volume level meter

akis · 10th May 2010, 05:37 AM

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.

bob91343 · 10th May 2010, 05:43 AM

You need to design it with comparators instead of analog amplifiers.

Mooly · 10th May 2010, 06:36 AM

Quote:

Originally Posted by bob91343

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

Nico Ras · 10th May 2010, 02:54 PM

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.

Mooly · 10th May 2010, 03:46 PM

Quote:

Originally Posted by Nico Ras

Simple task Mooly ................

Hi Nico,
I know

however it's not me you have to convince.

akis · 10th May 2010, 05:48 PM

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.

Mooly · 10th May 2010, 06:01 PM

You can use opamps as comparators too... I don't think you would notice a difference for this tbh

10th May 2010, 06:01 PM	#7
Mooly diyAudio Member Join Date: Sep 2007	You can use opamps as comparators too... I don't think you would notice a difference for this tbh __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

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10th May 2010, 05:43 AM	#2
bob91343 diyAudio Member Join Date: Mar 2010	You need to design it with comparators instead of analog amplifiers.

10th May 2010, 02:54 PM	#4
Nico Ras diyAudio Member Join Date: Nov 2005 Location: Amanzimtoti - East Coast of South Africa	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.

10th May 2010, 05:48 PM	#6
akis diyAudio Member Join Date: Jul 2008	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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