Any scopes that can display Db Volts in the under $500 range?

[Sparky Faraday]

Hi,
Just got my Siglent SDS 2104X-E and am trying to adapt it to my audio bench.

It can measure voltage in 25+ different ways, every way except dbV volts. Is there any DSO that has that feature? I was hoping to get my Leader ACVM off my bench but that won't happen with this.

I think in dbs when I measure gain or F response, every thing really.

Thanks

[vk6zgo]

Hi,
Just got my Siglent SDS 2104X-E and am trying to adapt it to my audio bench.

It can measure voltage in 25+ different ways, every way except dbV volts. Is there any DSO that has that feature? I was hoping to get my Leader ACVM off my bench but that won't happen with this.

I think in dbs when I measure gain or F response, every thing really.

Thanks

I don't know much about that model of 'scope, but I doubt that there is any way to show dB on the ordinary
display.
How about FFT-----maybe there is a log option for that?

[tautech]

Hi,
Just got my Siglent SDS 2104X-E and am trying to adapt it to my audio bench.

It can measure voltage in 25+ different ways, every way except dbV volts. Is there any DSO that has that feature? I was hoping to get my Leader ACVM off my bench but that won't happen with this.

I think in dbs when I measure gain or F response, every thing really.

Thanks

I don't know much about that model of 'scope,

Because there's no such model. 
Probably the OP means SDS1204X-E.

but I doubt that there is any way to show dB on the ordinary display.

Correct although IIRC you can select dB output levels in the AWG and in the Bode plot feature.

How about FFT-----maybe there is a log option for that?

Certainly, see below FFT menu from the 100 MHz SDS1104X-E:

[DaJMasta]

You can probably make it into a math function, though I think in most cases it's limited to math on the entire trace rather than math on a value (though maybe a math trace and cursors would do it for you).

I think scopes aren't so likely to have it because a typical one may only have ~50dB of actual dynamic range, in which case the log scales count for a lot less utility.  An alternative for a ballpark could just be Vrms and a table of some convenient values in dBV.

[rf-loop]

You can probably make it into a math function, though I think in most cases it's limited to math on the entire trace rather than math on a value (though maybe a math trace and cursors would do it for you).

I think scopes aren't so likely to have it because a typical one may only have ~50dB of actual dynamic range, in which case the log scales count for a lot less utility.  An alternative for a ballpark could just be Vrms and a table of some convenient values in dBV.

Think other way.
Also I think what OP say about leader what is possible analog one.

I was hoping to get my Leader ACVM off my bench but that won't happen with this.

If want measure dBV values reference value is 1V  (1V = 0dBV).
If user change measurement range just as he also select range with multimeters, automatically or manually, lets see how it go:

Most high sensitivity is 500uV/div and most low sensitivity is 10V/div if measured signal is connected to scope 1:1

In practice, example 1. 0.5mV peak sinewave give 2div p-p in 500uV/div range and example 2.  other end, using 10V/div there can be up to 40V peak sinewave.(80Vp-p).
Just like with multimeters it only need user select right range.
example 1. -69.03 dBV
example 2. +29.03 dBV

Whole usable range what can measure without external divider (probe) is roughly 98dBV  (-69 to +29dBm)
Of course this can bit stretch more if use high averaging and or other filtering in 500uV/div scale. So we can perhaps get up to 100dBV whole range.
(Using example FFT or SFRA it may give some amount more dynamics in one whole measurement and there is log scales but this is out from this question.)
Perhaps this is useful feature and we can wish some day in some model dBV measurement function is implemented....letter to Santa Claus.

Totally other question is one shot dynamic range. This is limited by 8 bit ADC resolution and other limiting things -- well under 45dB. Same with my multimeter, without range change it have more limited dynamic than with range change. Also my old HP analog meter have dB range and dynamic range is quite low without change measurement range. Without range change analog meters practical dynamic range is roughly 20dB
Example Leader ACVM here: (from   https://www.tapeheads.net/showthread.php?t=73600  )

[Sparky Faraday]

That's the Leader ACVM I use. I have 2. They are really good for audio. 1MHZ bandwidth which is why it's an audio meter, but only 1Mhz.

