Please read the description first for more & relevant information.
Video about the so called “ground loop hum” in audio amplifiers. A difficult problem that can be cured easily, when the setup of the audio amplifier is OK.
It is a persisting (small) hum on the background that is always there, whatever you do.
It has NOTHING to do with:
• shielding against E.M. influences, e.g. out of the supply AC 50/60 Hz transformer
• A too low value of the smoothing capacitor in the AC-DC setup, say with a bridge rectifier
• Ripple on the power supply lead
Again: these are no (!) reasons for a “ground loop hum” in a (homebrew) audio amplifier or pre-amplifier. Sometimes even in professional audio amplifiers it has to be cured.
This type of hum sounds different and has another character.
Also with somewhat sloppy (homebrew or not) setups of audio amplifiers this problem can be cured. More info in the video.
Reason that I publish this video now (2 July 2024) is that I have payed much attention to it in an earlier video (1 July 2024), but only in the textbox.
My idea was: perhaps I can explain it better in a new video. Because ground loop(s) hum can easily occur in homebrew audio amplifiers or pre-amplifiers, so an expensive audio project can fail, costing money.
Even in the more “modern” amplifiers, with High Q digital chips, because it is a classical problem in the development of analog circuits, especially the audio circuits.
It is all about wiring the ground wires (electrodes, shielding busses) to the 1 and only earth connection in the chassis, preferred made of steel (in audio amps).
On that “one and only” earth connection, also the supply electrolytic capacitor is mounted, with its minus to that chassis, in this case minus on ground. Minimum value in all cases of audio amplifiers (be it pre-amps or end-amps) is 4700 uF.
Its working Voltage depends on the electronic circuiit, always take the working voltage of the supply capacitor 20 % higher, compared to the voltage necessary (schematic) that must be used to supply the audio end amplifier.
NB: there are very “tricky” ways of ground loops that are not easy to detect, e.g. in the pre-amplifiers of a stereo amplifier.
When they are not completely identical, tiny currents can flow between the 2 pre-amps, that try to “elaborate/compare” their currents. It can lead to a ground loop with a tiny hum. That can also be cured in the way, showed in this video. Or via small compensating resistors in the order of 100 Ohm-1K, to make the 2 pre-amps (Left-Right) completely identical in their quiescent current, that is often the problem (their different quiescent currents (!), not the current when the pre-amps work and do their job).
You have to stick your ear completely into the loudspeaker to hear these differences and their cures.
But it is possible to get it completely free of hum.
More in my book “Schematics 2, audio amplifiers and lpoudspeaker boxes” on the Website of LULU. Search there for autor Ko Tilman.
My You Tube channel trailer is here: will follow
Type there the keywords that you like (e.g. radio/audio/amplifiers/test/filter/) in the “looking glass” = search function” and give “enter”. Via that you can find specific video’s (under the say 1500 published).
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You can also search via the “looking glass” on my Channel trailer via keywords like ”audio”, “radio”, “amplifier”, “filter”, “Shortwave”, “transistor”, “FET”, “oscillator”, “generator”, “switch”, “schmitt trigger” etc; so the electronic subject you are interested in.
My books about electronics & analog radio technology are available via the website of "LULU”, search for author “Ko Tilman” there. www.lulu.com/s....
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