Greetings all,
I could use some assistance with the following standard thru-hole VU design. I would like to modify the wattage points at which the LED's activate. What appears to be the variables n this example is at the Zener diodes in most of the LED circuits.
Can someone please tell me how to calculate what value Zener diodes are needed to attain activation at the predetermined wattage? I haven't been to school in 30 years and in all my efforts, in every calculation I try, I am unable to even simulate the circuit below to even get the values shown in this schematic. I am obviously missing something, and it's driving me bonkers.
Example:
LED #7, Zener diode value = 18v in this circuit, the LED activates at 50 watts and above.
- What calculation would I use to determine the Zener diode value needed to have the LED activate at 80 watts and above?
This example is using an 8-ohm speaker connected at points LS. (I am only interested in modifying LED's 5 thru 10, if that helps simplify)
Your assistance is GREATLY appreciated!
I could use some assistance with the following standard thru-hole VU design. I would like to modify the wattage points at which the LED's activate. What appears to be the variables n this example is at the Zener diodes in most of the LED circuits.
Can someone please tell me how to calculate what value Zener diodes are needed to attain activation at the predetermined wattage? I haven't been to school in 30 years and in all my efforts, in every calculation I try, I am unable to even simulate the circuit below to even get the values shown in this schematic. I am obviously missing something, and it's driving me bonkers.
Example:
LED #7, Zener diode value = 18v in this circuit, the LED activates at 50 watts and above.
- What calculation would I use to determine the Zener diode value needed to have the LED activate at 80 watts and above?
This example is using an 8-ohm speaker connected at points LS. (I am only interested in modifying LED's 5 thru 10, if that helps simplify)
Your assistance is GREATLY appreciated!
Normally they use a resistive divider to each LED driver. Probably the best thing to do is calculate the peak voltage for each trip point in the audio wave. The audio is processed, so you'll have to apply that voltage level and measure what comes out. I don't know off-hand if there is any compression in there, so simply doing this empirically might be the most effective. The input circuit may clip or compress.
Alternatively, just adjust the input divider to get the points you want assuming the ratios are okay for you. It's a self-powered thing, so do not expect linearity or accuracy!
-Chris
Alternatively, just adjust the input divider to get the points you want assuming the ratios are okay for you. It's a self-powered thing, so do not expect linearity or accuracy!
-Chris
Here's a rough calculation.
First calculate voltage for 50 watts into 8 ohms:
P = V * I = V * V / R
V = SquareRoot(R * P)
For 50 watts: V = SquareRoot( 8 * 50) = 20 Vrms
Vpeak = 1.4 * 20 = 28V
The LED drops approx. 2V so the zener should be about 28V - 2V = 26V.
The schematic shows a 27V zener.
First calculate voltage for 50 watts into 8 ohms:
P = V * I = V * V / R
V = SquareRoot(R * P)
For 50 watts: V = SquareRoot( 8 * 50) = 20 Vrms
Vpeak = 1.4 * 20 = 28V
The LED drops approx. 2V so the zener should be about 28V - 2V = 26V.
The schematic shows a 27V zener.
Hammerheadowner has nailed it 👍
Super quick simulation showing LED current for a 27 volt Zener. Only difference here is the input voltage at 31 volts (just coming into conduction) and 34 volts peak (fully on). An unknown with currents is the fact all the preceding stages will be on. Its easy to copy the LED section in the sim multiple times if anyone has the time.
Super quick simulation showing LED current for a 27 volt Zener. Only difference here is the input voltage at 31 volts (just coming into conduction) and 34 volts peak (fully on). An unknown with currents is the fact all the preceding stages will be on. Its easy to copy the LED section in the sim multiple times if anyone has the time.
You're welcome 🙂
I copied the LED's over and swapped the Zener's. No models for the 2v4 and 3v9 Zener so I've fiddled those. The LED current falls as expected but is still plenty with high efficiency LED's. The last two LED's here are at zero current (traces overlaid.
Currents in detail:
I copied the LED's over and swapped the Zener's. No models for the 2v4 and 3v9 Zener so I've fiddled those. The LED current falls as expected but is still plenty with high efficiency LED's. The last two LED's here are at zero current (traces overlaid.
