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The balanced line input will be used for long runs to eliminate noise. it is low impedance.the high impedance line (unbalanced) is ok for sort runs such as in a rack. if you were say running output from a mixer 50' away you want to use the balaced output on the board and the balanced input on the amp.
You do not mention whether you use one or several inputs on the SA620, but move the selector switch to & fro a few times to clean its contacts. Similarly, unpIug the phono plugs & replug (on Left channel). I aIso assume there is no left channel when using headphones. Also check the two thick wire links at the back are pushed in properly (take out & push back in to make sure), since these link the preamp to the power amp. All the above is done with mains power off.
On these old units, switches sometimes fail due to impurities on their
contacts, so operate them all (with mains OFF) a few times to wipe the
It would be informative to find out if the fault is in the preamp or power amplifier section. To do this, connect signal (eg external CD) to the TAPE 1 'PLAY' input (left) & switch front panel to TAPE 1. This bypasses the preamp section & injects the signal into the volume control. If there is still no left- hand channel, then the fault is likely to be in the power amplifier.
Only if you are technically competent, disconnect SA620 from mains, remove the SA620 lid, and with an insulated object eg a plastic screwdriver handle, tap the loudspeaker relay RL1 to release a possible sticking contact. If this does not cure the fault, then the same can be done with the unit turned on & a signal present.
If there is still no response, further fault finding in the power amp will be req'd.
The XTI 2k has lots of DSP options built into the front panel. If it's your intent to run the amp in bridge mono for subs be sure than you have all settings set correct for the DSP, it's very possible that channel 2 will render in-active.
This also applies in the case if you wanted to run your subs in stereo and the internal settings are set for bridged mono.
Another possibility would be if the DSP was set with a crossover. If you put a cross-over point (Low Pass Filter) on the high side of the sub, if becomes the High Pass Filter of Channel 2. Audio would pass if there was no other filter sets, but would not if you were using a crossover and then hitting the subs.
It sounds more like you are overdriving the speakers not clipping the amp. If the output rating for the amp is 1000W into 4 ohms, this is approximately 500W into an 8 ohm load. Your speakers are rated for 400W. If you are running the amp at full output, that is too much power for the speakers and either the speakers are warming up too much and failing or are being extruded too far and failing. Your best bet is to better match the amp/speaker setup. Crown amps have built in clipping indicators and I believe that the xti series also has a compression circuit that would prevent distortion on the output side.
To confirm my suspicions, in what manner are the speakers failing? Are they completely open or do they sound distorted?
This is most likely to be a heat issue where the amps overheat and shut themselves off then cool down and turn back on. Please check that the amps have proper ventilation and that any air ducts are clean.
The amplifier is going into protection. This may be caused by problems with speakers or wiring, or there may be internal problems in the amplifier. Start by connecting a known good speaker with a few feet of wire, and see if it runs without shutting down. If so, check the wiring and speakers. If the problem continues, the amp should be serviced.