reducing hum in high gain audio tube amp when no earth ground is connected? - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: April 21, 2021, 06:00:21 pm
content: so my "sound engineer" is very stuburn and wont listen to me when I tell him that he needs earth ground in his studio...so without the chassis grounded in my guitar amp, it buzzes quite a lot... I added an across the line cap (yes, I chose a proper type of cap for that) and that reduced it slightly, but it still buzzes.is there anything I can do to reduce this buzz? I thought about installed a not so-death cap, but idk I don't think that would help it a lot. and I don't want to drill another hole for a switch in the chassis without being sure it will do anything...so what should I do?maybe I smuggle a proper grounded power strip into the studio and just plug into an earthed outlet

author: mck1117
author_rank: Contributor
timestamp: April 21, 2021, 06:25:26 pm
content: earth ground exists for a reason, use it

author: Bassman59
author_rank: Super Contributor
timestamp: April 21, 2021, 07:34:28 pm
content: Quote from: ELS122 on April 21, 2021, 06:00:21 pmFire him immediately.Stop feeding his bullshit.

author: CaptDon
author_rank: Super Contributor
timestamp: April 22, 2021, 02:33:57 pm
content: Doesn't sound like much of an 'engineer'. Good grounding is the foundation of a great studio and despite the volumes of grounding techniques and theories in the end you go with whatever works best in the immediate situation. Sometimes star ground, sometimes distributed ground and sometimes even removing the 'ground pin' if the metal 19" rack itself is grounded. Now to fix your problem, I have used 600 ohm to 600 ohm line matching transformers which have a 'shield' wire between the two windings and I connect that shield to only the input device or only the output device, not both. Which ever gives less hum. You could also use an isolation transformer on the mains input of your amplifier. Sometimes a 120/240 'control' transformer of maybe 500va rating can work. They usually have 4 120 volt windings so they can be used at 120 or 240 as 'isolation'. Then definitely 'float' the ground of you amplifiers input. There is no danger of shock because the amplifier is now 'isolated' from real earth reference. I am both a guitar player for 3 different bands and styles of music and worked for 13 years as a professional broadcast engineer having built many studios over my career and played in dozens of other people's studios with all kinds of 'work-arounds' to reduce hum and digital noise. Best wishes!!

author: jonpaul
author_rank: Super Contributor
timestamp: April 22, 2021, 03:28:56 pm
content: Hello ELS122:The function of a chassis earth are many and SAFETY RELATED.Besides an RF shield and reducing ground current hum the earth ground is essential to provide a safe current return path if the device insulation line to chassis fails.DANGER, TOUCHING THE DEVICE WHILE YOU ARE STANDING ON A GROUNDED FLOOR (eg concrete, wet area) CAN RESULT IN A SHOCK OR DEATH.At least one famous R&R performe was electrocuted in this way.GROUND IT ASAP and get rid of your incompetent and dangerous "engineer"Bon Chance,Jon

author: jonpaul
author_rank: Super Contributor
timestamp: April 22, 2021, 06:26:13 pm
content: Rebonjour,Sorry for my excited note, but your post concerned me re safety.Having been "bitten" a few times by faulty equipment, I wanted to urge caution.Jon

author: jonpaul
author_rank: Super Contributor
timestamp: April 22, 2021, 06:28:31 pm
content: ELS122:we have used isolation transformers to reduce hum, either in the mains supplying the equipment (Stancor, Thardarson etc. 1:2 120V><120V) OR inline at the audio line, eg SesCom, Rane, Neutrik isolation adapters with 1;1 audio transformer.Bon ChanceJon

author: Someone
author_rank: Super Contributor
timestamp: April 23, 2021, 12:39:32 am
content: Quote from: jonpaul on April 22, 2021, 03:28:56 pmYes:https://en.wikipedia.org/wiki/Leslie_Harveyhttps://en.wikipedia.org/wiki/San_(band)https://en.wikipedia.org/wiki/Barbara_WeldensSafety standards are there for a reason, double insulated construction is possible if people really want to eliminate the ground reference.

author: coppercone2
author_rank: Super Contributor
timestamp: April 23, 2021, 06:04:09 pm
content: well given that I watch these videos, from how people love to leave as much original parts as possible in the device and how old the parts are, its a recipe for a disaster to run these with the chassis not grounded.you can easily get killed by some leaking overheating bullshit in a tube amp from 1940.Not even sure if I would trust it in a plastic enclosure because for 'sound reasons' they might leave things in there that can spill out, some of the old amp repair videos I see, its like opening a old refrigerator that someone unplugged in the garage. And I have seen alot of repairs where he takes it apart and there is old components left inside with new components taped on them and other bad stuff like that. Usually highly corroded and probobly conductive and corrosive stuff in there, plastic can be breached by something popping then leaking to make a circuit (i.e. it 'works' because it had a field repair in 1960 after being manufactured in 1940 by sticking something on with bubble gum scraped off the stage).

author: Terry Bites
author_rank: Super Contributor
timestamp: April 25, 2021, 10:58:34 am
content: Sack your sound engineer. He clearly knows nothing about "technical earthing" (as opposed to protective earthing).Now read this!https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjB7sn4m5nwAhW2ZhUIHcR0BB8QFjAAegQIBBAD&url=https%3A%2F%2Fwww.dalmura.com.au%2Fstatic%2FHum%2520article.pdf&usg=AOvVaw1FVvkocsvPOxkQO4q3ZDFH