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
DF96 - A sinewave of 2.5V peak to peak works out to an average of about 1.77V so will read +3dB on a meter configured for professional level.
Cheers
Mike
Cheers
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.
Oh dear. It seems there are quite a few mistakes.
I was trying to say 5V peak to peak in this case as most audio interfaces run off 5V and use a rail to rail op-amp for output.
I'll get these ironed out tonight.
Mike
I was trying to say 5V peak to peak in this case as most audio interfaces run off 5V and use a rail to rail op-amp for output.
I'll get these ironed out tonight.
Mike
Well I have a couple of USB audio interfaces and a CD player that give this sort of output.
The audio interface I use at the moment (an ESI U24XL) uses this means of driving the output.
Mike
The audio interface I use at the moment (an ESI U24XL) uses this means of driving the output.
Mike
All sorted now! Thanks for your help, man 😀 .
I wrongly thought that with a sinewave the RMS voltage was the same as the average voltage. Can't believe I got this far without knowing that was wrong!
Mike
I wrongly thought that with a sinewave the RMS voltage was the same as the average voltage. Can't believe I got this far without knowing that was wrong!
Mike
For a sinewave the average voltage is zero. However, for a full-wave rectified sine wave it is almost exactly 0.9 times the RMS value.
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
dBu vesus dB
The Vu drivers I made are calibrated to read 4dB at 1.228V.
The studio recording level (pro audio) of +4 dBu means a voltage of 1.228 volts.
Fair enough. But for pro use 0VU is always 1.228V RMS (with a sinewave). So 1.17V average (roughly).
From Wikipedia...
Of course as DIYers we can set our own standards 😀 .
Mike
From Wikipedia...
Of course as DIYers we can set our own standards 😀 .
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.
Hi,
Very elegant, and you wont get any distorted ground current either, but unfortunately you do not have pure current drive due to the resistive loading, I'm afraid.
Cheers,
Mike
Very elegant, and you wont get any distorted ground current either, but unfortunately you do not have pure current drive due to the resistive loading, I'm afraid.
Cheers,
Mike
Indeed, not a pure current drive, a 30K impedance good enough to deal with 1n914 threshold. Transistor reference is "any cheapest there is in store".
Old Vu meters were using germanium diodes, they have a handy lowest threshold, here one could use schottky diodes.
Old Vu meters were using germanium diodes, they have a handy lowest threshold, here one could use schottky diodes.
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Very true. In the very early days they were actually copper oxide rectifiers. There's a circuit in the article that has pure current drive. Highly recommended, if I say so myself!
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
Replying from work, apologies if you already covered it. A quick 'ctrl f' returned no results for 'ballistics' or 'weighting'. As I recall a true VU meter requires a specific drive impedance to maintain standard ballistics, otherwise it reads incorrectly on everything but sine waves.
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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