Hi 12B4A, nice build!
I wonder what is the model number of the XLR sockets you used. I like that they had a metal clip on top to enable grounding to the case right at the sockets. My sockets don't have the clips and I had to run separate ground wires to the chassis ground.
Here's the model# and data page:
NC3FD-L-B-1 - Neutrik
We had quite the discussion about XLRs earlier in this thread
Soldering does offer the better connection but I've found that using quick disconnect terminals are pretty handy in the long term when building projects that are comprised of several sub-assemblies. You never know when you'll want to reuse/repurpose something and I dislike desoldering.
NC3FD-L-B-1 - Neutrik
We had quite the discussion about XLRs earlier in this thread
Soldering does offer the better connection but I've found that using quick disconnect terminals are pretty handy in the long term when building projects that are comprised of several sub-assemblies. You never know when you'll want to reuse/repurpose something and I dislike desoldering.
Remaining parts finally arrived so I've finished the boards. I hooked the Power86 up to the variac and measured the voltage as instructed in Tom's guide. 35v both sides. The variac has no earth connector so I've just got L and N going to my fused (1 amp) power socket on the back of the case. Instructions for testing the Modulus 86 boards indicate there should be a ground connection.
Is this essential for testing purposes?
Is it OK to connect the amp boards to the Power86 one at a time so I can check each board individually in the first instance?
If ground is essential for testing then I suppose I could find a point on the variac case and connect this to earth on the input socket - would this be OK?
Thanks, Ian
Is this essential for testing purposes?
Is it OK to connect the amp boards to the Power86 one at a time so I can check each board individually in the first instance?
If ground is essential for testing then I suppose I could find a point on the variac case and connect this to earth on the input socket - would this be OK?
Thanks, Ian
Audio does not need a Safety Earth.
Look at all your double insulated audio equipment. Look at all your plastic cased audio equipment. Look at all the battery powered audio equipment. None of these require a Safety Earth to operate properly.
The Safety Earth is there only for safety. The Third wire is the Protective Earth and it must be permanently connected to the Chassis. If there is no chassis, then connect it to the biggest chunk of metal in the assembly.
Look at all your double insulated audio equipment. Look at all your plastic cased audio equipment. Look at all the battery powered audio equipment. None of these require a Safety Earth to operate properly.
The Safety Earth is there only for safety. The Third wire is the Protective Earth and it must be permanently connected to the Chassis. If there is no chassis, then connect it to the biggest chunk of metal in the assembly.
How to confuse. Call it two different names in 2 sentences. I know as the top poster on the forum you have to rattle em out, but in this case a proof read or clarification would have been very very very helpful to those who are learning from you!
OK, according to Tom's construction guide:
I think ! understand the difference between ground and earth in the sense that earth is the safety earth to hopefully protect me and ground is a reference point usually at 0V. My question really related to the circuits involved. In order to test the circuits do I need to connect them to ground or will the circuits be damaged if they are not so connected.
I think ! understand the difference between ground and earth in the sense that earth is the safety earth to hopefully protect me and ground is a reference point usually at 0V. My question really related to the circuits involved. In order to test the circuits do I need to connect them to ground or will the circuits be damaged if they are not so connected.
.....which is why I'm referring to the connection from the case to the circuit boards as ground. Do the circuits need to be grounded in order to test them?
You can test your amplifier without any safety earth.
But you do have to be aware that the protection afforded by a PE protected chassis is not there.
As an aside:
I build my amplifiers on the bench without a chassis.
The mains transformer is at one end and fed with fused supply.
The amplifer is in the middle of the bench.
I can see the mains transformer. If it is abused I should be able to hear. But I don't touch it.
The amplifier is on the isolated side of the mains transformer. As long as the mains transformer is not damaged, I am safe to touch any part of the low voltage amplifier.
Adding chassis to hold the completed and tested amplifier comes much later.
That is actually INCREASING the confusion as you have introduced another term.
I would recommend this Power Supply Wiring Guidelines as a good starter and less chewy that safety regs!
Thanks for the link, I'm reasonably confident I've done as suggested in this guide. However, there is one suggestion in there which I had been thinking about.
With an adonised case like mine I'd read elsewhere in this thread that to make a good chassis earth you need to scrape off the adonised coating. I did this on my case but then wondered about the earthing of the rest of the case as, when I checked for continuity between the panels of the case there was no electrical connection. I haven't seen anyone else concerned about this so should I ignore it?
With an adonised case like mine I'd read elsewhere in this thread that to make a good chassis earth you need to scrape off the adonised coating. I did this on my case but then wondered about the earthing of the rest of the case as, when I checked for continuity between the panels of the case there was no electrical connection. I haven't seen anyone else concerned about this so should I ignore it?
All exposed metal bits of the chassis should be grounded via the power cord (green or green/yellow wire).
An anodized chassis will usually offer connectivity through screws and other mounting hardware. Do verify this connectivity with an ohmmeter, though.
A powder coated chassis would probably not offer this connectivity. Whether you go through the trouble of scraping off the coating and connecting all the panels would depend on how much you feel like obeying the local electrical code and how much you love the people and pets you share your living quarters with. Personally, I'd rather take the time to scrape off the coating and ground the panels than having to deal with the emotional trauma having caused injury or death to a loved one. Never mind the legal issues.
Tom
That's a good practice to get into. Personally, I use a pair of lab supplies for the initial tests, but few are likely to have a pair of those at their disposal. A power transformer on a fused variac goes a really long way.
One note, though: Make sure you clean off all component lead clippings, wire, solder splashes, etc. from your workbench before you rig the amp for testing. Few things ruin your weekend like a strand of wire shorting out the supply, causing fireworks.
Tom
I have already checked this and found no connectivity hence my query. The fixing screws are coated black and the threads are anodized (their adenoids are fine!) I think I'll do some bonding between the plates of the case.
Thanks for advice, Ian
I have mentioned cross coupling the earth connection to separate panels in at least two previous posts.
I have also mentioned electrical continuity between panels in many posts.
The whole chassis must be protected. All exposed conductive parts should be connected to the protected chassis.
My supplies certainly wouldn't take that long. Not only would the amplifier survive because my noise filtering does include that case; but, also, the current delivered would have burned off that strand so quickly that nobody would have noticed. So, what's going on?
You may want to look at arcs. They can be rather nasty. Here's Wikipedia on the topic: https://en.wikipedia.org/wiki/Electric_arc
The question is what the arc destroys before it extinguishes, assuming it does extinguish.
Tom