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In Reply to: RE: 3 stage flywheel : mH choke damping resistor posted by deathtube 667 on October 18, 2016 at 18:44:43
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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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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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
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