Hello,

Any help here would be greatly appreciated. Very new to this.

I have a scenario where I have a large bank of speakers that I will be testing, and I want to be able to have an LED light up to show which speaker is on. I would have 1 LED for each speaker, and each speaker would be powered by it's own channel on an amplifier. There will be a variety of amplifiers (ranging from 100w to 400w).

It is my understanding that I will need to add a resistor with the LED.

Can anyone assist me in figuring out what parts I will need (outside of the speaker, speaker wire, and amplifier), and how to wire this to each speaker?

I currently have:
* Edgelec 10mm diffused LED 9v-12v
* Edgelec Film Fixed Resistor .25W 1.3K ohm Tolerance +l 1%

I have tried to connect this in the following manners already with the Resistor wired into the positive of the LED:
* Inline with the + speaker wire leading into the positive terminal of the speaker

* Tapped into the + and - of the speaker (I have also tried this without the resistor).

When I tried it with the resistor across the + and - of the speaker I thought I saw it flicker.

Again, if anyone could help it would be great! Also happy to provide any other information that I may be missing.

 

Welcome to AAC!
If your LED has a 9-12V rating then it already includes a series current-limiting resistor. However, the voltage across a 100W (or more) powered loudspeaker will almost certainly be much higher at times, so the LED would need extra protection.
What is the supply voltage of the output stages of these amplifiers?
Are they bridged amplifiers?
Can you post links to the amp specs?

 

Welcome to AAC.

If you are testing the speakers for fidelity adding the load of an LED to the circuit probably isn’t the best idea.

In parallel, across the terminals, the LED will change the characteristic impedance of the speaker causing the amplifier‘s performance to degrade. In series, in line with the speaker, the LED—being a diode—will change the AC signal the speaker needs to a pulsating DC signal completely destroying the audio. These both assume the LED could sustain the voltages needed to drive the speaker without failing.

You need a method of isolating the operation of the LED from the operation of the speaker. This means creating a high impedance connection to the speaker‘s drive signal so the LED is effectively invisible to the amplifier. To do this, you can’t rely on the power used to drive the speaker as the source to light the LED—only to switch it on.

So, you will need a separate power supply for the LEDs, and a way to ”monitor” the signal sent to the speaker. There are a number of strategies you can use to ”tap into” the speaker signal. Basically, you need to use a connection whose impedance (AC resistance (very roughly)) is so high the amplifier “doesn’t notice” that it is there.

Then you need a circuit that can be turned on when the tiny signal is present, and off when it isn’t. While this is much more complicated than just connecting an LED to the speaker terminals somehow, it also has advantages:

• You are guaranteed to avoid affecting the speaker’s performance because of the LED
• You can choose just how brightly, and for how long the LED lights when a signal is detected
• You won’t find LEDs suddenly dead if you turn up the volume to high
• You can use more than one LED if it helps the display’s visibility

The actual circuit can probably be very simple with only a few components. If you want to pursue this approach there are a number of people here who greatly enjoy working up circuits like this one and I am sure you will get some options.

Good luck with the project.

 

Thanks for responding! Here are the specs for the amp that would most commonly be connected to these speakers, but amps with different specs could also be connected.

These amps have the ability to be be bridged, but for our applications they will never be bridged.

As for the 2nd screenshot (Wisdom amps) there is a very small possibility that these amp could be bridged, but for that scenario we would not be using this test space to confirm that.

Hopefully this helps, and as I said earlier, if I can supply any other information, I will gladly do so!

 

Welcome to AAC.

If you are testing the speakers for fidelity adding the load of an LED to the circuit probably isn’t the best idea.

In parallel, across the terminals, the LED will change the characteristic impedance of the speaker causing the amplifier‘s performance to degrade. In series, in line with the speaker, the LED—being a diode—will change the AC signal the speaker needs to a pulsating DC signal completely destroying the audio. These both assume the LED could sustain the voltages needed to drive the speaker without failing.

You need a method of isolating the operation of the LED from the operation of the speaker. This means creating a high impedance connection to the speaker‘s drive signal so the LED is effectively invisible to the amplifier. To do this, you can’t rely on the power used to drive the speaker as the source to light the LED—only to switch it on.

