g9 grounding questions, questions, questions !

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maxime

Well-known member
Joined
May 27, 2005
Messages
156
Location
Brussels, Belgium
hello,
I'm currently debugging my brand new G9. I was wanting to get advice about the grounding method of the unit as I suspect mine to have this problem.
noise level is about at -60dB at full gain, the tone of it being really hiss+ 50hz harmonics (I suspect it being ground hum?). I also noticed it to be greater on the channel 2 (more 50hz harmonics)
At the moment changing the toroids and power caps place doesn't affect noise figures, as getting one of the xformer opposite to the other. my pcb, jacks and regulators is also isolated.

I only have one terminal chassis ground (at the side of the input 1 xlr). a strap goes from this to all the pins 1 of XLR, and is solered at the other end at the power inlet ground. so, just as prescribed by Jakob, our master, so no star ground here...

What makes me wonder is the fact that all inputs and outputs at the pcb grounds are connected to the xlr first pin, so creating multiple paths from the pcb to the chassis, no? should it be better with only pcb in or out to be grounded?

also about the cables coming from power transformers. I twisted every pair and pushed those close to the chassis (just as in those guitars amplifiers). Is it the right way to do it?
should the audio cables be the opposite (in the air)?
Is there a rule about the subject?

many questions, many questions, many questions,....
anyway, I want to thank you all about this super project that is the G9, and also all the discussions around it
best wishes
maxime
 

MrZpliff

Well-known member
Joined
Jun 15, 2005
Messages
399
Location
Sweden
I used shielded cable.
Pin 1 on the first xlr grounded.
2 extra caps for the heater.
No hum or hiss.

http://www.groupdiy.com/index.php?topic=11012&highlight=
 

maxime

Well-known member
Joined
May 27, 2005
Messages
156
Location
Brussels, Belgium
thanks for your reply
I can see my mistake... only xlr 1 should be grounded. no strap on this side...
will try it now..
my audio is of course shielded. and the HT caps are also two 330 MF.
ripple is really low (less than 2mV on the HT, less than 1 on the heaters fil.)
regards
maxime
 

maxime

Well-known member
Joined
May 27, 2005
Messages
156
Location
Brussels, Belgium
what gets the best results here is:
only one of the 2 input xlr tied to chassis.
both the output xlr tied to the chassis.(the outputs are not connected to ground rails at the pcb, but generate some noise if left n/c).
I still need to check with different equipment connected to it...
everythings seems ok and silent right now.
best regards
Maxime
 

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