Hi and sorry for the very basic question but i need to know better.
I see that many amps come with a two prongs only plug (no earth prong)
In this way it is not possible to connect the amp chassis to the mains Earth.
Is this really safe ? can i do this without risk on an amp i ma trying to assemble ?
Another question
I had an amp with the earth not connected
Then i connected the mains earth to the amp chassis and got a very loud hum
How is this possible ?
I know that earthing is a very important operation for safety.
Thanks a lot. Kind regards, gino
I see that many amps come with a two prongs only plug (no earth prong)
In this way it is not possible to connect the amp chassis to the mains Earth.
Is this really safe ? can i do this without risk on an amp i ma trying to assemble ?
Another question
I had an amp with the earth not connected
Then i connected the mains earth to the amp chassis and got a very loud hum
How is this possible ?
I know that earthing is a very important operation for safety.
Thanks a lot. Kind regards, gino
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Double insulated devices are not intended to be connected to mains earth. As you have found it usually results in an earth loop because the chassis is connected to internal 0V.
There is no benefit to be gained by earthing such an amplifier.
There is no benefit to be gained by earthing such an amplifier.
Hi and thanks a lot for the reply.
You mean i must connect the mains E to the amp chassis through a 10R resistor ? this is easy. Good !
Last think that i would want is to get hurt ...
By the way, i am proceeding with the destruction of the Doxa amp 😱
I think the real problem was in a relais in the power supply
In the weekend i will try to test the transformer
What i like very much of it are the very thick secondaries ... this suggests high current available on the secondaries ... very very good indeed.
I will check the VAC of the secondaries ...
The Rifa ps caps look beautiful and ok ... they are 40V/10.000uF pieces ... love them ... i know they are very good ... when new 🙁
I'll check the series.
To end all the rambling i strongly feel that a very good power amp starts with a great power supply and ends with a very robust but minimalist amp stage
On principle i love the F5 style ... but i would like something equally minimalist but with bjts (one single output pair) at the output and biased in class AB
And one day i will have it.
I just need max 10 strong and clean and transparent watts
I am moving to high efficiency speakers ... i am bored with little shoe boxes ...
I will be more precise after the weekend
Thanks a lot again, gino
A commercial product which is not connected to safety earth must be class 2 "double insulated", this is a set of rules meant to ensure that mains will never contact the chassis. You will see a logo in the sticker on the back, two squares one inside the other.
Such equipment is probably not designed against ground loops, so if you do connect it to earth, you can expect hum...
Such equipment is probably not designed against ground loops, so if you do connect it to earth, you can expect hum...
Hi and thanks for the valuable reply.
It is this double insulation that i do not understand well.
But no problem ... i will keep hands far away.
Kind regards, gino
Double insulated means the product is designed to be safe to the user under all conditions. There is no means for any fault to occur that cause a live wire or live mains voltage to come into contact with anything the user can touch. Components such as transformers will be safety specified (such as having thermal fuses) and there will be no way you can touch anything live or dangerous by poking metal implements into any accessible holes.
Grounding a double insulated amp chassis (provided that chassis is already user touchable) will cause no safety issue but could introduce hum in an audio component if other connected items are also mains grounded. That is because there is a wire "loop" formed from mains ground, through the amp, through the leads, into other components, and then back to the mains through other components. Yes 🙂 That loop of ground wire can have circulating currents within it that can cause audible hum... circuit dependent.
Grounding a double insulated amp chassis (provided that chassis is already user touchable) will cause no safety issue but could introduce hum in an audio component if other connected items are also mains grounded. That is because there is a wire "loop" formed from mains ground, through the amp, through the leads, into other components, and then back to the mains through other components. Yes 🙂 That loop of ground wire can have circulating currents within it that can cause audible hum... circuit dependent.
Yes.ginetto61 said:
Omitting a required earth connection is very dangerous.
Naively adding an unwanted earth connection can be very dangerous.
Before connecting equipment to the mains (especially DIY or DIY-modified) make sure you understand mains.
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Hi and thank you All very much indeed.
I will connect the mains E with the chassis like i have seen many times.
I am sure i will end with some ground loops ..
Regards, gino
I will connect the mains E with the chassis like i have seen many times.
I am sure i will end with some ground loops ..
Regards, gino
THIS THREAD IS CRAZY DANGEROUS.
DUBIOUS ADVICE IS GIVEN WITHOUT READING OR UNDERSTANDING THE OP PROBLEM.
1) ginetto specifically asked:
NO, with a 2 prong plug you can NOT connect the chassis to mains Earth, PERIOD.
You need to replace plug and cable with a 3 prong, 3 wire cmains cable and ground the ground wire to chassis, leave the other 2 alone
2)
WHERE is ginetto supposed to connect such Earth?
You don't mention using the proper 3 prong cable.
Taking that answer literally means connecting chassis through the network you suggest to plug Neutral ... a sure fire way to get Hum because it's often a few Volts away from true Earth.
DANGEROUS suggestion.
I ask Moderators to remove this entire dangerous thread.
Besides, Double Insulation applies to devices where there is no way users can touch or access internal chassis, such as power tools, kitchen appliances, remote control (or plastic button) operated TV, etc.
Amplifiers do NOT meet Double Insulated criteria because of audio signal grounding which directly connects internal chassis to external devices through audio cabling and connectors.
DF96 spells it clearly:
Thanks.
DUBIOUS ADVICE IS GIVEN WITHOUT READING OR UNDERSTANDING THE OP PROBLEM.
1) ginetto specifically asked:
the correct answer is:
NO, with a 2 prong plug you can NOT connect the chassis to mains Earth, PERIOD.
You need to replace plug and cable with a 3 prong, 3 wire cmains cable and ground the ground wire to chassis, leave the other 2 alone
2)
WRONG answer.
WHERE is ginetto supposed to connect such Earth?
You don't mention using the proper 3 prong cable.
Taking that answer literally means connecting chassis through the network you suggest to plug Neutral ... a sure fire way to get Hum because it's often a few Volts away from true Earth.
DANGEROUS suggestion.
I ask Moderators to remove this entire dangerous thread.
Not understanding mains issues is a BIG reason not to mess with it.
Besides, Double Insulation applies to devices where there is no way users can touch or access internal chassis, such as power tools, kitchen appliances, remote control (or plastic button) operated TV, etc.
Amplifiers do NOT meet Double Insulated criteria because of audio signal grounding which directly connects internal chassis to external devices through audio cabling and connectors.
DF96 spells it clearly:
but this does not hide dangerous / incomplete advice posted earlier, I suggest the entire thread is removed.
Thanks.
I'm posting now as a diy member, not a moderator and tbh I don't see any dangerous advice that has been given.
Many amplifiers are double insulated with a simple twin core mains lead (I have one in front of me now, a Rotel RA820). It has the recognised "Double Insulation" symbol against the mains inlet cable. The amplifier also has a full metal chassis and case complete with a user accessible earth screw terminal on the chassis rear. Any grounded source components will automatically ground the chassis via their RCA leads.
As I mentioned earlier, grounding an already user accessible chassis (and that it is already user accessible is important) carries no safety hazard.
Many amplifiers are double insulated with a simple twin core mains lead (I have one in front of me now, a Rotel RA820). It has the recognised "Double Insulation" symbol against the mains inlet cable. The amplifier also has a full metal chassis and case complete with a user accessible earth screw terminal on the chassis rear. Any grounded source components will automatically ground the chassis via their RCA leads.
As I mentioned earlier, grounding an already user accessible chassis (and that it is already user accessible is important) carries no safety hazard.
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