So, you will need a separate power supply for the LEDs, and a way to ”monitor” the signal sent to the speaker. There are a number of strategies you can use to ”tap into” the speaker signal. Basically, you need to use a connection whose impedance (AC resistance (very roughly)) is so high the amplifier “doesn’t notice” that it is there.

Then you need a circuit that can be turned on when the tiny signal is present, and off when it isn’t. While this is much more complicated than just connecting an LED to the speaker terminals somehow, it also has advantages:

• You are guaranteed to avoid affecting the speaker’s performance because of the LED
• You can choose just how brightly, and for how long the LED lights when a signal is detected
• You won’t find LEDs suddenly dead if you turn up the volume to high
• You can use more than one LED if it helps the display’s visibility

The actual circuit can probably be very simple with only a few components. If you want to pursue this approach there are a number of people here who greatly enjoy working up circuits like this one and I am sure you will get some options.

Good luck with the project.

Thanks for this information!!

I realized I somewhat misspoke in my original message.

These will be test speakers for multiple amps.

To give a little backstory, I am building out an equipment rack fabrication at a large residential AV company. We build and test equipment racks that will be sent out to the field, installed and will power equipment in very large residences that will have multiple audio zones. To simulate this in our facility, I will be setting up 2 "testing areas" with 16 zones of audio possible (32 speakers in each). So the speakers will be a constant, but the amplification will change. These will not be cranked all the way up to the max capacity of these amplifiers, but if possible and "easy" I would like to protect the LED's in the scenario that the amps ever are.

I am also not concerned with slight degradation in audio quality as we are not demoing the speakers to try to sell those. But I cannot have them degraded to the point of blatant degradation so that my techs are troubleshooting amps for an issue...lol.

 

Thanks for this information!!

I realized I somewhat misspoke in my original message.

These will be test speakers for multiple amps.

To give a little backstory, I am building out an equipment rack fabrication at a large residential AV company. We build and test equipment racks that will be sent out to the field, installed and will power equipment in very large residences that will have multiple audio zones. To simulate this in our facility, I will be setting up 2 "testing areas" with 16 zones of audio possible (32 speakers in each). So the speakers will be a constant, but the amplification will change. These will not be cranked all the way up to the max capacity of these amplifiers, but if possible and "easy" I would like to protect the LED's in the scenario that the amps ever are.

I am also not concerned with slight degradation in audio quality as we are not demoing the speakers to try to sell those. But I cannot have them degraded to the point of blatant degradation so that my techs are troubleshooting amps for an issue...lol.

Here are the specs to the speakers that we will be using in the "lab" and will be a constant.

 

Since this is for testing builds, I think it is worthwhile to spend a little extra—time and money—to create a reliable, universal solution. A small PCB can be designed easily and purchased very cheaply from any of several well known PCB fabs (we are talking <$1/pc).

This will allow you to have each speaker location to simple be a place you can hang a speaker and the LED indicator will be automatically included. One of the biggest advantages in your case will be the ability to make the LED light as brightly as needed to ensure the techs have no problem seeing which speaker is live, even from a distance and no matter the level of ambient light.

The circuit could be as simple as a single transistor and a few passives. The PCB design would be trivial and you could easily use the PCB fab’s online tools to lay it out. You can even have them do the assembly if you choose the right one. IN the end, you will have something people will thank you for, even if you are long gone*—rather than curse your name once you are no longer around to “fix” the LEDs when they don’t work for some reason.

In any case, aside from the various advantages above, one problem you will have if you take the passive approach is choosing just how hot you would have to make the speaker to get a visible indication. The brightness of the LED will completely depending on the position of the gain control on the amp, and it could be a very narrow range that ”works”.

*From your question, &c., you sound like someone that has been called “a rock star” by your management at some point. If you don’t program Crestron or Control4 (or whatever) you are probably less vulnerable to this, but if you are the one who fixes the installations of your fellow techs, being called “a rock star” is an excellent diagnostic indicator that you may not be long for your current company.

I am sure you have already received offers from competitors (perhaps you already jumped this current company from another). In any case, it’s nice to leave a legacy of well documented, reliable, scalable, and sustainable work when the time to move on comes. Your industry is not what I would call the most stable one, and with the current evolution of domestic installations becoming “mini commercial” ones, the same legacy problems (mostly variable skill levels and only a few really competent folks) is now coming home—so to speak.

