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Old 29th January 2009, 03:17 PM   #11
n_maher is offline n_maher  United States
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Default Re: Several misc scope questions

Quote:
Originally posted by boywonder
Are there any basic techniques to measure distortion without using FFT such as inverting a sigal and comparing it to another signal?
You could run the full set of RMAA tests on it. There is a free version of the software available for download.

Quote:
Is it possible (and reasonably safe) to measure a B+ of say 350V using a 300V probe?
I would not recommend exceeding the parameters the probe. Let's say you got a measurement, but damaged the probe. How would you know for sure? I'd just buy a HV probe if you expect to be measuring things that high on even an occasional basis.

Speaking of probes - would any one care to make some recommendations? Hopefully that isn't too much of a threadjack since I think it's a pretty common topic among scope newbies. Personally I'm looking at one of these - http://www.tequipment.net/CalTestCT2674A.html.
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Old 29th January 2009, 04:07 PM   #12
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Default Re: Re: Several misc scope questions

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Originally posted by n_maher
You could run the full set of RMAA tests on it. There is a free version of the software available for download.


Can you point me in the direction of the RMAA test software?
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Old 29th January 2009, 04:36 PM   #13
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Default Re: Re: Several misc scope questions

Quote:
Speaking of probes - would any one care to make some recommendations? Hopefully that isn't too much of a threadjack since I think it's a pretty common topic among scope newbies. Personally I'm looking at one of these - http://www.tequipment.net/CalTestCT2674A.html. [/B]

Frys has a Velleman 10x, 600volt, 60Mhz probe with all the accessories for only $19.99. I think the fry's part number is 5096285 and the Velleman PN is PROBE60S. I'm very happy with it.
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Old 29th January 2009, 04:56 PM   #14
jjman is offline jjman  United States
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Default Re: Several misc scope questions

Quote:
Originally posted by boywonder
.........................Are there advantages to using a scope instead of a DVM to adjust phase splitter balance?.............................
With the scope you can use the "add" button to sum the two probed outputs of a sine wave. Since they are out of phase you want to see a horizontal line as the sum. I checked this in one of my amps, with a LTPI and it was surprisingly balanced.

I also used it to fine tune a tremolo oscillator for speed and strength. Lotsa fun things you can do.

I built a cheap signal generator from a kit that works well except that I later discovered it has 4.5vdc on its output. This matches what the spec sheet says for the chip inside it. So I put a cap in there to block it.
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Old 29th January 2009, 05:16 PM   #15
n_maher is offline n_maher  United States
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Default Re: Re: Re: Several misc scope questions

Quote:
Originally posted by boywonder



Can you point me in the direction of the RMAA test software?

Sure - http://audio.rightmark.org/index_new.shtml - that's the place. Just click on the download section and you'll see where to go.
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Old 29th January 2009, 05:20 PM   #16
n_maher is offline n_maher  United States
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Default Re: Re: Re: Several misc scope questions

Quote:
Originally posted by Captn Dave



Frys has a Velleman 10x, 600volt, 60Mhz probe with all the accessories for only $19.99. I think the fry's part number is 5096285 and the Velleman PN is PROBE60S. I'm very happy with it.
While that certainly seems like a fair price I have a 100mHz scope so it seems a shame to throttle it with a lower bandwidth probe. Thankfully their 100mHz similar probe is only $29.99.
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Old 29th January 2009, 05:35 PM   #17
Osprey is offline Osprey  United States
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Quote:
What do people here use and recommend for a function generator?
Here's an inexpensive one that does go on sale periodically:

http://www.mcmelectronics.com/product/72-490

Output max is about 2V rms sine wave.
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Old 30th January 2009, 12:51 AM   #18
chrish is offline chrish  Australia
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I use one of these:

http://www.altronics.com.au/index.as...=item&id=K2544
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Old 30th January 2009, 11:51 AM   #19
kmaier is offline kmaier  United States
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You would be hard pressed to get a better sine/square generator than an old Heathkit IG-5218 unit... (IG-18 is the older version). They are usually reasonably priced on ebay and can deliver very low distortion output with a wide signal and frequency range. There were some modifications made many years ago that reduce distortion and improve overall quality. I still have the one I built over 30 years ago and it still performs flawlessly.

Regards, KM
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Old 31st January 2009, 12:03 PM   #20
Bitrex is offline Bitrex  United States
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IMO it is important to have a function generator that can go well above the audio frequency range, particularly when dealing with circuits involving negative feedback and multiple coupling capacitors. You could have a frequency in the ultrasonic range where the phase shifts through 180 degrees and there is still appreciable gain that will cause ultrasonic oscillations, and with a function generator that tops out at 20khz you'll never know about it other than that your amp performs like .
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