Reply to thread

Message

<blockquote data-quote="Bob Lee" data-source="post: 97562" data-attributes="member: 4707">Re: &quot;Interesting&quot; QSC RMX amp &quot;issue&quot;When you bridge an RMX amp, you must have channel 2&#039;s gain control turned all the way down OR have the inputs separate (i.e., in stereo). I always suggest doing both (unless you specifically need the inputs paralleled) to minimize the likelihood of user error.In bridge mono, channel 2 gets an inverse-polarity feed from channel 1, but if the inputs are paralleled and channel 2&#039;s gain control gets turned up, you&#039;ll also be summing what gets fed into channel 2&#039;s input (via the parallel inputs) with that inverse-polarity signal. If you turn the channel 2 gain control all the way up, you&#039;ll actually null out the normal-polarity and inverted-polarity signals, and channel 2&#039;s output will be zero. And then it will just act as a big virtual ground, sourcing and sinking the current from channel 1.However, there&#039;s also a bridged mono protection circuit that looks at the midpoint of the channel 1 and channel 2 outputs, which should be mirror images of each other. If that midpoint strays much from zero, it&#039;s likely that something&#039;s wrong in one of the channels and the circuit will mute the signal. (I don&#039;t think that&#039;s what&#039;s happening in the OP&#039;s situation; I just added it for informational purposes.)From Evan&#039;s description, it seems like the amp was not actually in bridged mono (or at least there was no feed from channel 1 to channel 2), but the inputs were parallel and the loudspeak(s) was connected across channel 1&#039;s and channel 2&#039;s hot outputs (i.e., the two red binding posts or 1+ and 2+ on the upper Speakon output); that&#039;s the only scenario I can think of that would cause such behavior.</blockquote>

[QUOTE="Bob Lee, post: 97562, member: 4707"] Re: "Interesting" QSC RMX amp "issue" When you bridge an RMX amp, you must have channel 2's gain control turned all the way down OR have the inputs separate (i.e., in stereo). I always suggest doing both (unless you specifically need the inputs paralleled) to minimize the likelihood of user error. In bridge mono, channel 2 gets an inverse-polarity feed from channel 1, but if the inputs are paralleled and channel 2's gain control gets turned up, you'll also be summing what gets fed into channel 2's input (via the parallel inputs) with that inverse-polarity signal. If you turn the channel 2 gain control all the way up, you'll actually null out the normal-polarity and inverted-polarity signals, and channel 2's output will be zero. And then it will just act as a big virtual ground, sourcing and sinking the current from channel 1. However, there's also a bridged mono protection circuit that looks at the midpoint of the channel 1 and channel 2 outputs, which should be mirror images of each other. If that midpoint strays much from zero, it's likely that something's wrong in one of the channels and the circuit will mute the signal. (I don't think that's what's happening in the OP's situation; I just added it for informational purposes.) From Evan's description, it seems like the amp was not actually in bridged mono (or at least there was no feed from channel 1 to channel 2), but the inputs were parallel and the loudspeak(s) was connected across channel 1's and channel 2's hot outputs (i.e., the two red binding posts or 1+ and 2+ on the upper Speakon output); that's the only scenario I can think of that would cause such behavior. [/QUOTE]

Verification