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We are currently running a Dolby CP 50 system. What are the cheapest options to uprade to Digital sound? I believe that DTS would be the cheapest, I heard their was an add-on that didn't require a new processor.

Should I go used or new? Do I need new speakers if I pump digital sound through them? Are new amps required? Finally, if anyone has a price estimate that would be great.
Thanks

First of all we need to know more about the system components you have now:
What cards are in the CP-50
Make & model of amplifiers
Make & model of stage speakers
Do you have a subwoof? Make/model?
Make, model, and how many surrounds?
Does soundhead have exciter lamp or has it got a LED reverse scan?
If you want to make use of the split (stereo) surrounds of DTS digital, you'll need to add one more amplifier.

DTS is the lowest cost digital sound system out there and a 'used' one works just as good as a new one. Some dealers have "B" stock units for a considerable discount. DTS has a small interface card that attaches and connects to the backplane of the CP-50. It has adjustments/jumpers to configure it to drop to Dolby A or SR, stereo or mono surrounds, etc. Your CP-50 MUST have a Cat 113-C automation card in it to work with DTS and a couple of traces must be cut/jumpered on the CP-50's backplane. It's easier to do this when the CP-50 is out of the rack.

The CP50 can be upgraded to run digital but
If you want the fader to control the level of the sub you have to instal the Cat 560 bass extension card. This also allows for split surrounds.
Also what is the room size you need about 10 db more headroom for any flavour of digital especially in the sub area
You are probably better off to look at the system as a whole