Author Topic: reducing hum in high gain audio tube amp when no earth ground is connected?  (Read 1369 times)

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Offline ELS122Topic starter

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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  ;D
 

Offline mck1117

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earth ground exists for a reason, use it
 

Offline Bassman59

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so my "sound engineer" is very stuburn and wont listen to me when I tell him that he needs earth ground in his studio...

Fire him immediately.

Stop feeding his bullshit.
 

Offline CaptDon

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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!!

 
Collector and repairer of vintage and not so vintage electronic gadgets and test equipment. What's the difference between a pizza and a musician? A pizza can feed a family of four!! Classically trained guitarist. Sound engineer.
 

Online jonpaul

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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
Jean-Paul  the Internet Dinosaur
 

Offline ELS122Topic starter

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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!!

I think you're talking about a ground loop... that's not the problem here, it's shielding that's the problem...

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

I know it's safety related, but I just don't see the huge deal about it in something that only I'm going to use and I have considered every percaution I can think of when wiring the amp, so there's an insanely minimal chance of something going wrong, except maybe for the power transformer shorting but it hasn't ever been in a humid or in other ways a bad environment that would damage the insulation.

Quote
DANGER, TOUCHING THE DEVICE WHILE YOU ARE STANDING ON A GROUNDED FLOOR (eg concrete, wet area) CAN RESULT IN A SHOCK OR DEATH.

well that's only if there's a current path between the Live wire, and Ground. and 'DEATH' is only really if there's some major failure in the circuit that connects the chassis to the live wire.
like for example: a shorted 'death cap' in an old amp that has a 'death cap', or just some live wire that's shorted to the chassis.

Quote
At least one famous R&R performe was electrocuted in this way.

Ace Frehley you mean? that was a railing that somehow was Live... I doubt it could just be Live because it had no earth on it. there must've been some cut wire or something that pressed against it. ofc if it was grounded it would've tripped the circuit breaker (or just melted the wire and someone would've noticed that there's a smoking wire there).
and in a way, most likely everyone who's played a vintage Fender amp has been electrocuted, it's basically in the design. if the 'death cap' is connected to Live and the chassis instead of Neutral, it would conduct around 2mA of current trough the cap, which would give you a pretty decent shock if you touched anything grounded. like for example wet concrete while bare foot, or a grounded cable, etc.


so in short, yes I understand the risks. I'm not THAT worried about it. and I've decided instead of adding a ground switch and a 'death cap', I'll just get a extension cord with a ground next time to a gig and plug it in into a grounded socket.


also the
Quote
and get rid of your incompetent and dangerous "engineer"
isn't really an option in my case... and I think I just can prove to him the benefits of having things grounded and make him ground everything.
 

Online jonpaul

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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
Jean-Paul  the Internet Dinosaur
 
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Online jonpaul

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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 Chance



Jon
Jean-Paul  the Internet Dinosaur
 

Offline ELS122Topic starter

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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 Chance



Jon


it probably would, since it's like a big inductor and may clean up any noise in the mains power.
you can probably plug it into a ballast and have an even bigger effect.

but I'd prefer just earthing the amp than buying an isolation transformer.
I can try adding a choke that I salvaged from a black plastic CRT TV, it was used in series with the line in the TV, so I guess it should do something? idk I see no reason to put like 500 chokes and 50000 capacitors in random places like I see in many consumer appliances from the 90s onward.
 

Online Someone

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At least one famous R&R performe was electrocuted in this way.
Yes:
https://en.wikipedia.org/wiki/Leslie_Harvey
https://en.wikipedia.org/wiki/San_(band)
https://en.wikipedia.org/wiki/Barbara_Weldens

Safety standards are there for a reason, double insulated construction is possible if people really want to eliminate the ground reference.
 

Online coppercone2

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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).
« Last Edit: April 23, 2021, 06:09:24 pm by coppercone2 »
 

Offline Terry Bites

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