Sorry for the discursive detour, this is just a thing that has some significance to me for personal reasons. I certainly wish you the best of luck and that your situation is an exception to my experience.

 

Since this is for testing builds, I think it is worthwhile to spend a little extra—time and money—to create a reliable, universal solution. A small PCB can be designed easily and purchased very cheaply from any of several well known PCB fabs (we are talking <$1/pc).

This will allow you to have each speaker location to simple be a place you can hang a speaker and the LED indicator will be automatically included. One of the biggest advantages in your case will be the ability to make the LED light as brightly as needed to ensure the techs have no problem seeing which speaker is live, even from a distance and no matter the level of ambient light.

The circuit could be as simple as a single transistor and a few passives. The PCB design would be trivial and you could easily use the PCB fab’s online tools to lay it out. You can even have them do the assembly if you choose the right one. IN the end, you will have something people will thank you for, even if you are long gone*—rather than curse your name once you are no longer around to “fix” the LEDs when they don’t work for some reason.

In any case, aside from the various advantages above, one problem you will have if you take the passive approach is choosing just how hot you would have to make the speaker to get a visible indication. The brightness of the LED will completely depending on the position of the gain control on the amp, and it could be a very narrow range that ”works”.

*From your question, &c., you sound like someone that has been called “a rock star” by your management at some point. If you don’t program Crestron or Control4 (or whatever) you are probably less vulnerable to this, but if you are the one who fixes the installations of your fellow techs, being called “a rock star” is an excellent diagnostic indicator that you may not be long for your current company.

I am sure you have already received offers from competitors (perhaps you already jumped this current company from another). In any case, it’s nice to leave a legacy of well documented, reliable, scalable, and sustainable work when the time to move on comes. Your industry is not what I would call the most stable one, and with the current evolution of domestic installations becoming “mini commercial” ones, the same legacy problems (mostly variable skill levels and only a few really competent folks) is now coming home—so to speak.

Sorry for the discursive detour, this is just a thing that has some significance to me for personal reasons. I certainly wish you the best of luck and that your situation is an exception to my experience.

Thanks for the above information. If you could provide me with more detail to your above statement, that would be very helpful.

While I have worked in Residential Electronics, this level of electrical wiring is not something I am familiar with or have ever really needed to use. So I definitely have a significantly smaller understanding for this aspect than I do the AV Field.

As for the portion in italics, I have been in this field for 23 years. I have been with my current company for a little over 11 years. I have started as a tech when I first joined, and then moved to Lead Technician, Project Manager, Field Supervisor, and my current position is Director of Production. My current company is very much like a family. That being said, I can be replaced tomorrow. But whenever I do something, I do it so that people have to address upgrading/repairing can say "whew, this information is helpful. The person who did this was really thinking about the next guy". I do not do things for "job security". I have been a tech that has had to fix things that others did with job security as their first thought, and it becomes a nightmare for all involved. Everyone is replaceable, I want to be kept at a compay because of what I bring/have brought to the table. Not because they cannot let me go because of the knowledge that I have. And to be fair, I have never seen someone let go at this company for any other reason than failure to perform, own desire to leave, or seriously messing something up, repeatedly. If I am ever let go, it will never be for any failure to try to better things for everyone.

 

Thanks for the above information. If you could provide me with more detail to your above statement, that would be very helpful.

While I have worked in Residential Electronics, this level of electrical wiring is not something I am familiar with or have ever really needed to use. So I definitely have a significantly smaller understanding for this aspect than I do the AV Field.

As for the portion in italics, I have been in this field for 23 years. I have been with my current company for a little over 11 years. I have started as a tech when I first joined, and then moved to Lead Technician, Project Manager, Field Supervisor, and my current position is Director of Production. My current company is very much like a family. That being said, I can be replaced tomorrow. But whenever I do something, I do it so that people have to address upgrading/repairing can say "whew, this information is helpful. The person who did this was really thinking about the next guy". I do not do things for "job security". I have been a tech that has had to fix things that others did with job security as their first thought, and it becomes a nightmare for all involved. Everyone is replaceable, I want to be kept at a compay because of what I bring/have brought to the table. Not because they cannot let me go because of the knowledge that I have. And to be fair, I have never seen someone let go at this company for any other reason than failure to perform, own desire to leave, or seriously messing something up, repeatedly. If I am ever let go, it will never be for any failure to try to better things for everyone.

