| Electronics > Beginners |
| Analog VU Meter & Volume Pot |
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| bob91343:
The problem with connecting the meter to the amplifier output is that its reading changes when you adjust the system volume. If you are willing to accept that, simply turn up the volume to a point you like and attach the meter to the amplifier output via a series resistor. You adjust the resistor to get the reading you like. If you decide to make the sound louder, the meter will peg and there is risk of damage to it. The internal rectifier would likely be copper oxide if it's an old meter; that was the standard for many years. You can get fancy and calibrate the meter in terms of amplifier power output. You drive it with a sine wave while measuring amplifier output and select a resistor to give the reading you choose. Then do it again for other power levels and finally put all the various resistors on a switch and mark it with the power needed for a 0 reading at each setting. |
| floobydust:
--- Quote from: vidarr on August 30, 2019, 10:54:51 pm ---Since this is a project just for learning's sake, what way would be the easiest to incorporate the VU meter? I don't fully understand the schematic you attached. I understand the VU meter and the resistor, but I don't see where the VU meter is inserted into the circuit. That is my primary question. THANK YOU! --- End quote --- I update the schematic, with a line around the VU meter and it's internal rectifier. Is this understandable? |
| vidarr:
Yeah, that is 100% clear now. But, if I put the VU meter after the input, before the amp chip, would the circuit look similar? I would just change the resistor? "The problem with connecting the meter to the amplifier output is that its reading changes when you adjust the system volume. If you are willing to accept that, simply turn up the volume to a point you like and attach the meter to the amplifier output via a series resistor. You adjust the resistor to get the reading you like. If you decide to make the sound louder, the meter will peg and there is risk of damage to it." Where do VU meters typically go to "avoid" this? Thank You |
| Audioguru again:
Your signal source might not have enough power to drive the VU meter then it will be distorted or at a low level. |
| floobydust:
What did you want the meter to show? It's like an AC voltmeter. Historically, people used them to prevent overload for the system. Going over +3dB or pegging the meter could mean things are distorting and clipping. It takes energy to move the meter's pointer, it does not move for free. If you are taking headphone output from something like a cellphone or mp3 player, it has enough power to drive a meter and you could connect the meter there with the same circuit. But a weaker line-level signal (PC soundcard, tape deck etc.), or the VU meter being AFTER the volume control, you would need to add an op-amp buffer to drive it, so it does not load down the signal and cause distortion. Found some info here: http://www.objectivesounds.co.uk/articles/driving-vu-and-other-ac-meters |
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