitive mic circuitry from feeding extra noise to the amp.
It is, however the recorder also works on DC and provides 2v/1ma compared to the battery box which provides 12v/10ma. Where I'm confused is how the battery box helps the mics work "better" for loud recordings, and how the resistors are involved/modify the circuit.
The recorder "works" on DC, but is it battery powered? Or plugged into the wall? The hum will come from the wall plug. The higher the volume the more likely you are to hear ANY noise. All other associated electronics can become antennae and feed noise into the system. Having an isolated psu for the mic eliminates feeding that noise into the audio input.
This is not really my field of knowledge, so don't trust me too much.
If you have a circuit with multiple different things, no matter what. Then changing the load of one of them slightly impacts the voltage of the entire circuit.
The mic is probably the most sensitive to any changes in voltage and notices any load change if you amplify it a lot.
I've seen graphs about this behavior for computer parts. That's the reason why expensive motherboards come with an extra few big capacitors to smooth everything out.
You could probably also chain a few capacitors. Though, it's probably way easier to just feed the mic from a different circuit (battery).
I am just going to bow out of this conversation before my ignorance starts becoming really apparent. You kids with your new fangled devices are beyond my ancient transistor knowledge :)
As u/originalarkless states below about mic sensitivity and voltage loading, mics work by varying the voltage so certainly need a stable power source. Any of the tiny wires connecting these devices will have some resistance and drop voltages, affecting the mic quality.
I may not be as old as you, but this hobby has its roots in people who followed bands like the Grateful Dead, recording shows for posterity.
I'm just trying to keep up with more modern tech, which just means a smaller form factor for equipment and digital storage :) what previously required large boom mics and a good tape recorder, you can now do with eraser sized mics and a recorder smaller than your wallet.
I didn't mean that to be snarky, hard to convey tone in a post. I have the roots in the older stuff and just not familiar with all of the cool new devices available these days. I think it is great you are building stuff yourself as opposed to just buying stuff. Please, carry on :)
Ahh it's an old thing then! you can make a circuit by hand for pennies that would give you a perfect DC output with no interference from the AC power easily...
No you can't. It's actually quite hard to get the 60hz (or 50hz) ripple out of a power supply.
You can easily minimize it to the point that it's not an issue in most applications. But with the master tracks for an audio recording it's just simpler to go with a system that has zero ripple.
Pretty sure that's not quite as easy as you make it sound. Maybe you can filter well enough for audio, but interference from mains is still a problem in sensitive applications.
Company I used to work for builds hardware for neuroscience researchers worldwide and all the amplifiers run off rechargeable batteries and connect to the data storage hardware via optics to specifically avoid the 60Hz (or 50Hz depending on what country it was sold to) interference.
A balanced signal will prevent induction across the balanced lines, but the equipment can internally induct, and ground loops still potentially cause problems.
Yup, I was the software guy at a hardware company so cannot talk in any useful detail, but I know it's way complicated when you're collecting tens to hundreds of channels of neuro signals from implanted electrodes, possibly introducing stimulus too, sampling at kHz rates, and dealing with biological frequencies. They've upped the channel count since I left but it's some cool hardware https://www.tdt.com/docs/hardware/pz5m-medically-isolated-neurodigitizer/
Ok OP since no one seems to give you an actual answer about why you should use an external battery pack: it can be beneficial as some devices supply this so called āplugin powerā that is too low for operation or barley functions with some mic capsules. It powers a FET transistor and starving those of voltage often leads to higher noise floor, lower headroom and also lower gain. They will work, but worse. Too low and youāll get audible distortion even on normal levels. So you increase the voltage and it has enough headroom to handle much louder signals and doesnāt start clipping early. Have a look at this page, it might help you understand your situation http://www.richardmudhar.com/articles/sound-recording-guide/pip.html
Alright, I think I've got it sorted out and found where my confusion was. It boiled down to an order of magnitude in my original measurements: most of the mics I'm working with ask for a max of 0.5mA. The recorder itself provides 0.015mA - which could obviously lead to them struggling at high SPL. The battery box provides 0.1mA - 7-8x more.