So, I would invoke the circuit… err… nerds, like @crutschow, @Audioguru again, @sghioto, @ericgibbs, @BobTPH, @Tonyr1084 and others—I am cure they can provide an excellent solution with a low component count. Similarly, there are many people here who use PCB fab services and love to help with them.

If we don’t seem to get a good response, I’ll poke at people as needed. It should be a fun and productive project and get you some new skills that you can reuse. Also, you will look like a wizard…

WIth your long tenure in the AV business, I don’t need to tell you what the state of things is. I have been involved in the business variously doing design and installation, as a large customer (specifying and managing the installation of classroom and conference room systems for a university as part of my rôle), and because one of my sons happens to be working in the field right now, having gone from commercial to residential and finding himself in the “rock star“ slot.

I am very glad to hear you have a solid position with a long employment, that’s excellent. It also sounds like your company is one of the rare ones that avoided being captured by the sales department and still has a priority on the engineering and technical side. I hope it stays that way for a long time. You would be the company cleaning up the mess left by the kinds of sales-driven fly-by-nights that are so common today.

 

So, I would invoke the circuit… err… nerds, like @crutschow, @Audioguru again, @sghioto, @ericgibbs, @BobTPH, @Tonyr1084 and others—I am cure they can provide an excellent solution with a low component count. Similarly, there are many people here who use PCB fab services and love to help with them.

If we don’t seem to get a good response, I’ll poke at people as needed. It should be a fun and productive project and get you some new skills that you can reuse. Also, you will look like a wizard…

WIth your long tenure in the AV business, I don’t need to tell you what the state of things is. I have been involved in the business variously doing design and installation, as a large customer (specifying and managing the installation of classroom and conference room systems for a university as part of my rôle), and because one of my sons happens to be working in the field right now, having gone from commercial to residential and finding himself in the “rock star“ slot.

I am very glad to hear you have a solid position with a long employment, that’s excellent. It also sounds like your company is one of the rare ones that avoided being captured by the sales department and still has a priority on the engineering and technical side. I hope it stays that way for a long time. You would be the company cleaning up the mess left by the kinds of sales-driven fly-by-nights that are so common today.

Thank so much for not only your help, but also tagging others that may be able to assist! I look forward to hearing any assistance than is able to be provided.

I have also been looking into:
Szliyands 3pcs Digital Display AC Current Indicator, 22mm Square Head LED Current Tester 0~100A Ammeter Monitor Green red Yellow from Amazon

Or similar displays, over the last few hours. What would your guys thought be on using something like this in place of an LED? I really just need something to trigger the visual that "this speaker is playing" and this seems to have circuitry already built into them

 

Here's my initial thought on a stand alone option. The LED would actually be a super bright 5mm WHITE LED as they are the easiest to see from a distance.

 

Just running some numbers:
100W, 8Ω implies 40V peak-to-peak across the speaker, so the power supply might be, say, 50V. The input current in the above circuit would then be less than the rated 50mA max for the PC814. Looks good.

Edit:
Some way of limiting the gate voltage of Q1, so as not to go above its rated value, would need to be added to the post #1 circuit if the circuit is powered by the amplifier instead of the battery

 

Here's my initial thought on a stand alone option. The LED would actually be a super bright 5mm WHITE LED as they are the easiest to see from a distance.
View attachment 313810

Thank you for your reply @sghioto

I can understand some of this drawing, and pardon my own ignorance, but you you break it down to a detailed parts and how they are wired.

I do not work with electronics at a board level, so this is very hard for me to understand. I think I see some resistors and capacitors in this drawing but don't really understand what it all means (insert line from Austin Powers, "what does it all mean Basil" here)

Does the battery truly mean a battery or alternate power source? Or is that to indicate the amplifier as the power source?

Thanks again though, your assistance is greatly appreciated!

 

Thanks again though, your assistance is greatly appreciated!

Sure no problem. Yes, the power source could be a battery or alternate power, possibly the amp if near by or what ever is practical in your setup.
The PC814 isolates the speaker from the LED circuit. Q1 is a mosfet transistor to drive the LED, value of R3 will be determined by the voltage source selected.
With sufficient output from the amp the LED will always be at max brightness.
Question? What is the minimum power these speakers will be tested at?

