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Virtual Oscilloscope vs Digital Oscilloscope

SIY

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#63
Most ADC's can give you 80 khz analog bandwidth. Scopes can give more, but is it really needed? I suppose it would be for good squarewaves much above 1 khz.
Yes, if you want to adjust the circuit to minimize ringing and risetime. A meg is not too much, which is why I use an analog scope for this. Likewise, with a 10x probe, you won’t perturb the measurement too much.
 

watchnerd

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#64
I'm of course aware of some of what you've been doing. I will ask more specifically, how would you use the O-scope to tell you something you can't find out with software and an ADC? Or what functions would an o-scope give that software and an ADC can't?
Are you referring to a virtual o-scope or a physical one?

Cartridge azimuth, for example, I'm pretty confident I could do with a virtual o-scope / software.

But square waves to check for ringing, etc?

If it can be done adequately via software, I'm not sure how to do it and what gear I would need.
 

SIY

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#65
If it can be done adequately via software, I'm not sure how to do it and what gear I would need.
Possible but not cheap. OTOH, you can buy a perfectly adequate used scope off eBay for like $100 or so.
 

watchnerd

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#66
Possible but not cheap. OTOH, you can buy a perfectly adequate used scope off eBay for like $100 or so.
Maybe I'm missing something, but it would seem ergonomically simpler, too.

If I bought a new o-scope, like the Rigol at the top of the thread, that's $349.

My laptop only has one USB port (USB C), so if I do it via software, and want to use my laptop, I need to get a portable interface cable of generating a good square wave, plus the software....my guess is the cost would be similar to the $349 of the digital oscope, at least.

Although now I'm wondering if I'm forgetting about probe costs....
 

solderdude

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#68
checking for oscillations for instance is something audio analyzers can't do.
Granted you need quite a few MHz bandwidth for that.
Like audio analyzers O-scopes have their place.
I have a TDS680P at work and Handyscope HS4 at home.
 
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watchnerd

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#69
checking for oscillations for instance is something audio analyzers can't do.
Granted you need quite a few MHz bandwidth for that.
Like audio analyzers O-scopes have their place.
Have a good scope at work and Handyscope at home.
Well, my job is at a software company....not many scopes at work. ;)
 

trl

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#70
I would be using it for analog purposes (vinyl, RTR).

How much does the bit limit matter that case?
If you want to check an analog amplifier, then a scope is really good, but if you have a vinyl test (with sinewaves recorded) I really think a second hand ASUS U7 (mkI, not mkII) could do the job very well with RMAA, ARTA and REW.
 

SIY

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#71
If you want to check an analog amplifier, then a scope is really good, but if you have a vinyl test (with sinewaves recorded) I really think a second hand ASUS U7 (mkI, not mkII) could do the job very well with RMAA, ARTA and REW.
Add in the cost of a good interface and it doesn't look so attractive for this use. Analog scopes still exist because there's things that they're just better for. Stuff like adjusting transformer loading, or looking for oscillations, or checking stability, or measuring AC voltages... they're the right tool.

I wrote a series of articles on using soundcards and software in audio testing, and there's things they're great for- distortion spectra, for instance. Far better than a scope. Different job, different tool.

The other thing an analog scope usually has built in is a square wave generator. It's there to adjust 10X probes and checking calibration, but can just as easily be used for things like transformer loading adjustment or amp stability tests. The square waves generated by a soundcard don't have the bandwidth for that.

If you look at my workbench, I have a soundcard data acquisition system. I have a stack of AP equipment. And sitting over that... an oscilloscope. It's 30 years old, similar to this one, and gets as much use as everything else. I made an analogy earlier about a scope being like a socket wrench set for mechanics. Yes, you can own a car and not own socket wrenches. But, if you want to start playing around with valve adjustments or changing plugs, or installing accessories, or the like, you need the basic tools. A scope and multimeter are the most basic tools before trying to be anything other than a buyer of appliances.
 

watchnerd

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#72
If you want to check an analog amplifier, then a scope is really good, but if you have a vinyl test (with sinewaves recorded) I really think a second hand ASUS U7 (mkI, not mkII) could do the job very well with RMAA, ARTA and REW.
Thanks, I don't need an ADC. My amp has USB out at 24bit/96khz.
 

watchnerd

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#73
"DS1000Z built-in signal source can output a variety of basic waveforms, including sine, square, ramp, pulse, DC and noise" - source: http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-050a/1/-/-/-/-/MSO1000Z&DS1000Z_UserGuide.pdf

You will not be able to do a proper FFT with such a scope, mostly because of a less than 16-bit internal resolution, but also because the signal generator's THD+N is usually higher than DUT's native THD+N.

I personally find a scope very useful to see if there's frequency roll-off or if there's post-ringing or pre-ringing, especially with speakers/headphones connected.
Okay, looking at the docs, I see a couple of concerns. For the signal generator:

"Set the amplitude Press Amplitude to set the amplitude of the signal. For the setting method, please refer to the introduction in "Parameter Setting Method". When the impedance is set to HighZ, the range is from 20 mVpp to 5 Vpp; when the impedance is set to 50 Ω, the range is from 10 mVpp to 2.5 Vpp."

So if I'm going to use this to push square waves into a step up transformer designed to take inputs in the <1mV range (specifically, .30mV, i.e. 1/30th of what is listed above), is that going to screw things up, either in the measurement arena or actually damage the transformer?