Currents in detail:
Hi @Mooly,
I was thinking of getting LTSpice. Do you like it? I am currently using EveryCircuit.com. Visually, it's good, but it has no canned components to pull from, so its manual entry 100%; and the parameters for Transistors and Diodes are non-conventional parameters that are driving me mad (meaning they don't correlate to datasheet parameters of said components). I would like to know your thoughts as to what you like about LTSpice, for comparison.
Also, with the Sim above, I noticed you dropped R12, and the circuit still sims. I'm just curious what drove that choice?
My ultimate goal is to find a way to Sim the circuit so that I change out the ZD's with various other values to see the net effect. I would like to be able to morph the LED's to approximate power levels of my choice.
Thank you for the info, btw!
I was thinking of getting LTSpice. Do you like it? I am currently using EveryCircuit.com. Visually, it's good, but it has no canned components to pull from, so its manual entry 100%; and the parameters for Transistors and Diodes are non-conventional parameters that are driving me mad (meaning they don't correlate to datasheet parameters of said components). I would like to know your thoughts as to what you like about LTSpice, for comparison.
Also, with the Sim above, I noticed you dropped R12, and the circuit still sims. I'm just curious what drove that choice?
My ultimate goal is to find a way to Sim the circuit so that I change out the ZD's with various other values to see the net effect. I would like to be able to morph the LED's to approximate power levels of my choice.
Thank you for the info, btw!
I've never used anything else tbh. Learning how to use one simulator is enough 😀 Lots of info here to get you started and the files I posted will just click and run in LT:
https://www.diyaudio.com/community/...rom-beginner-to-advanced.260627/#post-4025305
Purely an oversight. Well spotted. It seems to have little effect in practice and only altering slightly the current in an LED that is right on the edge of being driven on or not.
Try it in LT 🙂
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LT spice pretty common
Use Tina TI since it seems to have larger library
And much easier to actually do basic stuff like
drop in components and connect wires.
Importing models way easier.
Sounds silly maybe I am more use to it.
Switching to LT drives me nuts since pretty
basic functions are annoying.
Sub Circuits and macros are easier to implement
with Tina.
And can have virtual oscilloscope, function gen, meter
etc on screen. basically full virtual bench.
Of course bias and opinions vary and people get use
to what they are familiar with. Pretty easy to download both
since = free. TI just ask for user account. So just register with Email.
Pretty basic stuff.
Not sure what LT has for diodes in my library 47 series or 1N4728 goes down
to 3.3 volts and 52 series 1N5221 goes down to 2.4 volts
so 5222 is 2.5 volts, 5223 is 2.7 volts
also BZX79F series has 2.4 volts and 2.7
BZX79F2V4 , BZX79F2V7
Use Tina TI since it seems to have larger library
And much easier to actually do basic stuff like
drop in components and connect wires.
Importing models way easier.
Sounds silly maybe I am more use to it.
Switching to LT drives me nuts since pretty
basic functions are annoying.
Sub Circuits and macros are easier to implement
with Tina.
And can have virtual oscilloscope, function gen, meter
etc on screen. basically full virtual bench.
Of course bias and opinions vary and people get use
to what they are familiar with. Pretty easy to download both
since = free. TI just ask for user account. So just register with Email.
Pretty basic stuff.
Not sure what LT has for diodes in my library 47 series or 1N4728 goes down
to 3.3 volts and 52 series 1N5221 goes down to 2.4 volts
so 5222 is 2.5 volts, 5223 is 2.7 volts
also BZX79F series has 2.4 volts and 2.7
BZX79F2V4 , BZX79F2V7
This circuit is somewhat smarter, and doesn't require a flurry of different zeners:
https://www.diyaudio.com/community/threads/passive-led-vu-meter.237803/post-3531415
https://www.diyaudio.com/community/threads/passive-led-vu-meter.237803/post-3531415
Another plus is the loading: all LEDs are series-connected, meaning the load doesn't increase with the number of LEDs lit
That is a huge benefit Elvee. There are a few circuits that use series connected LEDs, but most have their own power supply.
Thank you, @WhiteDragon! I downloaded the Tina software, and the parts library had everything I needed! It had all the parameters necessary for the sim software I was using! It's also very functional. Much appreciated!
Hi @Elvee,
Thank you for this design! I modeled it in my animated sim program, and the LED lit up on my first try! Nice! 🙂
I did notice something that may cause issues, at least in my application.
- Since my design is meant to be placed in parallel with 4- or 8-ohm speakers, such variation will likely cause issues with the amplifier.