 

Here's my initial thought on a stand alone option. The LED would actually be a super bright 5mm WHITE LED as they are the easiest to see from a distance.
View attachment 313810

So an optoisolator (PC814), a MOSFET (Q1), 3 resistors, 1 capacitor, and a battery.

The optoisolator is a component with an LED and a phototransistor in one light-tight case (usually a small IC about the size of an 8-pin DIP package but with just four pins. It works by using the LED to signal there is current applied to it, which turns on the phototransistor. This provides galvanic isolation—that is, a connection that can’t conduct electricity at the voltages involved while still allowing action to take place.

The phototransistor is connected to the battery (this can be made a mains-powered DC power supply in practice) on one side, and the gate of the MOSFET on the other. A MOSFET is a specialized transistor (Metal Oxide Semiconductor Field Effect Transistor) which is especially well suited to operating as a switch. In this case it is an N-Channel MOSFET (also called an nMOS device). This means it works by making the connection from the positive to zero volt rail. That is it connects the circuit it is turning on—in this case the LED, to 0V or ground.

The passive components variously limit current and filter higher frequency signals which can be explained later.

 

So an optoisolator (PC814), a MOSFET (Q1), 3 resistors, 1 capacitor, and a battery.

The optoisolator is a component with an LED and a phototransistor in one light-tight case (usually a small IC about the size of an 8-pin DIP package but with just four pins. It works by using the LED to signal there is current applied to it, which turns on the phototransistor. This provides galvanic isolation—that is, a connection that can’t conduct electricity at the voltages involved while still allowing action to take place.

The phototransistor is connected to the battery (this can be made a mains-powered DC power supply in practice) on one side, and the gate of the MOSFET on the other. A MOSFET is a specialized transistor (Metal Oxide Semiconductor Field Effect Transistor) which is especially well suited to operating as a switch. In this case it is an N-Channel MOSFET (also called an nMOS device). This means it works by making the connection from the positive to zero volt rail. That is it connects the circuit it is turning on—in this case the LED, to 0V or ground.

The passive components variously limit current and filter higher frequency signals which can be explained later.

You can also see from the symbol for the PC814 that there isn’t just one, but two LEDs in it—wired in reverse of each other. This is very helpful because LEDs are diodes and like all diodes, light emitting or not, they only conduct in one direction.

This means that with AC (Alternating Current), liked your audio signal, if there was only one LED it would be lit up only half the time. With two, one lights when the signal is going from 0V to VMAX (the higher voltage above 0V) and the other when it goes from 0V to -VMAX (the lowest below 0V).

This will make the LED flicker less, and that can be reduced even further, should it prove necessary with a low pass filter that doesn’t let the current sent to the LED change quickly even if the MOSFET is switching on and off.

 

Nice write up Y. Thanks for providing the more detailed explanations.
I have some PC814s and will do a test here shortly.

 

With the values shown the LED is fully on with less then 3 volt peak to peak voltage. Thats 125 mw RMS into a 8 ohm load so plenty sensitive enough. This was using a 5 volt source with the LED at 20 ma.
The exact components listed here:

 

The LED would actually be a super bright 5mm WHITE LED as they are the easiest to see from a distance.

Just a nitpick, and not as a correction per se (and really, I should be able to resist saying this, but...)

The complete system involved in this application includes both the emitter (LED) and the sensor (human eye). When working out the efficiency of the system, both have to be taken into account.

As can see from the figure below visible light occupies a very small region in the electromagnetic spectrum with some interesting features. For example, notice how narrow the bands of cyan and blue, and on the other end, yellow and orange light appear, green seems pretty substantial, while the red looks far bigger than anything else.

But although this is an accurate accounting it doesn’t include a very important component—the varying sensitivity of the eye based on wavelength. Our eyes do not respond equally to all colors, some are “easier to see” than others. So, to determine the efficiency of an LED-to-eye signaling system both the cost (in power, and other things) and what each increment of cost is buying us in terms of efficacy must be combined.

the range of visible light
​

It turns out the human eye is substantially better at seeing green than other colors. In fact, around 565nm is the peak performance of the eye, a solidly green wavelength. In the plot below, if you draw a line at 80% pm the X axis, you can see it is mostly green, with a little yellow and orange—and no red or blue at all.

the spectral sensitivity of the human eye
​

We start to see the red at about 70%, but the blue is all the way down at 40% for a similar response. So, we see green, yellow. and orange well, red less so, and blue (and shorter) least of all. When it comes to LEDs, the high output InGaN blue LEDs are the king of output per watt. InGaN chemistry can be used to make UV, blue, or green emitters. The efficiency is inversely proportional to wavelength—so the very short wavelength (high frequency) UV types are most efficient, the blue less so, but the green dramatically less so.

