Modding an existing amp build (2 x nc250MP)

[Ykar]

Hi all,
I would need a quick advice please. I'm slighltly improving my amp through cable routing amonst other optimisations. There's a trigger input on the chassis which is connected to both Ncore blocs as on the diagram below.

Question is what are the 2 resitors here for, on each ground line ? is that to make sure any ground current would try to find another easier path (such as the Chassis, assuming the blocs are also grounded to chassis, near XLR socket)

As I can't use these resistors from the original build, and I don't have same value at hand, can I use 1 KOhms instead ? (and how to decide which value is best, depending on what they are here for ?...)


Thx

 

[Ykar]

ok well, I should have spend more time searching than posting, I think I've found the answer. That's to avoid ground loop with the triggering device as I suspected... any value "not too far away" should fit.
https://www.diyaudio.com/forums/solid-state/353500-12v-trigger-ground-loop.html

 

[Ykar]

Interested in experts view here : it seems NC...MP's input socket is quite sensisitive to proximity of onboard main SMPS noise "radiations". I did a bunch of tests with my tourist measurement setup and no grounding options helped to lower measured noise which looks like mains harmonics.

First measurment is input wires directly plugged to appropriate pins on J4 (original manufacturer circuit board bypassed, which was an improvement),
second measurement is with a piece of metal surrounding J4 as a sort of radiation shield.
I suspect good measurement system would reveal significantly more benefits as limitation probably comes from souncdard ADC input I use (Scarlett 2i2 Gen2, loopback SINAD measured to 95db and best SINAD with RME ADI2 feeding ADC at 98db...)

I know, none of this is audible but I can't get those spikes out of my head

All measurements are at 5w on 4ohms dummy load
1st :

metal shield surrounding J4 (Noise -1.1 db, mains spikes significantly decreased, SINAD improved by 0.5db)