I refer to differential breaker. In Italy they are mandatory and are commonly called "salvavita". According to what I see on Wikipedia, I guess they are called "RCDs" in your country. They works by detecting leakage current (to earth) and are very reliable. If a leakage current exists and exceeds the set threshold, they cut the mains power.
When the metal case is earthed, if there is an insulation fault allowing for some conduction between mains live and the case (or signal ground, or anything else somehow connected to the earth) there will be a leakage current. Thus the safety breaker will cut the power as soon as the defective appliance is connected to the mains.
To get an electrical shock there must be a current flow through your body. Which of course requires a return path (currents only flows in closed circuits...).
You must be touching a "live" circuit which is connected to earth on the other side (thus your body close the circuit through the earth), or TWO different parts of the circuit with a (dangerous) potential between them which you touch simultaneously.
If you only touch one side of a charged capacitor which is NOT connected to earth on the other side, no current will flow and no shock will result, no matter how high is the voltage on the cap.
If the metal case is connected to PE, unless you open the case (which is something which is NOT supposed to be done by people not knowing what they're doing) the only risk may be the signal and/or signal ground (in/out connectors) becoming at dangerous voltages WRT the earth. But! if the signal ground is connected to PE via a low value resistor, anti-parallel diodes, anti-series (low voltage) Zeners or other similar means, this simply can not happen.
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Unix,
well done.
Not to dilute what Unix has said, but I think in terms of current and circuits. Unix is telling us exactly that.
You need circuits and you need current to flow around those circuits.
This applies to power amplifiers and safety circuits and interconnects etc.......
well done.
Not to dilute what Unix has said, but I think in terms of current and circuits. Unix is telling us exactly that.
You need circuits and you need current to flow around those circuits.
This applies to power amplifiers and safety circuits and interconnects etc.......
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No, they are called GFCI here and we are talking about the same device.
In the context of DIY audio, chassis are being opened, hot capacitors have their negative leads connected to the chassis. A GFCI would not protect you in this case. Say you turn the switch of and leave it plugged in, there's your return path to ground. It took 2 seconds to come up with that scenario.
Yes if you have it unplugged you would have to make contact with the +voltage and the chassis. Again no GFCI protection there, That is my point, stranger things have happened.
Personally I would rather not have any resistive devices between ground, or any diode etc that I am not confident could handle all faults 100% of the time.
What ever happened to good quiet grounding schemes?
In the context of DIY audio, chassis are being opened, hot capacitors have their negative leads connected to the chassis. A GFCI would not protect you in this case. Say you turn the switch of and leave it plugged in, there's your return path to ground. It took 2 seconds to come up with that scenario.
Yes if you have it unplugged you would have to make contact with the +voltage and the chassis. Again no GFCI protection there, That is my point, stranger things have happened.
Personally I would rather not have any resistive devices between ground, or any diode etc that I am not confident could handle all faults 100% of the time.
What ever happened to good quiet grounding schemes?
I see that there is a My Ref (original) and a My Ref Rev C (BoM). How different is the "C" schematic, or is just a change in parts?
The schematic I've linked is the Rev C one, associated with the original stereo PCB.
The TP version is also Rev C but mono, so only the upper part of the schematic apply.
In addition some bypass caps and discrete diodes were added.
Just a word or two on the safty earth
If your using a toroidal transformer for your power supply, you are potentially one short circuit away from having mains AC on your power ground and therefor your 0 volt speaker cable, which, having very low impedance and high current capability can carry the full mains voltage and current outside the box. The power ground should to be connected directly to the safety ground
Earth leakage devises should be used in conjunction with, and not as a substitute for proper earthing, as safe and as simple and as reliable as they are, they are still capable of failing
If your using a toroidal transformer for your power supply, you are potentially one short circuit away from having mains AC on your power ground and therefor your 0 volt speaker cable, which, having very low impedance and high current capability can carry the full mains voltage and current outside the box. The power ground should to be connected directly to the safety ground
Earth leakage devises should be used in conjunction with, and not as a substitute for proper earthing, as safe and as simple and as reliable as they are, they are still capable of failing
TP don't sell them anymore.
You can:
- buy PCBs and/or kits from forum member LinuxGuru (slightly different PCB)
- use the Eagle files posted in this thread by Russ White of TP to order your own PCBs (costly).
- partecipate to the My_Ref Fremen Edition PCBs group buy in the next months
- search in the swap meet
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or you could etch them using single layer pcb. IINM there's 3 variation posted before.
absolutely.
Too often I see people claiming to care about "minimizing signal paths" but looking only at the "live" side, completely ignoring the return path, with ridiculously long (and usually wrong) grounding, etc. Or other ones making crazy things to avoid a capacitor "in the signal path" but failing to recognize that their PSUs (and caps) are in series with their audio circuits, etc.
