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Help: evaluation of a Beta 22 - Page 3

post #31 of 44
3/6/10 at 9:42pm
Quote:
Originally Posted by fishski13 View Post
any catastrophic failure of the TX would take out the o-22 and blow a fuse. the MOSFETs will not pass mains to the B22.
Not to mention the only failure that grounded the chassis is meant to prevent is to keep from causing the chassis having AC potential. The failure you describe would cause damage but not cause AC mains to make it to the chassis to many components between the transformers primary and chassis to make that happen without a very specific secondary failure in BOTH the sigma11 board and the b22 board.
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post #32 of 44
3/6/10 at 11:08pm
The point of the whole exercise is to stop someone touching a live chassis and an earthed one and electrocuting themselves. The safety of the electronics is immaterial.
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post #33 of 44
3/7/10 at 4:48am
Quote:
Originally Posted by m1abrams View Post
Really, so you plan to solder that wire to the bare metal on every panel? How do you plan to attach the wire to the panel?

Wire soldered to bare flat Al will not make a very good mechanical connection.
I said a screw is NOT an acceptable method for an electrical connection.

And I stick by what I said,ever pulled apart an old washing machine and wondered why all the panels are wired to earth,ever wondered why cars suffer from a multitude of electrical problems most caused by bad earths.

But hey its your amp and your life,do what you want.
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post #34 of 44
3/7/10 at 5:18am
The notion that there must be actual wires to every panel is absurd. Show me any commercial hi-fi gear that does this, even those that pass UL and CSA safety certification...
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post #35 of 44
3/7/10 at 10:15am
Quote:
Originally Posted by johnwmclean View Post
The anodized coating would insulate, but from my understanding there’s always components from stand off to jacks that have direct contact with the aluminum that would still conduct.
Sure, but where is the live AC going to be able to touch such that it will conduct through the whole case? There will only be a few very specific points where it can make it through the anodizing.

Not saying that you shouldn't earth anything of course, but that one connection to the base plate should be fine in the vast majority of cases. If the whole case doesn't have a 100% perfect connection to earth, it isn't life or death.
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post #36 of 44
3/7/10 at 7:51pm
Quote:
Originally Posted by amb View Post
The notion that there must be actual wires to every panel is absurd. Show me any commercial hi-fi gear that does this, even those that pass UL and CSA safety certification...
I don't have any examples that use actual wires, but there are plenty (in fact, the majority I'd argue) that have excellent grounding to each panel which is far superior to a screw. For example, look at even the cheapest DVD player out there, like the $100 Denon players. They have metal contacts that make connection to each of the panels as they are assembled. They are spring loaded contacts that make good contact when the panels are assembled.

I have seen one example (trust me, you only need one) where a live mains connection came loose and due to the way it was routed in the case, sprung up and was in contact with the top panel of the amplifier. The wire in question was not tinned and was attached to a screw connector (again, something you will not see in many UL and CSA safety certified pieces of equipment (again, if any), but are all over DIY projects). The wire was stranded and due to the lack of tin (and the strain that is described above) all the individual wires had broken at the connector... once this happened, well you can guess what happened.
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post #37 of 44
3/8/10 at 1:12am
Thread Starter 
Thanks all guys! I haven't thought the post would be 3 pages long.
May I conclude that other than the safety issue, the beta 22 is well built and worth to purchase? Since the seller finally replied my PM, I think I can negotiate the deal with him.
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post #38 of 44
3/8/10 at 1:56am
Quote:
Originally Posted by luvdunhill
look at even the cheapest DVD player out there, like the $100 Denon players. They have metal contacts that make connection to each of the panels as they are assembled. They are spring loaded contacts that make good contact when the panels are assembled.
Those are not for AC shock hazard protection. The spring contacts are there to reduce RFI leakage (to conform to FCC regulations).

Screws are definitely good enough to tie panels togetehr electrically. Most mid-fi commercial gear use self-tapping sheet metal screws, higher-end gear typically use machine screws with machine-threaded holes, pem nuts or nutserts. And there are typically many screws for each panel, providing redundancy. As long as most screws are properly fastened, they will provide good protection. In the event of live AC voltage touching the case inside, the fuse (or your house' mains breaker) should pop instantly.
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post #39 of 44
3/8/10 at 2:01am
A bit late to chime in, but oh well
Aside from the minor modifications (gain and zobel network), I am extremely happy with my B22, and Jason (oneplustwo) was a pleaure to deal with. I would buy from him again
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post #40 of 44
3/8/10 at 8:06am
Quote:
Originally Posted by amb View Post
The notion that there must be actual wires to every panel is absurd. Show me any commercial hi-fi gear that does this, even those that pass UL and CSA safety certification...
A lot of commercial equipment is double insulated.
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post #41 of 44
3/8/10 at 10:51am
Quote:
Originally Posted by luvdunhill View Post
I don't have any examples that use actual wires, but there are plenty (in fact, the majority I'd argue) that have excellent grounding to each panel which is far superior to a screw. For example, look at even the cheapest DVD player out there, like the $100 Denon players. They have metal contacts that make connection to each of the panels as they are assembled. They are spring loaded contacts that make good contact when the panels are assembled.
this is entirely for RFI and not for safety!

sorry to disagree but this is incorrect.
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post #42 of 44
3/8/10 at 11:04am
Quote:
Originally Posted by amb View Post
The notion that there must be actual wires to every panel is absurd. Show me any commercial hi-fi gear that does this, even those that pass UL and CSA safety certification...
I agree with what you're saying Ti but I've definitely had DIY chassis where the anodized coating was sufficient to isolate the front and back panels from the main chassis despite the fact that the entire thing was screwed together. Most Par Metals chassis that I've used have behaved this way. So while you don't need to wire the panels together builders need to be conscious of the fact that continuity should be verified and not assumed.
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post #43 of 44
3/10/10 at 1:23pm
Quote:
Originally Posted by fishski13 View Post
any catastrophic failure of the TX would take out the o-22 and blow a fuse. the MOSFETs will not pass mains to the B22.
But some things can fail open circuit rather short out and blow the fuse. If you are going to not earth the PCBs, then that is like double insulated equipment which is also able to get by without earthing things. There are other steps that you have to take to do this safely. Like transformers that have a built in thermal fuse. A different style or transformer that can still fail safely even if the insulation fails on all the transformer windings. Sealing the PSU so failure of the mains chassis wiring will still not allow for any stray wires to come into contact with the circuits or casework. You get the idea. I'm no expert or professional, it's just my understanding of how it's done and why. It's safer to just earth it, that's why some people get problems with ground loops. At least it's safe.

There are better ways of fixing ground loops rather than simply leaving off a vital earth connection. The 2 main ones I can think off are: 1) using a wall wart style double insulated PSU (3A at 12v AC is easily available which can be turned into +/- 12V DC quite easily)... 2) Balanced audio gear also solves it since the audio shield can be disconnected or connected with a capacitor to block the ground loop currents but still allow noise shielding while maintaining the safety earth to all the electronics.


BTW, screws are fine for tying panels together. Assuming the screws are not painted or coated themselves they can conduct huge currents easily.
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post #44 of 44
3/10/10 at 3:28pm
what if someone replaces all the screw with black aluminum oxide to look better? That's done all the time around here.

Also, I understand the point of RFI shielding but the point I was trying to make was that there is as a byproduct of this is the fact that electrically the case is also tied together.
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