Yes, I can print out a standard dbv table and get the difference between ins and outs off the scope and look that up in db BUT since this is a fancy pants scope, I was hoping it would make my life easier with a direct simple math function and save me another 1/2 sq foot of bench space. But alas . . .

I don't want parallel inputs with the scope and Leader - too much cable capacitance. In my all analogue setup I take outputs from the Leaders and run them into the scope as I did with the Hitachi 35 MHZ scope, and unhook a channel and go direct into the Hitachi when I need to use a scope direct probe. That worked fine for 35 years and will probably be how I go with Siggy.

The Siggy it has no dedicated trigger input so I have to use one channel for that so that leaves me one open scope channel. A minor improvement.

Fundamentally, the advantage for me of the scope is being able to record and analyze up to 4 channels of events. It already paid off for me in that respect. That and the FFT is useful, just tricky to use in the audio band. Oh, and saving the setups is cool.

Amazingly I can't find a DVM with dbv function either. Any one know of one? I can buy a cheap auto-ranging audiometer w/mic for sound measurement and chop that up to work, I guess.

And yes, I'm dyslexic. I have the SDS 1204X-E. I could have gotten the Rigol for $100 less but what - the - heck, I may actually need the extra BW and the math functions at some point.

Last scope I will buy.
Post covid vaccine rollout I go back to being a jazz bass player.

[commongrounder]

A Fluke 287 or 289 will read dBV directly. Pricey unit, though.  Another reasonably priced option is to find a good condition used Fluke 45 bench meter.  When you select the dBm range, the reference impedance can be set to 1000 ohms, which will give you dBV readings. Also, you can select 2,4,8,16 ohms reference impedances and have the meter calculate amplifier output power for you.  I have used two of these in my shop for years for this exact purpose. A dBm or dBV math function would be a nice addition to a digital scope for us audio people.

[bdunham7]

As already mentioned--have a good look at the FFT function and get good at setting it up.  It's likely that reading dBV from there will be more useful than directly from a trace.   dBV is typically measured as an RMS value, not an instantaneous one.  Using log math directly on the trace would be weird and confusing, although technically not impossible.  I can't think of any general-purpose scope I've seen that works like that.

As for DMMs, many meters with TRMS will read dBm and allow you to specify the reference impedance (the impedance of the meter does not actually change). Set that to 1000 ohms and you have dBV. 

As mentioned, the Fluke 289 has a direct menu option for dBV.  I see dB options on the panel in the math section of my HP 34401A, but it's not on the bench at the moment so I can't try it.  My BK Precision 2831E had a dBm + reference impedance function that would work for you.

[alsetalokin4017]

From the Rigol DS1000Z series user manual re FFT:

The unit of the vertical axis can be dB/dBm or Vrms which use logarithmic mode and linear mode to display vertical amplitude respectively. If you need to display the FFT frequency spectrum in a relatively larger dynamic range, dB/dBm is recommended.

[Sparky Faraday]

Thanks for the replies. I'll put some time in on the FFT.

What I generally need are gain measurements. In to out so just relative to each other, not absolute. When I open the fb loop I can see the difference and get the NFB amount from that.

I can still do it with my bench. I was hoping the scope can do that for me but not this one.

I do like that it can read phase shift directly but I'm not sure I can trust it yet.

[tautech]

Thanks for the replies. I'll put some time in on the FFT.

What I generally need are gain measurements. In to out so just relative to each other, not absolute. When I open the fb loop I can see the difference and get the NFB amount from that.

I can still do it with my bench. I was hoping the scope can do that for me but not this one.

I do like that it can read phase shift directly but I'm not sure I can trust it yet.