Nothing against your design, it obviously works just fine and is solid. I am only pointing out that I do not have these issues with my design in my Sim. My design ohms out between 3.87 and 3.99ohm when in parallel with a 4-ohm speaker, regardless of frequency (at least in my sim). I have built several live CCA's of my design and have them in use to this day, so I am confident in the design. I am sure that my issue here mainly lay with dusting off my brain and learning the sim software quirks so I can adjust my meter to my liking.
I appreciate you, and everyone that has helped me. I am blessed to have found this website and the great people here.
Thank you for this design! I modeled it in my animated sim program, and the LED lit up on my first try! Nice! 🙂
I did notice something that may cause issues, at least in my application.
- I noticed that the reaction time of the LED's activating was significantly slower than my schematic. (Could be an artifact of my Sim software, so may not be of significance).
- I also noticed that the circuit seems to be very reactive to variation of frequency of the sine wave. It reacted fine during 1Khz and above but burned the caps at 100hz and below.
- Since my design is meant to be placed in parallel with 4- or 8-ohm speakers, such variation will likely cause issues with the amplifier.
Nothing against your design, it obviously works just fine and is solid. I am only pointing out that I do not have these issues with my design in my Sim. My design ohms out between 3.87 and 3.99ohm when in parallel with a 4-ohm speaker, regardless of frequency (at least in my sim). I have built several live CCA's of my design and have them in use to this day, so I am confident in the design. I am sure that my issue here mainly lay with dusting off my brain and learning the sim software quirks so I can adjust my meter to my liking.
I appreciate you, and everyone that has helped me. I am blessed to have found this website and the great people here.
Hi HammerheadOwner,
You have to understand these things were not flat with frequency - ever. They were toys intended to create a light show and that's all. Even units with internal power supplies and better signal conditioning were not always that accurate or even flat with frequency. These were not intended as test instruments. Consumers always expected that of them.
The signal is very dynamic, and really they were intended to give you an idea how much output power you were delivering. They had no reason to be accurate.
Most meters on commercial amplifiers are not accurate, or flat. Ranging made calibration worse. Doing warranty on high end product, I got the most picky customers you can imagine. Just imagine trying to explain real life to these folks. Show me one with accuracy specs, or one including frequency response. If you find one, look at that circuit, then at anything you are looking at. Even meters on recording studio equipment isn't always flat. Studers were pretty good, other brands not so much! Now that is for recording studios and some techs used the meters for calibration.
You have to understand these things were not flat with frequency - ever. They were toys intended to create a light show and that's all. Even units with internal power supplies and better signal conditioning were not always that accurate or even flat with frequency. These were not intended as test instruments. Consumers always expected that of them.
The signal is very dynamic, and really they were intended to give you an idea how much output power you were delivering. They had no reason to be accurate.
Most meters on commercial amplifiers are not accurate, or flat. Ranging made calibration worse. Doing warranty on high end product, I got the most picky customers you can imagine. Just imagine trying to explain real life to these folks. Show me one with accuracy specs, or one including frequency response. If you find one, look at that circuit, then at anything you are looking at. Even meters on recording studio equipment isn't always flat. Studers were pretty good, other brands not so much! Now that is for recording studios and some techs used the meters for calibration.
Sorry but that schematic is wrong, or at least very poor.
ALL transistors activate at the same time 😱 since all bases are joined and all emitters are identical: 150 ohms to ground.
All zeners do is making higher power LEDs weaker or turn on later; you will get exact same results with a passive VU meter: only Leds, Zeners, and some current limiting resistors.
VERY crude.
Search around for much better VU Led schematics.
ALL transistors activate at the same time 😱 since all bases are joined and all emitters are identical: 150 ohms to ground.
All zeners do is making higher power LEDs weaker or turn on later; you will get exact same results with a passive VU meter: only Leds, Zeners, and some current limiting resistors.
VERY crude.
Search around for much better VU Led schematics.
These are all artifacts: the frequency response only depends on the 100µ capacitors, and if you want the circuit to work at very low frequencies, you simply need to increase them.
If the voltage rating of the caps is compatible with the power of the amplifier, there is no risk to blow them.
The value given by your ohmmeter is completely nonsensical: the impedance cannot go lower than the 10ohm series resistor.
You should use a less fanciful simulator, or even better breadboard the circuit