So here they are.......3 days from China....so I have a question. What is the grounding scheme on these amps? They have an external P.S. that has only a 2 prong cord. Then the DC output goes into the amp on 2 wires. But the amp has a 3 pin XLR/TRS combi jack. So where does pin 1/sleeve go?
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Topping LA90 Discrete Amplifier Review
- Thread starter amirm
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PC board ground plane? That's my speculation.
Hopefully also the chassis.
You need a reference between sending ground and receiving ground so as not to get an excessive common mode voltage differential, so pin 1 should go to chassis - but also the 0V reference of the circuit should also star to chassis.
See figure 24 here, and the reference to AES 48:
Roger...I know a lot about ground/grounding schemes. Just wondering how Topping handles it in these amps. So if pin 1 goes to the chassis then the chassis of this amp goes down the shield of the IC cable and ties to the chassis of sending equipment? Or do I need to add an external wire to the chassis of these amps to power ground?
No, the interconnect should do the job fine.
Incidentally there are many audio devices (or other consumer electronics) that are class II insulation, and hence have no connection to mains ground.
Roger that too...most are unbalanced interfaces.....or if balanced done incorrectly.
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I just measured mine. Pin 1 does indeed go to chassis ground.
I have one of mine still here at work on my bench. Going to dig into it later...you know in my "spare" time
And does that also go to the minus pin of the PS input?
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No.
On mine, the power supply input has no terminal for Earth ground, only two terminals for hot and neutral. Neither terminal connects to the chassis ground.
The power supply output has three pins, though, one of which does connect to chassis ground.
which one? the same one that is DC minus?
And yes of course I understand the AC input has no 3rd prong earth ground.
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There are three pins. Chassis ground only connects to one of them, the upper left pin if you are looking at the back of the amplifier. It is not shorted to either of the other two pins.
EDIT: also, on the other two pins, one measures -63V and the other measures 0V with reference to the pin that connects to chassis ground. But, again, the pin that measures 0V is not shorted to the chassis ground pin.
Your welcome.
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No.
OK, I just received my two units yesterday. I am assuming therefore they are the latest revision(if there have been revisions). I read 63.68 volts DC on the power supply sockets without it being plugged into the amp. + on pin 1, -on pin 2, nothing on pin 3. I read continuity on all pin 1s of the combi jacks to the chassis on amp. I read no continuity on any of the power supply pins to chassis. Very high resistance slightly fluctuating like stray capacitance. Also read continuity on the negative output speaker terminals to the chassis. Makes me wonder why a jumper between them is necessary to run amp in bridge mode, I mean if they are both already shorted to the chassis what is a jumper going to do?
to make the output clip? Or the input stage? I know for sure I can make the output clip
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