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Old 22nd July 2012, 04:35 PM   #51
miklos is offline miklos  Canada
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Could you please give a link to it?
OK, I found it.
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Old 22nd July 2012, 05:22 PM   #52
RNMarsh is offline RNMarsh  United States
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Go see Victor in Latvia for the low distortion oscillators.... viccc@ml.lv

[or hunt for him on eBAY -- would take me as long to find him again as it would for you to look.]
I didnt see this forum until long after I recieved the units or i would have kept more info on it to give to you. I just bought 2 of the 1KHz in case I smoke test one of them or it fails on its own accord someday.... and then I might not be able to find him/them again, later. After the 1KHz I asked him for a 10KHz and he made one of those too. I suppose he could do any frequency on special order.... ?

I havent got to using them yet. -RNM

Last edited by RNMarsh; 22nd July 2012 at 05:28 PM. Reason: Go see Victor for oscillators.
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Old 22nd July 2012, 06:00 PM   #53
1audio is offline 1audio  United States
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Can you share the ebay link since Richard no longer has it?

Sent from my myTouch_4G_Slide using Tapatalk 2
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Old 22nd July 2012, 08:13 PM   #54
miklos is offline miklos  Canada
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Ultra low distortion (<0.00005%) 1kHz sine generator assembled and tested PCB | eBay

Here it is.
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Old 23rd July 2012, 01:05 AM   #55
RNMarsh is offline RNMarsh  United States
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Can you share the ebay link since Richard no longer has it?

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I figure from what you wanted to do that telling about this would help you a lot in your R&D. especially the custom freqs you need. -RNM
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Old 23rd July 2012, 01:30 AM   #56
1audio is offline 1audio  United States
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Richard:
I am already working out the details with Victor. These will save some time mostly. I'll report back when they arrive.
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Old 23rd July 2012, 02:24 PM   #57
macboy is offline macboy  Canada
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@Richiem:
. . . I have several 6 digit DMM's and they don't agree. I sent the 8506 and the 732A out for cal. They came back and I finally checked them against each other to find they do not agree, not even close on the AC-DC comparison. Then I pull the certificates and find that the lab used a 5 digit portable meter to check the 732A and a calibrator no where near accurate enough for the 8506A. This all leaves me very unsure of the calibration. Needless to say they will be going back (the shop got close to $10K for calibration from that effort among all the instruments). As far as I can tell they did nothing to either except to see that they function. On DC they are 10 ppm apart when my shop is around 25C so I'll take that and build from it...
With all due respect, do you really expect that any two 6.5 digit meters are going to precisely agree, even when freshly calibrated? They will not. Your 8506A in DC mode has uncertainly of roughly 20 digits (full scale, most ranges) within 24 hours of calibration, and roughly 40 digits after only 90 days. And that assumes your lab is the same temperature as the calibration lab, and that you have warmed up the instrument for 4 hours! Furthermore, once you start to get resolution down into microvolts, thermal effects can be huge. Special test methods are required when taking such measurements, you can't just plug in some probes or leads and expect accuracy.
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Old 23rd July 2012, 03:25 PM   #58
1audio is offline 1audio  United States
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With all due respect, do you really expect that any two 6.5 digit meters are going to precisely agree, even when freshly calibrated? They will not. Your 8506A in DC mode has uncertainly of roughly 20 digits (full scale, most ranges) within 24 hours of calibration, and roughly 40 digits after only 90 days. And that assumes your lab is the same temperature as the calibration lab, and that you have warmed up the instrument for 4 hours! Furthermore, once you start to get resolution down into microvolts, thermal effects can be huge. Special test methods are required when taking such measurements, you can't just plug in some probes or leads and expect accuracy.

I am well aware of those issues and the total uncertainties involved. That's why I didn't go into the calibration issues initially. As I said I go through most of the gyrations to remove as many of those issues as I can. The 20 digits you mention are 20 ppm. (actually on the 10V range the total DC is 18 ppm for 90 days) The DC differences are within those uncertainties. The AC is way out. I gave up and am using the 540 which is 100 ppm AC-DC, where the 8506 seems to be more like 6000 ppm + (the spec is 160 ppm). I have some more precision converters but this is all way beyond anything valid for audio. Its really just obsession.

So far the the Fluke 510A seems to be as stable as they claim. It fluctuates in keeping with the temperature which is to be expected but otherwise it withing the claimed tolerances.
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Old 28th July 2012, 02:10 AM   #59
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@ Loudthud -- well, just as you might expect, lowering the signal 20dB with the attenuator raises the level vs THD plot by 20dB. So the red curve isn't real helpful. I'm not familiar with the specs on the Sys 1 -- is it 50 ohm output Z? If it's not, I would avoid using 50 ohm attenuators or terminated cables....
The attenuator was just a reality check to verify the noise is in the detector, not the oscillator. On the System 1 you can set the generator impedance to 50, 150 or 600 ohms.

I found an old Tektronix 7L5 Spectrum Analyzer to look at the Reading Monitor Output. There was a strong birdie at 48.5kHz when the Monitor was on. That was with a 22kHz filter on the distortion. Monitor on or off didn't make much difference. The options can set it at 22kHz, 30kHz, 80kHz or >500kHz. Those filter selections revealed harmonics of the 48.5kHz and an increase in the residual distortion at low signal levels. (There are also LF selections and tracking filters.)

What bandwidth filter is customary for distortion measurements?
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Old 28th July 2012, 02:42 AM   #60
1audio is offline 1audio  United States
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Usually distortion is reported with a 20 KHz filter (not meaningful for 10KHz source but. . ). Some even A weight the distortion which is really not meaningful. There are lots of philosophies on how best to understand the distortion measurement. First, with few exceptions its distortion + noise and with better stuff the noise dominates at real listening levels. Looking at the spectrum can be very helpful. Higher order harmonics are not good and in some cases (tubes?) low order harmonics can help sales.

The 7L5 is very useful for looking at the output of a DAC. There can be a lot more HF stuff that doesn't normally show when you stop the measurement at 100 KHz. I use mine a fair amount when developing DAC's.
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