Film-Tech Forum ARCHIVE: Dolby CP50 up grade to SR and Non sync switching problem

This is topic Dolby CP50 up grade to SR and Non sync switching problem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Warren Smyth (Member # 1838) on 08-21-2003, 07:23 AM:

Can I upgrade my CP50 processor to SR noise reduction by simply replacing the CAT 22 cards with CAT 280 ones. More precisely, is the circuit to and from the edge connectors holding the Dolby A cards compatible also with the SR cards. Maybe this is too simple to be true.

If an up grade is possible this way, is further calibration of the processor required, or do both types of cards process at unity gain negating need for further adjustment?

Another question - The audio level, when the CP50 is switched to non sync fades up. Can the ramp time be adjusted? The fade up is a little too slow for my application as I am also feeding the non sync input with the mono signal from 16mm. I cannot find any reference to an adjustment in the manual I have which is actually for an earlier series. The switching card is a CAT 113C.

There are ways round the problem such as not using the non sync input but they involve other complications.

I would really appreciate any advice.

Posted by William T. Parr (Member # 677) on 08-21-2003, 07:46 AM:

quote:
Can I upgrade my CP50 processor to SR noise reduction by simply replacing the CAT 22 cards with CAT 280 ones. More precisely, is the circuit to and from the edge connectors holding the Dolby A cards compatible also with the SR cards. Maybe this is too simple to be true.

Yes you can Simply replace the Cat 22 cards for the 280 cards. It is that simple.

quote:
If an up grade is possible this way, is further calibration of the processor required, or do both types of cards process at unity gain negating need for further adjustment?

It is recommnded that a A Chain and B Chain be done after any kind of upgrades to any sound rack

Posted by Steve Kraus (Member # 476) on 08-21-2003, 07:46 AM:

Yes, you can have SR by replacing the Cat.22's with Cat.280T's. Note the "T". This means the card has been modified (by cutting a jumper near the edge connector) to force it to stay in decode mode. Both the 22's and 280's are capable of encoding and decoding but whereas the 22 is automatically in decode mode when placed in a CP, an unmodified 280 will unfortunately go into encode mode, in other words making SR more SR. If you acquire stock 280's and cut the relevant jumper please mark them "Modified for playback only Cat.280T" so anyone handling them in the future will know.

There is no need for other adustment except this: SR tracks are recorded at a lower level on the film to trade a bit of the improved noise floor for greater headroom (not unlike the way A tracks are lower than mono). So you will need to turn up the fader a few dB from where you normally play films.

Posted by Peter Hall (Member # 695) on 08-21-2003, 07:50 AM:

Kia ora !
(ex Kiwi tech in London - what site are you on )

Yes - stick a couple of 280T or CC280s in and you have SR. Let us know if you need pricing on cards - we have recond in stock

Re fade times, you can change this (rather make the mute function lag) on the CP55 etc by changing a resistor. Looking at the C113C cct (I can hardly read it) it looks like j101 shorts out R136 which drives op amp IC106c to give direct switching. I dont have a card at hand - can you tell me what IC106 is ? Maybe change R136, or perhaps R135 136 and C116 form a timed cct (or it C116 for decoupling ??). Let us know - interested to help

Peter

Posted by Warren Smyth (Member # 1838) on 08-21-2003, 08:46 AM:

This is an amazing site. I was sitting here at 1am when everybody around me was asleep, I posted a couple of questions, one of which even certified Dolby engineers here couldn't answer and within about 25 minutes I had three replies.

While waiting I found that Film Tech actually has the manual for the switcher card CAT 113C including circuit diagrammes. You see being a new chum, I'm still finding my way around. Yes, it does look as if fade time constants can be altered by changing the value of c115 and c116. Thanks a million chaps.

