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  • 2 weeks later...
19 hours ago, sandyk said:

Not so.

 The transformer may be bolted to a metal chassis which is earthed for protective purposes, however many linear PSU powered devices do not have the  0 volts connected to the Safety ground. This includes many Preamplifiers, DACs etc. that may have their 0 volts side connected via their Interconnects to the Input of a Power Amplifier which may be earthed and provides the earth reference for them.

You are mixing several different functions.

* * * * * * * *

Wha do you mean by this provides the earth reference for them part?

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So let's clarify some of this:

  • Safety Ground. The Safety Ground is connected to the chassis near where the AC cord enters the chassis.  Exceptions being double insulated chassis (square with-in a square safety symbol) and wall-warts. The Safety Ground then makes its way back to the main breaker panel where it is connected to the Neutral.
  • Ground Rod. The ground rod is also connected to the Neutral at the main breaker panel (some locations have other methods).  But because the ground rod has no impact on day-to-day AC power quality, it is of little further interest to us.
  • DC Supply Common. The DC common is connected to the chassis of the unit it is powering at a single point. This is the same point as the audio circuit common.
  • Audio Circuit Common.  The audio circuit common is connected to the chassis at a single point near the signal input jacks. (the same point as the DC common). Sometimes there is a low value resistor network between the commons and the chassis.

Note that there is continuity between all these things, but each has it's own function.

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But Sandy, that's exactly what I wrote:

DC Supply Common. The DC common is connected to the chassis of the unit it is powering at a single point. This is the same point as the audio circuit common.

The DC is not connected to the DC supply chassis. It's attached to the chassis of the audio component.

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2 hours ago, sandyk said:

Are we even speaking the same language ?

I try to write in American engineering English (with a few British words added).

 

2 hours ago, sandyk said:

Are you able to read electronic schematics ?

With over a half century experience in broadcast engineering, recording engineering and industrial R & D electrical / electronic engineering I think that yes I can read schematics.

 

3 hours ago, sandyk said:

The use of the word "chassis" appears to be a problem here.

I think that it's the word 'ground' that is the problem. I try to use specific technical meaning for words.

"chassis" refers to the metal enclosure or base of whatever unit we are talking about at that moment.

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1 minute ago, gmgraves said:

Tell Me Alex, is their some reason why this design has the chassis ground (earth), the ±15 volt supply return and the 5 volt ground all isolated from one another?

The power supply drawing is completely correct. The DC grounding is taken care of at the audio circuit end.

Don't know if this supply is in the same enclosure as the audio circuit or not?

* * * * * * *

does 'sandyk' = Alex?

 

 

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  • The grounding symbol that looks like a lawn rake, indicates a connection to the metal chassis.  A requirement for the Safety Ground/Protective Earth.
  • The grounding symbol that looks like a triangle, indicates the circuit or circuits common. And most probably a PCB ground plain. Just how it gets connected to the chassis is determined somewhere else in the system.

* * * * * * * * *

In the context of the 'sandyk' power supply, because the +15/-15 and 5V supplies share a common, the will both connect to the chassis at the same point (wherever that might be).

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