Hello everyone,
Going to do some shameless self promotion here
. Just written an article on driving VU meters using simple effective circuitry. I've worked out a few really nifty ways of getting the job done.
Driving VU and other AC Meters - Simple High Performance Circuits
Gonna be writing a few more like this article so stay tuned!
Mike
Going to do some shameless self promotion here
. Just written an article on driving VU meters using simple effective circuitry. I've worked out a few really nifty ways of getting the job done.Driving VU and other AC Meters - Simple High Performance Circuits
Gonna be writing a few more like this article so stay tuned!
Mike
2.5V peak to peak is 1.25V peak. This is about 1.125V average after full-wave rectification. This is -0.76dB with respect to 1.228V average, not +3dB.
The https://en.wikipedia.org/wiki/Line_level article sheds some light on it, although it is not clearly written. 1.228V is the RMS value of a +4dBu sine wave signal, not the average value as you said.
The standard CD player output voltage always used to be 2V RMS (about 5.6V peak to peak), not 2.5V peak to peak as you said.
I suggest you carefully review your article, and get it checked by someone who knows the difference between peak, peak to peak, RMS and average - and how these relate to the VU standard.
The https://en.wikipedia.org/wiki/Line_level article sheds some light on it, although it is not clearly written. 1.228V is the RMS value of a +4dBu sine wave signal, not the average value as you said.
The standard CD player output voltage always used to be 2V RMS (about 5.6V peak to peak), not 2.5V peak to peak as you said.
I suggest you carefully review your article, and get it checked by someone who knows the difference between peak, peak to peak, RMS and average - and how these relate to the VU standard.
Ah, OK then. I think it's fairly obvious that in this case 'average' means the average rectified voltage. I will change it when I next get the chance.
In regards to output levels of various devices I just measured the output of my Armstrong ST3 which gives a scorching 20V pk-pk when listening to the loudest FM station in my area.
Mike
In regards to output levels of various devices I just measured the output of my Armstrong ST3 which gives a scorching 20V pk-pk when listening to the loudest FM station in my area.
Mike
My VU meter drivers do not use op amps.
I use LTP transistors: 2 transistors 5 résistors 4 diodes.
This simple circuit gives input impedance over 1 MegOhm and a current drive to the diode bridge. Current drive, because of the diodes thresholds.
I posted the schematic in "Chinese mini VU Meters"
The 2 base resistors are not a must, just extra input protection.
I use LTP transistors: 2 transistors 5 résistors 4 diodes.
This simple circuit gives input impedance over 1 MegOhm and a current drive to the diode bridge. Current drive, because of the diodes thresholds.
I posted the schematic in "Chinese mini VU Meters"
The 2 base resistors are not a must, just extra input protection.
I am not sure, pure current drive is worthwhile for two reasons.
_The Vu meter scale may be, takes care of the diode thresold. Who knows about chinese cheapos. I am quite sure old Vu meter scales were made for a single resistor and diode drive.
_The error from the threshold hides in the -20dB area where there not much to see.
_The Vu meter scale may be, takes care of the diode thresold. Who knows about chinese cheapos. I am quite sure old Vu meter scales were made for a single resistor and diode drive.
_The error from the threshold hides in the -20dB area where there not much to see.
I suppose so. But to me, pure current drive guarantees that the ground current will stay clean, which makes things much, much easier. Although in your circuit, this won't be an issue, if you are working with a single op-amp per meter it makes a big difference.
Most VU meters out there don't take the diode into account, unfortunately. Only the true types with internal rectifiers do. Have a look at the scales on some modern meters and compare the difference between -10 and -20dB. Usually the distance between -20 and the minimum line is half of the distance between -10 and -20, indicating that the diode has not been taken into account.
Mike
Most VU meters out there don't take the diode into account, unfortunately. Only the true types with internal rectifiers do. Have a look at the scales on some modern meters and compare the difference between -10 and -20dB. Usually the distance between -20 and the minimum line is half of the distance between -10 and -20, indicating that the diode has not been taken into account.
Mike
Well, the ballistics don't affect whether it measures average or RMS voltage. As I recall, a specific drive impedance (usually 3.6k, as mentioned in the article) is required on true VU meter to ensure correct ballistics, but with non-standard meters a parallel capacitor to damp the meter's movement is a much better choice.
Mike
Mike
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