Maybe @SIY knows...
 
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SIY

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#74
Okay, looking at the docs, I see a couple of concerns. For the signal generator:

"Set the amplitude Press Amplitude to set the amplitude of the signal. For the setting method, please refer to the introduction in "Parameter Setting Method". When the impedance is set to HighZ, the range is from 20 mVpp to 5 Vpp; when the impedance is set to 50 Ω, the range is from 10 mVpp to 2.5 Vpp."

So if I'm going to use this to push square waves into a step up transformer designed to take inputs in the <1mV range (specifically, .30mV, i.e. 1/30th of what is listed above), is that going to screw things up, either in the measurement arena or actually damage the transformer?

Maybe @SIY knows...
Take a look at the test setup I recommended in this article. And come at me with any questions. Basically, you set up a voltage divider having the same source impedance as the cartridge, and that will knock down the voltage to reasonable levels.
 
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watchnerd

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#75
Take a look at the test setup I recommended in this article. And come at me with any questions. Basically, you set up a voltage divider having the same source impedance as the cartridge, and that will knock down the voltage to reasonable levels.
Okay, not being an EE, I haven't an electronics class since freshman year in college as part of the applied physics curriculum.

Net result, I'm super rusty on reading circuit diagrams and calculating values.

How would I need to tweak this for a 10R cartridge?



Or does that even matter if I'm going to be testing via an oscilloscope?

I'd think I'd want the oscope impedance instead?
 

SIY

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#76
You can replace the lower 30k resistor with a short if you're running unbalanced (which 99.9% of vinyl setups are). Then the shunt resistor would be 10R to match the source resistance of the cartridge, since the 30k resistor is so large in comparison. The attenuation is 20 log(10/(10+30k)) = -70dB more or less. So drive this with a volt or so and your transformer will only see 0.4mV or so.
 

watchnerd

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#77
You can replace the lower 30k resistor with a short if you're running unbalanced (which 99.9% of vinyl setups are). Then the shunt resistor would be 10R to match the source resistance of the cartridge, since the 30k resistor is so large in comparison. The attenuation is 20 log(10/(10+30k)) = -70dB more or less. So drive this with a volt or so and your transformer will only see 0.4mV or so.
And I'm setting the shunt resistor to match the source resistance of the cartridge so that the square wave generator is simulating that circuit / load?
 

ajawamnet

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#78
I agree about the need for both analog and digital. Below is a pic of my bench...
IMG_20160114_140749.jpg

The one in the middle is one of the last analog CRT scopes Tek made a 4ch TAS475.

All the stuff in action (minus the newer Siglent spectrum) on this vid:

Note the out of phase audio in the crappy phone camera audio...

As to virtual scopes - most of the standalone digital scopes nowadays are just an ARM with a nice front-end, some speed rated ADC's , and an LCD/OLED.

Note that Rigol and Siglent were Asian manufactures that were building most of the low end stuff for Tek, Agilent, etc... overseas. Story I heard was that Rigol told Agilent to pound salt when they wanted to renew the contract. One thing Rigol did on their stuff was to speed grade, in-house, the ADC's and FPGA stuff they use. Most speed grading is done on the wafers and once the IC mfg hits allocation they stop. That means that most of the rest of the die is probably also speed grade.

One thing that analog scopes are better at - at least for me - is doing XY plots when I mix or test gear.

My mix setup:
ajawamsmst1.jpg

If I could fit one of my analog's on that shelf where the Tek digital is, I would...


Also note the small red Lissajous display. This is from AEA - the ribbon mic company founded by Wes Dooley who worked with Wally Heider back in the day. Called a "Winkie Blinkie, it's a bunch of LED arrays that does a Lissajous. Critical back back in the day of vinyl mastering since out-of-phase info would result in "lift out" - see this from Larry Boden's bible on mastering discs -

https://archive.org/details/BasicDiscMasteringLarryBoden600dpi:

liftout.jpg

... as well as this from the same book - shows the oscope patterns for various phase angles of a Lissajous display:
lissajous.jpg


Back at Opus One In Pittsburgh we always had an old Kenwood KC 6060 running in XY/Lissajous.
Kenwood-Solid-State-Audio-Lab-Scope-Kc-6060-Stereo-Oscilloscope.jpg

We had carpeted benches and you could see intermittent issues quite well - inject a mono signal and see if the diagonal line bounced.
 
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Panelhead

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#79
My needs are less than many here. Been testing the home system using the ADC built into a Focusrite Clarett, REW, and a Mac Mini.
The loopback testing showed a noise floor around -150 dBFS. Once my amplifiers were installed as DUT, it was evident that this changed to -130 to -120 dBFS. Working on improving this.
Did not have a signal generator, used the one in REW. Found that Akitka makes a 1KHZ sine wave generator kit. Lower noise, but higher distortion than the Mac Mini sound card.
The linearity, distortion, noise floor of the RTA function in REW is better than my equipment, for now.
 

DonH56

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#80
Nice setup, @ajawamnet . I always thought I'd have a nice home bench but never seem to have the time... I can bring stuff in to work but we don't have audio test equipment. I could bring a DSO home but shudder at the thought of schlepping home a 'scope worth more than my house.
 
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