[ 08-21-2003, 08:18 PM: Message edited by: Warren Smyth ]

Posted by John Hawkinson (Member # 1135) on 08-21-2003, 01:01 PM:

The jumper to cut is a short wire (.10") labelled J801 (not S801, or near it), and its adjacent to pin 1/pin A of the card-edge connector. It seems you might find it installed on either side of the PCB. The gain for Dolby SR should be 3dB higher than for Dolby A. It's a good idea to run Dolby Tone with the Cat 22, and then run it again with the Cat 280 -- you should get the same exact results.

Can someone explain to me why the Cat280 goes into record mode when pin 1 is hot, unlike the Cat22? It seems so weird that it wouldn't be exactly backwards-compatible.

Oh, also, the Cat280 cards draw more current than the Cat22 cards, and they may push the limit of the CP50 power supplies, so it's good to check to verify your supply is still putting out full voltage.

--jhawk

Posted by Steve Kraus (Member # 476) on 08-21-2003, 06:51 PM:

Good question, isn't it? I don't suppose it could simply be a mistake.

As for power supplies anyone interested can do a search as there was some discussion by Mark G. and others about substituting a beefier supply on a CP-50.

Posted by Mark Gulbrandsen (Member # 72) on 08-22-2003, 10:40 AM:

Yea, You have to keep an eye on the rails when you are installing all thode new cards in place. The rails will really start to sag when you plug in the 280T's. I installed a 350 watt switching supply in the CP-50 in my home screening room which has given rock solid performance since I made the original posting about it. I think the CP-50 also sounds ALOT better than it did and the S/N also seems a bit better. If you install a new type 108 preamp card in addition to the 280T's and 113C the CP-50 will become unusable with the original supply!!

Posted by Warren Smyth (Member # 1838) on 08-24-2003, 08:52 PM:

quote:
The rails will really start to sag when you plug in the 280Ts.

I have been thinking of trying to get an emergency power supply for the CP50 as a back up. However, given the apparent lack of surplus capacity to run a 280T on the existing one, it seems logical to build a 350 watt supply. If this is connected in the same way as an out board emegency supply, I can still switch to the existing one in an emergency, and go back to the Cat 22 cards if there is a significant drop in supply voltage.

I will have to check the circuit details but I think from memory, plus and minus 12 volts are required as well as plus 24 volts. Mark, are there any complications you can for see, or any advice you can give in building the supply?

Posted by Tom Wienholt (Member # 1510) on 08-24-2003, 09:03 PM:

I am currently operating a CP50 with an updated 108 preamp, 280T's and a 113c automation card. This unit has the original power supply and I have had no problems with it.

Posted by Steve Guttag (Member # 268) on 08-25-2003, 06:14 AM:

The Cat 114C shouldn't have any problems though any previous Cat. 114 will start to show problems in the +/- 12 volt rails...they start at 14 volts without load and will sag below 10 volts if you upgraded everything...the hum starts in the surrounds (with the Cat. 560 installed).

As to the Cat. 280T...they shouldn't start your humming...I'm pretty sure they only use the +24 rail which is relatively un-taxed. The +/- 12 rails take hits from most other cards and the newer cards like the 517 and 560 and 113C have LEDs on them soaking up 20mA a pop so you are cutting in on valuable current for the sound.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 08-25-2003, 09:37 PM:

Its also proven sonic fact that regulated supplies do improve sound quality overall. Unfortunately, much of the important analog circuitry in the CP50 was lacking any regulated supply of any type. There was definately mor than a hint of improvement after I installed the regulated switcher that I was able to get. Of course it could also be easily outboarded and may be safer to do so.
Mark @ CLACO

Posted by Steve Guttag (Member # 268) on 08-25-2003, 10:41 PM:

Hey Mark, no arguement here...Having a set of regulated supplied makes a lot of sense...the power rails shouldn't be sagging as the SPI LEDs come on! Analog sound NEEDs clean power...it is where the sound starts.

Steve

Posted by System Notices (Member # 2357) on 06-17-2005, 06:12 PM:

It has been 661 days since the last post.