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PostPosted: 23 Oct 2010, 05:45 
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Joined: 08 May 2009, 08:20
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Location: Duesseldorf, Germany
Hi again,

to complete the thread and the right answer about grounding systems i add some links to some WIKIs about the power line system. The WIKIs explain the consumer power line and the earthing system better than i could do it.

The main point on this is to show up how the earthing from power lines works. Usually the TN-C and TN-C-S / TT sytems are used in our households. On the pictures from the Wikis you can see, that L1, L2, L3 feed the loads and that PE (Protection Earth) and the N (Neutral) come together at the supply generator. As mentioned before, Earth and Neutral are splitted in the household. L1, L2, L3 are hooked up to the loads via circuit breakers. Neutral (N) is used as device / household grounding, the Earth (PE) re-combines the Neutral with the earthing and goes back to the PL Supply.

Earthing System

This is how GCFI (Residual current devices) works:
Residual current traps
Videos about GFCI

The neutral conductor and the live conductor go through a coil (balanced transformer core).
If a residual current (current due to a circuit failure) runs into the neutral, the transformer is inbalanced and switches the breaker.
Personal protections switch down at 4 to 6 mA - device protectors in the range of 40 to 80 mA (depends on the installed systems).

IMO - the basics of mains wiring are the most important things someone should know when building High Voltage circuits.

@Steven - i wish i could write like you :-).

Have fun ;-).

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 23 Oct 2010, 15:53 
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Joined: 05 Jan 2010, 21:16
Posts: 680
Location: Las Vegas Nevada USA
tombethe wrote:
IMO - the basics of mains wiring are the most important things someone should know when building High Voltage circuits.

@Steven - i wish i could write like you :-)

I agree completely. You shouldn't build or tinker with high voltage amps unless you understand how the protective devices work and how your house is wired in addition to using safe work practices. Working in the electric utility industry I have personally known people who have died from electrocution on the job. I guess that's why I may be a little preoccupied with protection and safety. It's part of my job and when somebody you know dies from electrocution it sticks with you.

And I wish I could READ like you! Maybe I wouldn't ask so many questions. But I'd rather ask and learn than just pretend I understand something when I don't. If I look foolish so be it. I don't think there are ANY stupid questions when it comes to safety. If you don't understand how a grounding scheme works, don't screw around with high voltage equipment that uses it until you DO IMHO.

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PostPosted: 23 Oct 2010, 22:54 
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Joined: 14 Oct 2010, 10:53
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Thank you guys for spelling this out. I have been thinking about this. While I understood the case was grounded to earth I was having a hard time wrapping my (admittitly feeble) mind around the DC to ground connection, in terms of safety. Can't build it till I understand it....

Paul


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PostPosted: 17 Nov 2010, 23:25 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi Everyone, Lots of good discussion here on grounding. The key point in all my designs is safety of the builder. There are several aspects to my designs that are included to safely deal with faults. The first is the power entry and filter. The type I use insures the proper connection to the AC mains and insures the chassis is at AC mains - earth ground potential. If there is a catastrophic failure in the equipment the fuse will blow. If there is a lessor failure - like a short in the B+, some of the resistors are sized so they will fail in seconds and protect the remainder of the circuit. Now on the operational side, just having a metal box with circuits that have no electrical connection to it will virtually guarantee hum and noise. Thus the often used method (one I use as well) is to connect a type X2 cap and parallel resistor between the signal (which includes the B+) ground and the chassis (at a single point). Then the chassis can act as a shield for the equipment it contains. If there is more than one connection you will usually get ground loops and hum. I encourage anyone that is unclear how the grounding and shielding works to keep asking as a mis-wiring in this area can be extremely dangerous.

Good listening
Bruce

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PostPosted: 26 Nov 2010, 23:11 
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Joined: 14 Oct 2010, 10:53
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Well I have "finished" my poddwatt. It sounds very nice - I'm looking forward to getting some real speakers on it. I have a couple of huge Magnaplaner speakers that my wife will not let in the living room (small house, 3 kids). I'm building some descent small speakers that will be allowed. Again, I have to say that the sound from the poddwatt is really nice, even from the crappy bookshelf speakers I have now. I know how bad they sounded with my previous amp (a nice Denon from the '80s). I had a few minor trouble shooting issues finishing the amp; the only thing I am a bit concerned about now is the amount of heat the power transformer is putting out. After about a half an hour or so the transformer reaches its full temp that seems quite hot. I can touch it but not comfortably for more that 5-10 seconds. Is this normal? If not what could be the problem?

I think I have made a fine looking case for the amp. I'll post some pics soon.

Paul


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PostPosted: 29 Nov 2010, 16:36 
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Location: Arizona, USA
Hi. That was one of my initial concerns as well, but consulting with Edcor it is OK. I have had the original amp running every day in my office for about 14-16 months now without any hint of a problem. If I were to do a redesign, I would probably pick a transformer that has a larger rating.

BTW, you may find the amp doesn't have enough muscle for the Maggies. I have Martin Logan Vistas and it is fine for casual listening, but will distort if pushed much. I had one diyer (Australian) say that Maggies need lots of drive.

Good listening
Bruce

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PostPosted: 30 Nov 2010, 12:51 
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Hi,

I'm not planning on using the Magnaplaners - I know from experience that they need a lot of push. I now have some quite good but smalish speakers on the Amp In Black (my daughter's name for the poddwatt). I am very impressed with the range and quality of the amp. Individual instruments really stand out. I would like to thank you for providing the design and advice. The kids were dancing to Pink Floyd last night - they give their approval. The amp is just enough for our living room (I have been wondering if the MP3 players could use bit of a boost) but the quality of the sound has me thinking about something bigger...

Still meaning to take a few pics but the Amp In Black sucks up what little light the rainy Portland skys have.

Paul


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PostPosted: 19 Jan 2011, 17:55 
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Joined: 03 Jan 2009, 10:44
Posts: 121
Need assistance! I can't seem to find an answer to this question so I'll burden you folks.

I noticed that the commercial version of the Poddwatt includes RCA outputs for (powered) subwoofer connections. Can anyone provide directions to a schematic showing how these outputs integrate with the original design? I am using the recommended transformers from Edcor.

I also have a pair of KT77 Oddwatts under construction and would like to add a subwoofer output to each of those as well.

Any assistance will be appreciated and generously rewarded with kind thoughts and/or a small cash award, whichever comes first.
Best regards,
Lofton


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PostPosted: 19 Jan 2011, 21:31 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi PM me with an address that can handle fair sized files and I'll send you the schematic.

Good listening
Bruce

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PostPosted: 10 Mar 2011, 15:04 
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Joined: 03 Jan 2009, 10:44
Posts: 121
Greetings, all.
My PoddWatt is finally done! I used the updated schematic sent by Bruce for the amp section and used the original schematic for the power supply. Might there be changes to the power supply schematic as well?

Initially I had horrific hum which was no doubt caused by a ground loop. To address this, at least temporarily, I removed the parallel X2 cap and resistor between signal ground, etc. and am using a single star ground. Hum is better, but evident. After about 45 minutes listening, the 1K resistor in the power section blew. This was not the first time this happened but with all my redoing wiring and such I figured I'd solved the problem, but apparently not.

What wattage resistor should I be using? The schematic says 1/2 watt, which is what I used.

Now for the dumb question: On the OddWatt there are two pair of test points for each channel. On the PoddWatt there's only one pair. How/where do I measure for adjusting the bias? I've read every thread here five or six times but am not finding answers.

Thanks for any guidance here, folks.

Lofton


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