# Sub amp input sensitivity question...



## vanderschel (Dec 27, 2012)

I've ordered a Crown X-3000 (same specs as the Crown XLi 2500) to power a pair of SVS 16-46 passive subwoofers. I'm currently using a QSC RMX850, but I have to step up the voltage for it to work w/ my Yamaha AVR. I'm using a Behringer Xenyx to do the step up, but I'd like to eliminate it from the signal path. Here's the info:

Yamaha subwoofer output: 1.0V
QSC input sensitivity: 1.15V

Crown input sensitivity (switchable): 0.775V or 1.4V

Will there be any problems using the Crown's input @ 0.775V?


----------



## AudiocRaver (Jun 6, 2012)

Looks like it should do exactly what you want it to.


----------



## tcarcio (Jun 27, 2007)

If your Yamaha has an output voltage of 1.4v or more than I would use that. I use 1.4 on my crown amp and it works perfectly.


----------



## vanderschel (Dec 27, 2012)

It doesn't, it only puts out 1.0V to all the pre-amp outs. I don't want to replace the Yamaha just yet, but I probably will in the near future. I'm just using it as a pre/pro for the most part, I only use it's amp to drive the surrounds.

Which Crown amp are you using? Didn't see it on your list.


----------



## Insearchof (Oct 21, 2014)

I'm using a Crown XLi with my Yamaha and have tried the amp input sensitivity switch at both settings. 
My Yamaha is also rated at 1volt at the preouts and it works fine with the Crown set to either. 
Most receivers output more than the preout spec.
I left it at .775 after trying both.


----------



## tcarcio (Jun 27, 2007)

vanderschel said:


> It doesn't, it only puts out 1.0V to all the pre-amp outs. I don't want to replace the Yamaha just yet, but I probably will in the near future. I'm just using it as a pre/pro for the most part, I only use it's amp to drive the surrounds.
> 
> Which Crown amp are you using? Didn't see it on your list.


I was useing the Crown CTS-600 but I recently replaced it with a QSC-GX5. I used the 1.4 volt for the input and got all the power out of that amp with ease. I am not sure if useing the lower voltage will reduce the output of the amp or not. I would call Crown to be sure.


----------



## vanderschel (Dec 27, 2012)

Thanks for the reply. I noticed a post on another forum that the lower input sensitivity resulted in a *noisier* signal, but they were driving mains. It appears that fan noise is negligible w/ the Crown.


----------



## tcarcio (Jun 27, 2007)

vanderschel said:


> Thanks for the reply. I noticed a post on another forum that the lower input sensitivity resulted in a *noisier* signal, but they were driving mains. It appears that fan noise is negligible w/ the Crown.


Yes the Crown I was useing was dead silent. If I didn't replace it I would still be useing it for sure. I am selling it now. If you decide to go with the 1.4v setting you can use a Rolls MB-15 to bump up the signal. They work great. I don't need them now so if you decide to do that I have 3 of them I am selling. So if your interested let me know.


----------



## Insearchof (Oct 21, 2014)

vanderschel said:


> It appears that fan noise is negligible w/ the Crown.


Mine is fairly quiet. If the living room is dead quiet, I can detect very slight fan noise when I have been really pushing it for an extended period but since this setup is in my living room that is open to an attached kitchen, I hear noise from the fridge more than I do the amp when watching movies. With music, it's loud enough that I never hear the fan.
If my setup was in an enclosed dedicated theater room I suspect it may be a bit more noticeable.


----------



## vanderschel (Dec 27, 2012)

That is good news about the fan noise! I had to put the QSC in a cabinet, and I could still hear it. 

I don't think the input sensitivity affects the power output, it does make the amp more vulnerable to spikes. If the amplifier captures the signal at a higher sensitivity rating, I'd probably leave it there. 
I'd prefer to leave the signal path as uncluttered as possible.

I'm a novice, so I'm not giving advice.

Thanks again for the feedback!


----------



## AudiocRaver (Jun 6, 2012)

The input sensitivity setting does not affect max power out, it is basically a gain setting. It CAN affect your ability to reach a desired volume level if it is improperly set, making it seem like power output is limited, but it is a gain mismatch only.

The simple approach is to use the 0.775 V setting and use the level controls for the Crown to fine-tune the gain as needed. There is no real advantage to using the 1.5 V setting, although there might be enough gain that it works just fine.


----------



## vanderschel (Dec 27, 2012)

Thanks for your inputs, folks! I used the 0.775 V input setting and was able to remove the line-level boost. I'm impressed w/ the Crown; no hum, no hiss, and virtually no fan noise.


----------



## AudiocRaver (Jun 6, 2012)

vanderschel said:


> and virtually no fan noise.


Wish I could say the same about my Crown - getting ready to mod it with low-noise fans.


----------



## vanderschel (Dec 27, 2012)

AudiocRaver said:


> Wish I could say the same about my Crown - getting ready to mod it with low-noise fans.


I had that problem w/ the QSC, it sounded like my wife's hair dryer. I'm not sure why the XLi series is so quiet, but I'm satisfied.


----------



## AudiocRaver (Jun 6, 2012)

Some have low or high flow depending on heat dissipation level, the normal low flow level can be very quiet. Mine is high all the time. A quiet AC-powered fan should do it, plus I never push the amp anything like it is built to handle, so super high flow rate is not vital.


----------



## vanderschel (Dec 27, 2012)

AudiocRaver said:


> Some have low or high flow depending on heat dissipation level, the normal low flow level can be very quiet. Mine is high all the time. A quiet AC-powered fan should do it, plus I never push the amp anything like it is built to handle, so super high flow rate is not vital.


Yes, the QSC fans ran high all the time, too. The specs for the QSC shows fan speed as variable. The QSC is rated down to 2 ohms, whereas the Crown is only 4 ohms. I was wondering if that might have something to do with it. I'm obviously in the low end of the learning curve on this stuff.


----------

