Lab instruments _ analog vs digital

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#21
stv said:
you have some mains signal (50 Hz + harmonics) in there.
make sure you have enough distance from any transformer and PSU circuit and check your ground connections (particularly for ground loops).
also, what is your 0 dB referenced to?
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The sound card is on the top of my pc ... maybe not the best place
And that can be some ground loops I understand now that my approach has been too not careful
Lab instruments need a lab Not a living room or a bed room
I am working on it I am looking for some quiet place to set up a little lab The only way it could work

0db= 0.707V
 
#22
ginetto61 said:
Hi thank you for the very valuable advice I can listen only to max 14k ... for me there is no need to go beyond that at my age
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It is more about checking out the amplifier's state and capabilties than the actual level we can hear up to 😉

And I was obviously mistaken above - the Uphoria can probably go higher than 20kHz - I was thinking about earlier versions of 202.

Your practical problem is to find loopback noise and distortion wise the optimum combo of card output and input gain/volume regulators and windows mixer level settings - both output and "mic" input. The results may vary greatly.
 
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#23
Elvee said:
Both are perfectly usable, and I could very well survive using only one of the varieties, but the clever thing to do is to use the best suited type for a given application.
Before my retirement several years ago, I used exclusively digital instruments because of the need to produce massive amounts of data, graphics, Excel files, etc.
In my own lab, I use both types equally: my main scope is a Fluke ana-digi, combining the best of both worlds, I have several multimeters ranging from pure analog (like the gold standard of the sixties, a senior Volt-ohmist VTVM made by RCA) to a pure digital Datron 7 digit dreadnought. I also have the ana-digi version of the multimeters, made by Metrix in the eighties. This one is not a success, unlike the Fluke scope: the analogue display merely serves as a subsidiary display for the digital meter and doesn't bring many advantages.
When you need great absolute accuracy (but does it actually occur in DIY?) digital is more straightforward (extreme accuracy is also possible with analogue, but it requires more intensive work).
For some very specialized measurements, only purely digital or analogue instruments can work, but the analogue niche is shrinking by the day.
For DIY, simply use what is easily available or cheap, and what you are comfortable with. There is no hard rule
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Hi thank you so much for your very helpful advice I am just starting and i want to start cheap an easy I like analog voltmeters because i can see more easily the variation of Volts instead of a numbers quickly changing If i had to build an amp i would place a analog voltmeter across the power supply caps to see if the voltage stays always steady even during peaks I have the feeling that with many commercial amps the needle would start dropping
Usually the power supply is where the major cost cuts are done Little VA transformers and small uF caps of also bad quality
 
#25
b_force said:
I don't think the approach and question here is the right way of getting proper equipment.
First ask yourself what you want to measure, how often you think you're gonna need that and what resolution/specs are needed for that.
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Hi ! thank you very much for your kind and valuable advice My main interest are line levels units like line preamps and headphone amps
I would like to see their THD+noise spectrum And i need an instruments I understand that many use usb sound cards at least not for pro uses
b_force said:
Next ask yourself more practical things, like budget and space on your desk.
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both limited In the meantime a friend will lend me to try another usb sound card that should be better An Audient ID14 mk II
I will get it tomorrow i hope It should be a better unit
b_force said:
Obviously older equipment needs more maintenance, so you need the experience and skills to repair those things as well.
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This is a very important point that makes me abandon this option I like maintenance free units And i am not a pro who uses them for the job
b_force said:
Except for samplerate/bandwith and measuring DC signals, it's pretty hard to beat a very good performing audio interfaces these days. Even in sense of THD+N and SNR. It's to unfortunate that most of them are limited around 25-40kHz even at the much higher samplerates.
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I think i have solved my doubts I will start with a usb sound card I understand that the qa403 would be the best option but i see its price 600USD a little on the high side I am not discussing its quality for sure I have seen impressive lab reports done with it to understand that it is a very high quality unity
Maybe in the future It is also very compact A very nice unit indeed
 
#26
There's a place for both types of scope imo but for signal generators used with audio it has to be digital for accuracy. There's no point using an old analogue signal generator if it's out of calibration and how would you know it is in-spec to begin with?
Analogue scopes can fail and go out of calibration too wheras even though digital scopes can have less resolution they usually have start-up calibration routines.
Swings and roundabouts.
 

