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Old 21st August 2002, 08:57 AM   #1
Eccu is offline Eccu  Finland
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Default My Crescendo amp pics

Couple of questions still open...

Number of the fuses:
a: Do I have put only one to the primary side?
b: Or also two fuses to secondary side? And where should these two fuses to be placed. Before rectifier or after rectifier or after capacitors?

Earthing:
a: Do I have connect the earth ( from wall socket ) merely to amplifier metal case? So speaker terminals and RCAs are isolated from case. And power supply zero point ( center point of PSU filter capasitors ) is separate from this earth.
b: Or do I have connect earth ( from wall socket ) to power supply zero point ( center point of capasitors ) and from there to metal case? And still keep speaker terminals and RCAs isolated from case. Or how I must do it?
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Old 21st August 2002, 09:03 AM   #2
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An another pic.
U see that I keep my filter capasitors in (empty) Ballantines whisky box...
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Old 21st August 2002, 09:34 AM   #3
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Hi Eccu,

looks nice!

You only need a fuse on the primary side. The original Crescendo had two extra fuses in the plus and minus feeds placed on the circuit boards.

Connect all of your grounds to one central point and from here with a resistor or NTC to the chassis. Connect chassis to wall socket (earth)
In some cases you must disconnect the input ground from the central point to avoid humm (it will still be connected through the 10ohms resistor)

william

P.S. Donīt you think you caps will smell when they get warm?
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Old 21st August 2002, 11:28 AM   #4
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BIG Thanks again Wuffwaff.

Do you mean this? (See attachment)

But should I connect speaker - (minus) to PSU capasitor center point or should I connect it to amplifier board (speaker -) like in schematic?



And now very stupid question: Is NTC same think as Thermistor?
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Old 21st August 2002, 02:05 PM   #5
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eccu,

yes, ntc and thermistor are the same. I would connect speaker - at the caps and not at the board (star earthing remember) just like in your drawing. The only connection thatīs missing in your drawing is inlet ground.

william
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Old 22nd August 2002, 06:04 AM   #6
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I think you mean that "OUTLET" in picture... that where purple wire is connected to ground point on the chasis.


I have still one question about NTC... so what is its meaning and function in this case?

And what kind of its got to be?



Dam my English is bad... I try make my best.
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Old 22nd August 2002, 05:42 PM   #7
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Eccu,

the NTC stands for "negative temperature coefficient" and means that the resistance of this part goes down to a few ohms when it gets hotter. So as long as your central earth point and chassis ground have almost the same potential thereīs no current flowing (NTC has a high resistance now) and no chance for ground loops and humm

As soon as the central earth point gets positive or negative, current will start flowing through the ntc and it will get lower resistance and even more current will be flowing

Now (or even before) your "differential switch" (donīt know the englisch name) will detect that thereīs more current going into your amp then is coming out and shut the whole house down

If you donīt have anything like a diff switch the high current to ground will activate the fuse in your amp and prevent other devices to get a lethal potential via the interconnect ground.

When I think about this itīs really time that I connect my central earth point to ground one of these days

william
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Old 23rd August 2002, 06:03 AM   #8
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Big thanks...
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