Film-Tech Forum ARCHIVE: Replacing Cat 108 with 108c

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Posted by Warren Smyth (Member # 1838) on 02-13-2004, 03:31 AM:

I have just received an exchange card for my faulty SPARE Cat 108 from Dolby. The new one is a 108c which I understand is an upgrade which is probably good news. If there is any benefit in so doing, I thought I might bring the 108c into active service and put the currently used pre-amp card which is a 108, into the spare backup slot

I'm using a CP50 which I have upgraded for SR with Cat 180s (after mods). Will the 108c perform better, will it draw more current? Are there any differences between the 108 and 108c that I need to allow for? Is the slit correction provision the same?

Posted by Mark Gulbrandsen (Member # 72) on 02-13-2004, 08:23 AM:

Do you also have a 113C automation card? This is the card with the touch buttons and an LED in each button. If so then in my case where I had a 113C,150E, 2 cat 280T's and then when I added added a 108C one of my power supply rails sank so low the unit would not function corectly. If you already have the upgraded power supply unit then you are ok though. In my case I installed a large switching power supply for tighter regulation of the DC rails. It was better quality and alot less expensive.

Maark @ CLACO

Posted by Warren Smyth (Member # 1838) on 02-14-2004, 06:44 AM:

Thank you Mark. Yes I do have the 113c Automation card. My processor cards are 150B/146B.

As to whether I have the upgraded power supply, I'm not sure. It has the number 8406 on it's back plate. It has three secondary fuses at the front - 2amp for 24 volts, 1 amp fuses for +/- 12 volts.

The primary fuse is at the rear - 600 mv for 115 volts and in my case, 300 mv for 240 volts.

The push on off switch at the front is recessed behind the round aperture on the front plate which hinges along the bottom. By the way, the plastic hinge sections which engage the pivoting rod are broken, do you know if replacements are available for these older units?

I believe the 113c card is original, not a latter upgrade so I may be lucky and have the gruntier power supply.

Posted by Mark Gulbrandsen (Member # 72) on 02-14-2004, 09:59 AM:

Warryn,
The upgraded power supply is the 114C. The orignal supply is simply a 114. If you are eurnning all those cards in there a 114C is almost a must. If you ahev the older 114 in there measure all the rail voltages to be sure they are with in plus or minus 5% to 10%. On the older 114 supply one of the rails will really start to sag down alot.
My power supply problems became apparent up when I plugged my 108C into my CP-50. I already had the 280T's and 113C in there. Some place here on Film-Tech there is a photo of my CP-50 switching supply upgrade. I did a search but couldn't get it to come up....

Mark @ CLACO

Posted by Warren Smyth (Member # 1838) on 02-15-2004, 05:13 AM:

I've removed the power supply and found that it is a 114c however I also checked the voltages and the results are not good.

With No load at all; -13.7v, +13.8v, +30.1v
with original cards(108,22,150b/146b,113c);-10.5v, +10.8v, +26.6v
with upgrades (108c,280T,150b/146b,113c); -10.3v, +10.6v,+26.1v

As you can see, the 24v rails are over and the 12v is well under even without the upgrades. Do you think I have a fault? There is no significant hum but I do have very slight distortion on very high peaks which is not apparent on bypass. (Dolby level is correct).

I found your details of the Power One supply with data sheet - looks good. I will check out availability over here.

Posted by Mark Gulbrandsen (Member # 72) on 02-15-2004, 10:59 AM:

Warren,
I think you'll be ok at those figures. Try it and see how it goes before replacing the power supply as the 114C is an expensive piece. The unloaded voltagesa re always higher by a considerable margin so that the voltages under load are still with in reason, I believe on mine the 12 volt rails actually went down to around 9 volts and the 24 volt rail was around 20 or so. The mod with the Power One supply has them rock solid at plus and minus 12 and 24. The advantage with a regulates supply such as the power one is that there is also over current and over temp protection. Although it does get hot during operation it has been just fine. I initally left it on for 6 months straight. Fitting it in is a bit tricky but it could be outboarded as well and then just plugged into the power connector on the back plane.

Posted by Matt Zeiner (Member # 1914) on 02-15-2004, 11:55 AM:

I would think that you would be losing some headroom running with +/- 9v rails...Mark - does the unit you have with the tightly regulated rails perform better? just curious.

Posted by Sam D. Chavez (Member # 1841) on 02-15-2004, 12:06 PM:

The cat. 108C is a slight improvement over the 108 and I believe the low pass filter was moved out for better HF response and perhaps improved LF response although I can't remember the details.

The main change was to fix a high freq. crosstalk problem on projector 2 having to do with the board layout.

I'm surprised you still have a healthy 150B working. An upgrade of this card to C and above would be very noticeable on channel separation.

Posted by Warren Smyth (Member # 1838) on 02-15-2004, 03:22 PM:

Mark, I will still look at getting a power supply as an out board spare backup. The one you suggest is probably cheaper than the Dolby out board spare.

quote:
I'm surprised you still have a healthy 150b working

The card is an exchange of about five years ago so may have been old new stock. The original was stuffed when I bought the CP50. Would have been nice if Dolby had upgraded it to a 150c for me but I suppose I can't be lucky all the time. It seems from your comments Sam, the 108c is slightly superior so I will use it as my primary pre-amp.

Many thanks.

Posted by Mark Gulbrandsen (Member # 72) on 02-15-2004, 04:27 PM:

Matt,
I don't really hear any difference at home, but you can almost bet that it increases the head room a bit on the 517 and 64's. This is all a good thing for high quality SR playback. I don't use the 50 for digital playback but it would certainly not hurt there either. Good audio circuitry is always built around tightly regulated, sometimes very sophisticated power supplies. Adding the Power One supply sure takes the CP-50 into the sophisticated power supply realm. It was also alot cheaper than the Dolby 114C replacement.

Mark @ CLACO