Film-Tech Forum ARCHIVE: Dolby CP55 help

This is topic Dolby CP55 help in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=010766

Posted by Tom Wise (Member # 6031) on 01-03-2011, 12:11 PM:

Hi,
A friend of mine has recently taken over a small cinema and asked me to take a look at the sound system. Following an initial inspection of the gear I noticed that the backplane of their CP55 had been modded. My background is in the pro-audio industry (live bands etc.) so I have a good idea what most of the equipment does, however my knowledge of cinema-specific kit is limited, so I was hoping someone here may be able to assist me in identifying what exactly has been done to the unit.

Fullsize image (c.567kB)

After some brief Googling on the subject it looks like there are a few mods available for CP55's, although none that I have found seem to match what has been done to this unit. I understand that some mods require changes to the cards, which I didn't know or think to check last time I was there. I can go and take photos of these as well if the attached photo is not enough to go on.

Any assistance or links to information would be gratefully received.
Many thanks in advance,
Tom

Posted by Steve Guttag (Member # 268) on 01-03-2011, 12:46 PM:

The red wire in your drawing is for the Cat 222SR/A modification.

The non-red wires (could be gray, could be white) are for the Cat 441 modification found in the DA10 or DA20 manual.

-Steve

Posted by Sam D. Chavez (Member # 1841) on 01-03-2011, 12:48 PM:

The CP55 backplane has been modified to install a Cat. No. 441 in place of the 241. The point of this mod is to allow stereo surrounds as well as an external subwoofer input for use with SR.D and/or DTS/SDDS.

Posted by Steve Guttag (Member # 268) on 01-03-2011, 12:53 PM:

Jeeez Sam, you're slow!

The most scary thing on this CP55 are the bypass relays...they are the cursed STC white relays...known the world over for dropping out signals. Reference Dolby Field Bulletin 161.

-Steve

Posted by Tom Wise (Member # 6031) on 01-03-2011, 01:29 PM:

Steve & Sam - many thanks to you both for the quick responses and invaluable information. I will try and absorb the manuals before going to have another look at the system. It's an exciting learning curve!

@Steve - thanks also for the tip-off about the relays. Any chance you could point me in the direction of FB-161? I couldn't find it in the Equipment Manual Warehouse.

Tom

Posted by Steve Guttag (Member # 268) on 01-03-2011, 02:22 PM:

Tom, FB161 predates the fancy schmancy PDF world...however, I suspect that you might see it appear in the up coming weeks...just a hunch.

-Steve

Posted by Tom Wise (Member # 6031) on 01-03-2011, 05:36 PM:

Hi Steve,
Thanks, I'll keep an eye out for it...

Tom

Posted by Sam D. Chavez (Member # 1841) on 01-03-2011, 06:37 PM:

Steve,

It's earlier out here and you hadn't yet posted when I began my thoughtful reply so excuse me. [Wink]

Posted by Steve Guttag (Member # 268) on 01-03-2011, 08:15 PM:

[Smile]

Posted by Brad Miller (Member # 2) on 01-05-2011, 12:19 AM:

Guess nobody noticed FB161 was added to the warehouse yesterday. [Razz]

Posted by Kenneth Wuepper (Member # 1174) on 01-05-2011, 07:30 AM:

Hello Brad,

I caught it in the header for newly added posts.

Even though there was a warehouse additions header in the original page, this is a more complete listing feature.

Thanks
KEN

Posted by Tom Wise (Member # 6031) on 01-05-2011, 03:27 PM:

Thanks Brad. I was actually out at the cinema yesterday so didn't notice the new file. I'll give Dolby a call and see if I can get some replacements before the STC's give up.

As for the CP55, turns out it has neither a Cat 241 or 441 installed, so I guess that means no stereo surrounds, even with the backplane modification. Another thing to add to the shopping list...

Tom

Posted by Steve Guttag (Member # 268) on 01-05-2011, 07:07 PM:

Yep, no stereo surrounds, no subwoofer and no "EQ" on the mono surrounds you have left.

Good luck on the STCs...This is a bulletin that dates back about 25-years. Dolby has formally announced the discontinuation of support for the CP55 (and the other analog processors except the CP45).

A good (better actually) substitute relay is an OMRON G5V series. It is a 24VDC relay. They make three relays in that model and voltage...the difference is the coil resistance. It shouldn't matter which you use...the lower current relays taxing the 24V rail just a bit less.

