hi,

I am looking for some ideas in relation to a system I have inhereited in
which there are several HY60 hybrid 30W audio amps connected to a split
power supply. They all share a common ground - one amp is physically located
some 10 metres away from the common point of the power supply.

When the system is fully powered this all works okay. The remotely located
amp can have the power removed from its two power rails leaving it still
attached to the signal ground - AND still with an input signal applied. When
this happens, popping is noticed after some time from the other amps
connected to that signal ground. The popping is intermittent and may be
30-60 secs apart.

I guess the long signal ground lead is less than ideal although system noise
is low when powered up. I am wondering if the open power rails allow some
sort of capacitive discharge originating either from the input signal or
from signal ground noise.

Any ideas appreciated.

Martin

In article
,
"Unknown" wrote:

hi,

I am looking for some ideas in relation to a system I have inhereited in
which there are several HY60 hybrid 30W audio amps connected to a split
power supply. They all share a common ground - one amp is physically located
some 10 metres away from the common point of the power supply.

When the system is fully powered this all works okay. The remotely located
amp can have the power removed from its two power rails leaving it still
attached to the signal ground - AND still with an input signal applied. When
this happens, popping is noticed after some time from the other amps
connected to that signal ground. The popping is intermittent and may be
30-60 secs apart.

I guess the long signal ground lead is less than ideal although system noise
is low when powered up. I am wondering if the open power rails allow some
sort of capacitive discharge originating either from the input signal or
from signal ground noise.

Any ideas appreciated.

Martin

The unpowered amp is clipping the line level input; sucking power from
it. It could be caused by input protection diodes that are designed to
prevent the input from exceeding the power rails, which are nearly zero
when it's off. It could also be the natural diode paths in junction
transistors.

You'll need a relay to disconnect the shared audio line or you'll need
an audio distribution amp to isolate the distortion.