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QSC 1804 "Parallel" Connection Question...

jokerjkny

jokerjkny

Jan 19, 2002
13,427
54
NY / NJ / PHL
www.instagram.com
#1
hey guys,

i'm sure mr. bob lee will chime in, but was wondering...

i know about using a TRS balanced .25" / .25" cable to connect the 1st and 2nd channels for a parallel output, but does it matter what i'm using into the 1st channel's input? in my case, its a TRS .25" / XLR female cable. course, its coming out the unbalanced output demeter hbp-1. ;)

kinda obvious i guess, but just want to make sure i dont blow anything up, cause i have, did, and most likely will. :p
 
#3
This surely will not hurt anything. If I'm not mistaken this will work but the signal will be unbalanced from one end to the other if the source is unbalanced. Basicly what Rick said.
 
#4
Yes, there's no way to (easily) turn the unbalanced signal into a balanced one.

Joker, a quick trick, if you can solder. Open the plug at the Demeter (unbalanced) end, and install a little shorting jumper between the Ring and Sleeve (ground) contacts. This will take care of it.

NOW make sure you mark the cable properly. The shorted end should go into the unbalanced device, and you don't want to accidentally use it for something else and get confused.
 
#5
nice guys,

my soldering skills suck. really. you DO NOT want to look at my last hatchet job.

the demeter pre does have a 1/4" balanced output jack, but i'm pretty sure the button in the back that flips XLR balanced output to the 1/4" balanced output, isolates each output, so its one or the other. cause i'd like to use the XLR out for PA use.

but do they make a *TS* .25"/XLR?

keep in mind, i'm already using the 1st channel's 1/4" jack to jumper to the 2nd channel's 1/4" jack.
 
#6
jokerjkny said:
nice guys,

my soldering skills suck. really. you DO NOT want to look at my last hatchet job.

the demeter pre does have a 1/4" balanced output jack, but i'm pretty sure the button in the back that flips XLR balanced output to the 1/4" balanced output, isolates each output, so its one or the other. cause i'd like to use the XLR out for PA use.

but do they make a *TS* .25"/XLR?

keep in mind, i'm already using the 1st channel's 1/4" jack to jumper to the 2nd channel's 1/4" jack.
Click to expand...

Hatchet job? You should have seen me trying to solder an LED today on a PCB that had a small Mini PCB on top of it so I could barely get to the Leads. Man what a pain that was. I remember one weekend while soldering a set of Patchbays into a local studio's console. I soldered 3,000 wires from Fri to Sunday. I was a nervous reck after that.


Yes they make a cable like that. It's the same as what Rick was saying by shorting the Ring to Ground it becomes TS.

I'm not familliar with your Preamp but I would think both outputs would be Low-Z and as soon as you plug in a 1/4" TS both become Hi-Z though maybe that is not correct. Most Power Amp inputs that I know of are like that and many Preamp Outs may be as well. Maybe the switch has something to do with loading.
 
#7
Just looked at the HPB-1 which switch are you talking about?


hbp1backlarge.gif


I believe the Line/Mic switch would have to do with db's and the Ground Lift is just taking off the ground from the output. The two Low-Z outputs should be coming from the same source and if you plug a Hi-Z (TS cable) in, the XLR would then be unbalnced as well. But looking at it you should be able to go Balanced all the way and still use the XLR for PA. Though if the two arent buffered there could be some loading. I'm not not real familiar with Lo-Z loading. perhaps someone could speak up about that.
 
#10
joker, I assume it's a PLX1804?

Rick Auricchio said:
You're fine, except that since the Demeter is unbalanced you'd be better to use a straight TS cable from Demeter to the QSC. This will properly ground the R (ring) contact, which is best when feeding an unbalanced signal.

If you use TRS, you may hear some noise picked up, because the R contact will be floating.
Click to expand...

What Rick said.

Yes, there's no way to (easily) turn the unbalanced signal into a balanced one.
Click to expand...

When you have an unbalanced source feeding a balanced input, you can get some of the noise immunity benefit of a balanced connection by using a quasi-balanced one:
quasi-balanced.gif


Of course, if you go this route, then the jumper joining the two channel inputs should also be balanced. If the connection between the power amp and preamp is short, though, there will probably be no noticeable improvement using a quasi-balanced connection instead of an unbalanced one.
 
#12
Bob Lee (QSC) said:
joker, I assume it's a PLX1804?



What Rick said.



When you have an unbalanced source feeding a balanced input, you can get some of the noise immunity benefit of a balanced connection by using a quasi-balanced one:
quasi-balanced.gif


Of course, if you go this route, then the jumper joining the two channel inputs should also be balanced. If the connection between the power amp and preamp is short, though, there will probably be no noticeable improvement using a quasi-balanced connection instead of an unbalanced one.
Click to expand...

yes, 1804! and i love it to pieces.

and again, big thx guys!
 

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