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Old 12th October 2011, 01:05 PM   #11
DF96 is offline DF96  England
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The link between the negative side of a bridge (or the secondary centre-tap) and the reservoir cap -ve terminal carries charging pulses. It should simply connect these two points together. There should be a separate link from the reservoir -ve to the smoother -ve, and then from there to the star point.

What many people do is connect the bridge (or CT), reservoir -ve and smoother -ve with three separate wires to the star. As a result the charging pulses go through the star. This would be OK if the star had zero resistance, but it doesn't. Even a few mm of thick connector is enough to generate a hum voltage if it has charging pulses through it.
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Old 12th October 2011, 01:08 PM   #12
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by DF96 View Post
Many people route the reservoir charging currents through their star ground, then wonder why they get hum.
Many Members recommend this fault in grounding.

It is asking for Hum & Buzz problems.

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Audio Component Grounding and Interconnection - diyAudio
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Old 13th October 2011, 04:10 PM   #13
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I am attaching the powersupply as a jpg file.Is anyone has any idea why I get 100 Hz hum

I have seperate trafos for each channel and different secondaries for the low power stages (regulated with lm317 - 337) and the output stage. Ths Power supply is used in a SE CLASS A amp with 2,3 Amp per rail tota 4.5 amp per channel.

thnx.
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Old 13th October 2011, 04:34 PM   #14
DF96 is offline DF96  England
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You have ground loops in your PSU.
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Old 13th October 2011, 05:00 PM   #15
AndrewT is offline AndrewT  Scotland
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There appear to be dead shorts across the secondary windings?

Is your schematic what you built?
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Old 13th October 2011, 05:46 PM   #16
DF96 is offline DF96  England
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Let us hope not! I hadn't spotted that. Maybe the ground loops aren't really there either?
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Old 13th October 2011, 05:50 PM   #17
AndrewT is offline AndrewT  Scotland
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He did say 4.5A per channel !
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Old 13th October 2011, 08:53 PM   #18
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you are right about the shorts inth picture but it is not reality. The secondaries are conected to the ac in the bridges. Where can someone see ground loops?
Why you are suprised about the current. 2 AMPERE in positive and 2 amp in negative side.
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Old 14th October 2011, 06:46 AM   #19
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I attach a new photo as it is. Do you think that the 100nf capacitors as they are connected accross the bridges contribute to the hum? I thought so and remove them, but the same situation. I have a week trying to find what is going on. What are your objections to this layout? Do I need more capacitance?
Any help it will be welcome.
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Old 14th October 2011, 08:08 AM   #20
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Also if someoune is noticing the low power rectification is done with one bridge and I connect the ground from the connection of the two secondaries to the ground coming from the rectification for the output stage (two bridges). Do you think that this action fills with dirty content the common ground?
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