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<blockquote data-quote="keep_hope_alive" data-source="post: 8656957" data-attributes="member: 576029">Whine is typically from a ground loop or voltage potential on the signal ground relative to chassis.  When you connect the sub amp RCA you create a loop, which may be why the issue is only when both amps are connected. The loop may exist because the amp grounds are tied together and the amps internally tie RCA ground to chassis ground or not (loop vs. floating)  They may also exist due to damage in the RCA itself.  I&#039;ve seen RCA&#039;s made with incorrect solder connections.What if you feed the sub amp from the RCA outputs on the 4channel?  You lose sub level control but it is worth a try to narrow down the loop location.What happens when you run a wire between the two amps&#039; RCA shields?  This shouldn&#039;t be a problem if everything is OK. You can also use a DMM to measure resistance from the RCA shield to amp/chassis ground in each amp, an also in the RCA shield to amp/chassis ground.</blockquote>

[QUOTE="keep_hope_alive, post: 8656957, member: 576029"] Whine is typically from a ground loop or voltage potential on the signal ground relative to chassis. When you connect the sub amp RCA you create a loop, which may be why the issue is only when both amps are connected. The loop may exist because the amp grounds are tied together and the amps internally tie RCA ground to chassis ground or not (loop vs. floating) They may also exist due to damage in the RCA itself. I've seen RCA's made with incorrect solder connections. What if you feed the sub amp from the RCA outputs on the 4channel? You lose sub level control but it is worth a try to narrow down the loop location. What happens when you run a wire between the two amps' RCA shields? This shouldn't be a problem if everything is OK. You can also use a DMM to measure resistance from the RCA shield to amp/chassis ground in each amp, an also in the RCA shield to amp/chassis ground. [/QUOTE]

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