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Old 6th November 2018, 09:16 PM   #151
craigtone is online now craigtone  United States
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I know this is a silly question but is anyone willing to part with one of these little beauties?
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Old 7th November 2018, 08:56 AM   #152
marconi118 is offline marconi118  Germany
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Hi Nelson
how do you measure these nice scope traces of H2?

using a notch filter to suppress the fundamental signal?
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Old 7th November 2018, 01:25 PM   #153
Mark Johnson is offline Mark Johnson  United States
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A pleasant and helpful youtube video is here
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Old 7th November 2018, 02:00 PM   #154
marconi118 is offline marconi118  Germany
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Quote:
Originally Posted by indra1 View Post
Try Dick Moore's Active Twin-T notch filter.
using this Active Twin-T notch filter between amp and scope will I have the nice distortion trace on the scope (the bottom one in the video or in pass pictures) ?

Or do I need a more complex distortion meter with a specific output for that? (mentioned in the video)
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Old 7th November 2018, 02:03 PM   #155
indra1 is offline indra1  Indonesia
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Yes, no need for additional meter.
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Old 17th December 2018, 04:19 PM   #156
Mark Johnson is offline Mark Johnson  United States
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I found this little figure in the Jan 2019 issue of Stereophile. It's part of the measurements section, in a review of a tube power amp.

Anybody want to positively state with confidence and complete certainty, whether this tube amp produces "positive phase" or "negative phase" distortion? And whether the distortion is H1, H2, H3, or something else?

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Old 17th December 2018, 04:27 PM   #157
Blues is offline Blues  United States
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Negative phase H2

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Old 17th December 2018, 06:23 PM   #158
oreo382 is offline oreo382  Canada
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Originally Posted by Blues View Post
Negative phase H2

I agree! When using LTSpice and viewing the harmonic distortion components the 2nd harmonic will be +45 degrees relative to the fundamental for a perfect neg. phase 2nd harmonic.I've used this method for tuning my F7 approximation and my ears like that setting more than all the others I have tried.

Last edited by oreo382; 17th December 2018 at 06:34 PM.
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Old 18th December 2018, 03:08 AM   #159
Loudthud is offline Loudthud  United States
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The ACA produces a positive phase 2nd harmonic. The speaker connections are inverted with the + speaker lead grounded. It squishes the top part of the waveform at the output. I verified this with an X-Y plot of the ACA output in the ACA thread.

Would an ACA built with P channel FETs produce a negative phase 2nd harmonic at the output ? Would you still need to invert the speaker connections ? Would this be better for head phones because of the common ground on the sleeve of the stereo phone plug ?
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Old 18th December 2018, 06:51 AM   #160
indra1 is offline indra1  Indonesia
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The ACA is inverting for both N and P channel FET. Speaker polarity connection is reversed (+ to ground) to maintain absolute phase in any case. Input to the ACA needs to be inverte to get both correct absolute phase and negative H2 from non inverted speaker connection. There are several ways to do that: a polarity plugin for foobar, an inverting preamp like the jBOZ, an 600 or 10k line matching transformer used with the output inverted and many others.
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