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PostPosted: 27 Apr 2011, 11:20 
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Joined: 05 Nov 2010, 21:07
Posts: 702
Location: South East US - Tennessee
Geek wrote:
Guh! Do you know how many commercial supposedly-CE-UL-CSA approved products I've found with the line/neutral backwards, or illegal wiring schemes (line straight to transformer, neutral switched, then to fuse, then to transformer. No X2 cap across switch)?

Neutral switching is actually common place and has sound basis IF you are an electrical engineer. The premis is that by switching the neutral side, as opposed to the hot side, is that there is lesser surge. I don't like it, I think that regardless of any pressumed difference of in-surge, putting the switch on the neutral leaves the circuit hot. With-in that argument is always the reminder to unplug the device while servicing. Under-Writers Labs (UL) has no problem with the sceme so long as the chassis and any exposed metal is properly ground via the ground wire of a typical 3-wire system. Can't speak for the other certifying labs for other countries. Under the premis, the capacitor would not be necessary. Let me reiterate - I DO NOT approve of this method nor agree with the premis ( I do have a reputation of arguing with so called engineers). My method places the in-fuse as close to the power input as practical (I will use a fused IEC receptical where feasable) and keep the wire to the mains switch and the location of said switch as close as practical to the in-line fuse, all on the HOT line. Power line to fuse to switch to rest of circuit. I always use 3 wire and chassis is ALWAYS grounded. The only exception is if my project uses a wall-wart or other external power supply.

I believe we may be wondering Off Topic, however.

:idea: How about an amp using a single tube (compactron) containing 2 disimilar triodes AND a pentode - the 6AF11 for example? Granted, the pentode section of this tube would not be practicle for a PP design, but should make a reasonable "flea power" SE.

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The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
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LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 27 Apr 2011, 17:14 
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Location: Chilliwack, BC
At a TV shop in the 80's, we were paid to switch the neutral back to line switching (and install the X2 cap) during a nation-wide recall of a certain brand amplifier. Maybe legal in the US, but it sure isn't here.

As for surge.... got any link on the data?


Back to topic...

Compactron amps! A place for info is Robert Casey, WA2ISE - http://pw2.netcom.com/~wa2ise/radios/compaa3.html While it's mainly talking about radio, he has curves there and talks about proper subbing.

Another place for info is here: http://www.junkbox.com/electronics/Comp ... ndex.shtml Nice selector to use your plinkers :D

Cheers!

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* Ratings are for transistors - tubes have guidelines*
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PostPosted: 28 Apr 2011, 00:07 
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Sorry Geek. The information is resultant of a personal argument I had with a corporate engineer of the manufacturer of the equipment I service. They used neutral switching in the equipment, both in the mains power and for control of AC driven parts - motors, heaters, etc. They also use DC ground switching for DC driven components. But, here's the reasoning given me:
By having neutral switching, the circuit remained powered (under potential), but since the neutral was open, no flow. By doing this, supposedly there would be less in-rush surge, which would necessarily reduce the arc over from switch closing. This also had the result of me getting zapped more than I liked by AC driven parts while in the process of troubleshooting failures - which is was spurred the argument. Please note that I clearly stated I didn't support the premise.


I am no stranger to electrical jolts. Before I started working on commercial equipment, I worked on consumer electronics, which included TVs. I got more than my fair share of hot chassis jolts and actually damaged an oscilloscope not realizing I was attaching to a hot chassis. Yeah, I really enjoyed working on Magnavox TVs. And yes, more often than not, I'd run in to an older TV that did not have a polarized plug - which meant that power switch may be on the hot side or the neutral side, depending on which way the cord was plugged in.

_________________
The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
_________________________________
LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 28 Apr 2011, 00:29 
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Joined: 24 Nov 2010, 14:39
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Location: California
Sorry to add to the OT, but I think this is important. :|

As a long-time electrician, hearing "neutral switching" makes me very nervous :eek: Switching should always be in the "hot" side of the mains (US National Electrical Code refers to it as the "ungrounded conductor") Ditto for the fusing - it should always be located in the hot side of the mains.
I don't think I buy the "lower surge" reasoning. I can't see any basis in fact. The neutral may be at ground potential, due to it's connection to ground at the buildings' main service panel and at the utility companys transformer, but it is still carrying the same amount of current (amperage) as the hot wire. So whichever one you interrupt with a switch, same amount of spark, same spike from the transformers magnetic field collapsing, etc.

I would be arguing with that engineer that says it's good to switch the neutral :shock:

It is permissable to use a double-pole switch that simultaneously interrupts both the neutral AND the hot, but I wouldn't advise it?

Anything that's mains-voltage electrical needs any metal parts, that are exposed in normal operation, to be grounded, generally meaning a 3 wire cord and 3-prong plug.

I'm not very familiar with codes and laws and customs outside of the U.S., but electrocution anywhere isn't good :hot:

Again, sorry for the OT. :bawling: Now where were we..... :)


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PostPosted: 28 Apr 2011, 04:26 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
I would dare say that engineer is extremely erroneous:
http://www.eng-tips.com/viewthread.cfm? ... 678&page=5

/me would argue with a god when I know I'm right..... and on the right side of the law to boot.

/me expects threadlock.

/me consults now with friend who is BscEE

;)

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
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PostPosted: 28 Apr 2011, 12:12 
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Joined: 04 Jun 2008, 20:59
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Hi, I had not checked this thread for a while and see some things in it that caught my attention. The bit about isolating chassis and signal grounds is really really important. If you don't there will almost certainly be ground loops. The second thing is interesting and perhaps a bit OT and maybe should be its own thread. I use three wire IEC connections to all my equipment and there are no ground loop issues. (this is true for both my own personal equipment and the Kits that Oddwatt Audio sells) I use commercial line filter / entry connectors on all equipment with the ground going directly to the chassis. Plus, internal to the equipment I use a 120-150 ohm resistor in parallel with a .1 to .2uf type X2 capacitor between the chassis and signal ground. the combination allows the chassis to both be the protective measure required by many countries electrical codes and provide a shield for the stuff inside. The ground loop problem is often from a different source and may well be from internal component arrangements and gounding. The best two solutions are a single point ground and a buss ground. Either can work. I like to have the single point if used tie together at the signal input. That is the area that is most sensitive.

There is one situation in which the three wire system can cause ground loops. That is if you attach some equipment to one outlet and some other equipment to a different one. The loop can occur through the house wiring. I highly recommend a power line filter as the main connection for all equipment. It need not be expensive and many reasonable ones have noise and transient filtering. A cheap form of insurance if you live in an area where lightning is present (I do :o ).

For those of you that tie the audio system into a home theater one, beware that the cable tv feed can be a source of a ground loop too. My local CATV ground is about 3.5 volts (no current as it is a hi Z ) different from the house mains ground.

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