Further to the above.
Some British separates manufacturers brought out speaker terminals that were shrouded in plastic insulating material and eliminated the "hole" into which an inquisitive child could poke a metal object. This special connector is disliked and fairly universally NOT adopted outside Britain.
It is a safety measure to protect our children from an obvious danger.
Why did we need this in Britain?
Because the speaker terminals are usually exposed conductive parts.
And the rule IS that they MUST be connected to Chassis.
The solution: make them NOT EXPOSED.
Why is the rest of the world ignoring this safety requirement?
Some British separates manufacturers brought out speaker terminals that were shrouded in plastic insulating material and eliminated the "hole" into which an inquisitive child could poke a metal object. This special connector is disliked and fairly universally NOT adopted outside Britain.
It is a safety measure to protect our children from an obvious danger.
Why did we need this in Britain?
Because the speaker terminals are usually exposed conductive parts.
And the rule IS that they MUST be connected to Chassis.
The solution: make them NOT EXPOSED.
Why is the rest of the world ignoring this safety requirement?
Safety measures will stop an be enough if the metal Chassis is grounded ( if needed ) to mains ground
CT comes from a transformer so it is isolated and probably do not apply to safety rules
We all have to learn from professional installations picture and problems are exactly the same only scale is far too smaller
Kind regards
Sakis
NO !!!!!!!
The correct way to wire the MISNAMED ground lift switch is NOT to break the safety connection.
I have written about this many times.
Read Jensen.
Because more and more class D amplifiers come in to the market, also many of them in various operating modes like bridged and more so speaker - will be no longer CT in this case but also for reasons of obvious short circuit
NO !!!!!
the route for the Fuse to blow when Fault Current passes is through the SAFETY connection.
The safety connection, (I call it the Disconnecting Network) must be able to pass Fault Current and survive long enough for the mains fuse to rupture and the arc to extinguish.
You cannot expect a 10r resistor to pass >1kA and survive !!!!!!
Now what if the internal hot wire comes lose for whatever reason and moves and touches a soldered heatsink of a supply, grounded invariably through the star point to the terminals on the back? And I proceed to touch the busses to disconnect the plugs? It will fry my fingers. AndrewT is right, if you follow regulations to the letter, at least your secondaries ground needs to be earthed as well.
If it is impossible for loose mains wires to hit any of the low voltage circuitries, I'm not sure if that would be an exception.
If it is impossible for loose mains wires to hit any of the low voltage circuitries, I'm not sure if that would be an exception.
SMPS does not use a conventional Centre Tapped transformer.
But it has nothing to do with CT.
It is all about
You are starting to describe Double Insulated or ClassII equipment.
Our ClassI equipment cannot meet the very onerous standards required of ClassII
Well Andrew regardless what you say for amplifier class AB till class H that works with a classic round or EI trafo the procedure is exactly as i described it world wide ...the switch is disconnecting audio signal from main protective ground
I can post over 1000 schematics with this approach ... all of them approved with CE and many more for Europe or US
Take it or leave it....
Expect though those rules to change or vary in the near feature for the reasons explained above
Rules like that exist from "the past " and need to be refreshed soon i think
Technics i think had on production amplifier that had mains on speaker cables ... by today's standards this could never see the light in Europe
Very correct the latest but old regulation is very very specific about the distribution of mains inside an amplifier for example ... To meet this type of regulation is the reason that you no longer have mains switch in the front panel and so on and on
For this regulation CT doesn't have to be Grounded
Interesting!
Is all this P.E. Regulation referring to AC only or DC or both?
The reason I ask is because I have at home a commercial valve pre (less than 12 mths old) where the chassis is NOT connected directly to Earth, but instead through a small (looks like ceramic capacitor).
Would anyone like to comment on that?
Kind Regards
Roy.
Is all this P.E. Regulation referring to AC only or DC or both?
The reason I ask is because I have at home a commercial valve pre (less than 12 mths old) where the chassis is NOT connected directly to Earth, but instead through a small (looks like ceramic capacitor).
Would anyone like to comment on that?
Kind Regards
Roy.
Roy, we are posting about the safety of Mains powered equipment.
Despite the regulations, East is still confused and does not understand
Quoting what others do with a "ground lift switch" but NOT understanding what the switch does, nor where it is placed relative to the regulated safety connections does not help convince me that he knows what he is talking about.
There is ONE way to make a Ground Lift Switch that complies. It is described and drawn by Jensen.
Jensen and many others have shown us that many manufacturers and even more uninformed Builders can get it unsafe.
One does NOT break the safety connection the the Chassis.
Despite the regulations, East is still confused and does not understand
Quoting what others do with a "ground lift switch" but NOT understanding what the switch does, nor where it is placed relative to the regulated safety connections does not help convince me that he knows what he is talking about.
There is ONE way to make a Ground Lift Switch that complies. It is described and drawn by Jensen.
Jensen and many others have shown us that many manufacturers and even more uninformed Builders can get it unsafe.
One does NOT break the safety connection the the Chassis.
Yes
probably belongs to what i said before and its ok not to , as long some other rules are kept like fused in the input , no mains switch or if one exists works with a rod ( plastic or other stick to provide distance ) and mains is distance bla from anything the user may touch ...
This is how it used to be world wide ...
Andrew i understand what you say , At the first place and to my opinion i dont agree with you . OK ?
In the second place no matter what my or your opinion is what i am posting has been common practice for many many years in the past either right or wrong either you or me like it or approve it ...
In the second place no matter what my or your opinion is what i am posting has been common practice for many many years in the past either right or wrong either you or me like it or approve it ...
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I don't need to understand anything Andrew ...just read a schematic I don't "promote " anything
I just repair amplifiers and read schematics Ok ?
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While we patiently wait for Nikosokey to repost his P3A I thought I'd share my experiences.
Well this is one of the first amplifiers I built, and for some reason I just can't stop tinkering with it. I'd conservatively estimate that over the past year, I've experimented with over a hundred different component substitutions in the quest for something different.
What I love about Rod's design is that it's so simple, yet produces very good sonics, and can be modified for even better performance.
For me the heart of the design is the bootstrapped voltage amplifier, and of course Rod's compound pair output stage. I've found that the best performance gain comes from simply substituting a better VAS transistor, reducing the miller cap and adding a phase lead.
Small input degeneration resistors seem to add some small refinement to the sound, without changing the sonic signature. This was most apparent when tested with the low noise & high gain BC550C LTP transistors shown. The added advantage of these degen resistors is that it make it trivial to balance the collectors by fine-tuning R4. I've tried adding a current mirror (with and without degeneration) - no difference in sound.
A high quality bootstrap cap is beneficial; I currently use a Nichicon KZ with excellent results. I've tried replacing it with an active current source, but prefer the sound with a good bootstrap cap.
I only listen to modern, digital sources, therefore, some of the other component values have been recalculated for a Low Impedance design.
The input filter shown is representative of my PCB design and a simplification of Rod's schematic. I don't advocate DC coupling per se., however my preamplifier (B1 buffer) has an output coupling cap so I've omitted the input cap on my PCB. HPF caps (when fitted) are soldered directly to the RCA connectors.
The circuit can be improved further but not without adding complexity. I like this version because its simple and still sounds like a P3A
