Thanks. I understood grounding metal cases, but was wrong on the need to ground the signal.
I was just curious about the basic scheme for full class 2. My Class 2 receiver has a direct connection from signal ground to case. Does it involve a special transformer that requires two failures to get a connection from primary to secondary? I notice that some of the surplus transformers that Steve (Apexjr) sells seem to have extra connections on the primary side.
I was just curious about the basic scheme for full class 2. My Class 2 receiver has a direct connection from signal ground to case. Does it involve a special transformer that requires two failures to get a connection from primary to secondary? I notice that some of the surplus transformers that Steve (Apexjr) sells seem to have extra connections on the primary side.
The data sheet for that transformer is http://www.apexjr.com/images/66938_sc7.pdf
So how would you ground banana jacks?
You say that the RCA jacks will be grounded because the shell part is ground, and the actual connector is signal.
Not sure but I believe banana jacks are just one big piece of metal...
And where would you connect them. To the star or directly to safety earth?
You say that the RCA jacks will be grounded because the shell part is ground, and the actual connector is signal.
Not sure but I believe banana jacks are just one big piece of metal...
And where would you connect them. To the star or directly to safety earth?
I think some transformers use a dual bobbin construction, so that there is physical separation between primary and secondary. You would then have to ensure that the mains wiring within the unit does not compromise safety e.g. all live metal covered so a stray signal wire cannot touch mains, mains leads too short to touch anything else if they break free. There are rules on physical separation distances too.
For the purposes of safety, any external metal connected to a circuit which is correctly grounded is deemed to be grounded too (assuming signal voltages are not too high). Otherwise you could not have signal ins/outs!
For the purposes of safety, any external metal connected to a circuit which is correctly grounded is deemed to be grounded too (assuming signal voltages are not too high). Otherwise you could not have signal ins/outs!
The speaker outputs would technically be grounded if I had one signal and one return (ground) per speaker, right?
Sorry. Don't feel like killing anyone.
I worry about crawlers (younger than toddlers) picking up a loose end of an interconnect or speaker wire and sucking it to find out if it tastes nice.
What if the other end is plugged into one of my creations that is not properly protected by the Safety Earth and that Safety Earth being permanently connected to PE all the way back to the distribution board.
How could I explain to my youngest sister that her 1year old should not have touched "my gear". Maybe the bigger problem is I am a pessimist and everyone one has better luck than me.
What if the other end is plugged into one of my creations that is not properly protected by the Safety Earth and that Safety Earth being permanently connected to PE all the way back to the distribution board.
How could I explain to my youngest sister that her 1year old should not have touched "my gear". Maybe the bigger problem is I am a pessimist and everyone one has better luck than me.
Yes, the speaker outputs are connected to a circuit that is properly grounded, so they are effectively connected to ground as DF96 said.
The speaker return is grounded if connected to your boards, the ground plane of which acts as a central ground once connected to the safety ground. You can also connect the speaker returns to the star formed by the center tap, safety ground and board ground.
Yes, Andrew it is much better to be safe than sorry. Although I am well past the creeper stage and my wooden box creations are placed out of guests range I am going to pull them out to properly ground them. Thank you again for setting me straight.
And thanks to DF96 for your insights, too. I had no intent to try to meet the Class 2 standard, just wanted to understand generally it was accomplished.
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It comes from my boss while I was indentured as a trainee "engineer".
Could you hand on heart stand in the dock and say to the jury "I did all in my power to protect others from errors in the implementation of my design"
That has stuck with me through six decades.
Could you hand on heart stand in the dock and say to the jury "I did all in my power to protect others from errors in the implementation of my design"
That has stuck with me through six decades.
Honor like that is one of those commodities that is becoming far too rare these days. How often would the answer be "I did all that the law requires" /OT rant
Hi,
I have always found the articles at ESP very helpful when I started with electronics. This specific article should help you with your question and give you some more background info: Power Supply Wiring Guidelines
Every professional "engineer" in the UK has to effectively vow to follow that "honor" code.
We risk being struck off if we hide behind a lesser moral stance.
