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Old 23rd February 2011, 12:32 PM   #1
BigE is offline BigE  Canada
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Default Phase linear 400 grounding help

I'd like to replace the RCA jacks and at this time, it looks like a good opportunity to change the grounding scheme.

The harness has already been replaced, as well as PS supply caps, PCB electrolytics, and 1 channel of the input differential pair has been swapped to MPSA06 (not heard the result of changing the diff pair yet).

The question is: What is the best routing for ground? Currently, the input (signal) and output (signal) grounds are connected together. Both input grounds on the PCB are connectet to a point between the input and output grounds.

Also, pin 5 on the harness is connected to this same point.

It seems to me that pin 5 ought to be connected to the PS '0' reference, along with the output grounds. The connection between input and output should then be cut -- assuming that pin 5 is connected to the input signal grounds too.....but that needs checking.

Has anyone changed this grounding scheme? Any comments?
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Old 31st March 2011, 03:31 PM   #2
BigE is offline BigE  Canada
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I changed the grounding to delete the direct conection between the output ground (speaker negative) and the input ground (Left and right channel sheilds).

Now, both the speaker negatives goes to power common, as do both input shields independently . The PCB ground - ie pin 5 on the PL14 board - also goes directly to power common.

Pin 2 is the signal ground (ie shield). It is connected to Pin 5 via R2, which has different values for each channel.

The PCB board itself shows two groups of grounds.

One group is connected to the signal ground to input differential pair reference ground, B+ bypass capacitor ground C3 for transistors Q3/Q4, emitter ground for Q3, and C6. In the original grounding scheme, the speaker negative was in this group too.

The second group is the pin 5 power common group, which is the ground reference for the protection circuit (between D11 and D12), the collector of Q5 and bias reference (via C10). In the original scheme, this group was connected to the speaker negative too.

The two groups are connected at the power common, and via R2. I can see no good reason for the R2 resistors to be different valued. In fact, I can't see why these two groups should be tied together at all.

In the original layout, pin2 (signal sheild) and pin5 are connected by R2 and the Pin 5 was connected to the input sheild.

Does that not mean R2 is simply unnecessary? Is it safe to delete R2? If I delete R2, will I blow up the amp?
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Old 13th June 2014, 08:01 PM   #3
BigE is offline BigE  Canada
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Does anyone know where the case is connected to power supply common? I cannot find it for some reason....
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Old 31st July 2014, 04:46 PM   #4
BigE is offline BigE  Canada
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FOUND IT.

There are two terminal strips on the back of the chassis. These are connected with a white wire to main audio gound (MAG) and are not isolated from the chassis. I disconnected them from the chassis, and connected MAG to safety earth with a ground loop breaker (yin yang diodes + 10R resistor all in parallel).

Safety earth is connected to chassis at the same point.
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Old 3rd August 2014, 12:51 AM   #5
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Are you just trying to make it safe for chassis faults or noise too?
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Old 4th August 2014, 12:29 AM   #6
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Chassis faults. I did install a ground loop breaker between main audio ground and safety earth too though.
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