Vu meters are designed to read only voltage. Maybe you should read the post again. The reference 0dBu is always computed as 0.775V into 600 ohms. That is what the vu meter is for, remember it originated in professional equipment and was adapted for use in domestic applications by the Japanese.
Because power amplifiers do not have a constant load - even 8 ohms load is not really 8 ohms - you cannot ever expect correct or close to correct reading from it.
Because power amplifiers do not have a constant load - even 8 ohms load is not really 8 ohms - you cannot ever expect correct or close to correct reading from it.
Calibrating
Greetings Pibull and Sangram.
First of all i want to thank you both for the efforts and the explanation for helping me calibrate the vu meters, which i find a bit less user friendly to do because i have not the adequate skills and knowledge to be comfortable enough to don’t damage the amplifier.
The way i make them all equal is finding a good amount of volume, 50 % i can handle, put a 60 Hrtz signal input and calibrate them manually do be at 90 degrees, that way, they all become equal but not accurate in db levels, I’m sure.
After all this is my first attempt of building such devices and i did not burned any component so far ;D.
Greetings Pibull and Sangram.
First of all i want to thank you both for the efforts and the explanation for helping me calibrate the vu meters, which i find a bit less user friendly to do because i have not the adequate skills and knowledge to be comfortable enough to don’t damage the amplifier.
The way i make them all equal is finding a good amount of volume, 50 % i can handle, put a 60 Hrtz signal input and calibrate them manually do be at 90 degrees, that way, they all become equal but not accurate in db levels, I’m sure.
After all this is my first attempt of building such devices and i did not burned any component so far ;D.
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Applying 35V dc directly to the high input of the vu meter will not blow it up ?
@AudioTag,
I will ask you something, because I don't have that board at home, will the output of the amp with let's say full power blow it (it also have swing of voltage between +30V and -30V)? I calculated this numbers with 10% ripple and 2V dropout on each transistor in the chips.
I wrote in my previous post that you should try with (very) short time connection to + rail (or -, whatever), if it is AC coupled. If you see that needle is at full scale, reduce the pot to lowest value. If that doesn't help, put at input another divider (potentiometer, or trimmer, value about 10kohm) and try to adjust what was described.
If it is DC coupled, then it function as DC voltmeter, so you can leave connected and adjust value.
Why I am not for Sangram option, when you will listen at 88dB, and your speakers are 88dB/W sensitive, you will have only 1W at output of your amp (or maybe 0,5W per channel), so when you decide to listen louder your VU will go to max of scale...
If you like to see needle to swing on lower power, you can do some switch with another attenuator for hi-power listening. That option I have on my amp, scale with x1 and x0,1. Latter value are for listening at low power and my scale is at 20W at 8ohm load. If it is at full range then I have 200W at 8ohm load. Calculate for practice what power I have on 4ohm load.
Load on output is only for better calibrating, you can do without load but you will achieve higher value of output voltage and you will lose "accuracy", then you can adjust to let say +6dB (or close to it) on scale.
As I wrote, +3dB means that you have music power from your amp, 0dB means full RMS power reached. It is simple description, when you understand that it will not be something scientific.
This amp has about 60-70W RMS on 8 ohm load with power rail +/-35V.
I will ask you something, because I don't have that board at home, will the output of the amp with let's say full power blow it (it also have swing of voltage between +30V and -30V)? I calculated this numbers with 10% ripple and 2V dropout on each transistor in the chips.
I wrote in my previous post that you should try with (very) short time connection to + rail (or -, whatever), if it is AC coupled. If you see that needle is at full scale, reduce the pot to lowest value. If that doesn't help, put at input another divider (potentiometer, or trimmer, value about 10kohm) and try to adjust what was described.
If it is DC coupled, then it function as DC voltmeter, so you can leave connected and adjust value.
Why I am not for Sangram option, when you will listen at 88dB, and your speakers are 88dB/W sensitive, you will have only 1W at output of your amp (or maybe 0,5W per channel), so when you decide to listen louder your VU will go to max of scale...
If you like to see needle to swing on lower power, you can do some switch with another attenuator for hi-power listening. That option I have on my amp, scale with x1 and x0,1. Latter value are for listening at low power and my scale is at 20W at 8ohm load. If it is at full range then I have 200W at 8ohm load. Calculate for practice what power I have on 4ohm load.
Load on output is only for better calibrating, you can do without load but you will achieve higher value of output voltage and you will lose "accuracy", then you can adjust to let say +6dB (or close to it) on scale.
As I wrote, +3dB means that you have music power from your amp, 0dB means full RMS power reached. It is simple description, when you understand that it will not be something scientific.
This amp has about 60-70W RMS on 8 ohm load with power rail +/-35V.
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