3 Leds Audio Level Indicator
- Thread starter darkcharly
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Help Support GroupDIY Audio Forum:
Yes it might... hard to tell from looking at the layout.
LM339 are popular quad comparator commonly used for simple meters.
JR
LM339 are popular quad comparator commonly used for simple meters.
JR
darkcharly
Active member
Thanks for the reply! I have seen that the PIN 3 is not connected. According to the datasheet of the LM339 is the input voltage. Is this a design error?
Show me a schematic and I will render an opinion... not worth my effort to reverse engineer from the layout.
JR
JR
darkcharly
Active member
Rob Flinn
Well-known member
R9 seems to be rather ineffective, it's wiper is not connected to anything ......
Rob Flinn said:
Might be connected to the ground side of the pot as overall sensitivity control?
OK I see one probably schematic mistake (wiper of r9 needs to be connected to one side or the other of the pot), and one design weakness... (?)
Not a mistake but I wouldn't trust it to always work reliably. While perhaps done on purpose, the diode D2 is biased on by the bias current of the Darlington PNP input devices. The 25 nA (nanno nanno) bias current is probably specified at equilibrium since when that input is low the bias current is probably less. This could be some free hysteresis or just sloppy design (or incorrect schematic documentation). A resistor to +V would make that diode Vref more repeatable.
That is more trimpots that I used in a few decades.
Yes, as your noticed pin 3 +V is not connected so that will not work. I would not trust that layout, It may have more errors.
JR
Not a mistake but I wouldn't trust it to always work reliably. While perhaps done on purpose, the diode D2 is biased on by the bias current of the Darlington PNP input devices. The 25 nA (nanno nanno) bias current is probably specified at equilibrium since when that input is low the bias current is probably less. This could be some free hysteresis or just sloppy design (or incorrect schematic documentation). A resistor to +V would make that diode Vref more repeatable.
That is more trimpots that I used in a few decades.
Yes, as your noticed pin 3 +V is not connected so that will not work. I would not trust that layout, It may have more errors.
JR
darkcharly
Active member
JR Thank you for your input!
It seemed important to ask for an opinion before starting to work on this project.
I was looking for an audio signal indicator 3 LEDs (signal, 0db and clip, or something simple) for use in the project SSL9K. Seeing that this layout does not seem reliable, I wonder if you know of any circuit that could work. Even better if it ran at 15 or 18v.
Thank you!
Cheers!
It seemed important to ask for an opinion before starting to work on this project.
I was looking for an audio signal indicator 3 LEDs (signal, 0db and clip, or something simple) for use in the project SSL9K. Seeing that this layout does not seem reliable, I wonder if you know of any circuit that could work. Even better if it ran at 15 or 18v.
Thank you!
Cheers!
The circuit could be made to work. while I agree with PRR I would not do it exactly that way...
For signal present, 0VU, and clip you are looking at pretty much known voltages so you don't need all the trim pots (a single resistor divider string could handle all three thresholds). Note: you want to indicate a few dB before actual clipping.
The 5.1V zener serves as a voltage reference so why all the trims..? If you have a regulated PS you can use that as your voltage reference.
The things I don't like about it are the extra expenses but for a one off DIY project not such a big deal for you.
If you do a search you will probably find many examples, if you are willing to stretch your brain a little and figure out how this works (you are part way there identifying the missing power connection ) you can learn from this.
The lm339 is a very popular quad comparator so a logical choice for your x3 meter. To make a meter that you can read (musical peaks are too short to see) You need a hold on the individual LEDs or a sample and hold on the input (what they did).
The three remaining comparators then handle the three thresholds
What is clipping for your gear? What is zero VU for your gear an d how small is signal present.
To make this exactly what you want is a wonderful learning opportunity.
JR
PS: the 470k LED current limit resistors seem large unless you have very high efficiency LEDs and a pretty high voltage PS. Green and yellow LEDs generally need more current than red for same brightness.
For signal present, 0VU, and clip you are looking at pretty much known voltages so you don't need all the trim pots (a single resistor divider string could handle all three thresholds). Note: you want to indicate a few dB before actual clipping.
The 5.1V zener serves as a voltage reference so why all the trims..? If you have a regulated PS you can use that as your voltage reference.
The things I don't like about it are the extra expenses but for a one off DIY project not such a big deal for you.
If you do a search you will probably find many examples, if you are willing to stretch your brain a little and figure out how this works (you are part way there identifying the missing power connection ) you can learn from this.
The lm339 is a very popular quad comparator so a logical choice for your x3 meter. To make a meter that you can read (musical peaks are too short to see) You need a hold on the individual LEDs or a sample and hold on the input (what they did).
The three remaining comparators then handle the three thresholds
What is clipping for your gear? What is zero VU for your gear an d how small is signal present.
To make this exactly what you want is a wonderful learning opportunity.
JR
PS: the 470k LED current limit resistors seem large unless you have very high efficiency LEDs and a pretty high voltage PS. Green and yellow LEDs generally need more current than red for same brightness.
RuudNL
Well-known member
I suppose with 470K in series with the LEDs you will barely see them glowing, even during the night...
Perhaps this is one of those real life IQ tests I talk about.
List all the mistakes in this design. 8) 8)
JR
List all the mistakes in this design. 8) 8)
JR
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