Dolby CP 200 diagrams !

[Mikael Christensen]

I have my CP200 up and running in the hometeater, and it sounds amazing.
Problem is I can't find a good diagram where I can read the text, the ones that is floating around on the WWW is in poor quality.
Does anyone know where to find a diagram one can read ?

[Mark Gulbrandsen]

Look in the Film-Tech warehouse. Also write to Bay Area Cinema Products. They may be able to help.

[Stefan Scholz]

Sounds amazing, ok, well... acoustical on indicator, break before make telephone exchange switches up to 4 times in signal path. Slow 741 circuitry opamps, unbalanced design... Not at all to my liking. Even in 1985 in electronics classes my professor asked: Seriously? Anybody actually builds THIS? And we had to discuss the design flaws in overtime after classes But thats just my 2 cents.
I can understand, it's a nice looking wall of rackmounts. So if I can help.
I do own an original printout of the schematic diagrams from the early 1980s somewhere in cabinet in my booth.
Thats hardcopy, no file, so scanning in good resolution is possible, if there's no other help for you.
Just let me know.

[Steve Guttag]

Bah...that's just snobbery on your professor's part. The CP200 was designed in the '70s with a debut in early 1980 (The Empire Strikes Back was its big debut). I don't recall any 741s in it. Mostly discrete transistors. The CP200 used as much pre-existing cards as possible...hence the CAT 108, CAT109, CAT150, CAT117 from the CP50; CAT64s from the E2 and the CAT22 from the 360 series (hand drawn traces and all).

Conversely, when my prof looked at its design and saw the TDA analog muxes...his first thought was "robust" using automotive components will stand up better in harsher environments. And, seriously, how many of them have died? You could move to DG series muxes but one needs to know their market. You are, primarily, playing a high noise source (optical sound or even magnetic) through a sheet of perforated vinyl using speakers designed in the 40s (primarily, when it came out). As with all Dolby products (through the CP750, for sure), the weakest link is its power supply...the PS1 (PS1B). That is one place that I rolled my own mod/upgrade and I have systems out there with switch-mode power supplies inside of the PS1B that significantly lowered the noise of it (no more ripple too) but you have to be careful...it was designed knowing the PS1 had a saggy power rail (12V relays, not 15V). Even the replacement output cards, CAT517 and CAT560 presumed a saggy power rail as they used the +24 and "-14" rails to get a bigger swing. I dial my 15V supplies down to 13V to ensure I'm within the spec of everything.

Everyone's a critic but the true test is how well they lasted and that, sonically, almost nobody complained about them. I still have CP200s in prominent places handling film sound. However, for digital cinema, I do bring that in further downstream as there is no reason to have that flow through a 40 year old piece of equipment. That said, I think the CP200 will outlast what it feeds.

[Mark Gulbrandsen]

Am pretty sure it used some NE5532's. Those were a more modern version of the 741, also sounded a heck of a lot better..

[Steve Guttag]

I don't recall NE5532 in the CP200...maybe on a line amplifier for something, if at all. They were a bit thirsty for current and generated a bit of heat. Panastereo used a crap-ton of them in their EQs and such. Dolby tended towards the TL072 and TL074 for their normal opamps for cinema.

...

I just flipped through a CP200 manual...it was all discrete and TL072 except for the CAT64B (EQ)...4538s, I believe. The CAT160 used NE5534 on its OBE output only (the rest of the opamps were TL072).

When you have a weak power supply (e.g. CP50, CP200), you can't afford to be feeding power sucking NE55xx chips. Definitely not in quantity. The NE5532 will set you back 8-16 mA per chip. With the TL072, you are going to be no more than 1.1mA. You could use 15 or more TL072 for every NE5532...when it comes to current consumption...and that isn't even taking into account the thermal impact (on a convection cooled system).

Again, one needs to know their market...the HVAC system will far drown out the benefits of the better opamp. Now, in screening rooms or theatres with very low noise floors, the benefits of the better components could indeed be heard. One of the reasons I used Panastereo in my screening rooms was due to the significant noise improvements that they had (that you could really hear). Another eye opener was doing A-chains where a Panastereo preamp will set up like text book responses, as compared to Dolby preamps. You'd really see it on both azimuth as well as HF response.

Correct me if I'm wrong...didn't Dolby (and by translation, the OEM projector companies) use a TL07x chip on the red readers for its output?

[Marcel Birgelen]

Both the 5532 and the TL072 were released somewhere around 1979. The 5532 is way more power hungry, but generally considered to be the best choice for high quality audio. The TL07x is more common in signal amplification circuits where noise isn't such a big issue. For an audio processor, you probably would expect to find more NE5532s than TL072s, but then again, you need to understand the entirety of the design to be able to judge those choices. Analog circuit design is not for the faint of heart and requires some actual knowledge and skill. I remember some story where even Steve Wozniak, who designed both the Apple I and Apple II himself, didn't dare to design the power supply for the Apple II...

I guess if Steve ever gets a contract to design a rocket to Mars, his designs will be based on a bunch of CP-200s. :P

[Mark Gulbrandsen]

You guys are right. TL072 is correct. I've seen so many schematics and circuit boards in my life that it's hard to remember who used what and where.