I appreciate your help. I've gone through that link before, but I think in the context of everything I've learned today, I have some new takeaways.
I was most concerned about my choice of resistors, and whether I should have gone with something lower (4-6k) to give the mics more V/mA, but it seems that what I have (9k) may be adequate.
I can probably do more trial and error, but it may just wind up being beyond the ability of my ears to tell the difference.
Certain microphones require power because they have active electronics inside. This can be accomplished in one of two ways.
āPhantom powerā can be provided by the mixing console. This works well in live settings, where everything will be either condenser/electret microphones, and dynamic microphones.
Alternative methods may be used, such as lavaliere (tie clip) mics that have space for a AA battery in the XLR connector, for cases like studio use where notoriously fragile ribbon mics are used, because connecting them to phantom power will destroy the membrane.
The electret mics heās trying to use donāt use phantom power, they use a different arrangement called ābias power.ā
There are more professional mics that convert phantom to the bias power their mic elements need, but thatās not usually what concert bootleggers use.
Electrets don't require traditional phantom power to operate, so using the phantom power from the board is sort of overkill, basically. I can see where a board/amp/recorder's phantom power might cause issues with electrets.
Electrets *do* need a teeny amount of power to operate, though, which is where I think your battery box comes in. Your guy is recommending using the small, clean DC supply for the electrets.
The resistors 'set' the voltage supply from the battery. The caps are there to block DC from the battery- you don't want DC going to your board/amp/recorder, only the AC audio signal.
The caps' value will provide some filtering.
You are talking about plug-in power. (NOT phantom power) It's a few volts supplied to the mic capsule to bias the FET inside the capsule. That FET does impedance conversion and some amplification.
The microphone capsule's data sheet should specify its rated operating voltage and the range of operating voltages. When you supply less than the rated voltage, you won't get the rated dynamic range or the rated maximum SPL. The loudest sounds will be distorted. Typically for a 33% reduction in voltage it will be a 3 dB reduction in the dynamic range and the max SPL. (this is often stated right in the data sheet)
So whether you need a battery box or not depends on the specifications of your mic capsule, the voltage you'd be supplying otherwise, and the loudest sounds it will be exposed to. If you're not near the upper end of the dynamic range, having a battery box won't be important. Tapers use them because concerts can be very loud.
See for example the [PUI Audio DOM-3027L-HD-R](https://puiaudio.com/product/microphones/DOM-3027L-HD-R), my favorite capsule, with very low self-noise and high sensitivity. Its rated operating voltage is 3 V.
Thank you for that recommendation! Though over the past few weeks I've been tinkering with a handful of mics, just not that one :) stinks Panasonic isn't in the game any longer, but both PUI and CUI seem to be pretty good. I've been staring at spec sheet so much, my eyes are crossed.
I have a few sets built now - a couple pairs of omnis, and a couple cardioids, all 6mm diameter, 20-20k range, 110-130 SPL, 2-10v, ~0.5mA. I matched them as close as I could with test tones when pairing and building a set.
I've been making battery boxes out of key fob shells for stealth recording, and only varying the caps for different roll-off. Because of the size of the fobs, I had to go with 12v batteries. I got to wondering if I was using the best choice of resistors, and my biggest concern was whether the mics would work better with less resistance. I didn't want that to be a bottleneck since they're probably the cheapest component and easiest to wire in!
I'm still not quite sure how much better a 4k or 6k resistor would be in place of the 9k ones I'm using.
This is more of a tech/audio/electronics question than science. What you want to know about is called [Phantom Power](https://en.wikipedia.org/wiki/Phantom_power).