-Steve

Posted by Tom Wise (Member # 6031) on 01-06-2011, 05:22 PM:

Hi Steve,

Many thanks for the relay info. I guess that trying to obtain a new Cat 441 card from Dolby is also going to be a dead-end. Apart from the Classifieds board here at Film-Tech, are there any other potential sources of cards for these old processors? Alternatively, are the schematics available?!

I can live without the EQ as it can be done further down the signal path, but the lack of split surround and sub outputs is a bit of a problem.
Does the lack of a subwoofer mean that the L, C & R channels are not being delivered in full-range (i.e. are the LCR outputs high-passed to cross-over with the subwoofer)?
Sub-question: Is this the case whether a Cat 241/441 card is installed or not (i.e. does the removal of the card switch the main outputs to full-range)?
Apologies for going off-topic. I can start another thread if this is deviating too much from the original thread title.

Tom

Posted by Gordon McLeod (Member # 33) on 01-06-2011, 05:58 PM:

The stage channels are always full range the sub foroptical is properly called optical bass extension(OBE) and is the sum of the Lt and Rt from the optical preamp it is passed through a filter and a downward expander and then a parametric eq

Posted by Tom Wise (Member # 6031) on 01-06-2011, 06:38 PM:

Many thanks for the clarification. I suspected it was something along those lines. I guess the front speakers really do sound that bad... [Roll Eyes]

Tom

Posted by Steve Guttag (Member # 268) on 01-07-2011, 05:37 AM:

There are Cat 441s floating around out there. I believe that BACP was to or perhaps is already producing Cat 441s. Sam Chavez could provide some more info on the status of that.

-Steve

Posted by Pete Naples (Member # 761) on 01-07-2011, 07:30 AM:

Tom, Dolby won't deal directly with you. You can only purchase through their dealer network.

Whilst I haven't supplied one for a while now, last time I asked there were new Cat441s available. This was probably 18 months ago now.

A well aligned CP55 with decent speakers etc, even without surround Eq and OBE shouldn't sound 'bad', not optimal but definitely not bad.

I'd suggest you contact a good local service engineer and have the system checked over from A chain to ears.

What's the projector sound head? Reverse scan? Jaxlite [Eek!]

Posted by Sam D. Chavez (Member # 1841) on 01-07-2011, 09:57 AM:

FYI, Dolby has 0 stock of CP65, 55, 200 and 50 parts. They were allowed to dwindle and the remainder discarded or sold off.

I have a little stock of repairiable boards and buy up used stock when I find it.

I usually don't sell boards outright as this depletes my repair stock but it does not hurt to check.

Posted by Tom Wise (Member # 6031) on 01-07-2011, 10:28 AM:

Thanks for the replies guys.

@Pete - I'm pretty sure it's the speakers that are the main weak link. They are old and too underpowered for the size of venue.
No idea what type of sound head it is. How do I tell? I'm new to the cinema game. Does this help? (Apologies for the image quality)

@Sam - thanks for the info, I'll drop you an email shortly.

Posted by Pete Naples (Member # 761) on 01-07-2011, 12:24 PM:

OK That is a Westrex or Monee, hard to tell from the photo. Essentially the same thing.

Judging by the wee yellow sticker on the exciter housing door, it's been fitted with an ACL Cine Laser, those stickers came as part of the kit. Now assuming it's in good alignment then that sound head is capable of more than acceptable results. We're the UK agents for those lasers so hopefully it was fitted by one of our guys.

As for that lamphouse..... [puke]

About the supply of Dolby cards, Sam are you sure that is the case worldwide? I obtained a Cat441 for a customer just 6 months ago from Dolby UK, and a Cat150F for the same customer just a month or so after the 441. They were new, old stock. Dolby were selling them with 90 day warranty.

There is a company here in the UK who are repairing the cards that Dolby won't touch, very useful!

Posted by Sam D. Chavez (Member # 1841) on 01-07-2011, 05:58 PM:

Glad to hear there is some stock from Dolby UK and happy to stand corrected.

I was told they were depleted and the remainder dumped as happened in the US. I was able to obtain what was left of the US repair stock for my own repair efforts.

Glad to hear there is a hoarder on your side of the pond.

Posted by Pete Naples (Member # 761) on 01-08-2011, 04:47 AM:

Might not still be the case, I'll find out for certain!

Posted by Tom Wise (Member # 6031) on 01-10-2011, 05:33 PM:

Thanks Pete & Sam. I'll keep checking the classifieds board for them...

Posted by Pete Naples (Member # 761) on 01-11-2011, 03:59 AM:

Sam, it is I who must stand corrected. They are now all gone [Frown]