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In Reply to: RE: Repost ... damping resistor ? posted by deathtube 667 on October 16, 2016 at 16:43:50
200 Ohms is a ballpark value that I arrived at by trial and error in SPICE. It was a compromise between reducing the impedance bump on the one hand, and rendering the 0.32H choke ineffective on the other. In this case, the filter with the resistor across the choke exhibits rejection at 1 kHz approximately 30dB better than with the choke bypassed. I concluded from this and the previous measurements that 200 Ohms is an effective value. By all means, feel free to try other values if you want, it's just a matter of achieving the right compromise.
The resistor type can be almost anything. It's inductance is relatively unimportant, and power dissipation will be well under 50 mW if the 0.32H choke is 10 Ohms DCR.
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Buy Chinese. Bury freedom.
Follow Ups:
Got a 220 ohm resistor (closest value to 200 ohms in my inventory) across the 320mH choke for a quick listen tonight.
There was a slight increase in AC ripple at the output from 3mV to 5mV.
The overall subjective sound is pretty smooth on my bookshelf speakers listening to some random classical music selections.
I'll need to do some bench testing with/without the damping resistor to see if I can detect any measurable changes/improvements.
In too much discomfort from a 3 hour trip to the dentist this afternoon to do much of anything tonight.
Sorry to hear you were tortured by the tooth doctor. That's never any fun. Well, I expected the 120 Hz energy to go up a little. The real problem in terms of overall ripple is the 2uF cap. It's just not large enough clean it up for a SET. Anyway, if ripple is acceptable without the 200/220 ohm but not OK when you install it, just add 20uF to C2 or C3 in your drawing.
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Buy Chinese. Bury freedom.
TK,
Not using any 2uF caps in my filter to the finals.
C1 = 8uF
C2,C3 = 50uF
Adding a bit more filtering if needed is not a problem.
dt 667
Just not sure that's enough to get it "SET quiet." You'll get it right over time though. You've got the tools and the smarts to steer it where you need it to go. :)
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Buy Chinese. Bury freedom.
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