Maybe you need study this thread where the limits of X-E Bode plots are explored:
https://www.eevblog.com/forum/testgear/siglent-sds1x04x-e-bodeplot-ii-(sfra)-features-and-testing-(coming)/

[rf-loop]

SDS1104X-E as also many other Siglent scopes can easy use just like logarithmic scale selective level meter.
Here example. Not SDS1000X-E but same things are also there even when User Interface have differences.
These scopes have very good FFT.  For using as selective level meter of course we need select right "window" and this is not rectangle. We want look levels not freq so best is perhaps FlatTop "filter"

If freq selectivity is not at all important and just want measure wide BW then Memory, samplerate and FFT length can select optimal for speed etc. All can set.
Then set unit what you want use. Here I have used dBm and in 50ohm impedance system.
If you want use example 600ohm system you can set scope input to 1M and not 50ohm. Then you add 600 ohm load (terminator) to scope input BNC and you connect your 600 ohm source to this then this source is loaded right. Then set FFT function EXT LOAD value  for 600ohm, so it can display right values spedcially important if your measurement unit is power as dBm is.  You can set vertical scale as needed. Here I have set scale for 10dB/div and reference level 10dBm. As can see noise level is outside of this display bottom but do not afraid, it sure is there. Display is jut only like small window to this whole area.
This have still far better dynamic range without vertical level range change.

1 image is only for show vertival units and scale selections. (different UI in SDS1000X-E but all these are also there)
2. I have measured signal in around 400Hz and first one amplifier OFF
3. Amplifier ON. As can note it amplify 43dB
There is marker in center of "filter" what follow this level.  (of course there is available more markers and two kind of markers and  tey can also search peaks etc..and harmonics but now I show selective level meter with Log scale so  it is here. Only what disappear is "needle" like in your analog meter. But if think this flat top is more wide it can be even straight line horizontally over display then you have this kind of level needle with dBm or dBV scale.
4. Just both, signal in time domain and with linear vertical scale and then level meter yellow horizontal line (FFT produce it) what moves vertically with LOG scale depending signal level and also marker tell its numerical dB value. In this image signal was  -6dBm level as yellow log scale level line show.

Any scopes that can display Db Volts in the under $500 range?

Of course and even very easy. Also can see this signal and this FFT level meter same time on the screen. As image 4. Of course different model bit doifferent and also depending how user set it.
But using these features so that they give somehow out what user want need that user is familiar with his instrument and its features.

[Sparky Faraday]

@rf-loop,
Thank you for your help.

I have to do some studying of your directions. And thank you.

What scope are you using? This is much hipper than mine.

BTW, is there a vertical auto-ranging function like a DVM? Can't find it in the instructions.

To everyone.

I spent some time with the FFT function and got it to show DbV at a fundamental of 1Khz. But it is not that convenient even with a setup recall function. I'm not sold on it's accuracy. It seems that the Rectangle Window is the most accurate. Here's pix of my work. Input: 1 Khz @ 1 V > Leader LMV-185 2 ch ACMV/ output > CH1, CH4 set to trigger from the trigger out on the osc.


I find I have to make sure the saves happen. I have assumed it was saving a setup only to find "file doesn't exist" when I go to recall it later.



So for now, living in the base band audio world, I'll probably use my old setup while I learn the FFT and bode plot functions.

Also, it appears I need to keep a notebook of what each setup is as the scope doesn't allow a readout of the settings. UNLESS i'm missing something? Also, it's very easy to overwrite and setting.

[rf-loop]

@rf-loop,
Thank you for your help.

I have to do some studying of your directions. And thank you.

What scope are you using? This is much hipper than mine.

BTW, is there a vertical auto-ranging function like a DVM? Can't find it in the instructions.

To everyone.

I spent some time with the FFT function and got it to show DbV at a fundamental of 1Khz. But it is not that convenient even with a setup recall function. I'm not sold on it's accuracy. It seems that the Rectangle Window is the most accurate. Here's pix of my work. Input: 1 Khz @ 1 V > Leader LMV-185 2 ch ACMV/ output > CH1, CH4 set to trigger from the trigger out on the osc.
(Attachment Link)

I find I have to make sure the saves happen. I have assumed it was saving a setup only to find "file doesn't exist" when I go to recall it later.



