On both boards, the left and right channels have grounds that are connected together instead of being kept separate.
That's why there are only 3 terminals, L, R, and G, on the connectors. This can cause ground loops and hum.
If this is the reason, there's not much you can do about it.
If I run a ground from the rca inputs directly to the preamp input ground and bypass the volume control module ground would that help?
Well I gave up and went back to the manual volume pot . I don`t know what could be wrong with it I tried different grounds different ps , with no success, just wondering should there be a power ground lead from the volume control board and not only audio signal grounds?
If it was a ground loop causing the problem would a ground loop isolator between the volume control module and the preamp board help
Try just one 10 Ohm resistor, and move it around to each possible ground connection.
See if it reduces the hum in any of the positions. It might make the hum worse in one of the positions
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What does this mean?
The 9VAC winding from the added power transformer is floating, unrelated to ground.
So it powers the proper "9-12VAC" terminals on your add-on module, which does have a ground terminal, you ground this together with other modules ground following established and time tested grounding rules.
That said, I don't much understand the logic behind mixing old Tech Tubes, modern Tech Digital stuff, etc. , but hey, it's *your* Birthday so you get to choose the cake.
Would love to help, but can't wrap my mind around conflicting requirements and Technologies.
Good luck/bonne chance-Merde, et tout ça q'applique ici 🙂
Well I gave the 10 ohm resistor a try with no success . the preamp with the standard pot has no hum , the remote module on its own has no hum, the 9 vac power supply floats on its own , put everything together we get a hum . not sure what to try next.
Remove the resistor entirely. Now try only connecting only the left channel and the ground all the way through,
from the input to the output. Is there hum now?
Next, try only the right channel all the way through.
Not sure how much more soldering and desoldering the preamp and rca can take things are looking rough ,also the hum or buzz comes out of both channels don,t understand by removing one channel then the other what it will tell me.
This is the schematic of the mvo4 can some one tell me what c 10 and r21 are for can,t seem to find them on the board
Those parts connect the alalog and digital circuit grounds together, through an impedance.
This could be related to your hum problem. Are there mounting positions for these parts
marked on the board? Are there wire jumpers installed in these positions instead?
Perhaps you have an earlier version of the board that omits these parts, and has no place
for them on the board.
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My guess is that this board does not have the analog and digital grounds separated
by the RC parts as in the schematic, but instead the analog and digital grounds are all
connected together, and cannot now be separated due to the board design.
This may be your problem. Can you discuss this with the mfr?
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Another thing to watch for is that the body of the pot is connected to gnd. If you attach it to your enclosure and your enclosure is connected to earth, you might create a groundloop.
I just installed a pair of these into amps made of hypex ucd180 (also without resistor in between the two grounds on the pcb) and this was the reason for some noise.
I just installed a pair of these into amps made of hypex ucd180 (also without resistor in between the two grounds on the pcb) and this was the reason for some noise.
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