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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I disagree Hen. Any spike on a sine wave will be smoothed by a capacitor.
The voltages and currents involved are pretty low, too, especially at the input stage, and thermal and shot noise can both be issues in solid state circuits, in particular.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Ash Small wrote ...
Now, a new question about shot noise in particular..... I've a hunch larger wattage resistors will result in less shot noise for a given current.
Does anyone have any 'opinion' either way on this?
I do not KNOW the answer, but from working with ham radio stuff; . I have never read of such an effect and if true I think that it would be known by now.
. the difference has mainly been between different resistor manufacturing techniques, from memory; carbon composition - carbon film - metal film in order of decreasing noise.
Registered Member #230
Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284
IMHO resistor type is more important than resistor size. Carbon composition being the worst and metal film being the best. In measurementsd i have done at UHF I can see the sifference in noise with a 51 ohm metal film cooled in liquid nitrogen and the same resitor @ 20 degree C so the major noise contributer was 4kTBR not shot noise
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I'm using film, metal film and wirewound resistors exclusively. virtually all are metal film or wirewound, except trim pots which will be replaced later with fixed resistors.
I'm getting some good results with low ESR capacitors.
I'm working on power supply smoothing at the moment, simulator says 1.6mA ripple @ 5A, with a five stage RC filter.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Your 5 stage filter yields hum level 70 dB down. However unless you construct your audio system with a balanced DC feed, your efforts will be skewered by the 5 amp drop across printed circuit foils.
-70 dB hum can be heard, if someone cranks the level and sticks an ear next to the cone.
Also wire wound resistors and capacitors have inductance, The Dyna 120 (classic solid state amplifier, circa 1970) wrapped a contra coil around the capacitors to buck out the inductance.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546
Balances amplifiers fed from a bipolar power supply, means the loudspeaker is fed with one terminal with positive going signal, while the other, a negative.
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Thermal and shot noise