So for now, living in the base band audio world, I'll probably use my old setup while I learn the FFT and bode plot functions.

Also, it appears I need to keep a notebook of what each setup is as the scope doesn't allow a readout of the settings. UNLESS i'm missing something? Also, it's very easy to overwrite and setting.

What is your SDS1204X-E    FW version?
Latest version 6.1.35R2

You need perhaps lot of training before you get all out from FFT.
There is many adjustment, sampling speed, scope time domain time base, memory length. FFT memory length.
Frequency span... center frequency and how wide range you wont look or start and stop frequency (just like zoom in more or less).
After then also need find how to set oscilloscope input channel level. And of course there is NO autorange.
After then you need find what mode you want... average FFT perhaps . Then you need find how to set and use markers for trace level and display value.
And always keep tight in mind basics about FFT. You need care that ADC do not see signals what have higher freq components than Nyquist limit is with cdurrent true sampling speed.

Scope what I use here for example was SDS2104XPlus, bit more advanced than SDS1104X-E what I have also used lot of but I do not have it now here.
But SDS1000X-E have roughly same features and functions in FFT. Bit less performance but difference is not big. 

Then you talk about BodePlot functions. What signal generator you have for it. It need Siglent generator (or something what have made compatible).
It is useless without suitable generator. It can work only with generator what is fully controlled by oscilloscope BP function, without any exception because it need be tightly synchronous with scope. Reason is, scope works in BP like frequency selective sweeping level receiver.
But BP function include full scale automatic auto range (ALC) system.


Here is one paper where can find how to select FFT window. Starting from page 10.
https://www.sjsu.edu/people/burford.furman/docs/me120/FFT_tutorial_NI.pdf

[Sparky Faraday]

Thanks again RF-loop.

I think I get it about the bode plot. It requires a sweep generator married to the scope, like what we used to align a tv or FM if stage. In the old days the sweep gen provided the Y output and the X came from the DUT. Simple.

I can do an adequate quick manual sweep of an audio amp just with my generator and meter, just hitting the F decade switch and spinning the dial at 10 or 100 khz. usually just looking for the -3 db point.

Continuing education. Is there a good tutorial article on FFT that I can reference?

Thanks.

[rf-loop]

Because previously I use some other scope than you have and you perhaps think it is much more advanced for FFT that your SDS1204X-E.  With your scope can do almost same if we look just this case.  SDS1000X-E/U series display is smaller. resolution is less so it also make some different and some other small things. FFT functions, features are lot of same.

Here some small examples using bit lower Siglent model, SDS1104X-U.

You need know that also User manual is same for these models X-E and X-U and most new manual version also have bit better about FFT.
Download it from Siglent side.  https://www.siglenteu.com/download/10068/
FFT starting from page 129.
And as told previously, you need be sure your scope have latest FW:  SDS1xx4X-E Firmware(4-Channel Models) – 6.1.35R2
If not, please first look carefully how to update.

Here some examples, something like previously but now with SDS1104X-U
Note that all signals are sinewave until there is told it is square wave.
I have not even tried to find most optimal settings for these small examples.
When use FFT as level meter it need always remember that it is not wide band level meter as old analog Leader in your case. Using FFT for this it need remember it is highly frequency selective. But of course it can adjust changing samplerate and FFT length and also selecting best possible FFT Window for level measurements what is "Flat Top".  Rectangle is... mostly forget if you do not know valid reason why you really need it.

Here just tiny examples what may give some imagine what it can do... yes it can do also lot of more.  I have no time to take it now on table and make some more examples about more wide frequency band width "level meter with dB scale" using FFT.

Image names may give also some some info

Think I have first -40dBm signal, image 1 and then I add 43dB amplifier and result is image 2

Note I have not used most high freq resolution. I used resolution and FFT window function what give more wide and flat top just for "Log scale Level meter" in mind and so that frequency can even drift some and I do not loose level.. Also f. band can be more wide. Bit it can not be this kind of wide band what is example your old Leader analog meter.This FFT method is and stay as selective level meter.