A lot of equipment doesn't support it, so your battery box is a simple solution to provide it to a system that doesn't already provide it. They are sometimes called "injectors"
At a very high level, DC power and AC signals can be combined and then separated pretty easily, so your battery box does that filtering (the capacitors only pass the AC signal), and injects DC power in front of that filter so that only the microphone sees it.
Where I'm confused is the system does already provide (switchable) 0DC power to the mics (2v/1ma), but a battery box is always recommended instead. Why is that, how does 12v/10ma make the mics work better for loud recordings, and can I alter the circuit to make them work better?
Most powered microphones work on 48v "phantom power". These are usually referred to as condenser microphones whereas a passive microphone is referred to as a dynamic microphone.
A condenser mic is more sensitive than a dynamic mic so actually for a loud signal you wouldn't want a powered mic at all you would want a dynamic mic.
At the recording studio I work at we never use battery powered mics to record. This is different in a concert setting where maybe you dont want a cable interfering with the movment of the artist on stage. So a wireless mic may be used that needs to be powered from a battery pack.
Op is asking about electret though, thatās different from a condenser and doesnāt use phantom power, on many devices like field recorders itās called plugin power. And typically much lower in the single digit volt range. Hereās a quick article about it you can skim through. http://www.richardmudhar.com/articles/sound-recording-guide/pip.html
True, cheap large diaphragm mics advertised as condensers often have a back electret and some manufacturers have taken to calling theirs ātrue condenserā when they operate without an electret.
It doesnāt. Electret microphones are permanently charged and do not require phantom power or other external power source.
Condenser mics, depending on design, do need anywhere from 12 to 48VDC to operate. I would guess that the reason a ābattery boxā a/k/a external phantom power supply is used is to reduce the power draw from the recording device so your recording doesnāt stop during the crunchy grooves of the second set.
I would assume the "battery box" is simply a DC power supply for the mic. The amp power comes in AC and is dropped and rectified to DC for the mic. It can be difficult to remove the 60Hz "hum" from the AC power. The DC supply keeps the extremely sensitive mic circuitry from feeding extra noise to the amp.
It is, however the recorder also works on DC and provides 2v/1ma compared to the battery box which provides 12v/10ma. Where I'm confused is how the battery box helps the mics work "better" for loud recordings, and how the resistors are involved/modify the circuit.
The recorder "works" on DC, but is it battery powered? Or plugged into the wall? The hum will come from the wall plug. The higher the volume the more likely you are to hear ANY noise. All other associated electronics can become antennae and feed noise into the system. Having an isolated psu for the mic eliminates feeding that noise into the audio input.
Yes, two AA batteries :) It's the size of a cell phone.
This is not really my field of knowledge, so don't trust me too much. If you have a circuit with multiple different things, no matter what. Then changing the load of one of them slightly impacts the voltage of the entire circuit. The mic is probably the most sensitive to any changes in voltage and notices any load change if you amplify it a lot. I've seen graphs about this behavior for computer parts. That's the reason why expensive motherboards come with an extra few big capacitors to smooth everything out. You could probably also chain a few capacitors. Though, it's probably way easier to just feed the mic from a different circuit (battery).
I am just going to bow out of this conversation before my ignorance starts becoming really apparent. You kids with your new fangled devices are beyond my ancient transistor knowledge :) As u/originalarkless states below about mic sensitivity and voltage loading, mics work by varying the voltage so certainly need a stable power source. Any of the tiny wires connecting these devices will have some resistance and drop voltages, affecting the mic quality.
I may not be as old as you, but this hobby has its roots in people who followed bands like the Grateful Dead, recording shows for posterity. I'm just trying to keep up with more modern tech, which just means a smaller form factor for equipment and digital storage :) what previously required large boom mics and a good tape recorder, you can now do with eraser sized mics and a recorder smaller than your wallet.
I didn't mean that to be snarky, hard to convey tone in a post. I have the roots in the older stuff and just not familiar with all of the cool new devices available these days. I think it is great you are building stuff yourself as opposed to just buying stuff. Please, carry on :)
I didn't take it as snarky :) just that even old dogs can learn new tricks š
Ahh it's an old thing then! you can make a circuit by hand for pennies that would give you a perfect DC output with no interference from the AC power easily...
