"Bleed" and grounding
2018-04-18 by Malte Rogacki
Hello everyone;
I've tried to delve a bit deeper into those issues. Turns out they are
somehow related (at least on my machine).
The "oscillator bleed" I described earlier (that was present even when
volume was fully turned down and the output switched off) and a lot of
other noises disappeared when using an audio isolation transformer (a cheap
Behringer "hum destroyer") between Polysix and amplifier.
This is somewhat remarkable since the whole Audio setup is pretty basic:
both the Polysix and the amp (I tried different ones) are powered from the
same outlet; there are no other devices involved. So the chance of getting
a bona fide ground loop causing such behaviour is pretty slim.
Hence I suspect that there still is someting wrong with grounding of this
particular unit. Even more so since there is another problem that the "hum
destroyer" did not get rid of:
While using the "hum destroyer" cleaned up the sound in a major way I
noticed clearly audible RFI (or something similar) when turning the volume
way up (with the volume switch in the "high" position). While working
inside the Polysix this was not much of a problem; the interference was
pretty low then. But when closing the lid it became clearly worse.
Closer observation seems to point at KLM-369 and/or KLM-370 as the source
of the noise (KLM-371 does not seem to play a role here).
Moving the audio connection between KLM-367 and KLM-368 did not seem to
make a major difference though it seems to me as if the interference is
picked up mostly by KLM-367.
Any ideas? Should I move all audio related boards into a different Polysix
to check this further? Or are those already clear signs of some grounding
issue?
I've tried to delve a bit deeper into those issues. Turns out they are
somehow related (at least on my machine).
The "oscillator bleed" I described earlier (that was present even when
volume was fully turned down and the output switched off) and a lot of
other noises disappeared when using an audio isolation transformer (a cheap
Behringer "hum destroyer") between Polysix and amplifier.
This is somewhat remarkable since the whole Audio setup is pretty basic:
both the Polysix and the amp (I tried different ones) are powered from the
same outlet; there are no other devices involved. So the chance of getting
a bona fide ground loop causing such behaviour is pretty slim.
Hence I suspect that there still is someting wrong with grounding of this
particular unit. Even more so since there is another problem that the "hum
destroyer" did not get rid of:
While using the "hum destroyer" cleaned up the sound in a major way I
noticed clearly audible RFI (or something similar) when turning the volume
way up (with the volume switch in the "high" position). While working
inside the Polysix this was not much of a problem; the interference was
pretty low then. But when closing the lid it became clearly worse.
Closer observation seems to point at KLM-369 and/or KLM-370 as the source
of the noise (KLM-371 does not seem to play a role here).
Moving the audio connection between KLM-367 and KLM-368 did not seem to
make a major difference though it seems to me as if the interference is
picked up mostly by KLM-367.
Any ideas? Should I move all audio related boards into a different Polysix
to check this further? Or are those already clear signs of some grounding
issue?