Let's see: in a 230V circuit with a 13A breaker, a short circuit would require a 10 Ohm resistor to deal with about 5000 Watts of power until the circuit breaker gets around to tripping.
The 10 Ohm resistor should be placed between the audio circuit common (aka ground) and the chassis. The PE/SG must be connected directly to the chassis.
This is right. My text is spaghetti although I meant the same.
However, in the given erroneous situation a short circuit from L to the casing would trip the breaker as 230/10=23A. A 13A breaker (they are 16A here) would trip immediately. The few kW are in milliseconds.
Still I reported my post to correct the phrasing.
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But he is right, a 10R resistor with 230V across it will result in 23A flowing, and a 13A fuse will last a LONG, LONG time under a small overload like that (Between 1 and ~500 seconds by the curves, which is probably longer then the resistor will survive).
10R between chassis and audio reference is fair enough if you trust your power transformer manufacturer, but the PE in a class I device MUST be connected directly to chassis.
10R between chassis and audio reference is fair enough if you trust your power transformer manufacturer, but the PE in a class I device MUST be connected directly to chassis.
For the slimline cases I strip the anodizing off the back panel counter sink holes, used a bright bolt, none anodized and this gives you continuity across the back, sides and front panel. I then strip off a small bit of anodizing on inside of top and bottom panels and counterink it from with a 6mm m3 stainless screw and connect this with a 3mm wire to the front panel brackets. This gives continuity across the whole case.
PE I connect to a contersunk m3 screw right next to the iec. I always keep audio gnd lifted from the chassis, rca sockets are insulated types and only connect at the preamp.
This is for a Paradise phono build. I never get any noise doing this. All builds are utterly silent.
PE I connect to a contersunk m3 screw right next to the iec. I always keep audio gnd lifted from the chassis, rca sockets are insulated types and only connect at the preamp.
This is for a Paradise phono build. I never get any noise doing this. All builds are utterly silent.
No we were talking breakers and short circuit. 23A with a 13A class B breaker is immediate tripping. A fuse would burn immediately too with such a short circuit. I don’t know what exactly a LONG, LONG time isbut 23A through a 13A fuse is a flash to the eye.
Check the curves, a type B MCB will instant trip between 3 and 5 times its rated current (On the magnetic trip), and at a 100% overload will hold for between about 50 seconds and several minutes (on the thermal trip).
A UK standard 13A fuse will as I said be anything from a second to almost 5 minutes at 26A, these are NOT precision devices.
Yes, I looked at the curves.
Not “AC ground” but PE. Let us use the correct names. PE is connected directly to the casing but audio GND is not. As indicated it is connected directly to PE in practically ALL devices in anglosaxon countries but that creates more problems than it solves.
You can lift audio GND with a 10 Ohm 5W resistor from PE. I leave audio GND floating in source devices or devices under 25 VA. I use the 10 Ohm to lift audio GND in power amplifiers. If you refer audio GND to PE in a power amp the audio GND of the source devices are also referred to PE in a way. A short from L to the casing is then also relatively safe for the user.
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thanks for commenting
could you clarify what you mean here? the countersink on the back panel or the thread it screws into on the side panel (or both)?
I'm still confused by how to actually lift audio ground and whether it's necessary when using a balanced input
I have
* an aluminium back panel to which some metal xlr connectors are attached , i.e. audio ground is connected to the chassis
* PE connected to the chassis
hence audio gnd is connected to PE, right?
if so...
do we expect this to cause hum? comments above refer to unbalanced so not sure it applies here
lifting audio ground means insulating the connector from the chassis and hence using something like NC3FAH | Neutrik (unless there is some other way to insulate a metal xlr connector from the chassis that I'm not aware of)?
I have
* an aluminium back panel to which some metal xlr connectors are attached , i.e. audio ground is connected to the chassis
* PE connected to the chassis
hence audio gnd is connected to PE, right?
if so...
do we expect this to cause hum? comments above refer to unbalanced so not sure it applies here
lifting audio ground means insulating the connector from the chassis and hence using something like NC3FAH | Neutrik (unless there is some other way to insulate a metal xlr connector from the chassis that I'm not aware of)?
that's kind of why i asked you earlier on if you where using a balanced connection if so current best practice is xlr pin 1 - chassis , pin 2 + or hot and pin 3 - or return (but the labeling is an intellectual mismomer to balanced operation)
is the source device balanced?
being from a pro audio background i like devices being designed with audio Gnd to chassis lift links but that's me!
is the source device balanced?
being from a pro audio background i like devices being designed with audio Gnd to chassis lift links but that's me!
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