John Curl's Blowtorch preamplifier part II - Page 3328 - diyAudio
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Old 22nd January 2013, 08:38 AM   #33271
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Quote:
Originally Posted by PMA View Post
One more, again 40dB gain, artifacts below -125dB are measurement artifacts rather than opamp's, same for previous measurement.
Aha! I can actually see the 7th! You failed miserably

BTW Pavel what (hardware or software) is this measurement done with?
Don't recognise the screen from one of the usual suspects.

jan
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Old 22nd January 2013, 09:27 AM   #33272
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Just got an email from Bourns support, a scanned page from an obvious older doc, saying that 'in general' cermet pots can take up to 100mA on the wiper.
.......
Jan,

Can you post that doc? If your not under NDA, of course ;-)

Thanks!
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Old 22nd January 2013, 09:31 AM   #33273
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Aha! I can actually see the 7th! You failed miserably
.....
Pavel's measurement results are also inconsistent, if setup stayed the same.
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Old 22nd January 2013, 09:33 AM   #33274
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Pavel, I must be missing something obvious- what's the difference in the test for the two spectra?
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Old 22nd January 2013, 10:11 AM   #33275
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Jan,

Can you post that doc? If your not under NDA, of course ;-)

Thanks!
Attached.
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File Type: pdf max wiper current.pdf (325.0 KB, 25 views)
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Old 22nd January 2013, 10:26 AM   #33276
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Pavel, I must be missing something obvious- what's the difference in the test for the two spectra?
The small difference is only in about 4dB of output amplitude. But it affects level of high order harmonics near -130dB, which is a measurement fault, not opamp's.

I can later measure more opamps like OPA134 etc. in the same setup, i.e. with gain +101.
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Old 22nd January 2013, 10:31 AM   #33277
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Originally Posted by jan.didden View Post
BTW Pavel what (hardware or software) is this measurement done with?
Don't recognise the screen from one of the usual suspects.

jan
Hi Jan,

the software is Virtins Technology, Multi-Instrument 3.2
Virtins Technology: Turn a PC into Virtual Instrument - Home
Virtins Technology: Turn a PC into Virtual Instrument - Products

Measured with SB X-Fi HD, USB soundcard. THD 0.002% is at the limit of the card.
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Old 22nd January 2013, 10:48 AM   #33278
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Default AD825 vs. AD797

This is the result of John's favorite AD825, compared to AD797. We can see higher noise (and distortion) with the AD825, but, as expected, much better immunity against interferences. But, it might be burried in noise for the AD825.
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File Type: png AD825_40dB.PNG (50.1 KB, 141 views)
File Type: png AD797_40dB.PNG (52.9 KB, 124 views)
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Last edited by PMA; 22nd January 2013 at 10:52 AM.
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Old 22nd January 2013, 11:33 AM   #33279
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Default AD844 vs. OPA134

AD844 and OPA134. NOW, yes know we can see higher order harmonics with the OPA134, namely the 5th, again as expected.
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File Type: png AD844_gain40dB.PNG (50.2 KB, 136 views)
File Type: png OPA134_gain40dB.PNG (49.3 KB, 134 views)
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Old 22nd January 2013, 11:40 AM   #33280
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Default OPA637

And finally, OPA637. Low distortion, low noise and low sensitivity to interference. My vote

No 7th!!
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File Type: png OPA637_gain40dB.PNG (49.0 KB, 141 views)
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Last edited by PMA; 22nd January 2013 at 11:48 AM.
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