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automatic tuned distortion analyser




 
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Author Topic: automatic tuned distortion analyser  (Read 922 times)
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« on: April 16, 2018, 03:17:29 PM »

There are several treads about AF quality, modulators amps etc. I did make quite a few tube HI-FI amps and had the desire to measure distortion, especially so that I could SEE what the source of the distorsion was. So I made a simple self-tuning notch filter based analyser that can measure from 10% down to 0.01%  The construcion has no PCB, the analyser is made at non etched PCBoard, many photos in the link. The analyser has an output after the notch filter so one can compare the amplified distorsion signal with the original signal at a two channel scope in order to see where the distortion originates. Real fun to play with and (for me) an extremely instructive experience
The analyser need a clean and reasonable stable AF generator tuned at 700 Hz. You ca use the analyser to see how clean the signal is. Small variations in frequency are automatically tuned by the analyser
Here is a link to the analyser
http://www.diyaudio.com/forums/equipment-and-tools/298895-simple-automatic-notch-filter.html
It did cost me approx 1 day to make the analyser, so acceptable
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MikeKE0ZUinkcmo
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« Reply #1 on: April 16, 2018, 06:38:30 PM »

Have to sign up and log in to see anything, are the pics posted on a public access photo site somewhere?
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Mike KE0ZU

Bold Text and PICS are usually links

https://mikeharrison.smugmug.com/
PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #2 on: April 16, 2018, 07:41:16 PM »

Hi Mike
It has been a while, I think that they are only at a few forums like the attached one. Also I can not enter at this  moment, because I changed country and Email address. So I am waiting for the new registration and than I can snipe the pics and resent at AMfone
But a new registration is free and fast, so that is an option as well.
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #3 on: April 17, 2018, 12:34:04 PM »

attached the first 3 pic of the distortion meter
ATTENTION
There is a small error in the second diagram Notch 2. The "NOTCH" signal enters an opamp which is coupled to a second opamp via 3.3 uF. There should be a resistor of 3k3 in series with this 3,3 uF capacitor. My error in drawing Sorry  Cry
As you will see in the next pics in the following post, the building is very simple. Just build in the same order as the diagram has been drawn. Super fast and the best ground plane possible. May be you should build a littlebit larger, I have a problem that I always tend to build too small...


* notch3.PNG (445.85 KB, 788x288 - viewed 49 times.)
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #4 on: April 17, 2018, 12:36:31 PM »

The diagrams and a pic how it has been build


* notch1.PNG (166.62 KB, 768x552 - viewed 72 times.)

* notch2.PNG (146.65 KB, 772x549 - viewed 56 times.)

* notch4.PNG (1078.19 KB, 786x478 - viewed 62 times.)
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PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #5 on: April 17, 2018, 12:46:15 PM »

Here an other build pic and two scope pics.
One of my Levell generator at the 0.1% distortion range. One can see that a part of the distortion results from compression of the negative peak. Total distortion 0,03%
The second pic is an LM386 amp at the 10% distortion range, total distortion 2,2%
Here the distortion peaks coincide more with the zero crossing and may be a combination of zero crossing and driver distortion.
It was for me very nice to adjust bias, cathode resistors, see the effect of decoupling cathode resistors, etc etc.  It helped me to learn and to optimize.


* notch6.PNG (1325.36 KB, 792x595 - viewed 38 times.)

* notch levell dist.PNG (764.3 KB, 777x572 - viewed 25 times.)

* notch LM386 dist.PNG (951.13 KB, 780x578 - viewed 25 times.)
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #6 on: April 17, 2018, 12:57:27 PM »


It's a neat project, but today it is excess effort, imo.

You can buy all sorts of distortion analyzers that go below 0.01% for next to nothing, especially
the HP series. Even Sound Technology units from 20+ years back are super inexpensive today.

But you can do even better with freeware, your laptop or desktop computer's sound card!
And you get FFT of the results as well!

If you're looking to get into the 0.001% class a used Quant Asylum box + laptop will do that
for under $200, no soundcard required.

My 2 cents worth.
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_-_- bear WB2GCR                   http://www.bearlabs.com
PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #7 on: April 17, 2018, 01:18:37 PM »

May be true in the USA, but in Europe it is very unlikely you find a distortion analyser for under 300$, if you can find one at all!!!. This did cost me approx 10$ and some junkbox stuff and approx half a day (hobby) work. Like to have a job where I can gain 200 $ in half a day
In addition, the sound card doesn't show you where the distortion comes from. Nice to know that it is e.g. third harmonics, but does it come from cross-over or from clipping? This shows you immediately for 10 bucks. And I enjoyed building a lot more than buying, it is my hobby
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WBear2GCR
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« Reply #8 on: April 18, 2018, 03:08:49 PM »


I see, so you want to use ur brain to analyze the residual waveform!?!?
Cheesy

They're all over ebay, dunno what shipping costs.
The HP and many other analog distortion analyzers are tuned notch filters, and they
have an analog output for a scope. FYI.

For basic stuff, I just invert one channel of my scope and invert... Cheesy

             _-_-bear
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_-_- bear WB2GCR                   http://www.bearlabs.com
PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #9 on: April 18, 2018, 03:53:47 PM »

Indeed bear, you'r smackon right. I love to use the brain for the hobby, design stuff etc, play around with it. I am not looking for those incredible low distortion factors, more practical stuff. It was very interesting to see how the compression at the sine peaks  change with bias or drive level of an amp, to find max output signal of circuits, see the effects of decoupling, see the effect of bias at cross-over etc. And all in the 0-1% distortion range. A scope doesn't do that Look at the pic of the LM386, the signal really looks nice, but still 2.2% distortion and not coming from the final stage. I think it will be quite hard to get that at a scope by subtracting signals. I did and do enjoy playing  with the set. I tried also to measure the modulated RF signal from a small 80 meter AM transmitter, and you could clearly see the distortion introduced by various factors. Learned a lot from it
I decided to design and build this little thing AFTER looking for an analyser at internet (while living in Spain). Including transport, could not find anything below 600$. Si I enjoyed my self a lot for 590 $ less  Grin
Here in Costa Rica it is worse, most people don't even sent to Costa Rica. And the transport and tax will very rapidly double the price. In addition, I have to drive 5 hour to the customs to pick it up (if it arrives at all) Like to buy a receiver, but the same problem, almost impossible or very expensive
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DMOD
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« Reply #10 on: April 18, 2018, 04:03:21 PM »

This might be a good place to post your DA:


http://amfone.net/Amforum/Index.php?board=51.0


Phil
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"What kind of Koolaid do they make you drink in the Physics Department?" Charlie Epps to Dr. Larry Fleinhardt, NUMB3RS   Smiley
PA0NVD
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Nico and Chappie (Chappie is the dog...)


« Reply #11 on: April 23, 2018, 11:59:47 PM »

So I did Phil
Regards
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