PJPro said:
The case will be almost invisible, I only need an enclosure to put the electronics in and hold them firmly in place. Additionally it will also be a Faraday cage. But all I need is the box and some sort of double bottom to allow me to mount bits and pieces without having to drill into the outer skin and have bolts sticking outside.
Well, even though I have not gone to lengths to buy expensive stuff, this guitar amp is going to cost quote a lot. I have not summed it all up yet but quite a lot. A box of this size (85cm x 40cm x 7cm) will cost 125+vat rock bottom price he said, as it will use almost a full sheet of metal.
akis said:Regarding the earth discussion:
"a direct mechanical link from the supply earth wire to the metal chassis".
The above, which is what was recommended above is not near good enough in my opinion. I am not trying to be awkward. The above should be something like:
"a direct mechanical link from the supply earth wire to the metal chassis AND to all other conductive elements on the chassis which the user may touch or work with, eg shielded wires, cables, probes, your electric guitar's lead, the electric guitar's strings, bridge and buckles, your amp's metal knobs and so on".
The advice to keep the RCA plugs and other interconnects separated from the earth (to avoid ground loops) kind of breaks it for me, I can imagine plugging a guitar into your amp and getting electrocuted.
Regrding the slow start circuit, would you like to be a guinea pig ?I have designed one and amabout to build it, the PCB should be arriving soon, it looks like this (I am sure I have posted this before somewhere here). What it does is provides a 12 V on-off switch, so you do not run 240V wires inside the enclosure and onto the front panel (imagine spilling your pint of beer) and additionally a slow start by the means of two relays.
See post #177.
As for the RCA's, in my experience their return (-ve) is usually insulated from the safety earth/chassis.
Stu
Yes, from memory the amp board has 'Out' and 'OG' (output ground) or something like that? 'Out' is to the inner terminal on the socket and 'OG' is to the outer. Subject to memory confirmation of the markings...
I'm sure there's just a misunderstanding of what is meant by 'keeping the RCA's separated from the earth', though.
Cheers
Stuey
I'm sure there's just a misunderstanding of what is meant by 'keeping the RCA's separated from the earth', though.
Cheers
Stuey
Hi,
connect the mains Earth Wire directly and permanently to chassis. This is the Safety Earth.
Connect all your Audio Grounds to the main Star Ground.
Connect the main Star Ground or the PSU Zero Volts to the Safety Earth.
You can do this with a direct wire connection,
or
through a High Power Thermistor with an appropriately low resistance,
or
through a Disconnecting Network that must include a High Power pair of inverse parallel diodes.
Any and all of these chosen connections MUST be capable of passing Fault Current to PE and survive longer than it takes the mains fuse to rupture and for the arc to extinguish.
The disconnecting network can optionally include a low power low value resistor and/or a low value capacitor and/or a ground lift switch. All of these optional components are in parallel to the inverse parallel High Power diodes.
connect the mains Earth Wire directly and permanently to chassis. This is the Safety Earth.
Connect all your Audio Grounds to the main Star Ground.
Connect the main Star Ground or the PSU Zero Volts to the Safety Earth.
You can do this with a direct wire connection,
or
through a High Power Thermistor with an appropriately low resistance,
or
through a Disconnecting Network that must include a High Power pair of inverse parallel diodes.
Any and all of these chosen connections MUST be capable of passing Fault Current to PE and survive longer than it takes the mains fuse to rupture and for the arc to extinguish.
The disconnecting network can optionally include a low power low value resistor and/or a low value capacitor and/or a ground lift switch. All of these optional components are in parallel to the inverse parallel High Power diodes.
PJ, I realised I ambiguously answered you.
To put it simply, all of what Andrew is saying (other than the disconnecting network or thermistor of course) will be achieved if you carefully follow the instructions given with the kit by Brian about wiring etc., and also connect the IEC socket Earth pin to the chassis as you mentioned previously.
The quote about the RCA sockets was about insulating these from the metal chassis at their mounting so there's only one path to safety earth from the RCA return (-ve) wire via the amp board and audio ground, as you allude to.
Cheers
Stuey
To put it simply, all of what Andrew is saying (other than the disconnecting network or thermistor of course) will be achieved if you carefully follow the instructions given with the kit by Brian about wiring etc., and also connect the IEC socket Earth pin to the chassis as you mentioned previously.
The quote about the RCA sockets was about insulating these from the metal chassis at their mounting so there's only one path to safety earth from the RCA return (-ve) wire via the amp board and audio ground, as you allude to.
Cheers
Stuey
Stuey said:
That is exactly what I was commenting on, if I were to plug my guitar to that amplifier I would be in constant touch with the "RCA return". In case of a fault, my guitar's strings , or some lead's connectors would be indirectly connected to the earth via some PCB tracks and solder connections and not directly with a screw and bolt. I am not an electrician so I would like to ask, is this legal in the UK? Why bother to connect the chassis to earth with a non-solder connection and no electronics in between, but having the shield of interconnecting cables and connectors NOT at ground level (if a bad solder joint/PCB track melts we would not be at ground level anymore).
Hi,
my quietest amplifiers are the prototypes that are NOT enclosed in a metal case.
All of my cased amplifiers are noisier than the uncased versions.
I do not believe there is a need to line your box with metal foil, if you have normal levels of transmitted signal around your system.
I do not have any transmitters in my house except for my mobile phone and even that does not interfere with an uncased amplifier
my quietest amplifiers are the prototypes that are NOT enclosed in a metal case.
All of my cased amplifiers are noisier than the uncased versions.
I do not believe there is a need to line your box with metal foil, if you have normal levels of transmitted signal around your system.
I do not have any transmitters in my house except for my mobile phone and even that does not interfere with an uncased amplifier
I believe the non-solder specification for the chassis earth is simply for strength, not related to solder melting. It prevents mechanical breakage of the connection, whereas soldering can easily deteriorate from flexing or cold joints as we know. I may be wrong. I both crimp and solder and then heatshrink mine.
I don't know if it's legal in the UK, but I know that many designs have the RCA's insulated from the chassis.
I suggest that if the audio ground circuit becomes mains-live, the relevant tracks will carry enough current to rupture the fuse if it's correctly minimally rated.
But, good question...
Stuey
I don't know if it's legal in the UK, but I know that many designs have the RCA's insulated from the chassis.
I suggest that if the audio ground circuit becomes mains-live, the relevant tracks will carry enough current to rupture the fuse if it's correctly minimally rated.
But, good question...
Stuey
the requirement is to connect all exposed conductive parts to Safety Earth.akis said:
A wire connection or a Thermistor connection or a Disconnecting Network complies with this requirement. If you assemble them correctly with the correct components.
If you don't and someone is injured or your house burns down then you, the builder, are in trouble.
I have opened up some commercial gear and found that every metal panel (3 + base) had a welded terminal, each connected back to Safety earth with a direct crimped wire connection.
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