Film-Tech Forum ARCHIVE: CP65 with no center speaker

This is topic CP65 with no center speaker in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Bernie Anderson Jr (Member # 410) on 04-21-2008, 04:37 PM:

I need an opinion on this. I have a theatre that only has a left, right and surround channel. The processor is a RGM industries processor. I can't find any manuals on this processor. It produces a phantom center channel using the left and the right channels. So its a L+R system that throws Center to both L+R. The sound is so bad in that theatre, I need to do something until we can get a center channel installed there.

So this is what I was thinking... Can I install a cp65 and jumper the center channel to both the left and right amps(remember there is only a L + R speaker behind the screen) and, still maintain a left and right channel at the same time? Does anyone have another suggestion?

Thanks

Bernie

Posted by Robert Minichino (Member # 3495) on 04-21-2008, 07:46 PM:

If you really need to do this, get a cheap mixer (something like this), and you can at least set your relative levels until you have a real center channel. Connecting the outputs of a CP65 directly together is a bad idea as you'll be shorting them together, potentially damaging the processor.

Posted by Steve Guttag (Member # 268) on 04-21-2008, 07:52 PM:

Oh, there is an even slicker solution than that...a CP65 can be wired C/S or L/R/S. Either way, it is done on the Cat 242 card.

When I'm back at the office, I'll look up the mods. Note, once moded, it is super-easy to restore the CP65 back to normal configuration.

Steve

Posted by Bernie Anderson Jr (Member # 410) on 04-21-2008, 09:41 PM:

Thanks Steve

That would be great and exactly what I need.

Bernie

Posted by Scott Norwood (Member # 30) on 04-22-2008, 09:50 AM:

I, too, would be interested in this mod.

Posted by Ken McFall (Member # 845) on 04-22-2008, 10:43 AM:

This mod was supplied to me recently when I asked for the same on a CP55.

see the topic : CP55 How to turn off matrix this is how UBB code keeps the page formatting normal

Remove the cat 150 card, the decoder card, as you will no longer require it for Left Right stereo use.

You then put a jumper on the Left & Right in on the back of the Cat 150 card and place the other end's onto the respective output terminal of the, now removed cat 150 card. This effectively bypasses the matrix but retains full noise reduction and normal operation of the CP65. It's also very easy to restore normal operation again by removing the jumpers and putting the card back in. This works perfectly in the location I've done it in.

I don't have a manual with the back plane of the CP65 to hand but it's very clear when you look at it.

Maybe Steve will be able to give the correct terminals to use.

[ 04-22-2008, 11:49 AM: Message edited by: Brad Miller ]

Posted by Steve Guttag (Member # 268) on 04-22-2008, 10:45 AM:

Well...I WAS going to tell you all and then Scott wanted it so forget it! [Embarrassed]

These mods work equally well for CP55 or CP65 since they are done on the same card...the Cat 242.

Center-Surround

Okay...the easy one For Center-Surround operation. Locate IC8. Jumper pins 5, 10 and 12 together and whola...it is Center-Surround processor. Left, Center and Right will all have the same signal at all times. When setting up the system, only use the Center channel from the Cat 85 to set 85dBc.

Left, Right and Surround

You will need two 6.8K resistors (1/4 or 1/8th watt should do).

Locate IC8. Place one of the resistors between pins 8 and 12.
Place the other resistor between pins 5 and 8.

When tuning up, first calibrate Left and Right for 85dBc each...when you turn on just the "C" channel on the Cat 85, you should also have 85dBc.

Since nothing is cut with either mod, they are completely reversable.

Steve

[Edit for response to Ken]

The CP-55 is wired a little differently than the CP-65 in this respect since the CP65 was SR aware.

For the CP55, Lt-in is pin 10, L-out is pin 4. Rt-in is pin 7, R-out is pin 6.

For the CP65, Dolby used both the 300mV and 500mV inputs simultaneously! So, from a gain structure standpoint, you have some differences and resistors in your way. I would start with pins 7 and 10 still for the inputs as they are the 500mV inputs...this is likely to be higher gain but some experimenting may be needed.

[ 04-22-2008, 12:43 PM: Message edited by: Steve Guttag ]

Posted by Brian Guckian (Member # 1678) on 04-24-2008, 03:30 PM:

quote: Bernie Anderson Jr
The sound is so bad in that theatre, I need to do something until we can get a center channel installed there.

FWIW, would it be OK to ask what the holdup is on doing that work? Is it possible to install the CP65 and add the speaker and / or amp at the same time? Do you have an available cable run already and / or a spare channel of amplification?

It's just that "temporary" mods have a terrible tendency to become permanent and the audience could end up stuck with "film done wrong" L/R/S for some time afterwards [Frown]

Also is your CP65 fitted with OBE so you can add a sub as well?