For completeness, do we need to discuss:
1. The cable gland. Are they still legal? If so, then the method of clamping the power cable is important and the earth wire must be longer than the active and neutral.
2. Should the fuses between the PSU and amp be shown.
3. Should the gender of the umbilical plugs and sockets be shown. Important if DC voltages are high.
4. What about countries with no earthing system?
regards
1. The cable gland. Are they still legal? If so, then the method of clamping the power cable is important and the earth wire must be longer than the active and neutral.
2. Should the fuses between the PSU and amp be shown.
3. Should the gender of the umbilical plugs and sockets be shown. Important if DC voltages are high.
4. What about countries with no earthing system?
regards
@AndrewT
As you are so hot on quoting (UK)regulations I am suprised that you are so selective in your choice.
The regulations only have legal force applied to articles offered for sale.
The word 'disconnect' has special significance in the regulations and that is not the 'disconnect network' discussed here.
@all
It is important to realise that a safety earth is intended to be 'an equipotential' system and should have no currents circulating in normal operation.
There are two ways that unwanted signal can appear at the output of a circuit via the ground or return line.
One is due to magnetically induced pickup which is avoided by the star system of grounding as the OP points out.
The other is for the output and input return ground to share a common line. The (large) return current from output generates significant millivolts variation along this common track or wire which is injected into the input and amplified.
Unfortunately the amplifiers, as drawn, appear to do exactly this second thing.
As you are so hot on quoting (UK)regulations I am suprised that you are so selective in your choice.
The regulations only have legal force applied to articles offered for sale.
The word 'disconnect' has special significance in the regulations and that is not the 'disconnect network' discussed here.
@all
It is important to realise that a safety earth is intended to be 'an equipotential' system and should have no currents circulating in normal operation.
There are two ways that unwanted signal can appear at the output of a circuit via the ground or return line.
One is due to magnetically induced pickup which is avoided by the star system of grounding as the OP points out.
The other is for the output and input return ground to share a common line. The (large) return current from output generates significant millivolts variation along this common track or wire which is injected into the input and amplified.
Unfortunately the amplifiers, as drawn, appear to do exactly this second thing.
I've always done my two-box GC's with a separate wire for safety earth. It just seemed logical to do so, leaving the other wiring 'unmodified' and therefore simpler for me to understand.
Another thought - if you use two rectifier bridges and want to leave the grounds separated until the amp stage, you will need five wires in the umbilical, and will almost certainly need to make up a lead rather than using something off-the-shelf. Unless using fairly small wires, choice of plug/socket will be a bit limited too.
Another thought - if you use two rectifier bridges and want to leave the grounds separated until the amp stage, you will need five wires in the umbilical, and will almost certainly need to make up a lead rather than using something off-the-shelf. Unless using fairly small wires, choice of plug/socket will be a bit limited too.
Studiot, AndrewT is not trying to 'sell' us anything, or mislead us. He is rightly concerned about the safety aspect of building mains-powered equipment, more so since many builders have little, or no training, in building this sort of stuff.
Although most of us will not be selling anything, it still makes sense to agree on a method of making these amps as safe as we can, if only for purposes of not invalidating our insurance.
It's not a court of law and he is free to quote what he likes.
Although most of us will not be selling anything, it still makes sense to agree on a method of making these amps as safe as we can, if only for purposes of not invalidating our insurance.
It's not a court of law and he is free to quote what he likes.
AndrewT said:
Andrew,
I think that the 4th wire for safety earth should go to both enclosures, if "the audio ground lead going to the disconnecting network does the duty of carrying fault current back to the PSU" then you could momentarily get a voltage difference between the 2 chassis, which would result in the bad kind of shock using 2 hands. Or, if the 2 enclosures were stacked or side by side and touching, you'd be shorting the disconnect network.
Questions I still have are if there should be any kind of connection between the amp chassis (safety earth) and audio ground in the amplifier, for example capacitors to the chassis from the shell of an RCA jack
This tread has helped me a lot to find the final solution for my amplifier.
AD826 Grounding Design
Most are common considerations but you will find few different ground connection that I found sounding better
AD826 Grounding Design
Most are common considerations but you will find few different ground connection that I found sounding better
studiot said:
Whilst I'm happy to use non-RoHS components and leaded solder in builds for my own use I still value the Regulations where electrical safety is the concern. Not all laws are written by *****.
Now, to put some values to parts mentioned, I put forward Rod Elliott's article for comment, which would apply to Australia and the UK; a parallel combination of
- 35A back-to-back diodes (using a 35A bridge)
- 10-ohm 5W resistor
- 100nF capacitor (X2?)
