Wikipedia:Reference desk/Archives/Science/2023 May 3

= May 3 =

Hum in headphone amplifier
I have a headphone amplifier that has some hum in it. If I put my hand on the metal case, the hum goes away - or at least so low that I can't hear it. Does it need to be grounded?

There is a post on the back for grounding it, but I don't know what to ground it to. Years ago I had my turntable grounded to a water pipe, when the pipes were metal. My current house has plastic pipes, so what can I ground it to? Run a wire to the actual ground? Bubba73 You talkin' to me? 04:03, 3 May 2023 (UTC)
 * It is most likely a ground loop problem. What are the headphones plugged into?  USB? If it's USB, then the device itself needs to be grounded; if it uses a 2-prong adapter or something, then there's your problem.  136.56.52.157 (talk) 06:29, 3 May 2023 (UTC)
 * They are Audeze CRBN electrostatic headphones. Bubba73 You talkin' to me? 06:31, 3 May 2023 (UTC)
 * At that price point, you should contact customer service for tech support: . 136.56.52.157 (talk) 06:40, 3 May 2023 (UTC)
 * P.s. this query from Audeze might be helpful, it suggests that it most likely relates to RFI. Not mentioned however, is that there are RFI filters for such problems. 136.56.52.157 (talk) 17:25, 3 May 2023 (UTC)

The hum goes away when I touch the metal case of the headphone amp, which is a Stax SRM-400S. Bubba73 You talkin' to me? 23:59, 3 May 2023 (UTC)


 * A couple a days ago I had this exact same issue with two guitar amps. Relocating the new amp from the campfire table to the bare ground stopped the 60HZ buzzing. Indoors, placing it on the floor reduced the hum only some, so I clamped a tape measure to it and wrapped that around a quart can of varnish I have. :-) Modocc (talk) 00:06, 4 May 2023 (UTC)
 * I'll try moving the cables and the amp around. Bubba73 You talkin' to me? 01:28, 4 May 2023 (UTC)

I think I'm going to try a ground-loop isolator, for the XLR inputs into the amp. Bubba73 You talkin' to me? 00:05, 4 May 2023 (UTC)

How did the ancients deal with mold and mildew in ancient aqueduct systems?
Modern drinking water systems rely on chlorine etc. to prevent mold from growing in water systems. Ancient aqueduct systems must have been exposed to the outside elements. Surely they would have accumulated mildew over time? Or did enough sunlight do the trick? Yanping Nora Soong (talk) 12:08, 3 May 2023 (UTC)
 * Does lead piping suffer from mildew? One just hopes it kills the bugs quicker than the humans! Martin of Sheffield (talk) 13:13, 3 May 2023 (UTC)
 * Pethaps continuously moving water is less prone to this (biologist required). A second hypothesis is that they didn't know or care about what was growing in their water supply. Dr John Snow was the first to realise that drinking water with sewage in it was a bad idea, and that wasn't until 1854. Alansplodge (talk) 13:56, 3 May 2023 (UTC)
 * Molds aren't the problem, bacteria are. And they aren't a problem within the system, but on either end. Abductive  (reasoning) 15:36, 3 May 2023 (UTC)
 * Not an issue. As an example Plymouth's drinking water was supplied via leats which are large drainage channels that drain Dartmoor. They are effectively canalised streams. The water in them is entirely drinkable, if a bit tannic. Greglocock (talk) 20:38, 3 May 2023 (UTC)
 * One may discover, just upstream and out of site from where you quenched your thirst, a dead sheep in the leat. DuncanHill (talk) 20:47, 3 May 2023 (UTC)
 * Correct, which is why you walk downstream before drinking. Survival101. Greglocock (talk) 00:35, 4 May 2023 (UTC)
 * Images in Egyptian tombs from the 15th to 13th century BCE show various water treatment devices. An ancient Sanskrit text on medicine the Sushruta Samhita specified various methods such as  boiling water under the sun and filtering it through sand and coarse gravel. Hippocrates c. 460 – c. 370 BC designed a crude water filter to “purify” the water he used for his patients. Later known as the “Hippocratic sleeve,” this filter was a cloth bag through which water could be poured after being boiled. Diophanes of Nicaea of the first century BC advised putting macerated laurel into rainwater, Paxamus proposed that bruised coral or pounded barley, in a bag, be immersed in bad tasting water and the eighth century Arabian alchemist, Gerber, described various stills for purifying water. Sir Francis Bacon in his compilation "A Natural History of Ten Centuries" 1627 discussed desalination and began the first scientific experimentation into water filtration. Philvoids (talk) 00:33, 4 May 2023 (UTC)
 * The best way to purify water is to warm it with some malt, boil it with some hops, let it cool and add the yeast. A few days later your water is fit for anyone! :-)  More seriously, much weak ("small") beer was drunk prior to 20C just because it was safe, unlike the water supply from wells next to cess pits (see  above. Martin of Sheffield (talk) 07:39, 4 May 2023 (UTC)
 * (Insert joke based on reading "20C" as a temperature in Celsius here.) --174.89.12.187 (talk) 18:17, 4 May 2023 (UTC)
 * (Point out that unlike 293K it would be 20°C.) Martin of Sheffield (talk) 19:38, 4 May 2023 (UTC)
 * 20C??? That's a lot of electrical charge! 73.162.86.152 (talk) 06:42, 5 May 2023 (UTC)
 * Equivalent to downing 3-1/3 six-packs of Mountain Dew in a second. DMacks (talk) 06:51, 5 May 2023 (UTC)

The ancient Greeks and Romans added wine to drinking water, which killed some of the bacteria, according to this article. Adding wine also improved the taste of stagnant water, according to this website. Cullen328 (talk) 20:08, 6 May 2023 (UTC)

So I actually found the best answer to my question - ancient Romans used a piscina limaria, or settling basin, to settle and remove crud at the intake and just before a city. They were also used in baths. I'll add that to the Roman aqueduct article with good sources soon. There is probably much also unsaid about the use of UVC-rich sunlight. Mold, odor and discoloration is easy to see (probably why the miasma theory had currency before the germ theory). Yanping Nora Soong (talk) 08:48, 7 May 2023 (UTC)