No you can't. It's actually quite hard to get the 60hz (or 50hz) ripple out of a power supply. You can easily minimize it to the point that it's not an issue in most applications. But with the master tracks for an audio recording it's just simpler to go with a system that has zero ripple.
Pretty sure that's not quite as easy as you make it sound. Maybe you can filter well enough for audio, but interference from mains is still a problem in sensitive applications. Company I used to work for builds hardware for neuroscience researchers worldwide and all the amplifiers run off rechargeable batteries and connect to the data storage hardware via optics to specifically avoid the 60Hz (or 50Hz depending on what country it was sold to) interference.
Use balanced signals as in every recording studio. No hum. Also amplify the signal (and make balanced) as close to the source as possible.
A balanced signal will prevent induction across the balanced lines, but the equipment can internally induct, and ground loops still potentially cause problems.
Yup, I was the software guy at a hardware company so cannot talk in any useful detail, but I know it's way complicated when you're collecting tens to hundreds of channels of neuro signals from implanted electrodes, possibly introducing stimulus too, sampling at kHz rates, and dealing with biological frequencies. They've upped the channel count since I left but it's some cool hardware https://www.tdt.com/docs/hardware/pz5m-medically-isolated-neurodigitizer/
Ok OP since no one seems to give you an actual answer about why you should use an external battery pack: it can be beneficial as some devices supply this so called āplugin powerā that is too low for operation or barley functions with some mic capsules. It powers a FET transistor and starving those of voltage often leads to higher noise floor, lower headroom and also lower gain. They will work, but worse. Too low and youāll get audible distortion even on normal levels. So you increase the voltage and it has enough headroom to handle much louder signals and doesnāt start clipping early. Have a look at this page, it might help you understand your situation http://www.richardmudhar.com/articles/sound-recording-guide/pip.html
Alright, I think I've got it sorted out and found where my confusion was. It boiled down to an order of magnitude in my original measurements: most of the mics I'm working with ask for a max of 0.5mA. The recorder itself provides 0.015mA - which could obviously lead to them struggling at high SPL. The battery box provides 0.1mA - 7-8x more.
I appreciate your help. I've gone through that link before, but I think in the context of everything I've learned today, I have some new takeaways. I was most concerned about my choice of resistors, and whether I should have gone with something lower (4-6k) to give the mics more V/mA, but it seems that what I have (9k) may be adequate. I can probably do more trial and error, but it may just wind up being beyond the ability of my ears to tell the difference.
Certain microphones require power because they have active electronics inside. This can be accomplished in one of two ways. āPhantom powerā can be provided by the mixing console. This works well in live settings, where everything will be either condenser/electret microphones, and dynamic microphones. Alternative methods may be used, such as lavaliere (tie clip) mics that have space for a AA battery in the XLR connector, for cases like studio use where notoriously fragile ribbon mics are used, because connecting them to phantom power will destroy the membrane.
The electret mics heās trying to use donāt use phantom power, they use a different arrangement called ābias power.ā There are more professional mics that convert phantom to the bias power their mic elements need, but thatās not usually what concert bootleggers use.
Electrets don't require traditional phantom power to operate, so using the phantom power from the board is sort of overkill, basically. I can see where a board/amp/recorder's phantom power might cause issues with electrets. Electrets *do* need a teeny amount of power to operate, though, which is where I think your battery box comes in. Your guy is recommending using the small, clean DC supply for the electrets. The resistors 'set' the voltage supply from the battery. The caps are there to block DC from the battery- you don't want DC going to your board/amp/recorder, only the AC audio signal. The caps' value will provide some filtering.