I believe "Eur Ing" has a similar code across Europe.
We risk being struck off if we hide behind a lesser moral stance.
I believe "Eur Ing" has a similar code across Europe.
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There's something like that here, only with a wink and a nudge "as long as it doesn't impact the bottom line."
Thanks guys.
I think I might just suck it up and get a metal enclosure to make things easier...
But I'm still learning the whole grounding thing so I'll probably be back.
Sorry to go off topic to heatsinks again, but, would it be effective at all to bolt/clip the amplifiers to the enclosure (aluminum), and then bolt a computer heatsink onto the back of the amp on the same panel where the amp chips are bolted to? Since the actual contact area on computer heatsinks is about the size of a half-dollar coin, would it be pointless?
Thanks again.
I think I might just suck it up and get a metal enclosure to make things easier...
But I'm still learning the whole grounding thing so I'll probably be back.
Sorry to go off topic to heatsinks again, but, would it be effective at all to bolt/clip the amplifiers to the enclosure (aluminum), and then bolt a computer heatsink onto the back of the amp on the same panel where the amp chips are bolted to? Since the actual contact area on computer heatsinks is about the size of a half-dollar coin, would it be pointless?
Thanks again.
It would be better to have a hole through which the chip could contact the heat sink. The ability of the chip to transfer heat depends on the surface area in direct contact. Smooth surfaces are not as smooth as you think, and adding another set of junctions just increases the thermal resistance.
Just connect everything the way you have it shown in post 13 and you will be safe. You connections to the exposed heat sinks take the place of the chassis connections shown in Rod's scheme.
Just connect everything the way you have it shown in post 13 and you will be safe. You connections to the exposed heat sinks take the place of the chassis connections shown in Rod's scheme.
Thanks. That's reassuring. So many things have been going through my mind over this project. It's kind of overwhelming, but I'll just slow down and get it right.
Wooden box it is then.
Can I use metallic based thermal compound or does it have to be non electrically conductive? I'm using the isolated chip...Is that stuff good to be on the plastic?
Don't pay attention to the previous question. Yes I can.
My real question is how to find exactly what NTC thermistor to put in. CL-60 you say, but how would I go about matching up the right one?
My real question is how to find exactly what NTC thermistor to put in. CL-60 you say, but how would I go about matching up the right one?
CL-60 is a part number, not a generic description of a class of parts, like NTC Thermistor would be.
CL-60 GE Sensing / Thermometrics Thermistors - NTC
CL-60 GE Sensing / Thermometrics Thermistors - NTC
Bob,
Yes. I know CL-60 is an exact part, but I mean is a CL-60 appropriate? What would be the advantage of using a CL-60 over a CL-50, CL-70 etc. What specs am I looking for?
Thanks.
Nelson Pass uses the CL-60 to separate the safety and power grounds in many Pass Labs amps.
All you really need is some resistance to reduce the likelihood of signal current flowing through your safety earth. In the A75 Pass and Thagard used 5R with diodes to limit the voltage across it (linked earlier). Compare it to a CL-30. Higher on resistance, so greater isolation. It's never going to carry a lot of current for long. Sure a CL-70 is higher cold resistance, but also a bit higher hot. Most any thermistor would work for this application.
So why choose one over another? CL-60s make good inrush limiters for 500-1KVA transformers, and buying multiples gets the unit cost down. I suspect that's at least a factor in Pass Labs' use of CL-60s for ground isolation.
All you really need is some resistance to reduce the likelihood of signal current flowing through your safety earth. In the A75 Pass and Thagard used 5R with diodes to limit the voltage across it (linked earlier). Compare it to a CL-30. Higher on resistance, so greater isolation. It's never going to carry a lot of current for long. Sure a CL-70 is higher cold resistance, but also a bit higher hot. Most any thermistor would work for this application.
So why choose one over another? CL-60s make good inrush limiters for 500-1KVA transformers, and buying multiples gets the unit cost down. I suspect that's at least a factor in Pass Labs' use of CL-60s for ground isolation.
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