Connecting unbalanced source to balanced inputs (paging bob lee?)

ThrashMaster · #1 07-08-2010, 09:35 AM

I have an older QSC RMX 1450. The only inputs it has are balanced trs connectors. I currently use an SWR sm400s bridged mono. Id like more power, hence the seperate power amp. The SWR has a balanced xlr DI output and an unbalanced preamp output. What is the best way for me to connect these two. Id really like to keep the DI output for sending to mixing boards, as I think its one of the best sounding DIs out there.

Suggestions?

BassmanPaul · #2 07-08-2010, 09:58 AM

Plug the unbalanced 1/4 inch plug into the TRS of the power amp. Simple as that.

Paul

M0ses · #3 07-08-2010, 09:59 AM

+1. I don't think that the XLR would do a good job of driving the amp anyway, it's Hi-Z.

ThrashMaster · #4 07-08-2010, 10:01 AM

haha, really? I just assumed id need to have a balanced signal going into the balanced inputs. I tend to waaaaaaay overthink things so....thanks

BassmanPaul · #5 07-08-2010, 10:16 AM

Quote:

Originally Posted by M0ses

+1. I don't think that the XLR would do a good job of driving the amp anyway, it's Hi-Z.

It's not the impedance that's problem it's the amount of signal level. BTW DI XLRs are designed to feed a low impedance input at line level (usually) of a PA mixer.

Paul

bongomania · #6 07-08-2010, 10:26 AM

The only issue with connecting unbalanced 1/4" to a balanced input on a power amp is there is typically 6dB less signal going to the power amp that way. So if you fire it up and find that it sounds not quite as loud or ballsy as you expected, or if the signal indicator lights on the power amp aren't lighting up as much as you expected, then the reason is probably the unbal->bal connection. To fix that, Rapco, Whirlwind, and [sfx] make boxes which convert line-level signals from unbal to bal.

ThrashMaster · #7 07-08-2010, 10:33 AM

could you give a link to one such product? All i seem to find online for converting unbal to bal are di boxes...

Bob Lee (QSC) · #8 07-08-2010, 10:35 AM

The RMX1450 has XLR balanced and TRS (1/4") balanced inputs. Balanced inputs can be run unbalanced, too, so if you have a preamp with, say, an unbalanced 1/4" output, a good way to connect it would be to use a short shielded cable with 1/4" TS plugs.

bongomania · #9 07-08-2010, 10:51 AM

Quote:

Originally Posted by ThrashMaster

could you give a link to one such product? All i seem to find online for converting unbal to bal are di boxes...

http://whirlwindusa.com/catalog/blac...r-and-balancer

http://www.sfxsound.co.uk/mainpage.asp?page=thumpinator

Note though that you'll only need something like this if there's an issue with the levels. There may be no problem in any one specific case.

Bob Lee (QSC) · #10 07-08-2010, 10:56 AM

Quote:

Originally Posted by ThrashMaster

could you give a link to one such product? All i seem to find online for converting unbal to bal are di boxes...

I don't think you'll need anything other than a cable.

RickenBoogie · #11 07-08-2010, 05:24 PM

It hasn't been mentioned, but I assume you want more power because you want more volume? If so, more speakers are what you really need- unless the SWR has it's own cab, and now this poweramp will also have it's own cab to run.

ThrashMaster · #12 07-09-2010, 09:54 AM

the swr head will be running a goliath sr and the qsc will be pushing a 2 2x15 subwoofer cabs

Rick Auricchio · #13 07-09-2010, 10:11 AM

I presume you have a crossover to feed the subs only the range they cover, and to limit subsonic frequencies that can destroy them.

Most subs cover up to perhaps 250Hz; feeding anything above that just heats them up. The thump from a slapped string can overextend a sub's cone.

ThrashMaster · #14 07-09-2010, 10:22 AM

the subs are getting everything between 30 and 100hz. Over that goes to the swr, and I have a rumble filter already that kills everything below 30.