Without further analysis, it would seem the blue LEDs would be the choice for maximum signaling bang for your power buck—but that leave out the other end of our system.

​

The figure below has the wavelength ranges of various colors. The typical high efficiency InGaN green LED has a peak wavelength of 535nm while the typical high output blue LED peaks at ~470nm. A Quick Look at the chart above will show that 525nm corresponds closely to peak color vision while 470nm os at about 20%.

Color vs. Wavelength
​

White LEDs... kind of don’t exist. What I mean is that a “white LED” is a blue LED covered in a phosphor that produces the white light we see. This its why early examples, and current garbage white LEDs have a very pronounced blue cast. The blue light is what is making the white light—and not for free.

The figure below shows the relative intensities of a white LED based on a Ce:YAG (Cerium doped Yttrium Aluminum Garnet) phosphor pumped by a blue InGaN LED. The first peak is the output of the blue LED, the second of the composite white one. Note the relative difference with the blue being much more intense. Of course, that power is used in generating the white light by fluorescence.

The relative outputs of the InGaN blue pump and the white Ce:YAG phosphor in a white LED
​

Notice that the white output has a nice peak about 550nm—solidly green. This is good for making the light useful to humans. You might have noticed that although old school high K (6000+) fluorescent tubes are very “bright”, the light just doesn’t seem as useful for seeing as something like an incandescent halogen bulb (~4000K). This is because that blue light doesn’t use the main sensitivity of your eye in the green as much as it stimulates the blue.

In any case, if we take the power we are putting into the blue LED and, instead, put it into a high efficiency green emitter, while the pure photons per watt favors the the blue LED, the usefulness of the output favors the green which means effective luminous flux per watt goes to the green.

All of this said, any modern, high brightness LED with a narrow angle reflector should serve. The narrow angle is very important because it will do more than anything to make the LED visible by concentrating the light in the direction of the viewer.

 

So an optoisolator (PC814), a MOSFET (Q1), 3 resistors, 1 capacitor, and a battery.

The optoisolator is a component with an LED and a phototransistor in one light-tight case (usually a small IC about the size of an 8-pin DIP package but with just four pins. It works by using the LED to signal there is current applied to it, which turns on the phototransistor. This provides galvanic isolation—that is, a connection that can’t conduct electricity at the voltages involved while still allowing action to take place.

The phototransistor is connected to the battery (this can be made a mains-powered DC power supply in practice) on one side, and the gate of the MOSFET on the other. A MOSFET is a specialized transistor (Metal Oxide Semiconductor Field Effect Transistor) which is especially well suited to operating as a switch. In this case it is an N-Channel MOSFET (also called an nMOS device). This means it works by making the connection from the positive to zero volt rail. That is it connects the circuit it is turning on—in this case the LED, to 0V or ground.

The passive components variously limit current and filter higher frequency signals which can be explained later.

@Ya’akov

Thank you for this response. I will say that while I somewhat understand what is being said here, by the time I get about half way through, my brain begins to feel like it is being tied in knots...lol.

Your explanation is great! And your parts listed are very helpful. I have always been able to comprehend things better with an exact parts list, a drawing with those parts called out and being told to figure it out. Then I learn from my mistakes until I get it working and then I not only understand how to properly do something, but also why not to do certain things.

Please forgive me for not fully understanding this.

I do feel like the steps listed above, while they may not take long to do for 1 speaker, will take a considerable amount of time to do for 64 speakers.

Would you happen to know if there is a product that I could buy that would have the majority of this already put together?

Would something like this work as an all in one solution for a visual que as to which speaker is currently playing?

diymore 10pcs Mini Digital Voltage Meter DC 2.5~30V 0.28" 2 Wire Digital Voltmeter Gauge Tester Green LED Display Panel Mount Car Motorcycle Battery Monitor Led https://a.co/d/0UycpTb