OK,
A friend at the monthly HAM swap meet has a very clean, restored and calibrated AC millivolt meter. Dual channel 30uV to 100V. (the meter actually has two pointers). Meter has AC and dB scales.
I understand that these meters really just do one thing, probably very well, for measuring minute levels of average AC present.
What can I use this for? I was thinking along these lines:
1) Quickly evaluating power supply ripple while breadboarding and tweaking.
2) Having two channels to compare input to output.
3) Maybe some applications in negative feedback?
4) Finding crosstalk?
Is this a boat anchor, or could it be handy tweaking things? I'd have to learn it, but it seems easy.
A friend at the monthly HAM swap meet has a very clean, restored and calibrated AC millivolt meter. Dual channel 30uV to 100V. (the meter actually has two pointers). Meter has AC and dB scales.
I understand that these meters really just do one thing, probably very well, for measuring minute levels of average AC present.
What can I use this for? I was thinking along these lines:
1) Quickly evaluating power supply ripple while breadboarding and tweaking.
2) Having two channels to compare input to output.
3) Maybe some applications in negative feedback?
4) Finding crosstalk?
Is this a boat anchor, or could it be handy tweaking things? I'd have to learn it, but it seems easy.
I have one, and I find it (moderately) useful. Unlike the one you covet, which seems at the very top of the top-end, mine is the poor man's version, made by Levell.
Despite its unbeatable cheapness, it is a well designed, quite usable instrument and I use it for various purposes: for example here it is used to measure the residual noise of a supply (scroll to the end of the post):
D-Noizator: a magic active noise canceller to retrofit & upgrade any 317-based V.Reg.
It was actually insufficient to measure the true performance of the scheme under test, but it provided a first glimpse of the improvements.
I later complemented it with a proper LNA, but having an instrument ready, capable of roughing out the job is very convenient.
I also find the built-in, crude filters useful, and I frequently use the auxiliary output to push my scope's sensitivity down to µV level.
Thus, I could easily do without it, use my lab instruments and amplifiers to do the same, but it is a convenient piece of kit.
If you can have one for cheap, and if it isn't too bulky, I would go for it
Despite its unbeatable cheapness, it is a well designed, quite usable instrument and I use it for various purposes: for example here it is used to measure the residual noise of a supply (scroll to the end of the post):
D-Noizator: a magic active noise canceller to retrofit & upgrade any 317-based V.Reg.
It was actually insufficient to measure the true performance of the scheme under test, but it provided a first glimpse of the improvements.
I later complemented it with a proper LNA, but having an instrument ready, capable of roughing out the job is very convenient.
I also find the built-in, crude filters useful, and I frequently use the auxiliary output to push my scope's sensitivity down to µV level.
Thus, I could easily do without it, use my lab instruments and amplifiers to do the same, but it is a convenient piece of kit.
If you can have one for cheap, and if it isn't too bulky, I would go for it
Assuming it measures RMS values, it can be handy for noise measurements when you combine it with an A-weighting filter. I have an old distortion meter that also works as a millivoltmeter and a homemade A-weighting filter.
The last time I used it, it was just to check the AC heater voltage of a valve circuit.
The last time I used it, it was just to check the AC heater voltage of a valve circuit.
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Useful for all sorts of things.
Other simple uses - connecting across your speaker terminals and finding out how much power your preferred listening level amounts to,in RMS terms. Always instructive as to how little this might really be...
and then - use it to work on your amplification until the idle noise, vol at normal, at the speaker terminals gets down below the 100uV level. go for delivering all the dynamic range your sources are capable of!
There are many other things that having an ACmv meter is complementary too. It's actually the kind of uses that cheap DVMs are very poor at, so if this piece of equipment piques your interest - yes, buy it. You'll find new uses, the more you play.
Other simple uses - connecting across your speaker terminals and finding out how much power your preferred listening level amounts to,in RMS terms. Always instructive as to how little this might really be...
and then - use it to work on your amplification until the idle noise, vol at normal, at the speaker terminals gets down below the 100uV level. go for delivering all the dynamic range your sources are capable of!
There are many other things that having an ACmv meter is complementary too. It's actually the kind of uses that cheap DVMs are very poor at, so if this piece of equipment piques your interest - yes, buy it. You'll find new uses, the more you play.
Thanks, I'll pick it up in a few weeks then. An analog meter can do things a DMM cant when it comes to seeing minute changes. So far I have power supply ripple as maybe worth it alone, or to test if old filter caps are doing their job in a repair. Putting on an audio test CD (or even just music since it is averaging the AC) and using it to measure RMS listening levels. The idle noise check is cool too. I really like to breadboard, so quick and dirty is nice.
For example I recently wanted to just see the inrush current and quiet down time that happens when I switch on an amp... The DMM failed miserably at this. So I wired an old Simpson 3A AC panel meter I had in series with the mains. It told me tell right away the peak inrush current and how long it took it to quiesce, just by watching the needle. Using that value and timespan one can look up the best thermistor. And even go ahead and do it over with different thermistors until the inrush gets handled best. It even shows the little jump that happens when the shorting relay removes the thermistor. The DMM cant do any of that!