...but here we're goin' way too OT.
If you are working "inside" an appliance, you MUST always know exactly what you're doing and take appropriate measures to protect yourself.
No standard safety measure will protect you against your own misbehavior. Having the circuit GND directly connected to PE will NOT give you any extra safety WRT the two being separated by a small R, diodes, etc.
BTW, this applies (almost only) to tube circuits. With most SS designs (like this very project) there are simply no dangerous voltages around (other than the mains AC voltage up to the primary of the PT). Of course there is always the risk of a PT or other isolation failure bringing the mains AC where it should not be... but this have nothing to do with capacitors and "stored voltages".
...that's exactly why you want (need) to "decouple" GND to PE at audio frequencies.
Ground loop (electricity) - Wikipedia
true. But you have to accept some compromise between paranoid safety and good sound...
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How do LinuxGuru's boards compare to the ones at Jim's Audio?
LM3886 x2 + opamp preamplifier 68W 4 ohm amplifier PCB | eBay
Siva's boards are derived from TP design so they're monoblocks.
Jim's Audio PCB is simply a buffered Gainclone, probably also copied from a previous Penasa's work.
On eBay there's a My_Ref C clone (Nimo e-store) but it's not the one sold by Jim's audio.
I've bought one just to try, the PCB seems good quality (2mm FR4), can be populated (almost) with my BOM and it performs quite well.
But, sincerely, I'm rather annoyed by the fact that Nimo e-store is making money by using, without author's permission (I suppose), a design given to the community by Mauro Penasa...
Attachments
Is "Siva" also known as LinuxGuru?
That's the general description of ALL these variations floating around here.
Please give an internet address for Nimo; it doesn't come up on eBay e-store directory.
I agree with you in principle, but I've been searching for this (so far) illusory PC board for several days without success. Let's say I'm annoyed that the originator has not made a source available and that going to Jim's is more-or-less my last resort. There's not even an "Official Current Version" posted by the originator. Same thing with "The Wire" amplifiers - many threads, but no boards.
absolutely.
Too often I see people claiming to care about "minimizing signal paths" but looking only at the "live" side, completely ignoring the return path, with ridiculously long (and usually wrong) grounding, etc. Or other ones making crazy things to avoid a capacitor "in the signal path" but failing to recognize that their PSUs (and caps) are in series with their audio circuits, etc.
...but here we're goin' way too OT.
If you are working "inside" an appliance, you MUST always know exactly what you're doing and take appropriate measures to protect yourself.
No standard safety measure will protect you against your own misbehavior. Having the circuit GND directly connected to PE will NOT give you any extra safety WRT the two being separated by a small R, diodes, etc.
BTW, this applies (almost only) to tube circuits. With most SS designs (like this very project) there are simply no dangerous voltages around (other than the mains AC voltage up to the primary of the PT). Of course there is always the risk of a PT or other isolation failure bringing the mains AC where it should not be... but this have nothing to do with capacitors and "stored voltages".
...that's exactly why you want (need) to "decouple" GND to PE at audio frequencies.
Ground loop (electricity) - Wikipedia
true. But you have to accept some compromise between paranoid safety and good sound...
First of all power caps are not in the "audio" path. Last time I checked, audio was an A/C current, power caps hold a DC current reserve just like a battery. They filter out 60hz "audio" when working correctly.
You have to draw a practical line somewhere.
What is "WRT"?
You know here in Canada, all devices must be safe for the highest voltage used in the device. It does not matter if YOU view 50v as "harmless".
What happens when a fault imposes 120v on your "50v" parts, then what? I guess you don't have a low-voltage device anymore.
I still don't see how a couple of diodes or a little resistor are going to survive a 1800watt surge, maybe that's just me.
I find your lack of imagination careless. You should be paranoid.
Yes
No, the My_Ref is a unique design with nested feeedback and the only amp where a power opamp is used as current pump.
This topology has it's roots on Musical Fidelity A370 which have similarities with Quad 405 and Pass' STASIS.
All of them are among the best sounding amps...
It seems that you finded it by yourself.
This is not true.
As I've said Siva has always PCBs for the My_Ref.
Few weeks ago I've organized a beta GB for my derivate amp.
There's not even an "Official Current Version" posted by the originator. Same thing with "The Wire" amplifiers - many threads, but no boards.
Also not true, the official schematic and gerbers (stereo single sided) have been published by the author and thread starter.
This is the one and only official thread.
Also the TP version (same schematic, different PCB) has been posted here and Eagle files and gerbers are available.
And when you asked I've indicated you all fair sources.
Nimo e-store is not a fair source, IMHO.