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24.140.192.106
Did a few overlay plots in ARTA to look for differences when using TK's 220 ohm damping resistor across 320mH L3 choke . Refer to previous thread on this subject.Also tested at 5KHz , overlay difference of 0.
Adding an extra 15uF to C2 dropped the mVAC at the amp speaker posts from 5mV to 3mV with the damping resistor installed.
Edit: I took individual spectral graphs with and without the 220 ohm damping resistor across L3.
The new graphs seem to match the spice B+ vs. Hz plots by TK.
I probably had the overlay color mixed up on the now deleted graph I posted previously.
The energy spike that appeared below 60Hz was a random event that occurs from time to time on the analyzer , not sure what causes it. It happened with or without the damping resistor installed.
Edits: 10/19/16Follow Ups:
Thanks for posting those - I feel vindicated! :) Now, the question remains as to whether the improvement in low frequency PS output Z is audible. The first step toward that would be to do a frequency sweep to see if low frequency response is affected. But, even if you don't see it, there might still be an audible difference. Musical transients can elicit a different response from an amp than constant-amplitude RMS sweeps.
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Buy Chinese. Bury freedom.
Differences @ 60Hz = .37db, 50Hz = 2.19dB, 40Hz =.48dB , 30Hz = 1.17dB
Differences @ 120Hz = 0dB, 240Hz = 0dB, 480Hz = .22dB
I didn't add the extra 15uF of filtering @ C2 for this test.
I ran the green (no damping) resistor plot first, then the orange (220 ohm damper ) overlay plot. The difference is in yellow near the 0dB line.
dt 667
There's a lot of "ripple" in all those plots. It's not a small deviation, looks like +/- 2dB or so from the average. I think those must be artifacts of the measurement, but they make it difficult to tell what's really going on. Do you think the dip in output just above 30 Hz (without dampening resistor) is real? It doesn't seem to correlate with any of the sims, but it could be related to some characteristic of the output transformer.
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Buy Chinese. Bury freedom.
New graph. Low bandwidth sweep to 20Hz with 1/3 smoothing.
That looks much better. I think you would only want to turn off smoothing if short-term anomalies (spikes and transients) are likely to be involved.
I was very surprised to see such a small delta in the plots with and without dampening. Then I realized the effect of PS impedance bumps on output amplitude probably can't be measured so easily in an amp with NFB. The feedback will mask any small variations in gain that occur as a result of the power supply. I think you'll need to remove the feedback to see what's happening in those terms. Otherwise, you're limited to evaluation by ear or the use of very specialized and expensive test gear.
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Buy Chinese. Bury freedom.
Some of the reports of poor performance of low DCR filters (flywheel/LSES) might be dependent on the application of signal circuits, use of feedback or other things we can't or don't know how to measure.
Subjectively, the 3 LC section (to finals) flywheel filter I am using sounds well enough to my ears that I will just leave it as is for now.
Thanks for helping with the measurements.
dt 667
no text
Do you have a hypothesis regarding the increase in energy below 60 Hz? Is it present without the 1 KHz signal? It's pretty small, roughly -93 dB relative to 1W, but the increase runs counter to "before-after" SPICE results in that region.
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Buy Chinese. Bury freedom.
"Do you have a hypothesis regarding the increase in energy below 60 Hz?"
At the moment, no. It does run counter to the spice results.
"Is it present without the 1 KHz signal?"
Didn't notice anything unusual.
I ran another overlay where the 220 ohm damping resistor was in place and I compared C2 with 50uF vs. 65uF. The increase in energy below 60Hz didn't appear on that graph.
I'll run the test again when I get home from work to see if this low HZ energy was some sort of bogey or a result I can reproduce.
2006
Fortunately, I had some examples of how to model the flywheel LC section saved on my PC (not the step current tests).
Thanks for posting the link.
dt 667
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