Film-Tech Forum ARCHIVE: Breakout Boards for D-Cinema

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Posted by William T. Parr (Member # 677) on 04-21-2013, 08:54 PM:

I am looking to see if there are currently any breakout boards that would allow the 15pin and 25pin cables to beused with an older, Ultra Stereo CM35 or CM60 booth Monitor? I need need to know if I can get away with purchasing something or if I cam goin to have to fabricate something to intergrate a Dolby CP750 into an existing soundrack.

Posted by Tony Bandiera Jr (Member # 2365) on 04-21-2013, 10:27 PM:

Odessey is your friend:

LINKY

Great products that save a lot of time...they can be a little pricey but compare that to the time you'll waste fabricating custom cables.

EDIT: Sorry, re-read your post and noticed you are talking about breakouts to a monitor...they also do custom fabrications, use the "Products" tab and select Custom Products.

In reality, What I have done is used a 25-pin "Gender changer block" (it has 2 each male and female DB25 connectors in a metal chassis) ..Fry's Electronics had them...yep, here it is:

FRYS

Use a standard DB25 cable (male/female) from the processor to this block, then your custom cables to the monitor and out to the amps.

I have the military grade machined pin crimper and make my own cables.

Posted by Scott Norwood (Member # 30) on 04-23-2013, 07:18 AM:

So, how does everyone deal with a balanced processor output feeding an unbalanced monitor input? Do you wire everything as unbalanced? Do you add transformers at the monitor end? Do you throw away the old monitor and get a modern one? Does the CP750 have a separate monitor output (which would eliminate this whole problem)? Something else?

Posted by Tony Bandiera Jr (Member # 2365) on 04-23-2013, 01:09 PM:

quote: Scott Norwood
So, how does everyone deal with a balanced processor output feeding an unbalanced monitor input?

The same way we always have.

quote: Scott Norwood
Do you wire everything as unbalanced?

Nope. For example, the Component Engineering CM 100 always was unbalanced. I wired them in hundreds of locations by feeding the (+) of Center to center, the (-) of Center to the "GND" terminal of the input end, and all shields were floated at the monitor end. ALL other channels had only the (+) side connected, the (-) sides were unconnected at both ends. (CP-50/65/200 and Ultra*Stereo Processors) I have done the same with CP 500 and 650 with no ill effects. Amps are wired balanced. (No jumpers from (-) to shield are used.)

quote: Scott Norwood
Do you add transformers at the monitor end?

Nope, never. Observe good grounding and shield connection tactics and you won't have to use transformers.

quote: Scott Norwood
Do you throw away the old monitor and get a modern one?

In any upgrade, yes. I use the QSC DCM Series monitors and for CP-650 and 750 it is a simple matter of a single DB 25 cable to connect. For CP 50/65/200/500 I use a DB 25 cable with one end cut off and the appropriate wires connected to fanning strips.
I have also used the DB25 Gender Changer block I linked to above at UC Irvine for my CP650 in HIB 100. One cable from the CP-650 to the block, one from a DCM-1 to the block, and my balanced feeds to the amps backstage had a DB25 connector installed on them and plugged in to the block.

quote: Scott Norwood
Does the CP750 have a separate monitor output (which would eliminate this whole problem)?

No and as I posted above there never was a problem.

quote: Scott Norwood
Something else?

Yeah, most monitor's designs have very high impedance inputs so the loading effect on the line level side is nil....which is why the "mixed" style of connections works without issues.

Posted by Steve Guttag (Member # 268) on 04-24-2013, 05:24 AM:

quote: Tony Bandiera Jr
Nope. For example, the Component Engineering CM 100 always was unbalanced. I wired them in hundreds of locations by feeding the (+) of Center to center, the (-) of Center to the "GND" terminal of the input end, and all shields were floated at the monitor end.

Hold on a minute there partner. By doing that, you just unbalanced the center channel since you tied the "-" output to ground. You now have the entire signal above ground (unbalanced).

There are different methods of creating a "balanced" output too. Some merely use an inverting op-amp to generate the "-" side. If one ties the "-" terminal of that sort of output to ground, you effectively are shorting out the op-amp. This is a poor design to begin with but on has to know the type of output stage before tying "-" to ground. In the case of the CP650, they use a proper differential/balanced output stage that pretty well mimics a transformer (except for isolation) so one can indeed get away with tying the "-" to ground and merely unbalancing the whole output (just like if it was a true transformer output).

An alternate way that will maintain the balanced nature of the output is to tie the signal ground of the CP650 (or other similar type transformerless differential output) to the signal ground of the unbalanced monitor. This will provide the signal return path for the monitor yet maintain the balanced characteristics of a true differential system. It will have 6-dB less level, however, since you are only looking at half of the signal.

A better solution is to use a transformer set on the input of the unbalanced monitor since they will effectively turn the monitor into a differential input...which will lower the noise of the system. Odyssey Products makes a suitable such board...originally designed to isolate the 6-channel inputs on processors like the CP650.

As others have said, if the system is being changed out anyway for digital...then going to a new monitor with balanced inputs (and often the right pinout on the DB25) is a wise move for maintaining the best signal path all of the way through.

Posted by Dave Macaulay (Member # 813) on 04-24-2013, 06:40 AM:

When installing digital systems with a modern processor that has balanced outputs to a legacy sound system, I prefer not to connect the processor end because that will unbalance the signals. The monitor still has the amplifier output monitoring function, really old monitors (Altec etc) don't even have a processor monitoring capability. Degrading the main output signal quality to achieve the processor monitoring function doesn't make sense to me, it isn't that vital a function.
Sometimes the amps used are unbalanced input only. In that case I connect the monitor as well.
Connecting the monitor with transformers is possible but expensive.
Using a QSC DCM is great on an upgrade where the sound equipment is replaced. Not all theatres can afford that, especially under VPF deals - where there is no money for sound upgrades.
The Odyssey monitor is effective and economical when I need a new monitor but don't need the extensive (and expensive) capabilities of a DCM. With a DB25+terminals breakout card for the processor and a flat cable jumper to the monitor, input hookup is fast and simple if the existing amp input cables are wired correctly.
Amp output connections to the Odyssey monitor are a bit of a pain since Odyssey has the amp monitor inputs balanced as well: the right way to do it since a bridge-mono amp can be accurately monitored (for the first time I think), but still a pain to wire up.

Posted by Steve Guttag (Member # 268) on 04-24-2013, 04:10 PM:

The Panastereo CM230-EX had differential inputs on the amp side.

Note, some have differential on the subwoofer only since that is the likely candidate for bridged output.

Posted by Marco Giustini (Member # 4544) on 04-24-2013, 04:50 PM:

quote: Tony Bandiera Jr
I use the QSC DCM Series monitors and for CP-650 and 750 it is a simple matter of a single DB 25 cable to connect

I know I'm being fussy here, but wouldn't a proper balanced cable be recommended for such connection? I mean with all the channels on a twisted shielded pair.

Posted by Steve Guttag (Member # 268) on 04-24-2013, 05:50 PM:

To get the full benefit of balanced audio, yes, twisted cable should be used since it will maximize the suppression of induced noise/crosstalk. That is one of the key benefits of a differential system.

However, the typical run between the processor and monitor is small and in an enclosed system. The odds one gets away with straight/ribbon cable for the monitor are pretty high.