Any scopes that can display Db Volts in the under $500 range? - Page 1
Forum section: electronics / testgear

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 05, 2021, 04:46:23 am
content: 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

author: vk6zgo
author_rank: Super Contributor
timestamp: February 05, 2021, 06:00:07 am
content: Quote from: Sparky Faraday on February 05, 2021, 04:46:23 amI don't know much about that model of 'scope, but I doubt that there is any way to show dB on the ordinarydisplay.How about FFT-----maybe there is a log option for that?

author: tautech
author_rank: Super Contributor
timestamp: February 05, 2021, 06:15:19 am
content: Quote from: vk6zgo on February 05, 2021, 06:00:07 amBecause there's no such model.Probably the OP means SDS1204X-E.QuoteCorrect although IIRC you can select dB output levels in the AWG and in the Bode plot feature.QuoteCertainly, see below FFT menu from the 100 MHz SDS1104X-E:

author: DaJMasta
author_rank: Super Contributor
timestamp: February 05, 2021, 07:03:54 am
content: 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.

author: rf-loop
author_rank: Super Contributor
timestamp: February 05, 2021, 09:49:23 am
content: Quote from: DaJMasta on February 05, 2021, 07:03:54 amThink other way.Also I think what OP say about leader what is possible analog one.Quote from: Sparky Faraday on February 05, 2021, 04:46:23 amIf 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 1:1In 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 dBVexample 2. +29.03 dBVWhole 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 20dBExample Leader ACVM here: (fromhttps://www.tapeheads.net/showthread.php?t=73600)

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 07, 2021, 07:08:05 pm
content: 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.

author: commongrounder
author_rank: Frequent Contributor
timestamp: February 07, 2021, 08:17:27 pm
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: February 07, 2021, 09:17:12 pm
content: 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.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 07, 2021, 09:32:13 pm
content: From the Rigol DS1000Z series user manual re FFT:Quote

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 08, 2021, 03:25:24 am
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: February 08, 2021, 03:37:37 am
content: Quote from: Sparky Faraday on February 08, 2021, 03:25:24 amMaybe 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)/

author: rf-loop
author_rank: Super Contributor
timestamp: February 08, 2021, 07:52:09 am
content: 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 OFF3. Amplifier ON. As can note it amplify 43dBThere 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.

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 09, 2021, 06:11:14 am
content: @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.

author: rf-loop
author_rank: Super Contributor
timestamp: February 09, 2021, 11:39:29 am
content: Quote from: Sparky Faraday on February 09, 2021, 06:11:14 amWhat is your SDS1204X-E FW version?Latest version 6.1.35R2You 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

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 09, 2021, 05:55:36 pm
content: 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.

author: rf-loop
author_rank: Super Contributor
timestamp: February 10, 2021, 07:57:16 am
content: 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) – 6.1.35R2If not, please first look carefully how to update.Here some examples, something like previously but now with SDS1104X-UNote 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 infoThink I have first -40dBm signal, image 1 and then I add 43dB amplifier and result is image 2NoteI 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.

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 11, 2021, 03:24:10 am
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: February 11, 2021, 04:01:12 am
content: 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.

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 11, 2021, 04:27:21 am
content: tautech - I was wondering about that. Yes indeed, that will help!Thanks,Sparks

author: Performa01
author_rank: Super Contributor
timestamp: February 11, 2021, 02:28:29 pm
content: Quote from: Sparky Faraday on February 11, 2021, 03:24:10 amOne 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 thedisplayparameters, i.e. vertical reference level and scale as well as horizontal start/stop frequencies doesnotalter 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.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 11, 2021, 02:36:32 pm
content: Quote from: rf-loop on February 05, 2021, 09:49:23 amWould 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?

author: rf-loop
author_rank: Super Contributor
timestamp: February 11, 2021, 04:08:01 pm
content: Quote from: SilverSolder on February 11, 2021, 02:36:32 pmExternally 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.

