Is Gainclone Direct Coupled? Appropriate Preamp? - Page 4 - diyAudio
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Old 10th April 2011, 06:39 AM   #31
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Sure, why not, I think with Andrew's help we might even perfect the deadbug layout; the chipamp everyone should start with.

Hi Andrew, regarding the diodes and cap to ground, I know Rod Elliot uses a similar config, BUT, he seems to use it to bridge Between case ground terminal and power ground star. (image attached)

So my question is, do you think the disconnect network should be where you suggested, or as Rod suggested. I know you are very good at this, but maybe it was late and seeing only a piece of the layout you got confused... just want to doublecheck.

Your way would give protection to the SG but leave the PG with an uninterupted ground path, but as it is not the route to PG, would one still need to use such big components, i.e. 5A diodes, and high power resistor?
Its a might fine subcircuit and saved my bacon a few times.

I have empty space on that side of my board, so it would not be a problem to insert it. Actualy, together with the larger film input cap we discussed earlier, it will nicely balance out the protection components, and slowstart/DC cutoff relay on the other side.
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Old 10th April 2011, 10:48 AM   #32
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This is an extra Disconnecting Network.

The Chassis is permanently connected to PE at the Safety Earth. This must never be compromised.

Then the Main Audio (Star) Ground (MAG) is connected to chassis. This connection can be direct wire or via a big Disconnecting Network. An optional extra is a parallel switch that shorts across the Disconnecting Network. If opening/closing the switch makes no difference to the audio output then leave the switch closed. Note if the switch is left open the MAG is still connected to Chassis. This is the safe ground lifting switch.
You must never implement a ground to chassis "breaking" switch. This could kill you.

Now look at what is left, if you keep the 10r between the Signal Ground and the MAG.
If a Fault current gets onto the Signal Ground then the 10r will rupture open and anyone touching the shield or RCA could be electrocuted.
To comply with the "all exposed conductive parts must be connected to Earth" the 10r must be bypassed with something that can pass fault current. If you add the 10r as a ground loop current limiter then you must add an extra Disconnecting Network.
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Last edited by AndrewT; 10th April 2011 at 10:54 AM.
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Old 10th April 2011, 01:13 PM   #33
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Why not just use a monolithic 35A Bridge Rectifier for the ground loop isolator for 2-3 bucks? Is there a point to the 10ohm resistor? Ive seen a couple of kinds of ground loop isolators, this is the first one ive seen that uses both a resistor the diodes.
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Old 10th April 2011, 01:19 PM   #34
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Night.
do you realise what fault current means?
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Old 10th April 2011, 05:18 PM   #35
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The chassis is grounded So that if its gets energized It doesnt drop the next person who touches it. The ground loop isolator is to lift the signal ground above earth while not limiting current flow. For if the signal ground gets energized it doesnt drop the next person who touches it. Again in either situation the amp would run fine if it where not grounded.

I normally use this:
http://i232.photobucket.com/albums/e...ges/Safety.png

I have also seen the huge 10ohm resistor with cap.
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Old 10th April 2011, 07:01 PM   #36
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Ni,
touch the RCA exposed terminal just a couple of inches along from the mains input on the back panel. Inside the mains hot has broken and flipped across to touch the RCA outer from the inside and blown the 10r ground lift resistor while you were not looking but heard the amp apparently go off.
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Old 11th April 2011, 05:58 AM   #37
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The diodes offer the resistor some protection, not the other way around, as far as I understand.
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Old 11th April 2011, 08:53 AM   #38
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The diodes pass the fault current.
The resistor makes the voltage reference.

Quite different jobs.

The resistor alone or resistor//cap can never pass fault current. To say that one has never seen diodes (along with resistor) in these locations indicates that we have Member who does not read safety advice and is a danger to anyone around who may operate his/her badly assembled mains powered equipment.
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Old 11th April 2011, 09:46 AM   #39
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I'd highly recommend the Rod Elliot article for anyone who wants to understand more about saftey earth, and the use of earth loop breakers. Earthing (Grounding) Your Hi-Fi - Tricks and Techniques In fact IMO it should be mandatory reading for anyone doing a mains powered project

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Old 11th April 2011, 02:42 PM   #40
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Hi Andrew, me again, with a new question...

I see the schematic calls for a 1M resistor from input to SG.
If I wanted to put a pot infront of the amp, can I use my standard old 10k log pots or should one use 1M pots? and remove the resistor...? I know if use a too big pot on other schematics, I have issues with sensitivity.
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