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Old 9th October 2011, 05:59 PM   #51
klewis is offline klewis  United States
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I hooked up the K-H 4402B to my computer sound card this morning through Pete Millett's sound card adapter. I have the Juli@ card in the balanced mode and didn't have an adapter from the BNC to Balance, so, went through the adapter instead. I adjusted it as close to 0dB as I could, but, when I got close, the 3rd harmonic started to rise up in an unusual way. I just remembered that their is an adjustement I have to make in the software. The results are shown below.

I also tried it with the Twin-T, but, it didn't seems very happy. I will look into the Arta software and a BNC to Balance cable.

The other piece of news is that the K-H did not measure as well this morning on the 3562A as it did yesterday. The adjustments don't seem to hold. There are a few electrolitic caps in the unit, maybe they are at the end of their life. The unit manufacture date is 1997.

Ken
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Old 9th October 2011, 09:23 PM   #52
richiem is offline richiem  United States
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RE post #50: Yep.

RE post #51: I'm not familiar with Millet's adapter -- is it described here at DIYAudio? Intrinsically, for balanced inputs you just ground one of the inputs and feed signal into the other one.

The Juli@ card looks interesting to me; I think it and the ARTA software should be a good match. ARTA is free to use with no time limit in demo mode with very few restrictions -- you just can't save setups and a few other things. Highly recommended. The AudioTester app has a nice display and obviously lots of options -- I'll take a look at their page. The amount of spurious stuff in the plot is troubling, as is the rise in the noise floor above 40kHz -- I can't really come up with a reason for these artifacts. A sharp rise in 3rd H. should be accompanied with a similar but even sharper rise in 2nd if the issue is dynamic range of some part of the gain chain.

Last edited by richiem; 9th October 2011 at 09:38 PM.
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Old 10th October 2011, 03:09 AM   #53
klewis is offline klewis  United States
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Quote:
Originally Posted by richiem View Post
RE post #50: Yep.

RE post #51: I'm not familiar with Millet's adapter -- is it described here at DIYAudio? Intrinsically, for balanced inputs you just ground one of the inputs and feed signal into the other one.

The Juli@ card looks interesting to me; I think it and the ARTA software should be a good match. ARTA is free to use with no time limit in demo mode with very few restrictions -- you just can't save setups and a few other things. Highly recommended. The AudioTester app has a nice display and obviously lots of options -- I'll take a look at their page. The amount of spurious stuff in the plot is troubling, as is the rise in the noise floor above 40kHz -- I can't really come up with a reason for these artifacts. A sharp rise in 3rd H. should be accompanied with a similar but even sharper rise in 2nd if the issue is dynamic range of some part of the gain chain.
So, I tested the signal analyzer up to about -91db. Past that point the next step in the attenuator was 20db and the 8903 ran out of gas. The analyzer and the 8903 matched within +-0.7 dB on two test. I think the 4402b is in need of a serious tune up. When in the 1k to 10k (1k x) range and trimmed for .1v at 1k then moved to 10k the trim is out of tolerance. When I put it in the 10k x range the lowest reading I get is 25kHz. So, either bad resistors or caps for this range. Will measure in the next few days.

Pete's adapter is in the Tube forum. I'll find the link... I haven't been able to master AudioTester's calibration. Arta seems worth a try. I believe the noise at 40k and beyond is the switchmode supply in the computer. As it is, I unplug my monitor before running the test otherwise you would see two off scale spikes at about 44 and 46 kHz.

I've decided that the rise in the third harmonic came from overloading the adapter which was set in the 2v range and has diode voltage limiters. I think the voltage was at about 2.3Vrms when I was trying to get 0db AT.
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Old 10th October 2011, 06:01 AM   #54
richiem is offline richiem  United States
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Seems like the bug squashing is working out -- good luck on the 4402B fix.

Thx for the tip on the monitor noise. I've had noise in the 44kHz range as well, but it didn't seem to be the computer -- I hadn't thought of the monitor -- I'll try turning it off once measurements are set up....
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Old 10th October 2011, 03:00 PM   #55
klewis is offline klewis  United States
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Here's the link for Pete's soundcard interface:
Test & Measurement interface for Soundcard
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Old 10th October 2011, 05:25 PM   #56
AndrewT is offline AndrewT  Scotland
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I tried again on Pmillet's links and they all worked this time.
A few minutes ago I tried them and three out of four were "no service available". When I re-tried the working one, it too reported "no service available".

Can anyone explain why links drop out and come back without apparent reason?
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Old 11th October 2011, 02:28 AM   #57
klewis is offline klewis  United States
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Looks like the Juli@ will go to 90kHz. First plot is a 1kHz signal, 2nd an 80kHz and third a 90khz signal all at a similar amplitude generated by the HP8903A. (I set it at 0.5Vrms at 1kHz and by 90kHz it was down to 0.279Vrms) The last plot, I turned of the fluorescent lights and the computer monitor.
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File Type: png 1k_100-100k_test.png (65.3 KB, 239 views)
File Type: png 80k_sig_100-100k.png (64.6 KB, 236 views)
File Type: png 90k_sig_100-100k.png (64.8 KB, 230 views)
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Old 11th October 2011, 04:25 AM   #58
richiem is offline richiem  United States
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Hi Ken -- the level reading below the plot shows -8dB at 80kHz and -66dB at 90kHz, and yet the spectra and S/N ratios look essentially identical -- do you know why that is? Anyway good news on BW for Juli@. Thanks.
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Old 11th October 2011, 04:27 AM   #59
Frex is offline Frex  France
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Hello Klewis,

Do you use symetric or asymetric inputs of the Juli@ ?


FRex.
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Old 11th October 2011, 02:31 PM   #60
klewis is offline klewis  United States
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Quote:
Originally Posted by richiem View Post
Hi Ken -- the level reading below the plot shows -8dB at 80kHz and -66dB at 90kHz, and yet the spectra and S/N ratios look essentially identical -- do you know why that is? Anyway good news on BW for Juli@. Thanks.
Hi Dick,

I noticed the same thing. I'm just guessing, but maybe 90kHz is just beyond the limits of either the card of the software. I didn't try 86kHz, being half the 192kHz might be the limit.

Ken
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