Film-Tech Forum ARCHIVE: QSC USA 900 question.

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Posted by Paul G. Thompson (Member # 655) on 09-08-2002, 12:37 AM:

I don't have documentation on that amplifier. Dip switch No. 1 and 2 indicates the amplifier is configured for a "Parallel mode". Am I to presume the parallel configuration will allow me to drive the left channel only and have an output from both sides of the amplifer? This amplifier is used as a split surround amplifier. The DTS6AD died, and I have to finish temporarly replacing it with a Dolby CP-55.

Thanks

Posted by Daryl C. W. O'Shea (Member # 1303) on 09-08-2002, 12:46 AM:

I've never seen a USA amp but on any other amp I've ever used parallel mode does exactly what you have presumed. The left input is output on both sides (left and right) of the amp outputs.

Posted by Antonio Marcheselli (Member # 373) on 09-08-2002, 04:43 AM:

And what is the difference between "parallel" and "bridge" mode? Impedance range?

Bye
Antonio

Posted by Brad Miller (Member # 2) on 09-08-2002, 04:50 AM:

Antonio,

Stereo...2 inputs, 2 outputs

Parallel...1 input (usually the left channel), 2 separate outputs (this is just like using a "Y" cable and sending the same signal into the left and right inputs with the amp in stereo mode)

Bridge...1 input, 1 output, but using "both sides of the amp".

Paul,

Wish I could help, but I stick to QSC's MX and DCA line.

Posted by Phil Hill (Member # 371) on 09-08-2002, 05:34 AM:

Documentation can be found at the excellent QSC website by clicking on the "LINKS" at the left.

Posted by Steve Guttag (Member # 268) on 09-08-2002, 02:41 PM:

Note, with Crown amps, parrallel means for driving low current (down to 1-Ohm) on some models. QSC has always used it for omitting the y-cable as Brad described.

Steve

------------------
"Old projectionists never die, they just changeover!"

Posted by Dave Macaulay (Member # 813) on 09-09-2002, 10:34 AM:

Parallel sends the same signal to both channels, this is just like using a Y-cord as already mentioned. There should be no output signal measured between the 2 channel's "hot" terminals.
Bridge turns a stereo amplifier into a mono amplifier. Both channels get the same signal, but one is inverted so that the output is taken from between the 2 "hot termionals and the ground terminals are not used. This mode requires that all wiring is separate with no ground returns or common lines - but separate wires are standard in theatre installations as far as I know.

Posted by Antonio Marcheselli (Member # 373) on 09-09-2002, 12:29 PM:

Brad, Thanks

Steve, I understand now! I only saw the parallel mode on my crown 2401 and means exactly what you wrote. I didn't knwo that is just a crown option. Thanks!

P.S. Noone answered my previous post, let me try again! How can I found the circuit schematics of my crown 2401?

Bye
Antonio

Posted by Paul G. Thompson (Member # 655) on 09-09-2002, 12:36 PM:

Thanks, Gentlemen. It worked as suspected. One signal drives both channels when configured with the dip switches.

Posted by Gordon McLeod (Member # 33) on 09-09-2002, 10:14 PM:

Some manufacturers do not release there schematics so you must contact them

Posted by Manny Knowles (Member # 1171) on 09-09-2002, 10:56 PM:

Dave wrote:

quote:
This mode requires that all wiring is separate with no ground returns or common lines - but separate wires are standard in theatre installations as far as I know.

Please explain this for me. I'd like to understand it better.

Posted by Paul G. Thompson (Member # 655) on 09-10-2002, 01:02 AM:

Manny, I think Dave is saying that no speaker wiring is referenced to ground.

With most amplifiers I have seen operating in the bridged mode (it has to be a bridging amplifier) one side of the speaker goes to the positive post of the left channel, and the other side of the speaker connects to the positive post of the right channel. You ignore the black output posts of the amplifier in the bridged mode.

In the parallel mode, both sides operate separately but are common to the input on either channel. Just like connecting a "Y" cable as someone suggested earlier.

Gordon said:

quote:
Some manufacturers do not release there schematics so you must contact them

That really frosts my you-know-what! I ranted about that subject in an earlier thread. I hate that type "protectiveness" on the manufacturer's part when I am trying to get something running!

Manufacturers who pull that stupid head game are the ones I try to stay clear of. I wish they would wake up!

Posted by Antonio Marcheselli (Member # 373) on 09-10-2002, 02:28 AM:

Gordon,

Do you know that Crown do not public their schematics (so I'll stop searching) or is it just a thought?

Crown has helped me much by e.mail but, as often happen, they stopped replying after few messages...

Bye
Antonio

Posted by Manny Knowles (Member # 1171) on 09-10-2002, 08:13 AM:

Thanks, Paul. I understood that part about using the positive terminals only. I was curious about the other stuff...separate wires, common lines, etc.