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[Doug Moran]

I was helping a local school this evening with their older auditorium sound system.  The subs were not working.  The amp rack has four Crown Com-Tech power amplifiers.  The subs are driven by a Com-Tech 1600.  This amp is in Parallel-Mono mode, and the IOC yellow lights are lite on the front panel.  After power cycling the amps, only the 1right IOC light was on (channel 2, which looks to be what the manual I found on-line mentions).  Still the subs did not work.

The output wiring to the subs do not follow the manual.  The jumper between channel 1 and channel 2 positive (+) terminals is present (and nicely formed), but the installer years ago wired both channel 1 and channel 2 output terminals with 4 different wires.  I understand you only use the channel 1 output terminals in parallel-mono mode on these Crown amps.

It is a mono system, and everything is under the floor/stage with feeds coming out for the subs.  I cannot meter anything to see what is going where due to the distance between the wire ends.  Any idea why the channel 2 output terminals were wired, and perhaps to what?

Thanks - Doug

[Ivan Beaver]

I was helping a local school this evening with their older auditorium sound system.  The subs were not working.  The amp rack has four Crown Com-Tech power amplifiers.  The subs are driven by a Com-Tech 1600.  This amp is in Parallel-Mono mode, and the IOC yellow lights are lite on the front panel.  After power cycling the amps, only the 1right IOC light was on (channel 2, which looks to be what the manual I found on-line mentions).  Still the subs did not work.

The output wiring to the subs do not follow the manual.  The jumper between channel 1 and channel 2 positive (+) terminals is present (and nicely formed), but the installer years ago wired both channel 1 and channel 2 output terminals with 4 different wires.  I understand you only use the channel 1 output terminals in parallel-mono mode on these Crown amps.

It is a mono system, and everything is under the floor/stage with feeds coming out for the subs.  I cannot meter anything to see what is going where due to the distance between the wire ends.  Any idea why the channel 2 output terminals were wired, and perhaps to what?

Thanks - Doug

If you are talking about the mode where you can drive a 1 ohm load, the OUTPUTS of the channels must be strapped together.

Run a 12 ga wire between both + (red) terminals.

The inputs don't matter-only channel 1 is used.

The switch puts the output sections together from the channel 1 drive.

So if 1 sub is on channel 1 and the other on channel 2 (which it sounds like), the one on channel 2 is not getting any signal unless the output strap is in place.

It is a simple case of 2 subs (1 on each channel), I WOULD NOT run it in parallel mono mode.

I would put it in "dual" mode, and tie the inputs together (which it sounds like is already done).

That way each sub has its own channel and they are driven by a common input.

[Doug Moran]

If you are talking about the mode where you can drive a 1 ohm load, the OUTPUTS of the channels must be strapped together.

Run a 12 ga wire between both + (red) terminals.

The inputs don't matter-only channel 1 is used.

The switch puts the output sections together from the channel 1 drive.

So if 1 sub is on channel 1 and the other on channel 2 (which it sounds like), the one on channel 2 is not getting any signal unless the output strap is in place.

It is a simple case of 2 subs (1 on each channel), I WOULD NOT run it in parallel mono mode.

I would put it in "dual" mode, and tie the inputs together (which it sounds like is already done).

That way each sub has its own channel and they are driven by a common input.

Thanks Ivan.  I think it is set up correctly for Crown's Parallel mode, with the exception of the output of channel 2 being wired up.  If I put the amp in dual mode, and had the same input to both channels, I would need to remove the jumper currently installed from the plus terminals of both channels output. 

My initial question is why they wired anything to the output terminals of channel two.

There is a PIP card installed that I don't have the model number of right now.  It has an XLR input and an XLR output on it.

I suspect the Com-Tech 1600 needs some repair.  The front filters on all the amps in the racks are full.

Thanks - Doug

[Doug Moran]

I think I found the answer in an old post on the Crown forum:

"When set for Parrallel-Mono and the jumper is in place all the output jacks are the same output as they are combined. The speaker load is then connected to a positive and negative, like normal, as the amp is now a large MONO amplifier."

Most likely the installer used the outputs from both channels simply to allow them to use two separate runs to the subs.   All is good in my mind now, well, almost.  :-)

Thanks again - Doug

[Jean-Pierre Coetzee]

I believe this would just run the subs in parallel same as if you looped though from one to the next with a normal cable.

Whether this is actually the best possible solution would depend entirely on the rest of the setup.

From what I know running the two channels in parallel gives you the same voltage but double the current at the outputs, if this is any better than just running the amp in stereo I don't know.

[Ivan Beaver]

I believe this would just run the subs in parallel same as if you looped though from one to the next with a normal cable.

Whether this is actually the best possible solution would depend entirely on the rest of the setup.

From what I know running the two channels in parallel gives you the same voltage but double the current at the outputs, if this is any better than just running the amp in stereo I don't know.

If there are 2 speakers, with 2 cables, then the "total outcome" would be same whether you run it in 2 channel or the parallel mono mode-ASSUMING they are low freq devices.

What is not "talked about" is that the amp starts to fall apart around 5Khz when in the parallel mono mode.

That is why I suggest the 2 channel mode.

If you only have 1 cable and 2 speakers, THAT is where the parallel mono mode comes in handy.

Despite what some people want to believe, you do not get any power increase into a specific load when in parallel mono.  You ONLY get the "extra power" when you add more speakers.

[Doug Moran]

I think we have this figured out, at least for now.  Both of the IOC lights were on initially.  What happened after coming back the next day and powering everything up was only the channel 2 IOC light was on, which matched the Crown manual instructions.  Using my DI's and input source, everything worked.  Someone had the sub amp output level all the way up, and the system was not balanced at all, all boom.  Turning down the level helped tremendously, and we settled on about a 25% reduction.  I suggested they lock the amp rack cabinet for those visitors using the system.

This issue came to light when the "subs didn't work with the CD player" up in the booth.  That was still the case after what we did in the paragraph above.  Testing each of the 24 inputs on the EV BK-2442 mixer (I think that is the model number) showed the line lever inputs sounded like they were going through a severe low pass filter, and the mic pre-amps (using DIs) sounded fine.

I suggested they look at buying a new mixer and consider getting someone in to look at the amplifiers, perhaps give the system a little TLC.

Thank you for your help!

Doug

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