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Old 4th January 2013, 10:40 PM   #21
Pano is offline Pano  United States
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Thanks for the update!

For me it would be worth the 1.5dB loss to have the grounded secondary. But I like a slow, sloping rolled-off response, anyway.
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Old 8th January 2013, 09:53 PM   #22
rrrs is offline rrrs  United States
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Hi, there is some “weirdness” I am founding out with this transformer; there seems to be pronounced rise in distortion from 2K up.
Here are THD measurements I did in ARTA, all at 1W into 5.7ohm load (this are measurements of actual amplifier, not just OPT):

40Hz – 0.4%
100Hz – 0.31%
1KHz – 0.31%
2KHz – 0.37%
4KHz – 0.55%
6KHz – 0.77%
8KHz – 0.98%
10KHz – 1.2%
12KHz – 1.33%
14KHz – 1.37%
16KHz – 1.34%
18KHz – 1.17%

Then I did vey same measurement with Chinese made transformers that came with amp originally and got higher distortion (around 0.7% at 1KHz), but it would remain pretty consistent with higher frequency (getting higher once you go below 200Hz).

Here are figures I got from Chinese 10K OPT, 1W into 5.7ohm load on 8 ohm tap:

40Hz – 1.03%
100Hz – 0.72%
1KHz – 0.63%
10KHz – 0.79%

Then, on 4 ohm tap, again 1W into 5.7ohm load:

40Hz – 0.74%
100Hz – 0.36%
1KHz – 0.23%
10KHz – 0.46%

Would anyone have idea why is Lundahl distortion is rising at higher frequency while; would this be the function on higher primary (20K vs 10K for Chinese OPT)?
Lundahl has higher inter-winding capacitance which makes it roll-off earlier at HF; but would this influence distortion?
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