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volume level meter
volume level meter
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Old 10th May 2010, 05:37 AM   #1
akis is offline akis  United Kingdom
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Default volume level meter

Hi I have built the circuit below to help me see when my amp is about to clip, or clipping. It works fine but on a dummy load viewed on the scope, the amp clips more or less suddenly, whereas my LEDs are very linear and progressive.

Which means if I adjust so that the red LED is full on when the amp clips, then it will also be on well before it clips, just a bit less bright.

So I am after a design that would perhaps go on suddenly, if possible. The circuit below still works and does provide indication of level but it rather depends on the ambient light in the room to be able to see the various levels of yellow and red LEDs.
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Old 10th May 2010, 05:43 AM   #2
bob91343 is offline bob91343  United States
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You need to design it with comparators instead of analog amplifiers.
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Old 10th May 2010, 06:36 AM   #3
Mooly is offline Mooly  United Kingdom
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volume level meter
Quote:
Originally Posted by bob91343 View Post
You need to design it with comparators instead of analog amplifiers.
Agreed... and also check out the LM3914 LM3915 and LM3916 LED/Bargraph drivers.
Worked examples and datasheets here,
http://www.datasheetcatalog.org/data...r/DS007970.PDF

http://www.datasheetcatalog.org/data...r/DS005104.PDF

http://www.datasheetcatalog.org/data...r/DS007971.PDF
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Old 10th May 2010, 02:54 PM   #4
Nico Ras is offline Nico Ras  South Africa
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Simple task Mooly, use a comparator with the amp power supply as reference and measuring the output swing with reference to the power supply. Your amp depending upon the design will start to clip when it reaches some point close to the rail, which is dynamic anyway. All you need to add is a monostable that would keep the LED on for at least long enough so you can see it.
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Old 10th May 2010, 03:46 PM   #5
Mooly is offline Mooly  United Kingdom
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volume level meter
Quote:
Originally Posted by Nico Ras View Post
Simple task Mooly ................
Hi Nico,
I know
however it's not me you have to convince.
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Old 10th May 2010, 05:48 PM   #6
akis is offline akis  United Kingdom
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For one reason or another this circuit is on the pre-amp, not on the amp itself. To adjust it I use the scope and the amp on a dummy load.

I looked up comparators and it seems that's the way to go, so I will replace the LED transistors with a comparator. I have no idea which comparators to use - the LM393 is one option, it is dual so I could use it for the yellow and red, the green can be driven from a tranny as above since it is not critical.
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Old 10th May 2010, 06:01 PM   #7
Mooly is offline Mooly  United Kingdom
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volume level meter
You can use opamps as comparators too... I don't think you would notice a difference for this tbh
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