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#28
Thank you to You all I have fixed some requirements considering that i am a beginner
  • easy of use
  • not much space needed
  • no maintenance required
  • link to a pc
  • below 200USD cost
From what i have understood the best option could be the qa403 that could provide semipro results and it is not very challenging to use
It should satisfy perfectly any of the above requirements cost aside
If i really will fall in love with measurements i could purchase one But i have to try first some measurements
It could be just a silly infatuation and not passion
By the way 600USD can buy probably an excellent sound card usable also for music A very interesting option
 
#29
ginetto61 said:
I have fixed some requirements considering that i am a beginner
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I started out from (almost) that position about a decade ago and Picoscope was the first one that I bought (my ancient analogue scope had just one channel and fading focus but I needed stereo and FFT and saved screenshots/measurement results and ...).
It is still my fastest to use and first choice when I need to measure something on my ordinary level at my becnh where it is wired up:

https://www.picotech.com/oscilloscope/2000/picoscope-2000-overview
 
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#30
madis64 said:
It is more about checking out the amplifier's state and capabilties than the actual level we can hear up to 😉
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You are right I am always self centered I should realize better what is the real goal of testing
madis64 said:
And I was obviously mistaken above - the Uphoria can probably go higher than 20kHz - I was thinking about earlier versions of 202.
Your practical problem is to find loopback noise and distortion wise the optimum combo of card output and input gain/volume regulators and windows mixer level settings - both output and "mic" input. The results may vary greatly.
Click to expand...
I see My understanding is that the first thing is to check for the noise A sound card with a high noise floor is not usable
Then pass to distortion If the noise is low but the HD is high i could think of buying a digital signal generator decent in HD and not very expensive and using the sound card for signal acquisition
the first time i saw a scope i was 13 in a guided visit to a technical school I wanted to study electronics but my performance at maths blocked me and i decided for chemistry But also in chemestry the only decent results were in the lab But chemicals can be very very dangerous
Some Volts cannot do any harm Cyanides can
 
#31
madis64 said:
I started out from (almost) that position about a decade ago and Picoscope was the first one that I bought (my ancient analogue scope had just one channel and fading focus but I needed stereo and FFT and saved screenshots/measurement results and ...).
It is still my fastest to use and first choice when I need to measure something on my ordinary level at my becnh where it is wired up:
https://www.picotech.com/oscilloscope/2000/picoscope-2000-overview
Click to expand...
This is very very interesting I am thinking about it very very seriously
i have seen the video on the web site and if i understand right the unit can work as scope, signal generator and also as spectrum analyzer ? that would be just perfect
I wonder which would be the exact model to look at to get both low price and decent performance ? (i cannot understand clearly the specs)
My goals would be just some THD noise measurements on low level units and stop
I like this product very much indeed and my guess is that it would be much better than a usb sound card that after all is intended for other uses
In the past i had a cheap Hantek but i cannot find it anymore I think i have lost it during one of my relocations 😢
This should be a step above ? the Hantek was very cheap but also cute and convenient
I like this one very much.
Thank you very much again.
 
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#34
Thanks a lot again I will check also RMAA and REW
I am using Arta right now and seems quite good and above all easy
P.S. i have tried using RMAA but the sound is intermittent ... strange Nice SW indeed
I will look for a tutorial
 
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#36
Hi thanks a lot again So it is not like Arta where there is a spectrum analyzer option and a signal generator ?
i need a simple tool Arta seems quite user friendly at least for THD checks
If i get the pico 2204 i see that it comes with a dedicated SW That is very good
RMAA seems more tricky to visualize a THD spectrum of a sine test signal
 
#38
Please sorry to bother you but i am slow to understand
Lets say that i want to see the THD spectrum of a 1kHz sine generated by the sound card
I have connected card outs with card ins
Then i open RMAA and what i have to do ?
On the bottom left corner i see the buttons here below

1718040711125.png

and i am lost at this point
 
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