Uni-T UT81B Scope-meter question / Sound distortion

[giavra]

Today I'm starting wondering if this low cost Item Uni-T UT81B Scope-meter Oscilloscope with around 200$ including the post cost for Greece is a crack in the market or not.I'm also wondering if this scope-meter can provide the distortion point through his sine wave presentation when you want for example to check the output sound level of your amplifier putting the pot to the level that the sound start distorts.Also as a multimeter may to accurate?

[Kiriakos GR]

Dear @giavra
First of all I need to inform you that even with EMS (ELTA) your item will receive taxation 23%.
Currently I have some instruments in the customs on hold, because of the new changes.

About the Uni-T UT81B Scope-meter I do have access to one of those, it is in the hands of a close friend of my.

What I disliked on it is the low resolution of the screen, it can help as Scope-meter if you wish to measure the volts of one waveform, but by my opinion is not capable to offer the needed visual detail for fine measurements over distortion.
Especially when it comes about High End audio systems which has tremendously low distortion in their specifications.   

Probably you are aware that what you need is one spectrum analyzer, and I will agree that the cost is extremely high for a hobbyist.

The advice that I have to offer to you it will very specific, you need one oscilloscope which will have an high accuracy factor, equal to the level of the distortion that you need to measure.

I am aware about the low distortion levels of preamplifier s, and that the final stages are more prone to cause an significant distortion.
But just think that with out the proper tool, you will be unable to test the quality of the preamplifier it self.
You have mention that you are making amplifiers with tubes, that the tolerances in them it is known to vary by allot. 
Even so my advice is the same as to was made by modern technology.

Today I was playing with an 40 years old scope with 3% accuracy. 
This is not even close to be called as acceptable performance in our times. 

[Phyllomedusa]

well, I do have an Higher-Range Digital Oscilloscope (Scopemeter) the Hantek DSO1202B.

First off all: If you just want to use it in a lab, you're better off with a Labscope. Well, they do need more space, but the controls are more intuitive and the performance (in the same price-range) is usually better.

The Handhelds are very nice if you need to carry them around (like I do) and can help you a lot. Unless you need the portability I would consider a Handheld scope but not as a "must-have".

I can't tell you anything about the distortion, but I can at least tell you that these Handheld normally have a very slow screen-update-rate and get pretty lazy if you use a high memory option (which some have....like 1M for 1CH/512K for 2CH).
So for finer details on your signal you could use this high memory mode (normally a Labscope starts at 1M ), record a period and check it on the scope (that's what I normally do if I need high res.).
Eventually that is far from a smooth workflow

I would say the UT81B is nice for general checks in rough signals....like putting it in your Toolbag for testing automotive sensors..... but not a High precision Instrument.
Probably you're better off with a used Lab-Scope form ebay. The Rigols are very popular and a lot on the used-market right now.

Another thing: What Signal do you want't to compare your output to? Do you use a Function Generator or some audio-input?

[giavra]

Thanks all members for their answers which much appreciate  by me.Yes Kyriakos probably a spectrum analyzer is more accurate unit to test the output signal.I want to take a clear audio signal in the 1000Hz range via a test audio cd signal  and take the necessary references .

[Phyllomedusa]

OK. So that's fine. Yes, a Spectrum Analyzer may be helpful here. Otherwise..... most modern DSO's have a FFT mode which could help as well..... as kind of cut down Spectrum Analyzer.

[gameru]

The Uni-t ut81 it can be used  to analyze Voltage from outlet (230V 50Hz) with test leads?
I saw on youtube, a real oscilloscope i need Differential Probes to measure voltage from outlet,and are very expensive.

[Kiriakos GR]

Basically any battery powered oscilloscope this is safe to use for mains voltage, if it input specifications aloud it.

GDS-320 this can accept 300V RMS at 1X   ( this is almost 1000V pp )
Speaking of other limits,  one oscilloscope probe even at 10x  this can accept max 600V RMS.

I am not aware of UT81B Max input voltage, or if this comes with quality probes for high voltages.

 

[gameru]

I saw your video on youtube about GDS-320.I like the presentation and Oscilloscope,but the price it is not attractive (1850 euro +VAT)
On manul of UT81B says - maximum input voltage 1000Vp-p,RMS i think 300V
But,have only DC coupling
The UT81B come only with test leads,not end oscilloscope probe.I'm curious if it works with test leads to analyze AC Voltage (230V 50Hz)

[Kiriakos GR]

Pricing comparisons them have value when compering two similar items.
GDS-200 (70MHz) this is close to 1000 EUR that is close to what a GDS-2102A worth.
 
I will agree that starting price for buying a helicopter seems totally unreasonable to me either. 

Here is a fresh example of what true tools them can do 
http://www.ittsb.eu/forum/index.php?topic=1108.0


 

[Kiriakos GR]

By a second read of the questions for UT81B,  I have to say that my personal quick testing with it for few minutes, (as also the date of this topic indicating) this was at 2012.

The limitations of it, this made me to stop thinking of it and move on.
Few pictures from it over the web, them indicating that when sine-wave displayed this is only frequency measurement.
Quick reviews by others them mentioning mediocre performance of square-wave above 1MHz.

According to my personal opinion, one oscilloscope this must be able to serve (or comply with)  thee important applications.
1) This must have low volts sensitivity at ACV so this to be able to measure ripple at DC power supply.
2)  This must have bandwidth of 100MHz so this to be able to assist at repairing anything working up to 20MHz.
Rule of thump this is oscilloscope bandwidth this must be five times higher than the signal that you are going to review.

3) This must have a size of screen above 3 inch, and to be fast, so this to be  keeper in long term.

I am aware of cash flow difficulties of hobbyist.
But again in 2015 one professional in electronics repairs he have to invest a minimum of cash at buying several tools, so him to work as freelancer and this is close 20000 EUR.
The average investment in tools (and I am included) this is 40000 EUR , and I am lucky as around 20000 EUR of tools, I got them due the family business, as my father he was also an electrician.

In our times one dentist he must invest 100,000EUR  so him to accept a customers and start making money.
Therefore nothing comes easy to any one.