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Topic: QSC SF-3 compatibility?

Amanda Mundin
Expert Film Handler

Posts: 122
From: Belper, Derbyshire, UK
Registered: Sep 2005

posted 02-22-2007 06:23 AM

I have a QSC ISA 750 amplifier operating in bridge mono powering my JBL 4642a subwoofer and purchased a QSC SF-3 subwoofer filter hoping to extend the bottom end response.

The QSC website states:

"The SF-3 subwoofer filter allows the addition of subwoofers to an existing full-range system, offering adjustable low-pass filtering and high-pass subsonic filtering with optional B6 boost and mono-summing. The unit mounts to the rear panel of a two-channel DCA, CX, or ISA amplifier to save cost and rack spack. "

Yet when asking a QSC engineer how I configure the SF-3 to install it onto the ISA750 I was told that the SF-3 is incompatible with the ISA series of amplifiers, and that even though there is a dataport on the back of the ISA amps that it won't supply enough power to work the SF-3 correctly.

Does anyone have an SF-3 running on an ISA series amp, and if so does it run successfully? And has it been powered by an external source?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 02-22-2007 08:12 AM

The ISA amps do have a crippled Data port but it should work with the XC-3 and SF-3 modules. The amplifier does supply it power and that should be present on the ISA series. The ISA does not provide complete information for the DCM monitors though and other devices that utilize the port for things other than just feeding a signal in.

For the SF-3 there are very few features. You will want to turn the B-6 filter on (LF Boost).

You will also want to make sure the proper SIP resistor network is installed. For the 4642A I normally go with the 25Hz HPF since the system really is starting to push it down to 22Hz however it is rated down to 22Hz with a boost. If you want to get that extra 3Hz then filter at 20Hz and know that what it can't reproduce comes off of power handling.

I normally also leave the LPF in at 250Hz...this keeps it well out of either optical or digital subwoofer region but also knocks down any hiss the cinema processor may have.

Steve

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Samuel Hynds
Film Handler

Posts: 50
From: Riverside, CA, USA
Registered: Aug 2004

posted 02-22-2007 12:47 PM

Just to set things right.

The ISA's DataPort is a not fully utilized version. This is why it is called a V2. It has 2 channels in & out (reduced version of the amplifier output) & limited 15VDC output. About 50mA - just enough to power the EX-3, LF-3 or SF-3 units - BUT we have seen some ISA not wake-up correctly with these units attached. Meaning the amplifier will not come out of 'protect' mode (with the clip L.E.D. dim). This could be due to the line voltage or age of the amplifier.

So - an ISA should work with a SF-3 (or XC-3, LF-3) attached; but just be aware of this issue.

Sorry for the conflicting information. [Wink]

Ciao,

Sam Hynds
Product Specialist, Cinema
QSC Audio Products, Inc.

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