For example I recently wanted to just see the inrush current and quiet down time that happens when I switch on an amp... The DMM failed miserably at this. So I wired an old Simpson 3A AC panel meter I had in series with the mains. It told me tell right away the peak inrush current and how long it took it to quiesce, just by watching the needle. Using that value and timespan one can look up the best thermistor. And even go ahead and do it over with different thermistors until the inrush gets handled best. It even shows the little jump that happens when the shorting relay removes the thermistor. The DMM cant do any of that!
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Exactly! The first and greatest thing actual analogue meters give you - is a clear impression of trend. Flickering digits cannot do this. Am I watching noise, a cyclical problem, a drift, a trend or ...what ? For very quick insight into such issues, an analogue meter is fantastic; irreplaceable, in fact
and
I've a couple of rather old AvoMeters. Apart from being simply lovely things - the fact that they require no batteries on the 0-3Vac and other scales is inherently useful; I can plug one into the back of my headphone amp as a giant VU meter so I'm aware of how hard (or not) I am driving whatever headphone set I have in use; useful ditto with the speaker system. Free amusement - from a seriously useful tool.
I hope the set proves useful to you.
and
I've a couple of rather old AvoMeters. Apart from being simply lovely things - the fact that they require no batteries on the 0-3Vac and other scales is inherently useful; I can plug one into the back of my headphone amp as a giant VU meter so I'm aware of how hard (or not) I am driving whatever headphone set I have in use; useful ditto with the speaker system. Free amusement - from a seriously useful tool.
I hope the set proves useful to you.
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My Levell TM3B is an average-measuring/RMS-calibrated instrument (it is cheapest among the cheaps), but for "ordinary" noise profiles, it agrees almost perfectly with true RMS instruments.
In fact, I do not even bother to check the true RMS value when the noise profile is not pathological: the displayed value is accurate to a few %, which is normally perfectly sufficient for most measurements.
For an instrument maker like Keysight or Tektro, it is important to get the specs right down to the tenth of dB, but for ordinary, DIY and troubleshooting work, the average method is mostly sufficient (not the case for power converters, and anything else that produces extreme waveforms obviously)
I also have 2 channel meter (Kenwood VT-176)
Kenwood VT-176 2-Channel AC Voltmeter Manual | HiFi Engine
... and four others single channel (2 in operation, 2 spare/possible donor). 🙂
Measuring transfer functions it's basic instrument.
The quick -and dirty- transfer measuring: signal generator- DUT (device under test)-mV meter.
It's quicker, and more vivid, than using computer aided measuring.
The other function of mV meter is using as "preamp" before the soundcard metering (transfer, FFT, THD etc.): it have fixed level (below 1V) output.
With this layout (and 100MHz 1:1, 1:10, or 1:100 high voltage oscilloscope probe) becomes possible measuring within tube equipments (with great caution!).
Kenwood VT-176 2-Channel AC Voltmeter Manual | HiFi Engine
... and four others single channel (2 in operation, 2 spare/possible donor). 🙂
Measuring transfer functions it's basic instrument.
The quick -and dirty- transfer measuring: signal generator- DUT (device under test)-mV meter.
It's quicker, and more vivid, than using computer aided measuring.
The other function of mV meter is using as "preamp" before the soundcard metering (transfer, FFT, THD etc.): it have fixed level (below 1V) output.
With this layout (and 100MHz 1:1, 1:10, or 1:100 high voltage oscilloscope probe) becomes possible measuring within tube equipments (with great caution!).
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Good point, you are only about 1 dB off.
Normally distributed noise:
RMS value is sqrt(pi/2) times the average absolute value, with sqrt(pi/2) ~= 1.25331414
Sine wave:
RMS value is sqrt(2) pi/4 times the average absolute value, with sqrt(2) pi/4 ~= 1.11072073
Ratio: 1.12837917, so you only underestimate Gaussian noise by about 1 dB.
Kenwood made good stuff back in the 80's. Made in Japan at the peak of when they were obsessed with quality! My friend has a Leader, same era made in Japan.
If the instrument really has 30uV sensitivity full scale you should go for it.
I suspect it is 300uV, good enough most of the time.
I suspect it is 300uV, good enough most of the time.
Good luck with that!
HP, GenRad and others made quite sensitive tuneable voltmeters, i.e. "wave analyzers" -- you can measure distortion by first tuning to the fundamental, then dialing up the values of the harmonics.
HP, GenRad and others made quite sensitive tuneable voltmeters, i.e. "wave analyzers" -- you can measure distortion by first tuning to the fundamental, then dialing up the values of the harmonics.
Some decades ago I would have been happy to afford an AC-millivoltmeter with A+C weighting. Today with my tiny cellar man cave I am happy with my Rigol Scope, some soundcards and laptops. All in all it is a matter of taste. If you love these stylish pointer instruments, go for it😉
I had to check that again too, its actually 100uV to 300V in 12 ranges. I somehow got 30uV in my head just seeing it at his table last month. Still at 1/10th of a mV I'd have to begin to worry about stray AC just using it.