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 12, 2021, 05:21:12 am
content: 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

author: tautech
author_rank: Super Contributor
timestamp: February 12, 2021, 06:25:53 am
content: Quote from: Sparky Faraday on February 12, 2021, 05:21:12 amJust 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.

author: Performa01
author_rank: Super Contributor
timestamp: February 12, 2021, 10:16:38 am
content: Quote from: Sparky Faraday on February 12, 2021, 05:21:12 amWell, 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.

author: rf-loop
author_rank: Super Contributor
timestamp: February 12, 2021, 10:55:45 am
content: Quote from: Performa01 on February 12, 2021, 10:16:38 amThis rolling average is perhaps not implemented optimally for step response. How long it takes before error is below resolution after large step in input.

author: Performa01
author_rank: Super Contributor
timestamp: February 12, 2021, 11:30:55 am
content: Quote from: rf-loop on February 12, 2021, 10:55:45 amThis is something I've been noticing a long time ago: the Average mode takes much longer to settle than expected according to the selected parameter.For instance, a 4x Average takes at least 16 full scans (FFT calculations) to settle - if it were the classical sliding average, one would expect that the final result is available after 4 scans.So my verdict on this: since we cannot go any lower than 4x averaging (which in reality looks much more like a 16x sliding average), we should avoid Averaging mode unless we have a good reason to use it anyway (like the reasons I've mentioned in my last post).

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 12, 2021, 04:22:06 pm
content: Thanks. I can see the average mode would take a long time. Will try your suggestions.Can someone suggest a current book or website that can walk me through FFT from the ground up?I'll try to map out the menus and sub menus for the machine. I'll post it when I get it done.73s

author: Performa01
author_rank: Super Contributor
timestamp: February 12, 2021, 05:59:06 pm
content: I can't suggest a website for the FFT fundamentals (I guess professor Google might yield something), but can offer a checklist specific for Siglent DSOs (reply #23):https://www.eevblog.com/forum/testgear/rohde-schwarz-rtb2002-vs-siglent-sds2104x-plus/msg3239832/#msg3239832Some corrections/additions:ad 2. Line trigger is even better, because it will trigger 50 or 60 times per second even with signals below the trigger sensitivity at slow timebases, where the auto trigger rate can be rather slow.Topics 6 and 7 should be swapped, obviously, whereas the order of topics is flexible to a certain degree otherwise.

author: wilhe_jo
author_rank: Regular Contributor
timestamp: February 12, 2021, 06:25:52 pm
content: There's a book which can be read online...http://www.dspguide.com/pdfbook.htmIts pretty basic, but I guess that's what you wantedIt covers DFT, FFT and several other topics.Another reference would be "Digital Signal Processing" by Oppenheim & Schäfer.But that's more what you would read at university... so its very detailed on the mathematics73

author: horo
author_rank: Regular Contributor
timestamp: February 12, 2021, 07:51:24 pm
content: Even very cheap devices can show this if it has the right software - preferable a softwarethat you can adapt on your own.Bottom lines show besides some DC/AC values also the dBV level, the power dissipation for a selectable load, the THD of the signal as well as the frequency.

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 12, 2021, 08:26:08 pm
content: Again, thanks for great advice and patience for a DSO newbie.@ horo: "Even very cheap devices can show this if it has the right software - preferable a software that you can adapt on your own."Well, I can make your stereo sound great and spin a great bass line for a tune, not sure about that.I have to do some research. So thinking it through, and on my bench I have surrendered to the fact that my ACVMM into my scope will be more than adequate for measuring sine waves through an audio amp.What will be of interest is seeing the FFT breakdown of distortion components from my THD setup.I still welcome any continuing advice. I actually got a FFT readout on the output of my THD analyzer, really a filter, when I first set up the scope.

author: bdunham7
author_rank: Super Contributor
timestamp: February 12, 2021, 09:15:11 pm
content: I still welcome any continuing advice. I actually got a FFT readout on the output of my THD analyzer, really a filter, when I first set up the scope.Well, not to discourage you in any way, but a typical DSO has significant limitations in audio work because it usually has 8-bit resolution and a bandwidth 100 to 1000X what is appropriate. This means that things like noise and THD are well above the acceptable floor for any decent audio equipment. A decent soundcard in a PC and the right software will greatly outperform a standard DSO as well as DDS-based signal generators. A DSO is useful for examining gross errors, such as in the repair process, but I wouldn't be using it for most types of fine tuning. Level comparison might be one exception where they are good enough.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 12, 2021, 09:32:52 pm
content: You could do a lot worse than downloading the WaveForms software from Digilent - this software normally powers the Analog Discovery, but it actually works great with a PC sound card! - and it is 100% free!https://reference.digilentinc.com/reference/software/waveforms/waveforms-3/startUsed with a decent sound card, you can do a LOT of cool things at audio frequencies that a scope has no chance of keeping up with.

