So I understand the star topology and why they would ground the op amp and first input drivers separately, but alas something is amiss!
In the schematic, both op amps are wired the same and tied to case ground (0v on the primary), while the rest of the driver is tied to 0v on the secondary. However in the diagram, L and R are wired differently. Am I going crazy or is there a reason they did this? I verified the traces on the board and they agree with the diagram rather than the schematic. Many thanks.
I have highlighted the grounds and the ground-ties. The red circles are 10ohm resisters between the two grounding arms.
In the schematic, both op amps are wired the same and tied to case ground (0v on the primary), while the rest of the driver is tied to 0v on the secondary. However in the diagram, L and R are wired differently. Am I going crazy or is there a reason they did this? I verified the traces on the board and they agree with the diagram rather than the schematic. Many thanks.
I have highlighted the grounds and the ground-ties. The red circles are 10ohm resisters between the two grounding arms.
That would ultimately the be goal they wanted to achieve if this wasn't a mistake, but I can't understand how rando this board seems with respect to ground. Can we recognize out of this what is best practice?
I ask because I'm rebuilding the whole amp, and right now I'm just running 4 separate ground wires (2 for each channel driver) right to the secondary caps. Just wondering if that's enough or I should be cloning this ground-L-resisitor-0v-R- loop weirdness above.
I ask because I'm rebuilding the whole amp, and right now I'm just running 4 separate ground wires (2 for each channel driver) right to the secondary caps. Just wondering if that's enough or I should be cloning this ground-L-resisitor-0v-R- loop weirdness above.
It looks like the pins tied to ground are for an unused channel of a dual opamp. Doing it differently for left and right may not be pretty but isn't functionally relevant.
Not sure why they would link the two "brown grounds" together like that, perhaps reducing ground return impedance on there (for better crosstalking or something)? Perhaps a look at the schematic would be illuminating, what model is it? SM-6100SA, never heard of that one. Seems to be only 20 years old, why'd it need a rebuild already? It let the magic smoke out bigtime?
Ah, so "brown ground" appears to be a power ground, and "green ground" is signal ground. Always good to have them separate. They're linked by W802 in the power supply, and again with these 10 ohm resistors. Not sure why, perhaps an inductance-related thing... 10 ohms may be high enough to avoid a ground loop at audio frequencies but low enough to counteract RF issues. I may be talking out of my rear end here, but unless you can get ahold of the original designers it can be hard to determine why they did things a certain way.
Not sure why they would link the two "brown grounds" together like that, perhaps reducing ground return impedance on there (for better crosstalking or something)? Perhaps a look at the schematic would be illuminating, what model is it? SM-6100SA, never heard of that one. Seems to be only 20 years old, why'd it need a rebuild already? It let the magic smoke out bigtime?
Ah, so "brown ground" appears to be a power ground, and "green ground" is signal ground. Always good to have them separate. They're linked by W802 in the power supply, and again with these 10 ohm resistors. Not sure why, perhaps an inductance-related thing... 10 ohms may be high enough to avoid a ground loop at audio frequencies but low enough to counteract RF issues. I may be talking out of my rear end here, but unless you can get ahold of the original designers it can be hard to determine why they did things a certain way.
Thank you sgrossklass for your insight. You have authoritative knowledge without being arrogant, so I'll take your guesses over mine any day of the week 🙂
The SM6100Sa is identical to the PM6100/PM8200 with all of the digital controls stripped out (I'm actually using the PM8200 service manual). This amp worked when I started lol. The sound had fallen flat and there was a very faint hum in the left side so I knew it needed at least caps. When I opened it I realized it had all the active ingredients for a great Japanese SS amp and the weakest link was the circuit board.
So here I am. I have the thing 95% rebuilt with UKZ,WIMA,MICA, all 1% resistors, etc in separate mono blocks that are electrically identical to the schematics. Just have to work these ground returns out.
The SM6100Sa is identical to the PM6100/PM8200 with all of the digital controls stripped out (I'm actually using the PM8200 service manual). This amp worked when I started lol. The sound had fallen flat and there was a very faint hum in the left side so I knew it needed at least caps. When I opened it I realized it had all the active ingredients for a great Japanese SS amp and the weakest link was the circuit board.
So here I am. I have the thing 95% rebuilt with UKZ,WIMA,MICA, all 1% resistors, etc in separate mono blocks that are electrically identical to the schematics. Just have to work these ground returns out.
"They're linked by W802 in the power supply, and again with these 10 ohm resistors. Not sure why, perhaps an inductance-related thing... 10 ohms may be high enough to avoid a ground loop at audio frequencies but low enough to counteract RF issues."
Thank you sgrossklass for letting me learn how to explain the 'ground loop' issue to my other friends. I'm always learning.
Thank you sgrossklass for letting me learn how to explain the 'ground loop' issue to my other friends. I'm always learning.