[Sparky Faraday]

Hi RF,
Thanks for your time to get me started with this.

It took me an hour of fussing around with hidden menus but I finally got the first 2 or 3 picture on my scope.

When it come to measuring it takes about a minute for the everything to settle down when I change the input 10 db so that's fine if I need to run to the bathroom but my ACMVM is immediate and accurate enough. I assume more $$$ is faster.
My setup is Gen>ACMVM>scope. The ACMVM (millivoltmeter) is instantaneous.

BTW, I have the manual downloaded and the scope is running 6.1.35R2, Uboot OS 8.1, FPA Version 2019-11-15, Hardware V 01-05.

Also, yes I know the FFT is not wide band and for the most part I'm measuring sine waves. Occasionally I need a noise or hum measurement but I know my meter well and I'm always looking at it on the scope. The Siggy will give me a much deeper look at it, for sure but I've gone 35 years without it.

This exercise was great to get me better acquainted with FFT. or really SFT.

Here's my homework.

I'll try the others later.

[tautech]

Sparky, use the blue Print button for screenshots straight to a USB stick which has the massive advantage of displaying the feature menu instead of the Save/Recall menu.
Being able to see your menus setting helps immensely to give proper advice on usage.

[Sparky Faraday]

tautech - I was wondering about that. Yes indeed, that will help!
Thanks,
Sparks

[Performa01]

When it come to measuring it takes about a minute for the everything to settle down when I change the input 10 db so that's fine if I need to run to the bathroom but my ACMVM is immediate and accurate enough. I assume more $$$ is faster.

One minute doesn’t sound credible for your settings. When I replicated your case, the response time of the FFT was 1 second at the most.

The speed of measurement has nothing to do with $$$, but with the effort that goes into a measurement.

A simple AF-millivoltmeter measures wideband average voltage, calibrated in RMS (valid for pure sine waves only) and its response time depends on the lower frequency limit, because the time constant of the averaging has to be long enough to average out several periods of the lowest input frequency.

The modern DSO on the other hand does frequency selective true RMS measurements – and not just one, but a multitude of them at the same time. Luckily, we just need to know some basics and then be able to configure the measurement so that it suits our needs.

In your example the FFT bandwidth is unnecessarily wide for audio: 2.5 MHz. At the same time, the frequency step is very small, just 19.07 Hz. That means that your FFT has to process 2.5 MHz / 19.07 Hz = 131095 bins for every single scan. This is in accordance to what is displayed on the screen: 262144 points … divide that by two and you get the number of bins. In other words, 131095 individual 19.07 Hz wide sections of the total bandwidth are processed during one single scan. Do you still think the instrument is slow?

And it’s so easy to speed it up considerably. For example:

Limit the FFT length to 16 k and speed up the timebase to 1 ms/div.

Now you get an effective sample rate for the FFT of 2.5 MSa/s, thus reducing the bandwidth to 1.25 MHz, which should still be plenty for AF. At the same time, the frequency step has increased to 152,59 Hz, which is meaningless as long as your benchmark is a wideband measurement.

Keep in mind that changing the display parameters, i.e. vertical reference level and scale as well as horizontal start/stop frequencies does not alter the measurement in any way. It is just the way how you look at your data, including extreme zoom views.

A few simple rules:
•   The upper frequency limit of the FFT is half the effective (FFT) sample rate.
•   The lower frequency limit is determined by the reciprocal of the timebase divided by the number of horizontal divisions. 1ms/div corresponds to 1000 Hz / 14 ~ 71.42 Hz. The lower you get here, the longer the timebase and the smaller the frequency step, where both will considerably slow down the measurement.
•   Make sure the upper frequency limit as defined above includes all possible input frequencies (including harmonics and spurs), not just the ones you are interested in. Use the horizontal display settings to define center frequency and span to zoom into narrowband structures.
•   Always use flattop window for best amplitude flatness and accuracy in the passband and be aware that the -3dB bandwidth of this particular window is roughly about 4 frequency steps. In the example above, the -3dB bandwidth would be about 600 Hz.