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 13, 2021, 01:32:38 am
content: You may have hit the nail on the head. This is the wrong hammer for my nails. Audio minimum today is 16 bits deep at 44.1Khz sample - cd quality (mp3 is irrelevant for me) and CD quality is not really listenable for orchestral string listening. Going to 24 bits solves a lot of problems. No arguing here.I downloaded the Waveforms software and it looks like I can do a lot with a 192Khz interface box, relatively cheaply. Although no dbV scaling. Gets me to 96K. The only thing I need to look at above that is bandwidth of my amps, usually 250Khz -3db point but I can get that with my analogue setup.The 4 ch did solve a warmup mute timer problem. Maybe Return it and get Rigol 4 ch just to have it. I have an OTL Futterman that has a problem with the screen grids arcing or doing something that I can't catch so maybe I can capture the problem. Max volts I would deal with would be 500 v or more likely 420. Might be a bit too hot for the probes?Again, thank you for all the help and I'm still open to other suggestions. I've only done this audio thing for 36 years so I'm still getting the hang of it.

author: bdunham7
author_rank: Super Contributor
timestamp: February 13, 2021, 01:45:34 am
content: Quote from: Sparky Faraday on February 13, 2021, 01:32:38 amThat would be a significant step backwards, IMO. And I've had both.QuoteYou really ought to have 100X HV probes for that, and certainly not use the included 1X/10X switchable kind. Here are two I recommend, one cheapie (but actually pretty good) and one very good one.https://www.ebay.com/itm/P2301C-High-Voltage-Oscilloscope-Passive-Probe-5kV-100X-300MHz-For-Tektronix-HP-/332835001398https://www.amazon.com/Probe-Master-4910-2-Passive-Voltage/dp/B01D13ILOO

author: SilverSolder
author_rank: Super Contributor
timestamp: February 13, 2021, 04:08:18 am
content: Quote from: Sparky Faraday on February 13, 2021, 01:32:38 amThat's exactly what I do - I have a decent quality 192KHz audio interface and you can get very nice stuff in and out of Waveforms with that.If Digilent ever gets their products in stock again, I might buy an Analog Discovery just for fun - but they have been out of stock since Covid began.QuoteSure there is!QuoteI hear you. Somehow it never ends. And that's a good thing, or it would get boring around here, right?

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 13, 2021, 05:30:47 am
content: Silver: Very cool and thanks.What 192khz gizmo are you using to get in and or out? Does it sound any good? Chesky Records owes me some HDTracks that I want to check out. Can I put tubes in it?Sparks

author: SilverSolder
author_rank: Super Contributor
timestamp: February 13, 2021, 06:04:12 am
content: I've got an old E-mu 0404 USB, but I don't recommend it because drivers don't always work on every PC... not supported for years, I am going to have to get another interface due to "unplanned" obsolescence... Kind of sad, the sound and dynamic range is crazy good, even today... the 117 dB signal to noise is pretty impressive too.These days I'd look at a USB recording audio interface like a Behringer U-PHORIA UMC202HD or a Focusrite Scarlett 2i2, there may be other contenders. For audio use, it is kind of cool that these prosumer units have microphone amps built in for speaker measurements etc.Note, though, that you'd have to research carefully whether a particular box shows up in Windows as a regular sound card would, i.e. that there aren't any driver "gotchas" so it can't be used with other applications than specific pro audio ones. Maybe buy from Amazon so it can be returned! (I believe the Behringer is "plain" USB compliant)You can and should put tubes everywhere, especially in winter!

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 13, 2021, 07:00:38 am
content: I have Macs. 2011 and 2012 Macbook Pros with firewire and USB 2 an 3. Macs are usually compatible with most audio boxes.I have Focusrite 8 ch that does 96/24. I don't know how I can assign it.If these boxes can go down to DC then an appropriate attenuator would let you get into the higher voltages to look at regulator noise and get a good picture of it. Better than a scope in the audio band.I've thought about it. I think I have a motu 2408 box somewhere that could probably go to dc with a few less caps. Only goes to 48, though. Tricky without a schematic.I still think I'll keep the Siggy although it's sale price just dropped another $25 on amazon. Now $425. I got mine on 2/1 for $449. I wonder if they are selling them off in anticipation of a replacement model?