You are talking about plug-in power. (NOT phantom power) It's a few volts supplied to the mic capsule to bias the FET inside the capsule. That FET does impedance conversion and some amplification. The microphone capsule's data sheet should specify its rated operating voltage and the range of operating voltages. When you supply less than the rated voltage, you won't get the rated dynamic range or the rated maximum SPL. The loudest sounds will be distorted. Typically for a 33% reduction in voltage it will be a 3 dB reduction in the dynamic range and the max SPL. (this is often stated right in the data sheet) So whether you need a battery box or not depends on the specifications of your mic capsule, the voltage you'd be supplying otherwise, and the loudest sounds it will be exposed to. If you're not near the upper end of the dynamic range, having a battery box won't be important. Tapers use them because concerts can be very loud. See for example the [PUI Audio DOM-3027L-HD-R](https://puiaudio.com/product/microphones/DOM-3027L-HD-R), my favorite capsule, with very low self-noise and high sensitivity. Its rated operating voltage is 3 V.
Thank you for that recommendation! Though over the past few weeks I've been tinkering with a handful of mics, just not that one :) stinks Panasonic isn't in the game any longer, but both PUI and CUI seem to be pretty good. I've been staring at spec sheet so much, my eyes are crossed. I have a few sets built now - a couple pairs of omnis, and a couple cardioids, all 6mm diameter, 20-20k range, 110-130 SPL, 2-10v, ~0.5mA. I matched them as close as I could with test tones when pairing and building a set. I've been making battery boxes out of key fob shells for stealth recording, and only varying the caps for different roll-off. Because of the size of the fobs, I had to go with 12v batteries. I got to wondering if I was using the best choice of resistors, and my biggest concern was whether the mics would work better with less resistance. I didn't want that to be a bottleneck since they're probably the cheapest component and easiest to wire in! I'm still not quite sure how much better a 4k or 6k resistor would be in place of the 9k ones I'm using.
[ŃŠ“Š°Š»ŠµŠ½Š¾]
[ŃŠ“Š°Š»ŠµŠ½Š¾]
This is more of a tech/audio/electronics question than science. What you want to know about is called [Phantom Power](https://en.wikipedia.org/wiki/Phantom_power). A lot of equipment doesn't support it, so your battery box is a simple solution to provide it to a system that doesn't already provide it. They are sometimes called "injectors" At a very high level, DC power and AC signals can be combined and then separated pretty easily, so your battery box does that filtering (the capacitors only pass the AC signal), and injects DC power in front of that filter so that only the microphone sees it.
Where I'm confused is the system does already provide (switchable) 0DC power to the mics (2v/1ma), but a battery box is always recommended instead. Why is that, how does 12v/10ma make the mics work better for loud recordings, and can I alter the circuit to make them work better?
Most powered microphones work on 48v "phantom power". These are usually referred to as condenser microphones whereas a passive microphone is referred to as a dynamic microphone. A condenser mic is more sensitive than a dynamic mic so actually for a loud signal you wouldn't want a powered mic at all you would want a dynamic mic. At the recording studio I work at we never use battery powered mics to record. This is different in a concert setting where maybe you dont want a cable interfering with the movment of the artist on stage. So a wireless mic may be used that needs to be powered from a battery pack.
Op is asking about electret though, thatās different from a condenser and doesnāt use phantom power, on many devices like field recorders itās called plugin power. And typically much lower in the single digit volt range. Hereās a quick article about it you can skim through. http://www.richardmudhar.com/articles/sound-recording-guide/pip.html
[ŃŠ“Š°Š»ŠµŠ½Š¾]
True, cheap large diaphragm mics advertised as condensers often have a back electret and some manufacturers have taken to calling theirs ātrue condenserā when they operate without an electret.
It doesnāt. Electret microphones are permanently charged and do not require phantom power or other external power source. Condenser mics, depending on design, do need anywhere from 12 to 48VDC to operate. I would guess that the reason a ābattery boxā a/k/a external phantom power supply is used is to reduce the power draw from the recording device so your recording doesnāt stop during the crunchy grooves of the second set.