[SilverSolder]

[...]
Perhaps this [logarithmic range] is useful feature and we can wish some day in some model dBV measurement function is implemented....letter to Santa Claus.
[...]

Would it be possible to knock up a small log converter that could be used externally for (DC) dBV measurements?

It seems to me the low dynamic range of the scope inputs makes it very difficult to build this into the scope itself?

[rf-loop]

[...]
Perhaps this [logarithmic range] is useful feature and we can wish some day in some model dBV measurement function is implemented....letter to Santa Claus.
[...]

Would it be possible to knock up a small log converter that could be used externally for (DC) dBV measurements?

It seems to me the low dynamic range of the scope inputs makes it very difficult to build this into the scope itself?

Externally can do what ever math (analog) even very complex.
Old times it was fun and more fun it was when analog computer need sometimes calibrate. I do not have experience with these big machines but in factory in some production line there was small (except size and weight because it have also analog memory for make delays) E.I.A made analog number cruncher doing part of product testing.
Always when factory product lines was stopped due to holidays  we need do  deep check and calibrate-fine adjust it for best possible accuracy including some predict because always we have previous record and we know main things how it drift due to some ageing etc. In normal production  we only look after it if some problems.  This amount of trimmers inside.. and all was bit better tempco and overall best available. Also front panel huge amount of normal 10 turn potentiometers with dial, switches etc for normal users to set parameters what need when these things change what it measure and calculate..

So, answer is of course yes and it is even easy as eating if we talk low frequencies.

[Sparky Faraday]

Here is an attempt to copy RF's first snapshot a few posts back.
Some notes: I'm using ch 2 for input and ch 4 for sync off the back of the generator. Gen into ACVM into scope. So a click of the meter knob is 10 db.
Whatever else I'm doing would be in the picts.

Also some bugs taking pics with the print button. I don't think this should happen.

I'm beginning to think the scope has some problems, not just from this.

Also, I timed the scope when I increased or decreased the input by 10 db and either way it is roughly 40 seconds of settling time.

Is there a map of the layers of menu items for these things? I know each feature is laid out in the manual but a quick reference would be very helpful. Not asking anyone to do it, just asking if it exists.

Also my bench. I just put white leds in the meters so I can read them. Brightens the bench, too.

Thanks

[tautech]

Also some bugs taking pics with the print button. I don't think this should happen.

Just press Print don't hold it and wait for the saved to *** message to appear. Holding down any button pops up the Help message for that button.
Pressing Print again too rapidly will capture where the last screenshot was saved to.

Sub menus will remain up for a short period and with practice they are easy to capture into a screenshot.

[Performa01]

Also, I timed the scope when I increased or decreased the input by 10 db and either way it is roughly 40 seconds of settling time.

Well, as I've spotted you are using Average mode and this slows down settling time considerably indeed.
Nevertheless, my test using your settings on an SDS2354X Plus took less than 12 seconds to be fully settled in 4x Average mode. So it remains mysterious how your setup appears to be so much slower. I do not think there can be a significant difference to the SDS1000X-E series, nor have I experienced it in the past (I know the SDS1000X-E fairly well, just don't have a specimen at hand right now).

Anyway, only use Average mode in an attempt to precisely measure noisy signals; for reasonably clean and stable signals, Normal mode does the job much faster.

EDIT: Forgot to mention: Instead of the peak table, it is more convenient to enable an automatic max() measurement for the math (FFT) trace. You are fully independent of the FFT settings and can have full measurement statistics on top of that - i.e. the statistics average of that measurement can replace the Average mode in the FFT settings in many instances. This way you get the instantaneous value together with the long time average at the same time. You can define the averaging period by simply pushing "Clear Sweeps" on the front panel, which will reset the measurement statistics.
On the other hand, FFT markers can only be placed within the constraints of the frequency step raster, so they can be off considerably when you are using wide frequency steps.