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 13, 2021, 07:03:57 am
content: It starts to get expensive at 384K and 768k is in the kilobuck region.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 13, 2021, 02:52:17 pm
content: I'm not sure they will respond to DC (as in actually measuring it) but they seem to go down quite deep in frequency, 10Hz or so. They might tolerate some DC on the input but probably not outside the range of the expected AC... - No problem that a capacitor (and perhaps a resistor to ground afterwards) won't cure, when it comes to "listening" to regulator noise!

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: February 13, 2021, 04:47:45 pm
content: Well, for ADCs with a mic pre there are caps to keep the phantom power out of the op amps. There are usually caps before the adc chips to keep the dc component at 0.Got any schematics of any of these things? More homework.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 13, 2021, 08:49:31 pm
content: Quote from: Sparky Faraday on February 13, 2021, 04:47:45 pmI don't have schematics, - but I did find this young German chap that does very technical and objective reviews of audio interfaces:https://www.youtube.com/c/JulianKrause/videos

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: April 24, 2021, 01:37:22 am
content: I bought a UR22MKIId1 Demo 2x2 USB2 Interface from Sweetwater. Unusable. 192Khz interface but there is unbelievable amount of RF noise coming out of the output, the whole box really, that puts way too much tall grass on the scope. I measured 40 mv at idle on a 1mhz acvm. $149 as a used item. Don't bother with it.Also it's all brick walled at 22kz so can't be used for anything above that. I didn't bother with LF cutoff.I just wish my Siglent could record hours of roll. Jeez, 128 g card is $20. You'd think they could use that and then play it back on the scope. Maybe this is not the last scope I own!

author: SilverSolder
author_rank: Super Contributor
timestamp: April 24, 2021, 02:49:48 am
content: Oh no, what a pain! Was that measurement done at high impedance? Maybe the noise is more benign at lower impedances?Julian Krause reviews that interface, and his scope trace doesn't look terrible?

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: April 24, 2021, 03:36:19 am
content: Single ended into a 1meg of the ACmvm, a Leader. But I fussed with grounding and trying to do a THD measurement was impossible. No that I think of it I did try a simple RC lowpass filter on the output but still too noisy into the THD meter.My Leader audio oscillator is still in use. .03% 3rd harmonic distortion and quiet so nothing is different than before.The other thing I tried was using it as an input to the Mac thru the usb. I used Waveforms and it works. But my Mac laptop is noisy and shows up on the scope when I touch it. I have the power supply plugged into a line filter in a different outlet which helps. But RF noise doesn't like long wires to ground so there you go.I was interested in measuring very low distortion levels and noise so for now it's 8Bits on the Siglent which is pretty quiet, but not as quiet as analogue.I work in the world of tubes and have had very good success without a DSO. But it's been useful using the roll function watching turn on/off sequences to see how circuits come to life and turn off which helps to time muting circuits and find weird behavior.Thanks for the reply and interest. Do you have a link to the review?

author: SilverSolder
author_rank: Super Contributor
timestamp: April 24, 2021, 01:50:38 pm
content: Steinberg UR22mkII Audio Interface Review (with noise measurements)Is normal audio input impedance 1Meg though? - maybe lowering it with a resistance is enough to quiet things down a little?I have seen "digital garbage" in the outputs of digital audio equipment, for example Class D amplifiers can be terrible above the audible range. I'm surprised they let that go in an audio interface... it has one job... !

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: April 24, 2021, 07:39:06 pm
content: Thanks. The reviewer used it exclusively through the USB. He did not scope it so all noise over 22Khz is heavily suppressed through the analogue brick wall filter.I was hoping to adapt it as test equipment but 22khz BW limit and noise makes it unusable.Here are some screenshots off the scope. Granted the noise is way out of band but it's noise and shows how poorly shielded the thing is.Here are screenshots off the Steinberg.

author: Sparky Faraday
author_rank: Regular Contributor
timestamp: April 24, 2021, 07:42:47 pm
content: BTW for tube circuits and fet inputs 1meg input Z is not uncommon. Usually no less than 100K.